Broadband Modem Mixed-Signal Front End
Data Sheet
AD9865
Rev. B Document Feedback
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FEATURES
Low cost 3.3 V CMOS MxFETM for broadband modems
10-bit D/A converter
2×/4× interpolation filter
200 MSPS DAC update rate
Integrated 23 dBm line driver with 19.5 dB gain control
10-bit, 80 MSPS A/D converter
−12 dB to +48 dB low noise RxPGA (< 3.0 nV/rtHz)
Third order, programmable low-pass filter
Flexible digital data path interface
Half- and full-duplex operation
Backward-compatible with AD9975 and AD9875
Various power-down/reduction modes
Internal clock multiplier (PLL)
2 auxiliary programmable clock outputs
Available in 64-lead chip scale package or bare die
APPLICATIONS
Powerline networking
VDSL and HPNA
FUNCTIONAL BLOCK DIAGRAM
10
XTAL
RX–
4
6
AD9865
10
0 TO –7.5dB
04493-0-001
0 TO –12dB
REGISTER
CONTROL
CLK
SYN.
ADC
80MSPS
2-4X IOUT_G+
IOUT_N+
IOUT_N–
IOUT_G–
CLKOUT_1
CLKOUT_2
OSCIN
RX+
IAMP
TxDAC
IOUT_P+
IOUT_P–
2M CLK
MULTIPLIER
2-POLE
LPF 1-POLE
LPF
0 TO 6dB
∆ = 1dB – 6 TO 18dB
∆ = 6dB –6 TO 24dB
∆ = 6dB
SPI
AGC[5:0]
RXCLK
RXE/SYNC
ADIO[9:4]/
Tx[5:0]
ADIO[3:0]/
Rx[5:0]
TXCLK
TXEN/SYNC
MODE
PWR DWN
Figure 1.
GENERAL DESCRIPTION
The AD9865 is a mixed-signal front end (MxFE) IC for
transceiver applications requiring Tx and Rx path functionality
with data rates up to 80 MSPS. Its flexible digital interface,
power saving modes, and high Tx-to-Rx isolation make it well
suited for half- and full-duplex applications. The digital inter-
face is extremely flexible allowing simple interfaces to digital
back ends that support half- or full-duplex data transfers, thus
often allowing the AD9865 to replace discrete ADC and DAC
solutions. Power saving modes include the ability to reduce
power consumption of individual functional blocks, or to power
down unused blocks in half-duplex applications. A serial port
interface (SPI®) allows software programming of the various
functional blocks. An on-chip PLL clock multiplier and
synthesizer provide all the required internal clocks, as well as
two external clocks from a single crystal or clock source.
The Tx signal path consists of a bypassable 2×/4× low-pass
interpolation filter, a 10-bit TxDAC, and a line driver. The
transmit path signal bandwidth can be as high as 34 MHz at an
input data rate of 80 MSPS. The TxDAC provides differential
current outputs that can be steered directly to an external load
or to an internal low distortion current amplifier. The current
amplifier (IAMP) can be configured as a current- or voltage-
mode line driver (with two external npn transistors) capable of
delivering in excess of 23 dBm peak signal power. Tx power can
be digitally controlled over a 19.5 dB range in 0.5 dB steps.
The receive path consists of a programmable amplifier
(RxPGA), a tunable low-pass filter (LPF), and a 10-bit ADC.
The low noise RxPGA has a programmable gain range of
−12 dB to +48 dB in 1 dB steps. Its input referred noise is less
than 3 nV/rtHz for gain settings beyond 36 dB. The receive path
LPF cutoff frequency can be set over a 15 MHz to 35 MHz
range or simply bypassed. The 10-bit ADC achieves excellent
dynamic performance over a 5 MSPS to 80 MSPS span. Both
the RxPGA and the ADC offer scalable power consumption
allowing power/performance optimization.
The AD9865 provides a highly integrated solution for many
broadband modems. It is available in a space saving 64-pin chip
scale package and is specified over the commercial (−40°C to
+85°C) temperature range.
AD9865 Data Sheet
Rev. B | Page 2 of 48
TABLE OF CONTENTS
Features .............................................................................................. 1
Applications ....................................................................................... 1
Functional Block Diagram .............................................................. 1
General Description ......................................................................... 1
Specifications ..................................................................................... 3
Tx Path Specifications .................................................................. 3
Rx Path Specifications .................................................................. 4
Power Supply Specifications........................................................ 5
Digital Specifications ................................................................... 6
Serial Port Timing Specifications ............................................... 7
Half-Duplex Data Interface (ADIO Port) Timing
Specifications ................................................................................ 7
Full-Duplex Data Interface (Tx and Rx Port) Timing
Specifications ................................................................................ 8
Explanation of Test Levels ........................................................... 8
Absolute Maximum Ratings ............................................................ 9
Thermal Resistance ...................................................................... 9
ESD Caution .................................................................................. 9
Pin Configuration and Function Descriptions ........................... 10
Typical Performance Characteristics ........................................... 12
Rx Path Typical Performance Characteristics ........................ 12
TxDAC Path Typical Performance Characteristics ............... 16
IAMP Path Typical Performance Characteristics .................. 18
Serial Port ........................................................................................ 19
Register Map Description .......................................................... 21
Serial Port Interface (SPI) .......................................................... 21
Digital Interface .............................................................................. 23
Half-Duplex Mode ..................................................................... 23
Full-Duplex Mode ...................................................................... 24
RxPGA Control .......................................................................... 25
TxPGA Control .......................................................................... 27
Transmit Path .................................................................................. 28
Digital Interpolation Filters ...................................................... 28
TxDAC and IAMP Architecture .............................................. 28
Tx Programmable Gain Control .............................................. 30
TxDAC Output Operation ........................................................ 30
IAMP Current-Mode Operation .............................................. 30
IAMP Voltage-Mode Operation ............................................... 31
IAMP Current Consumption Considerations ........................ 32
Receive Path .................................................................................... 33
Rx Programmable Gain Amplifier ........................................... 33
Low-Pass Filter ............................................................................ 34
Analog-to-Digital Converter (ADC) ....................................... 35
AGC Timing Considerations .................................................... 36
Clock Synthesizer ........................................................................... 37
Power Control and Dissipation .................................................... 39
Power-Down ............................................................................... 39
Half-Duplex Power Savings ...................................................... 39
Power Reduction Options ......................................................... 40
Power Dissipation....................................................................... 42
Mode Select upon Power-Up and Reset .................................. 42
Analog and Digital Loop-Back Test Modes ............................ 43
PCB Design Considerations .......................................................... 44
Component Placement .............................................................. 44
Power Planes and Decoupling .................................................. 44
Ground Planes ............................................................................ 44
Signal Routing ............................................................................. 44
Evaluation Board ............................................................................ 46
Outline Dimensions ....................................................................... 47
Ordering Guide .......................................................................... 47
REVISION HISTORY
9/2016—Rev. A to Rev. B
Changed Thermal Characteristics Section to Thermal
Resistance Section ............................................................................ 9
Changes to Thermal Resistance Section ....................................... 9
Added Table 9; Renumbered Sequentially .................................... 9
Changes to Figure 2 and Table 9 ................................................... 10
Changes to Ordering Guide .......................................................... 47
11/2004—Rev. 0 to Rev. A
Changes to Specifications Tables ..................................................... 3
Changes to Serial Table .................................................................. 19
Changes to Full Duplex Mode section ......................................... 24
Change to TxDAC and IAMP Architecture section .................. 29
Change to TxDAC Output Operation section ............................ 30
Insert equation ................................................................................ 37
Change to Figure 84 caption ......................................................... 42
11/2003—Revision 0: Initial Version
Data Sheet AD9865
Rev. B | Page 3 of 48
SPECIFICATIONS
Tx PATH SPECIFICATIONS
AVDD = 3.3 V ± 5%, DVDD = CLKVDD = DRVDD = 3.3 V ± 10%; fOSCIN = 50 MHz, fDAC = 200 MHz, RSET = 2.0 kΩ, unless otherwise
noted.
Table 1.
Parameter Temp Test Level Min Typ Max Unit
TxDAC DC CHARACTERISTICS
Resolution Full 10 Bits
Update Rate Full II 200 MSPS
Full-Scale Output Current (IOUTP_FS) Full IV 2 25 mA
Gain Error1 25°C I ±2 % FS
Offset Error 25°C V 2 µA
Voltage Compliance Range Full −1 +1.5 V
TxDAC GAIN CONTROL CHARACTERISTICS
Minimum Gain 25°C V −7.5 dB
Maximum Gain 25°C V 0 dB
Gain Step Size 25°C V 0.5 dB
Gain Step Accuracy 25°C IV Monotonic
Gain Range Error 25°C V ±2 dB
TxDAC AC CHARACTERISTICS2
Fundamental 0.5 dBm
Signal-to-Noise and Distortion (SINAD) Full IV 62.0 63.1 dBc
Signal-to-Noise Ratio (SNR) Full IV 62.5 63.2 dBc
Total Harmonic Distortion (THD) Full IV −77.7 −67.0 dBc
Spurious-Free Dynamic Range (SFDR) Full IV 67.1 79.3 dBc
IAMP DC CHARACTERISTICS
IOUTN Full-Scale Current = IOUTN+ + IOUTN− Full IV 2 105 mA
IOUTG Full-Scale Current = IOUTG+ + IOUTG− Full IV 2 150 mA
AC Voltage Compliance Range Full IV 1 7 V
IAMPN AC CHARACTERISTICS3
Fundamental 25°C 13 dBm
IOUTN SFDR (Third Harmonic) Full IV 43.3 45.2 dBc
IAMP GAIN CONTROL CHARACTERISTICS
Minimum Gain 25°C V −19.5 dB
Maximum Gain 25°C V 0 dB
Gain Step Size 25°C V 0.5 dB
Gain Step Accuracy 25°C IV Monotonic dB
IOUTN Gain Range Error 25°C V 0.5 dB
REFERENCE
Internal Reference Voltage4
25°C
I
1.23
V
Reference Error Full V 0.7 3.4 %
Reference Drift Full V 30 ppm/oC
Tx DIGITAL FILTER CHARACTERISTICS (2× Interpolation)
Latency (Relative to 1/fDAC) Full V 43 Cycles
−0.2 dB Bandwidth Full V 0.2187 fOUT/fDAC
−3 dB Bandwidth Full V 0.2405 fOUT /fDAC
Stop-Band Rejection (0.289 fDAC to 0.711 fDAC) Full V 50 dB
AD9865 Data Sheet
Rev. B | Page 4 of 48
Parameter Temp Test Level Min Typ Max Unit
Tx DIGITAL FILTER CHARACTERISTICS (4× Interpolation)
Latency (Relative to 1/ F
DAC
)
Full
V
96
Cycles
−0.2 dB Bandwidth Full V 0.1095 fOUT/fDAC
−3 dB Bandwidth Full V 0.1202 fOUT /fDAC
Stop Band Rejection (0.289 fOSCIN to 0.711 fOSCIN) Full V 50 dB
PLL CLK MULTIPLIER
OSCIN Frequency Range Full IV 5 80 MHz
Internal VCO Frequency Range Full IV 20 200 MHz
Duty Cycle Full II 40 60 %
OSCIN Impedance 25°C V 100//3 ΜΩ/pF
CLKOUT1 Jitter5 25°C III 12 ps rms
CLKOUT2 Jitter6 25°C III 6 ps rms
CLKOUT1 and CLKOUT2 Duty Cycle7 Full III 45 55 %
1 Gain error and gain temperature coefficients are based on the ADC only (with a fixed 1.23 V external reference and a 1 V p-p differential analog input).
2 TxDAC IOUTFS = 20 mA, differential output with 1:1 transformer with source and load termination of 50 Ω, FOUT = 5 MHz, 4x interpolation.
3 IOUN full-scale current = 80 mA, fOSCIN = 80 MHz, fDAC =160 MHz, 2x interpolation.
4 Use external amplifier to drive additional load.
5 Internal VCO operates at 200 MHz , set to divide-by-1.
6 Because CLKOUT2 is a divided down version of OSCIN, its jitter is typically equal to OSCIN.
7 CLKOUT2 is an inverted replica of OSCIN, if set to divide-by-1.
Rx PATH SPECIFICATIONS
AVDD = 3.3 V ± 5%, DVDD = CLKVDD = DRVDD = 3.3 V ± 10%; half- or full-duplex operation with CONFIG = 0 default power bias
settings, unless otherwise noted.
Table 2.
Parameter Temp Test Level Min Typ Max Unit
Rx INPUT CHARACTERISTICS
Input Voltage Span (RxPGA Gain = −10 dB) Full III 6.33 V p-p
Input Voltage Span (RxPGA Gain = +48 dB) Full III 8 mV p-p
Input Common-Mode Voltage 25°C III 1.3 V
Differential Input Impedance 25°C III 400
4.0
Ω
pF
Input Bandwidth (with RxLPF Disabled, RxPGA = 0 dB) 25°C III 53 MHz
Input Voltage Noise Density (RxPGA Gain = 36 dB, f
−3 dBF
= 26 MHz)
25°C
III
3.0
nV/rtHz
Input Voltage Noise Density (RxPGA Gain = 48 dB, f−3 dBF = 26 MHz) 25°C III 2.4 nV/rtHz
RxPGA CHARACTERISTICS
Minimum Gain 25°C III −12 dB
Maximum Gain 25°C III 48 dB
Gain Step Size 25°C III 1 dB
Gain Step Accuracy 25°C III Monotonic dB
Gain Range Error 25°C III 0.5 dB
RxLPF CHARACTERISTICS
Cutoff Frequency (f−3 dBF ) Range Full III 15 35 MHz
Attenuation at 55.2 MHz with f−3 dBF = 21 MHz 25°C III 20 dB
Pass-Band Ripple 25°C III ±1 dB
Settling Time to 5 dB RxPGA Gain Step @ fADC = 50 MSPS 25°C III 20 ns
Settling Time to 60 dB RxPGA Gain Step @ f
ADC
= 50 MSPS
25°C
III
100
ns
ADC DC CHARACTERISTICS
Resolution NA NA 10 Bits
Conversion Rate Full II 5 80 MSPS
Data Sheet AD9865
Rev. B | Page 5 of 48
Parameter Temp Test Level Min Typ Max Unit
Rx PATH LATENCY 1
Full-Duplex Interface
Full
V
10.5
Cycles
Half-Duplex Interface Full V 10.0 Cycles
Rx PATH COMPOSITE AC PERFORMANCE @ fADC = 50 MSPS2
RxPGA Gain = 48 dB (Full-Scale = 8.0 mV p-p)
Signal-to-Noise and Distortion (SNR) 25°C III 43.7 dBc
Total Harmonic Distortion (THD) 25°C III −71 dBc
RxPGA Gain = 24 dB (Full-Scale =126 mV p-p)
Signal-to-Noise (SNR) 25°C III 59 dBc
Total Harmonic Distortion (THD) 25°C III −67.2 dBc
RxPGA Gain = 0 dB (Full-Scale = 2.0 V p-p)
Signal-to-Noise and Distortion (SINAD) Full IV 58 59 dBc
Total Harmonic Distortion (THD) Full IV −66 −62.9 dBc
Rx PATH COMPOSITE AC PERFORMANCE @ fADC = 80 MSPS3
RxPGA Gain = 48 dB (Full-Scale = 8.0 mV p-p)
Signal-to-Noise (SNR) 25°C III 41.8 dBc
Total Harmonic Distortion (THD) 25°C III −67 dBc
RxPGA Gain = 24 dB (Full-Scale = 126 mV p-p)
Signal-to-Noise (SNR)
25°C III 58.6 dBc
Total Harmonic Distortion (THD) 25°C III −62.9 dBc
RxPGA Gain = 0 dB (Full-Scale = 2.0 V p-p)
Signal-to-Noise (SNR)
25°C II 58.9 59.6 dBc
Total Harmonic Distortion (THD) 25°C II −69.7 −59.8 dBc
Rx-to-Tx PATH FULL-DUPLEX ISOLATION
(1 V p-p, 10 MHz Sine Wave Tx Output)
RxPGA Gain = 40 dB
IOUTP± Pins to RX± Pins 25°C III 83 dBc
IOUTG± Pins to RX± Pins 25°C III 37 dBc
RxPGA Gain = 0 dB
IOUTP± Pins to RX± Pins 25°C III 123 dBc
IOUTG± Pins to RX± Pins 25°C III 77 dBc
1 Includes RxPGA, ADC pipeline, and ADIO bus delay relative to fADC.
2 fIN = 5 MHz, AIN = −1.0 dBFS , LPF cutoff frequency set to 15.5 MHz with Reg. 0x08 = 0x80.
3 fIN = 5 MHz, AIN = −1.0 dBFS , LPF cutoff frequency set to 26 MHz with Reg. 0x08 = 0x80.
POWER SUPPLY SPECIFICATIONS
AVDD = 3.3 V, DVDD = CLKVDD = DRVDD = 3.3 V; RSET = 2 kΩ, full-duplex operation with fDATA = 80 MSPS,1 unless otherwise noted.
Table 3.
Parameter Temp Test Level Min Typ Max Unit
SUPPLY VOLTAGES
AVDD Full V 3.135 3.3 3.465 V
CLKVDD Full V 3.0 3.3 3.6 V
DVDD Full V 3.0 3.3 3.6 V
DRVDD
Full
V
3.0
3.3
3.6
V
IS_TOTAL (Total Supply Current) Full II 406 475 mA
POWER CONSUMPTION
IAVDD + ICLKVDD (Analog Supply Current) IV 311 342 mA
IDVDD + IDRVDD (Digital Supply Current) Full IV 95 133 mA
AD9865 Data Sheet
Rev. B | Page 6 of 48
Parameter Temp Test Level Min Typ Max Unit
POWER CONSUMPTION (Half-Duplex Operation with fDATA = 50 MSPS)2
Tx Mode
IAVDD + ICLKVDD 25°C IV 112 130 mA
IDVDD + IDRVDD 25°C IV 46 49.5 mA
Rx Mode
IAVDD + ICLKVDD 25°C IV 225 253 mA
IDVDD + IDRVDD 25°C IV 36.5 39 mA
POWER CONSUMPTION OF FUNCTIONAL BLOCKS1 (IAVDD + ICLKVDD)
RxPGA and LPF 25°C III 87 mA
ADC 25°C III 108 mA
TxDAC 25°C III 38 mA
IAMP (Programmable) 25°C III 10 120 mA
Reference 25°C III 170 mA
CLK PLL and Synthesizer 25°C III 107 mA
MAXIMUM ALLOWABLE POWER DISSIPATION Full IV 1.66 W
STANDBY POWER CONSUMPTION
IS_TOTAL (Total Supply Current) Full 13 mA
POWER DOWN DELAY (USING PWR_DWN PIN)
RxPGA and LPF 25°C III 440 ns
ADC 25°C III 12 ns
TxDAC 25°C III 20 ns
IAMP
25°C
III
20
ns
CLK PLL and synthesizer 25°C III 27 ns
POWER UP DELAY (USING PWR_DWN PIN)
RxPGA and LPF 25°C III 7.8 µs
ADC 25°C III 88 ns
TxDAC 25°C III 13 µs
IAMP 25°C III 20 ns
CLK PLL and Synthesizer 25°C III 20 µs
1 Default power-up settings for MODE = HIGH and CONFIG = LOW, IOUTP_FS = 20 mA, does not include IAMP’s current consumption, which is application dependent.
2 Default power-up settings for MODE = LOW and CONFIG = LOW.
DIGITAL SPECIFICATIONS
AVDD = 3.3 V ± 5%, DVDD = CLKVDD = DRVDD = 3.3 V ± 10%; RSET = 2 kΩ, unless otherwise noted.
Table 4.
Parameter Temp Test Level Min Typ Max Unit
CMOS LOGIC INPUTS
High Level Input Voltage Full VI DRVDD – 0.7 V
Low Level Input Voltage
Full
VI
0.4
V
Input Leakage Current 12 µA
Input Capacitance Full VI 3 pF
CMOS LOGIC OUTPUTS (CLOAD = 5 pF)
High Level Output Voltage (IOH = 1 mA) Full VI DRVDD – 0.7 V
Low Level Output Voltage (IOH = 1 mA) Full VI 0.4 V
Output Rise/Fall Time (High Strength Mode and CLOAD = 15 pF) Full VI 1.5/2.3 ns
Output Rise/Fall Time (Low Strength Mode and CLOAD = 15 pF) Full VI 1.9/2.7 ns
Output Rise/Fall Time (High Strength Mode and CLOAD = 5 pF) Full VI 0.7/0.7 ns
Output Rise/Fall Time (Low Strength Mode and CLOAD = 5 pF) Full VI 1.0/1.0 ns
RESET
Minimum Low Pulse Width (Relative to f
ADC
)
1
Clock
cycles
Data Sheet AD9865
Rev. B | Page 7 of 48
SERIAL PORT TIMING SPECIFICATIONS
AVDD = 3.3 V ± 5%, DVDD = CLKVDD = DRVDD = 3.3 V ± 10%, unless otherwise noted.
Table 5.
Parameter Temp Test Level Min Typ Max Unit
WRITE OPERATION (See Figure 46)
SCLK Clock Rate (fSCLK)
Full IV 32 MHz
SCLK Clock High (tHI)
Full IV 14 ns
SCLK Clock Low (tLOW)
Full IV 14 ns
SDIO to SCLK Setup Time (tDS)
Full IV 14 ns
SCLK to SDIO Hold Time (tDH)
Full IV 0 ns
SEN to SCLK Setup Time (tS)
Full IV 14 ns
SCLK to SEN Hold Time (tH)
Full IV 0 ns
READ OPERATION (See Figure 47 and Figure 48)
SCLK Clock Rate (fSCLK)
Full IV 32 MHz
SCLK Clock High (tHI)
Full IV 14 ns
SCLK Clock Low (tLOW)
Full IV 14 ns
SDIO to SCLK Setup Time (tDS)
Full IV 14 ns
SCLK to SDIO Hold Time (tDH) Full IV 0 ns
SCLK to SDIO (or SDO) Data Valid Time (tDV)
Full IV 14 ns
SEN to SDIO Output Valid to Hi-Z (tEZ)
Full IV 2 ns
HALF-DUPLEX DATA INTERFACE (ADIO PORT) TIMING SPECIFICATIONS
AVDD = 3.3 V ± 5%, DVDD = CLKVDD = DRVDD = 3.3 V ± 10%, unless otherwise noted.
Table 6.
Parameter Temp Test Level Min Typ Max Unit
READ OPERATION1 (See Figure 50)
Output Data Rate
Full II 5 80 MSPS
Three-State Output Enable Time (tPZL)
Full II 3 ns
Three-State Output Disable Time (tPLZ)
Full II 3 ns
Rx Data Valid Time (tVT)
Full II 1.5 ns
Rx Data Output Delay (tOD) Full II 4 ns
WRITE OPERATION (See Figure 49)
Input Data Rate (1× Interpolation) Full II 20 80 MSPS
Input Data Rate (2× Interpolation) Full II 10 80 MSPS
Input Data Rate (4× Interpolation) Full II 5 50 MSPS
Tx Data Setup Time (tDS)
Full II 1 ns
Tx Data Hold Time (t
DH
)
Full
II
2.5
ns
Latch Enable Time (t
EN
)
Full
II
3
ns
Latch Disable Time (tDIS)
Full II 3 ns
1 CLOAD = 5 pF for digital data outputs.
AD9865 Data Sheet
Rev. B | Page 8 of 48
FULL-DUPLEX DATA INTERFACE (Tx AND Rx PORT) TIMING SPECIFICATIONS
AVDD = 3.3 V ± 5%, DVDD = CLKVDD = DRVDD = 3.3 V ± 10%, unless otherwise noted.
Table 7.
Parameter Temp Test Level Min Typ Max Unit
Tx PATH INTERFACE (See Figure 53)
Input Nibble Rate (2× Interpolation) Full II 20 160 MSPS
Input Nibble Rate (4× Interpolation) Full II 10 100 MSPS
Tx Data Setup Time (tDS)
Full II 2.5 ns
Tx Data Hold Time (tDH)
Full II 1.5 ns
Rx PATH INTERFACE1 (See Figure 54)
Output Nibble Rate Full II 10 160 MSPS
Rx Data Valid Time (tDV) Full II 3 ns
Rx Data Hold Time (t
DH
)
Full
II
0
ns
1 CLOAD =5 pF for digital data outputs.
EXPLANATION OF TEST LEVELS
I 100% production tested.
II 100% production tested at 25°C and guaranteed by design and characterization at specified temperatures.
III
Sample tested only.
IV Parameter is guaranteed by design and characterization testing.
V Parameter is a typical value only.
VI 100% production tested at 25°C and guaranteed by design and characterization for industrial temperature range.
Data Sheet AD9865
Rev. B | Page 9 of 48
ABSOLUTE MAXIMUM RATINGS
Table 8.
Parameter Rating
ELECTRICAL
AVDD, CLKVDD Voltage 3.9 V maximum
DVDD, DRVDD Voltage 3.9 V maximum
RX+, RX−, REFT, REFB −0.3 V to AVDD + 0.3 V
IOUTP+, IOUTP− −1.5 V to AVDD + 0.3 V
IOUTN+, IOUTN−, IOUTG+,
IOUTG−
−0.3 V to +7 V
OSCIN, XTAL
−0.3 V to CLVDD + 0.3 V
REFIO, REFADJ −0.3 V to AVDD + 0.3 V
Digital Input and Output Voltage −0.3 V to DRVDD + 0.3 V
Digital Output Current 5 mA maximum
ENVIRONMENTAL
Operating Temperature Range
(Ambient)
−40°C to +85°C
Maximum Junction Temperature 125°C
Lead Temperature (Soldering, 10 s)
150°C
Storage Temperature Range
(Ambient)
−65°C to +150°C
Stresses at or above those listed under Absolute Maximum
Ratings may cause permanent damage to the product. This is a
stress rating only; functional operation of the product at these
or any other conditions above those indicated in the operational
section of this specification is not implied. Operation beyond
the maximum operating conditions for extended periods may
affect product reliability.
THERMAL RESISTANCE
Thermal performance is directly linked to printed circuit board
(PCB) design and operating environment. Careful attention to
PCB thermal design is required.
The exposed pad (EPAD) must be soldered to the ground plane
for the 64-lead LFCSP. The EPAD provides an electrical,
thermal, and mechanical connection to the board.
Junction temperature (TJ) can be estimated using the following
equations:
TJ = TT + (ΨJT × P),
or
TJ = TB + (ΨJB × P)
where:
TT is the temperature measured at the top of the package.
P is the total device power dissipation.
TB is the temperature measured at the board.
ΨJT and ΨJB are thermal characteristic parameters obtained with
θJA in still air test conditions.
Table 9. Thermal Resistance
Package θJA θJC Unit
CP-64-31 23.32 0.7 °C/W
1 Test condition 1: typical θJA and θJC values are specified for a 4-layer, JESD51-7
high effective thermal conductivity test board for leaded surface-mount
packages. θJA is obtained in still air conditions (JESD51-2). Airflow increases
heat dissipation, effectively reducing θJA. θJC is obtained with the test case
temperature monitored at the bottom of the exposed pad.
ESD CAUTION
AD9865 Data Sheet
Rev. B | Page 10 of 48
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
4493-0-002
ADIO9/Tx[5]
ADIO8/Tx[4]
ADIO7/Tx[3]
ADIO6/Tx[2]
ADIO5/Tx[1]
ADIO4/Tx[0]
ADIO3/Rx[5]
ADIO2/Rx[4]
ADIO1/Rx[3]
ADIO0/Rx[2]
NC/Rx[1]
NC/Rx[0]
RXCLK
TXCLK/TXQUIET
TXEN/TXSYNC
RXEN/RXSYNC
DRVDD
DRVSS
CLKOUT1
SDIO
SDO
SCLK
SEN
GAIN/PGA[5]
PGA[4]
PGA[3]
PGA[2]
PGA[1]
REFB
AVSS
RESET
PGA[0]
AVSS
AVSS
IOUT_N–
IOUT_G–
AVSS
AVDD
REFIO
REFADJ
AVDD
AVSS
RX+
RX–
REFT
AVSS
AVDD
AVSS
DRVDD
DRVSS
PWR_DWN
CLKOUT2
DVDD
DVSS
CLKVDD
OSCIN
XTAL
CLKVSS
CONFIG
MODE
IOUT_G+
IOUT_N+
IOUT_P–
IOUT_P+
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
64
63
62
61
60
59
58
57
56
55
54
53
52
51
50
49
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
NOTES
1. THE EXPOSED PAD (EPAD) MUST BE SOLDERED TO T HE GRO UND P LANE FOR THE 64- LEAD LF CSP.
THE EPAD P ROVIDES AN ELE CTRI CAL, THERM AL, AND MECHANICAL CONNECTI ON TO T HE BOARD.
48
47
46
45
44
43
42
41
40
39
38
37
36
35
34
33
AD9865
TOP VIEW
(Not to Scal e)
Figure 2. Pin Configuration
Table 10. Pin Function Descriptions
Pin No. Mnemonic Mode1 Description
1 ADIO9 HD MSB of ADIO Buffer
Tx[5] FD MSB of Tx Nibble Input
2 to 5 ADIO8 to 5 HD Bits 8 to 5 of ADIO Buffer
Tx[4 to 1] FD Bits 4 to 1 of Tx Nibble Input
6 ADIO4 HD Bit 4 of ADIO Buffer
Tx[0] FD LSB of Tx Nibble Input
7 ADIO3 HD Bit 3 of ADIO Buffer
Rx[5] FD MSB of Rx Nibble Output
8, 9 ADIO2, 1 HD Bits 2 to 1 of ADIO Buffer
Rx[4, 3] FD Bits 4 to 3 of Rx Nibble Output
10 ADIO0 HD LSB of ADIO Buffer
Rx[2] FD Bit 2 of Rx Nibble Output
11 NC HD No Connect
Rx[1] FD Bit 1 of Rx Nibble Output
12 NC HD No Connect
Rx[0] FD LSB of Rx Nibble Output
13 RXEN HD ADIO Buffer Control Input
RXSYNC FD Rx Data Synchronization Output
14 TXEN HD Tx Path Enable Input
TXSYNC FD Tx Data Synchronization Input
Data Sheet AD9865
Rev. B | Page 11 of 48
Pin No. Mnemonic Mode1 Description
15 TXCLK HD ADIO Sample Clock Input
TXQUIET
FD
Fast TxDAC/IAMP Power-Down
16 RXCLK HD ADIO Request Clock Input
FD Rx and Tx Clock Output at 2 x fADC
17, 64 DRVDD Digital Output Driver Supply Input
18, 63 DRVSS Digital Output Driver Supply Return
19 CLKOUT1 fADC/N Clock Output (L = 1, 2, 4, or 8)
20 SDIO Serial Port Data Input/Output
21 SDO Serial Port Data Output
22 SCLK Serial Port Clock Input
23 SEN
Serial Port Enable Input
24 GAIN FD Tx Data Port (Tx[5:0]) Mode Select
PGA[5] HD or FD MSB of PGA Input Data Port
25 to 29 PGA[4 to 0] HD or FD Bits 4 to 0 of PGA Input Data Port
30 RESET
Reset Input (Active Low)
31, 34, 36, 39, 44, 47, 48 AVSS Analog Ground
32, 33 REFB, REFT ADC Reference Decoupling Nodes
35, 40, 43 AVDD Analog Power Supply Input
37, 38
RX−, RX+
Receive Path − and + Analog Inputs
41 REFADJ TxDAC Full-Scale Current Adjust
42 REFIO TxDAC Reference Input/Output
45 IOUT_G− −Tx Amp Current Output_Sink
46 IOUT_N− −Tx Mirror Current Output_Sink
49 IOUT_G+ +Tx Amp Current Output_Sink
50 IOUT_N+ +Tx Mirror Current Output_Sink
51 IOUT_P− −TxDAC Current Output_Source
52 IOUT_P+ +TxDAC Current Output_Source
53 MODE Digital Interface Mode Select Input
LOW = HD, HIGH = FD
54 CONFIG Power-Up SPI Register Default Setting Input
55 CLKVSS Clock Oscillator/Synthesizer Supply Return
56 XTAL Crystal Oscillator Inverter Output
57 OSCIN Crystal Oscillator Inverter Input
58 CLKVDD Clock Oscillator/Synthesizer Supply
59 DVSS Digital Supply Return
60 DVDD Digital Supply Input
61 CLKOUT2 fOSCIN/L Clock Output, (L = 1, 2, or 4)
62 PWR_DWN Power-Down Input
EPAD Exposed Pad. The exposed pad (EPAD) must be soldered to the ground
plane for the 64-lead LFCSP. The EPAD provides an electrical, thermal,
and mechanical connection to the board.
1 HD = half-duplex mode; FD = full-duplex mode.
AD9865 Data Sheet
Rev. B | Page 12 of 48
TYPICAL PERFORMANCE CHARACTERISTICS
Rx PATH TYPICAL PERFORMANCE CHARACTERISTICS
AVDD = CLKVDD = DVDD = DRVDD = 3.3 V, fOSCIN = fADC = 50 MSPS, low-pass filter’s f−3 dB = 22 MHz, AIN = −1 dBFS,
RIN = 50 Ω, half- or full-duplex interface, default power bias settings.
04493-0-040
FREQUENCY (MHz)
INPUT REFERRED SPECTRUM (dBm)
0 6.25 12.50 18.75 25.00
10
–100
–90
–80
–70
–60
–50
–40
–30
–20
–10
0FUND = –1dBFS
SINAD = 59.1dBFS
ENOB = 9.53 BITS
SNR = 60.2dBFS
THD = –65.2dBFS
SFDR = –64.9dBc (THIRD HARMONIC)
RBW = 12.21kHz
Figure 3. Spectral Plot with 4 k FFT of Input Sinusoid with
RxPGA = 0 dB and PIN = 9 dBm
04493-0-041
FREQUENCY (MHz)
INPUT REFERRED SPECTRUM (dBm)
0 5 10 15 20 25
–30
–130
–120
–110
–100
–90
–80
–70
–60
–50
–40 RBW = 12.2kHz
Figure 4. Spectral Plot with 4 k FFT of 84-Carrier DMT Signal
with PAR = 10.2 dB, PIN = −33.7 dBm, and RxPGA = 36 dB
04493-0-042
INPUT AMPLITUDE (dBFS)
0dBFS = 2V p-p
SINAD (dBFS)
THD (dBFS)
–21 –18 –15 –12 –9 –6 –3 0
66
45
48
51
54
57
60
63
–50
–92
–86
–80
–74
–68
–62
–56
SINAD @ 3.14V
SINAD @ 3.3V
SINAD @ 3.46V
THD @ 3.14V
THD @ 3.3V
THD @ 3.46V
Figure 5. SINAD and THD vs. Input Amplitude and Supply
(fIN = 8 MHz, LPF f−3 dB = 26 MHz; Rx PGA = 0 dB)
04493-0-043
RxPGA GAIN (dB)
SINAD (dBFS)
ENOB (Bits)
–6 0 6 12 18 24 30 36 42 48
62
41
44
47
50
53
56
59
10.0
6.5
7.0
7.5
8.0
8.5
9.0
9.5
1MHz
5MHz
10MHz
15MHz
20MHz
Figure 6. SINAD/ENOB vs. RxPGA Gain and Frequency
04493-0-044
RxPGA GAIN (dB)
THD (dBFC)
–6 0 6 12 18 24 30 36 42 48
–55
–85
–80
–75
–70
–65
–60
1MHz
5MHz
10MHz
15MHz
20MHz
Figure 7. THD vs. RxPGA Gain and Frequency
04493-0-045
RxPGA GAIN (dB)
SINAD (dBFS)
THD (dBc)
–6 0 6 12 18 24 30 36 42 48
62
41
44
47
50
53
56
59
–45
–80
–75
–70
–65
–60
–55
–50
SINAD @ +25C
SINAD @ +85C
SINAD @ –40C
THD @ +25C
THD @ +85C
THD @ –40C
Figure 8. SINAD/THD Performance vs. RxPGA Gain
and Temperature ( fIN = 5 MHz)
Data Sheet AD9865
Rev. B | Page 13 of 48
Rx PATH TYPICAL PERFORMANCE CHARACTERISTICS
AVDD = CLKVDD = DVDD = DRVDD = 3.3 V, fOSCIN = fADC = 80 MSPS, low-pass filter’s f−3 dB = 30 MHz, AIN = −1 dBFS,
RIN = 50 Ω, half- or full-duplex interface, default power bias settings.
04493-0-046
FREQUENCY (MHz)
INPUT REFERRED SPECTRUM (dBm)
0 10203040
10
–100
–90
–80
–70
–60
–50
–40
–30
–20
–10
0FUND = –1dBFS
SINAD = 59.3dBFS
ENOB = 9.56 BITS
SNR = 59.8dBFS
THD = –69.1dBFS
SFDR = –70.3dBc (THIRD HARMONIC)
RBW = 19.53kHz
Figure 9. Spectral Plot with 4k FFT of Input Sinusoid
with RxPGA = 0 dB and PIN = 9 dBm
04493-0-047
FREQUENCY (MHz)
INPUT REFERRED SPECTRUM (dBm)
0 10203040
–30
–130
–120
–110
–100
–90
–80
–70
–60
–50
–40 RBW = 19.53kHz
Figure 10. Spectral Plot with 4k FFT of 111-Carrier DMT Signal with
PAR = 11 dB, PIN = −33.7 dBm, LPF f−3 dB = 32 MHz, and RxPGA = 36 dB
04493-0-048
INPUT AMPLITUDE (dBFS)
0dBFS = 2V p-p
SINAD (dBFS)
THD (dBFS)
–21 –18 –15 –12 –9 –6 –3 0
66
45
48
51
54
57
60
63
–50
–92
–86
–80
–74
–68
–62
–56
SINAD @ 3.14V
SINAD @ 3.3V
SINAD @ 3.46V
THD @ 3.14V
THD @ 3.3V
THD @ 3.46V
Figure 11. SINAD and THD vs. Input Amplitude and Supply
(fIN = 8 MHz, LPF f−3 dB = 26 MHz; RxPGA = 0 dB)
04493-0-049
RxPGA GAIN (dB)
SINAD (dBFS)
ENOB (Bits)
–6 0 6 12 18 24 30 36 42 48
62
41
44
47
50
53
56
59
10.0
6.5
7.0
7.5
8.0
8.5
9.0
9.5
5MHz
10MHz
15MHz
20MHz
30MHz
Figure 12. SINAD/ENOB vs. RxPGA Gain and Frequency
04493-0-050
RxPGA GAIN (dB)
THD (dBc)
–6 0 6 12 18 24 30 36 42 48
–
55
–85
–80
–75
–70
–65
–60
5MHz
10MHz
15MHz
20MHz
30MHz
Figure 13. THD vs. RxPGA Gain and Frequency
04493-0-051
RxPGA GAIN (dB)
SINAD (dBFS)
THD (dBc)
–6 0 6 12 18 24 30 36 42 48
62
41
44
47
50
53
56
59
–
40
–75
–70
–65
–60
–55
–50
–45
SINAD @ +25C
SINAD @ +85C
SINAD @ –40C
THD @ +25C
THD @ +85C
THD @ –40C
Figure 14. SINAD/THD Performance vs. RxPGA Gain and Temperature
( fIN = 10 MHz)
AD9865 Data Sheet
Rev. B | Page 14 of 48
04493-0-052
INPUT FREQUENCY (MHz)
SNR (dBFS)
THD (dBc)
–6 0 6 12 18 24 30 36 42 48
61.0
60.5
60.0
59.5
59.0
58.5
58.0
57.5
57.0
56.5
56.0
–
52
–54
–56
–58
–60
–62
–64
–66
–68
–70
–72
SNR @ 3.13V
SNR @ 3.3V
SNR @ 3.47V
THD @ 3.13V
THD @ 3.3V
THD @ 3.47V
Figure 15. SNR and THD vs. Input Frequency and Supply
( LPF f−3 dB = 26 MHz; RxPGA = 0 dB)
04493-0-053
RxPGA GAIN (dB)
INTEGRATED NOISE (V rms)
NOISE SPECTRAL DENSITY (nV/ Hz)
–6 0 6 12 18 24 30 36 42 48
109.4
98.5
87.5
76.6
65.6
54.7
43.8
32.8
21.9
10.9
0
20
18
16
14
12
10
8
6
4
2
0
AD9865: +25C
AD9865: +85C
AD9865: –40C
Figure 16. Input Referred Integrated Noise and Noise Spectral Density vs.
RxPGA Gain (LPF f−3 dB = 26 MHz)
04493-0-054
GAIN (dB)
DC OFFSET (% of full-scale)
–6 0 6 12 18 24 30 36 42 48
5
–5
–4
–3
–2
–1
0
1
2
3
4
DEVICE 1
DEVICE 2
DEVICE 3
DEVICE 4
Figure 17. Rx DC Offset vs. RxPGA Gain
04493-0-055
INPUT FREQUENCY (MHz)
SNR (dBFS)
THD (dBc)
20 30 40 50 60 70 80
60.0
55.0
–20
–70
–60
–50
–40
–30
55.5
56.0
56.5
57.0
57.5
58.0
58.5
59.0
59.5
SNR @ 3.13V
SNR @ 3.3V
SNR @ 3.46V
THD @ 3.13V
THD @ 3.3V
THD @ 3.46V
Figure 18. SNR and THD vs. Sample Rate and Supply
(LPF Disabled; RxPGA = 0 dB; fIN = 8 MHz)
04493-0-056
CUTOFF FREQUENCY (MHz)
SNR (dBc)
0 1020304050607080
45
44
43
42
41
40
39
38
Figure 19. SNR vs. Filter Cutoff Frequency
(50 MSPS; fIN = 5 MHz; AIN = −1 dB; RxPGA = 48 dB)
04493-0-057
RxPGA GAIN (dB)
GAIN STEP ERROR (dB)
–6 0 6 12 18 24 30 36 42 48
0.5
–0.5
–0.4
–0.3
–0.2
–0.1
0
0.1
0.2
0.3
0.4
AD9865: GAIN STEP ERROR @ +25C
AD9865: GAIN STEP ERROR @ +85C
AD9865: GAIN STEP ERROR @ –40C
Figure 20. RxPGA Gain Step Error vs. Gain (fIN = 10 MHz)
Data Sheet AD9865
Rev. B | Page 15 of 48
Rx PATH TYPICAL PERFORMANCE CHARACTERISTICS
AVDD = CLKVDD = DVDD = DRVDD = 3.3 V, fOSCIN = fADC = 50 MSPS, low-pass filter disabled, RxPGA = 0 dB, AIN = −1 dBFS,
RIN = 50 Ω, half- or full-duplex interface, default power bias settings.
04493-0-058
TIME (ns)
CODE
0 80 160 240 320 400 480 560 640 720
512
64
128
192
256
320
384
448
Figure 21. RxPGA Settling Time −12 dB to +48 dB Transition for DC Input
(fADC = 50 MSPS, LPF Disabled)
04493-0-059
INPUT FREQUENCY (MHz)
AMPLITUDE RESPONSE (dB)
0 5 10 15 20 25 30 35 40 45 50
0
–18
–15
–12
–9
–6
–3
3.3V
3.0V
3.6V
Figure 22. Rx Low-Pass Filter Amplitude Response vs. Supply
(fADC = 50 MSPS, f−3 dB = 33 MHz, RxPGA = 0 dB)
04493-0-060
FREQUENCY (MHz)
ATTEN @RxPGA = 0dB (dB)
0 5 10 15 20 25 30 35
140
60
70
80
90
100
110
120
130 TxDAC ISOLATION @ 0dB
IAMP ISOLATION @ 0dB
Figure 23. Rx to Tx Full-Duplex Isolation @ 0 RxPGA Setting
(Note: ATTEN @ RxPGA = x dB = ATTEN @ RxPGA = 0 dB − RxPGA Gain)
04493-0-061
TIME (ns)
CODE
0 80 160 240 320 400 480 560 640 720
352
320
288
256
224
192
160
128
96
64
Figure 24. RxPGA Settling Time for 0 dB to +5 dB Transition for DC Input
(fADC = 50 MSPS, LPF Disabled)
04493-0-062
INPUT FREQUENCY (MHz)
FUNDAMENTAL (dB)
0 5 10 15 20 25 30 35 40 5045
0
–20
–16
–18
–14
–12
–10
–8
–6
–2
–4
–6dB GAIN
0dB GAIN
+6dB GAIN
+18dB GAIN
+30dB GAIN
+42dB GAIN
Figure 25. Rx Low-Pass Filter Amplitude Response vs. RxPGA Gain
(LPF's f−3 dB = 33 MHz)
04493-0-090
FREQUENCY (MHz)
RESISTANCE ()
CAPACITANCE (pF)
5 105958575655545352515
420
320
10
0
1
2
3
4
5
6
7
8
9
330
340
350
360
370
380
390
400
410
R
IN
C
IN
Figure 26. Rx Input Impedance vs. Frequency
AD9865 Data Sheet
Rev. B | Page 16 of 48
TxDAC PATH TYPICAL PERFORMANCE CHARACTERISTICS
AVDD = CLKVDD = DVDD = DRVDD = 3.3 V, fOSCIN = 50 MSPS and 80 MSPS, RSET = 1.96 kΩ, 2:1 transformer coupled output
(see Figure 63) into 50 Ω load half- or full-duplex interface, default power bias settings.
04493-0-072
FREQUENCY (MHz)
dBm
0 5 10 15 20 30
10
–80
–70
–60
–50
–40
–30
–20
–10
0
Figure 27. Dual-Tone Spectral Plot of TxDAC's Output
(fDATA = 50 MSPS, 4× Interpolation, 10 dBm Peak Power,
F1 = 17 MHz, F2 = 18 MHz)
04493-0-073
2-TONE CENTER FREQUENCY (MHz)
IMD (dBFS)
(RELATIVE TO PEAK POWER)
0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0
–65
–90
–85
–80
–75
–70
10dBm
7dBm
4dBm
Figure 28. 2-Tone IMD Frequency Sweep vs. Peak Power
with fDATA = 50 MSPS, 4× Interpolation
04493-0-074
2-TONE CENTER FREQUENCY (MHz)
SFDR (dBFS)
(RELATIVE TO PEAK POWER)
0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0
–65
–90
–85
–80
–75
–70
10dBm 7dBm
4dBm
Figure 29. 2-Tone Worst Spur Frequency Sweep vs. Peak Power
with fDATA = 50 MSPS, 4× Interpolation
04493-0-075
FREQUENCY (MHz)
dBm
0 5 10 15 20 25 30 35 40
10
–80
–70
–60
–50
–40
–30
–20
–10
0
Figure 30. Dual-Tone Spectral Plot of TxDAC's Output
(fDATA = 80 MSPS, 2× Interpolation, 10 dBm Peak Power,
F1 = 27.1 MHz, F2 = 28.7 MHz)
04493-0-076
2-TONE CENTER FREQUENCY (MHz)
IMD (dBFS)
(RELATIVE TO PEAK POWER)
0 5 10 15 20 25 30
–65
–90
–85
–80
–75
–70
10dBm
7dBm
4dBm
Figure 31. 2-Tone IMD Frequency Sweep vs. Peak Power
with fDATA = 80 MSPS, 2× Interpolation
04493-0-077
2-TONE CENTER FREQUENCY (MHz)
SFDR (dBFS)
(RELATIVE TO PEAK POWER)
0 5 10 15 20 25 30
–65
–90
–85
–80
–75
–70
10dBm
7dBm
4dBm
Figure 32. 2-Tone Worst Spur Frequency Sweep vs. Peak Power
with fDATA = 80 MSPS, 2× Interpolation
Data Sheet AD9865
Rev. B | Page 17 of 48
04493-0-078
FREQUENCY (MHz)
dBm
0 5 10 15 20 25
–20
–30
–40
–50
–60
–70
–80
–90
–100
PAR = 11.4
RMS = –1.4dBm
Figure 33. Spectral Plot of 84-Carrier OFDM Test Vector
(fDATA = 50 MSPS, 4× Interpolation)
04493-0-079
FREQUENCY (MHz)
dBm
0 25 50 75 100 125 150 175 200
–20
–30
–40
–50
–60
–70
–80
–90
–100
PAR = 11.4
RMS = –1.4dBm
Figure 34. Wideband Spectral Plot of 88-Subcarrier OFDM Test Vector
(fDATA = 50 MSPS, 4× Interpolation)
04493-0-080
AOUT (dBFS)
SNR AND 2-TONE IMD (dBFS)
(RELATIVE TO PEAK POWER)
–24 –21 –18 –15 –12 –9 –6 –3 0
100
55
60
65
70
75
80
85
90
95 2-TONE IMD
SNR
Figure 35. SNR and SFDR vs. POUT
(fOUT = 12.55 MHz, fDATA = 50 MSPS, 4× Interpolation)
04493-0-081
FREQUENCY (MHz)
dBm
0 5 10 15 20 25 30 35 40
–20
–100
–90
–80
–70
–60
–50
–40
–30
PAR = 11.4
RMS = –1.4dBm
Figure 36. Spectral Plot of 111-Carrier OFDM Test Vector
(fDATA = 80 MSPS, 2× Interpolation)
04493-0-082
FREQUENCY (MHz)
dBm
0 20 40 60 80 100 120 140 160
–20
–100
–90
–80
–70
–60
–50
–40
–30
PAR = 11.4
RMS = –1.4dBm
Figure 37. Wideband Spectral Plot of 111-Carrier OFDM Test Vector
(fDATA = 80 MSPS, 2× Interpolation)
04493-0-083
AOUT (dBFS)
SNR AND 2-TONE IMD (dBFS)
(RELATIVE TO PEAK POWER)
–24 –21 –18 –15 –12 –9 –6 –3 0
95
55
60
65
70
75
80
85
90
SNR
2-TONE IMD
Figure 38. SNR and SFDR vs. POUT
(fOUT = 20 MHz, fDATA = 80 MSPS, 2× Interpolation)
AD9865 Data Sheet
Rev. B | Page 18 of 48
IAMP PATH TYPICAL PERFORMANCE CHARACTERISTICS
AVDD = CLKVDD = DVDD = DRVDD = 3.3 V, fOSCIN = 50 MSPS, RSET = 1.58 kΩ, 1:1 transformer coupled output (see Figure 64 and
Figure 65) into 50 Ω load, half- or full-duplex interface, default power bias settings.
04493-0-084
FREQUENCY (MHz)
dBm
0 5 10 15 20 25
20
–60
–55
–50
–45
–40
–35
–30
–25
–20
–15
–10
–5
0
5
10
15 RBW = 2.3kHz
Figure 39. Dual-Tone Spectral Plot of IAMPN Output
(IAMP Settings of I = 12.5 mA, N = 4, G = 0,
2:1 Transformer into 75 Ω Loader, VCM = 4.8 V)
04493-0-085
FREQUENCY (MHz)
dBm
0 5 10 15 20 25
0
–80
–70
–60
–50
–40
–30
–20
–10
PAR = 11.4
RMS = 10.3dBm
Figure 40. Spectral Plot of 84-Carrier OFDM Test Vector Using IAMPN in
Current-Mode Configuration
(IAMP Settings of I = 10 mA, N = 4, G = 0; VCM = 4.8 V)
04493-0-086
FREQUENCY (MHz)
dBm
0 5 10 15 20 25
0
–80
–70
–60
–50
–40
–30
–20
–10
PAR = 11.4
RMS = 10.4dBm
Figure 41. Spectral Plot of 84-Carrier OFDM Test Vector Using IAMP in
Voltage-Mode Configuration with AVDD = 5 V
(PBR951 Transistors, IAMP Settings of I = 6 mA, N = 2, G = 6)
04493-0-087
VCM (V)
OIP3 (dBm)
3.0 3.5 4.0 4.5 5.0
48
5MHz
10MHz
15MHz 20MHz
2.5MHz
30
46
44
42
40
38
36
34
32
Figure 42. IOUTN Third-Order Intercept vs. Common-Mode Voltage
(IAMP Settings of I = 12.5 mA, N = 4, G = 0, 2:1
Transformer into 75 Ω Load)
04493-0-088
VCM (V)
OIP3 (dBm)
3.0 3.5 4.0 4.5 5.0
42
5MHz
10MHz
15MHz
20MHz
2.5MHz
30
40
38
36
34
32
Figure 43. IOUTG Third-Order Intercept vs. Common-Mode Voltage
(IAMP Settings of I = 4.25 mA, N = 0, G = 6,
2:1 Transformer into 75 Ω Load)
04493-0-089
FREQUENCY (MHz)
dBm
0 5 10 15 20 25
0
–80
–70
–60
–50
–40
–30
–20
–10
PAR = 11.4
RMS = 9.8dBm
RBW = 10kHz
Figure 44. Spectral Plot of 84-Carrier OFDM Test Vector Using IAMP in
Voltage-Mode Configuration with AVDD = 3.3 V
(PBR951 Transistors, IAMP Settings of I = 6 mA, N = 2, G = 6)
Data Sheet AD9865
Rev. B | Page 19 of 48
SERIAL PORT
Table 11. SPI Register Mapping
Address
(Hex)1
Bit
Break-
down Description
Width
Power-Up Default Value
Comments
MODE = 0 (Half-Duplex) MODE = 1 (Full-Duplex)
CONFIG = 0 CONFIG = 1 CONFIG = 0 CONFIG = 1
SPI PORT CONFIGURATION AND SOFTWARE RESET
0x00
(7)
4-Wire SPI
1 0 0 0 0 Default SPI configuration is
3-wire, MSB first.
(6) LSB First
1 0 0 0 0
(5) S/W Reset
1 0 0 0 0
POWER CONTROL REGISTERS (via PWR_DWN pin)
0x01
(7) Clock Syn. 1 0 0 0 0 PWR_DWN = 0.
Default setting is for all
blocks powered on.
(6) TxDAC/IAMP
1 0 0 0 0
(5) Tx Digital
1 0 0 0 0
(4) REF
1 0 0 0 0
(3) ADC CML
1 0 0 0 0
(2) ADC 1 0 0 0 0
(1) PGA Bias
1 0 0 0 0
(0) RxPGA
1 0 0 0 0
0x02
(7) CLK Syn. 1 0 0 0 1* PWR_DWN = 1.
Default setting* is for all
functional blocks powered
down except PLL.
*MODE = CONFIG = 1.
Setting has PLL powered
down with OSCIN input
routed to RXCLK output.
(6) TxDAC/IAMP
1 1 1 1 1
(5) Tx Digital
1 1 1 1 1
(4) REF
1 1 1 1 1
(3)
ADC CML
1
1
1
1
1
(2)
ADC
1
1
1
1
1
(1) PGA Bias 1 1 1 1 1
(0) RxPGA
1 1 1 1 1
HALF-DUPLEX POWER CONTROL
0x03
(7:3) Tx OFF Delay
5
0xFF 0xFF N/A N/A
Default setting is for TXEN
input to control power
on/off of Tx/Rx path.
Tx driver delayed by 31
1/fDATA clock cycles.
(2) Rx _TXEN
1
(1) Tx PWRDN
1
(0) Rx PWRDN
1
PLL CLOCK MULTIPLIER/SYNTHESIZER CONTROL
0x04 (5) Duty Cycle Enable 1 0 0 0 0 Default setting is Duty Cycle
Restore disabled, ADC CLK
from OSCIN input, and PLL
multiplier × 2 setting.
*PLL multiplier × 4 setting.
(4) fADC from PLL
1 0
0 0 0
(3:2) PLL Divide-N
2 00
00 00 00
(1:0) PLL Multiplier-M
2 01
10* 01 01
0x05
(2) OSCIN to RXCLK
1 0 0 0 1* Full-duplex RXCLK normally
at nibble rate.
*Exception on power-up.
(1) Invert RXCLK
1 0 0 0 0
(0)
Disabled RXCLK
1
0
0
0
0
0x06 (7:6) CLKOUT2 Divide 2 01 01 01 01 Default setting is CLKOUT2
and CLKOUT1 enabled with
divide-by-2.
*CLKOUT1 and CLKOUT2
disabled.
(5) CLKOUT2 Invert 1 0 0 0 0
(4) CLKOUT2 Disable 1 0 0 0 1*
(3:2) CLKOUT1 Divide
2 01 01 01 01
(1) CLKOUT1 Invert
1 0 0 0 0
(0) CLKOUT1 Disable
1 0 0 0 1*
AD9865 Data Sheet
Rev. B | Page 20 of 48
Address
(Hex)1
Bit
Break-
down Description Width
Power-Up Default Value
Comments
MODE = 0 (Half-Duplex) MODE = 1 (Full-Duplex)
CONFIG = 0 CONFIG = 1 CONFIG = 0 CONFIG = 1
Rx PATH CONTROL
0x07
(5) Initiate Offset Cal.
1 0 0 0 0 Default setting has LPF ON
and Rx path at nominal
power bias setting.
*Rx path to low power.
(4) Rx Low Power
1 0 1* 0 1*
(0) Rx Filter ON
1 1 1 1 1
0x08 (7:0)
Rx Filter Tuning
Cut-off Frequency
8
0x80 0x61 0x80 0x80 Refer to Low-Pass Filter
section.
Tx/Rx PATH GAIN CONTROL
0x09
(6)
Use SPI Rx Gain
1
0x00 0x00 0x00 0x00
Default setting is for
hardware Rx gain code via
PGA or Tx data port.
(5:0)
Rx Gain Code
6
0x0A
(6)
Use SPI Tx Gain
1 0x7F 0x7F 0x7F 0x7F Default setting is for Tx gain
code via SPI control.
(5:0)
Tx Gain Code
6
Tx AND Rx PGA CONTROL
0x0B
(6) PGA Code for Tx
1 0 0 0 0 Default setting is RxPGA
control active.
*Tx port with GAIN strobe
(AD9875/AD9876-compatible).
** 3-bit RxPGA gain map
(AD9975-compatible).
(5) PGA Code for Rx 1 1 1 1 1
(3) Force GAIN strobe
1 0 0 0 0
(2) Rx Gain on Tx Port
1 0 0 1* 1*
(1) 3-Bit RxPGA Port
1 0 1** 0 0
Tx DIGITAL FILTER AND INTERFACE
0x0C
(7:6)
Interpolation
Factor
2 01 00 01 01 Default setting is 2×
interpolation with LPF
response. Data format is
straight binary for half-
duplex and twos
complement for full-duplex
interface.
*Full-duplex only.
(4) Invert
TXEN/TXSYNC
1 0 0 0 0
(3) Tx 5/5 Nibble* 1 N/A N/A 0 0
(2)
LS Nibble First*
1
N/A
N/A
0
0
(1) TXCLK neg. edge
1 0 0 0 0
(0) Twos complement
1 0 0 1 1
Rx INTERFACE AND ANALOG/DIGITAL LOOPBACK
0x0D
(7) Analog Loopback
1 0 0 0 0 Data format is straight
binary for half-duplex and
twos complement for full-
duplex interface.
Analog loopback: ADC Rx
data fed back to TxDAC.
Digital loopback: Tx input
data to Rx output port.
*Full-duplex only.
(6) Digital Loopback* 1 0 0 0 0
(5) Rx Port 3-State
1 N/A N/A 0 0
(4) Invert
RXEN/RXSYNC
1 0 0 0 0
(3) RX 5/5 Nibble
1 N/A N/A 0 0
(2) LS Nibble First*
1 N/A N/A 0 0
(1) RXCLK neg. edge
1 0 0 0 0
(0) Twos complement
1 0 0 1 1
DIGITAL OUTPUT DRIVE STRENGTH, TxDAC OUTPUT, AND REV ID
0x0E
(7) Low Drive
Strength
1 0 0 0 0 Default setting is for high
drive strength and IAMP
enabled.
(0) TxDAC Output
1 0 0 0 0
0x0F
(3:0)
REV ID Number
4 0x00 0x00 0x00 0x00
Tx IAMP GAIN AND BIAS CONTROL
0x10
(7)
Select Tx Gain
1
0x44 0x44 0x44 0x44
Secondary path G1 = 0, 1, 2,
3, 4.
Primary path N = 0, 1, 2, 3, 4.
(6:4)
G1
3
(2:0)
N 3
Data Sheet AD9865
Rev. B | Page 21 of 48
Address
(Hex)1
Bit
Break-
down Description Width
Power-Up Default Value
Comments
MODE = 0 (Half-Duplex) MODE = 1 (Full-Duplex)
CONFIG = 0 CONFIG = 1 CONFIG = 0 CONFIG = 1
0x11
(6:4)
G2 3
0x62 0x62 0x62 0x62
Secondary path stages:
G2 = 0 to 1.50 in 0.25 steps
and G3 = 0 to 6.
(2:0)
G3 3
0x12
(6:4)
Stand_Secondary
3 0x01 0x01 0x01 0x01 Standing current of primary
and secondary path.
(2:0)
Stand_Primary
3
0x13 (7:5) CPGA Bias Adjust 3
0x00 0x00 0x00 0x00
Current bias setting for Rx
path’s functional blocks.
Refer to page 41.
(4:3) SPGA Bias Adjust 2
(2:0) ADC Bias Adjust 4
1 Bits that are undefined should always be assigned a 0.
REGISTER MAP DESCRIPTION
The AD9865 contains a set of programmable registers described
in Table 11 that are used to optimize its numerous features,
interface options, and performance parameters from its default
register settings. Registers pertaining to similar functions have
been grouped together and assigned adjacent addresses to
minimize the update time when using the multibyte serial port
interface (SPI) read/write feature. Bits that are undefined within
a register should be assigned a 0 when writing to that register.
The default register settings were intended to allow some
applications to operate without the use of an SPI. The AD9865
can be configured to support a half- or full-duplex digital
interface via the MODE pin, with each interface having two
possible default register settings determined by the setting of
the CONFIG pin.
For instance, applications that need to use only the Tx or Rx
path functionality of the AD9865 can configure it for a half-
duplex interface (MODE = 0), and use the TXEN pin to select
between the Tx or Rx signal path with the unused path
remaining in a reduced power state. The CONFIG pin can be
used to select the default interpolation ratio of the Tx path and
RxPGA gain mapping.
SERIAL PORT INTERFACE (SPI)
The serial port of the AD9865 has 3- or 4-wire SPI capability
allowing read/write access to all registers that configure the
device’s internal parameters. Registers pertaining to the SPI are
listed in Table 12. The default 3-wire serial communication port
consists of a clock (SCLK), serial port enable (SEN), and a bi-
directional data (SDIO) signal. SEN is an active low control
gating read and write cycle. When SEN is high, SDO and SDIO
are three-stated. The inputs to SCLK, SEN, and SDIO contain a
Schmitt trigger with a nominal hysteresis of 0.4 V centered
about VDDH/2. The SDO pin remains three-stated in a 3-wire
SPI interface.
Table 12. SPI Registers Pertaining to SPI Options
Address (Hex) Bit Description
0x00
(7)
Enable 4-wire SPI
(6)
Enable SPI LSB first
A 4-wire SPI can be enabled by setting the 4-wire SPI bit high,
causing the output data to appear on the SDO pin instead of on
the SDIO pin. The SDIO pin serves as an input-only throughout
the read operation. Note that the SDO pin is active only during
the transmission of data and remains three-stated at any other
time.
An 8-bit instruction header must accompany each read and
write operation. The instruction header is shown in Table 13.
The MSB is an R/W indicator bit with logic high indicating a
read operation. The next two bits, N1 and N0, specify the
number of bytes (one to four bytes) to be transferred during the
data transfer cycle. The remaining five bits specify the address
bits to be accessed during the data transfer portion. The data
bits immediately follow the instruction header for both read
and write operations.
Table 13. Instruction Header Information
MSB
LSB
17 16 15 14 13 12 11 10
R/W
N1
N0
A4 A3 A2 A1 A0
The AD9865 serial port can support both MSB (most
significant bit) first and LSB (least significant bit) first data
formats. Figure 45 illustrates how the serial port words are built
for the MSB first and LSB first modes. The bit order is con-
trolled by the SPI LSB first bit (Register 0, Bit 6). The default
value is 0, MSB first. Multibyte data transfers in MSB format
can be completed by writing an instruction byte that includes
the register address of the last address to be accessed. The
AD9865 automatically decrements the address for each succes-
sive byte required for the multibyte communication cycle.
AD9865 Data Sheet
Rev. B | Page 22 of 48
SCLK
SDATA
SCLK
SDATA
R/W N1 A1
A2
A3A4 A0
N2 D71D61D1ND0N
R/W
N1
A1 A2 A3 A4
A0 N2 D01D11D7N
D6N
4493-0-003
DATA TRANSFER CYCLE
INSTRUCTION CYCLE
DATA TRANSFER CYCLE
INSTRUCTION CYCLE
SEN
SEN
Figure 45. SPI Timing, MSB First (Upper), and LSB First (Lower)
When the SPI LSB first bit is set high, the serial port interprets
both instruction and data bytes LSB first. Multibyte data trans-
fers in LSB format can be completed by writing an instruction
byte that includes the register address of the first address to be
accessed. The AD9865 automatically increments the address for
each successive byte required for the multibyte communication
cycle.
Figure 46 illustrates the timing requirements for a write opera-
tion to the SPI port. After the serial port enable (SEN) signal
goes low, data (SDIO) pertaining to the instruction header is
read on the rising edges of the clock (SCLK). To initiate a write
operation, the read/not-write bit is set low. After the instruction
header is read, the eight data bits pertaining to the specified
register are shifted into the SDIO pin on the rising edge of the
next eight clock cycles. If a multibyte communication cycle is
specified, the destination address is decremented (MSB first)
and shifts in another eight bits of data. This process repeats until
all the bytes specified in the instruction header (N1, N0 bits) are
shifted into the SDIO pin. SEN must remain low during the data
transfer operation, only going high after the last bit is shifted
into the SDIO pin.
D7 D6
A0 D1
SEN
N1 N0
t
S
SCLK
SDIO
1/
f
SCLK
t
LOW
t
HI
t
DS
t
DH
R/W D0
t
H
4493-0-004
Figure 46. SPI Write Operation Timing
Figure 47 illustrates the timing for a 3-wire read operation to
the SPI port. After SEN goes low, data (SDIO) pertaining to the
instruction header is read on the rising edges of SCLK. A read
operation occurs, if the read/not-write indicator is set high.
After the address bits of the instruction header are read, the
eight data bits pertaining to the specified register are shifted out
of the SDIO pin on the falling edges of the next eight clock cycles.
If a multibyte communication cycle is specified in the instruction
header, a similar process as previously described for a multibyte
SPI write operation applies. The SDO pin remains three-stated
in a 3-wire read operation.
D7 D6
A0 D1
SEN
N1
tS
SCLK
SDIO
1/
fSCLK
tLOW
tHI
tDS tDH
R/W D0
tEZ
A2 A1
tDV
4493-0-005
Figure 47. SPI 3-Wire Read Operation Timing
Figure 48 illustrates the timing for a 4-wire read operation to
the SPI port. The timing is similar to the 3-wire read operation
with the exception that data appears at the SDO pin, while the
SDIO pin remains high impedance throughout the operation.
The SDO pin is an active output only during the data transfer
phase and remains three-stated at all other times.
A0
SEN
N1
t
S
SCLK
SDIO
1/f
SCLK
t
LOW
t
HI
t
DS
t
DH
R/W
t
EZ
A2 A1
t
DV
D7 D6 D1
SDO D0
t
EZ
4493-0-006
Figure 48. SPI 4-Wire Read Operation Timing
Data Sheet AD9865
Rev. B | Page 23 of 48
DIGITAL INTERFACE
The digital interface port is configurable for half-duplex or full-
duplex operation by pin-strapping the MODE pin low or high,
respectively. In half-duplex mode, the digital interface port
becomes a 10-bit bidirectional bus called the ADIO port. In
full-duplex mode, the digital interface port is divided into two
6-bit ports called Tx[5:0] and Rx[5:0] for simultaneous Tx and
Rx operations. In this mode, data is transferred between the
ASIC and AD9865 in 6-bit (or 5-bit) nibbles. The AD9865 also
features a flexible digital interface for updating the RxPGA and
TxPGA gain registers via a 6-bit PGA port or Tx[5:0] port for
fast updates, or via the SPI port for slower updates. See the
RxPGA Control section for more information.
HALF-DUPLEX MODE
The half-duplex mode functions as follows when the MODE
pin is tied low. The bidirectional ADIO port is typically shared
in burst fashion between the transmit path and receive path.
Two control signals, TXEN and RXEN, from a DSP (or digital
ASIC) control the bus direction by enabling the ADIO port’s
input latch and output driver, respectively. Two clock signals are
also used: TXCLK to latch the Tx input data, and RXCLK to
clock the Rx output data. The ADIO port can also be disabled
by setting TXEN and RXEN low (default setting), thus allowing
it to be connected to a shared bus.
Internally, the ADIO port consists of an input latch for the Tx
path in parallel with an output latch with three-state outputs for
the Rx path. TXEN is used to enable the input latch; RXEN is
used to three-state the output latch. A five-sample-deep FIFO is
used on the Tx and Rx paths to absorb any phase difference be-
tween the AD9865’s internal clocks and the externally supplied
clocks (TXCLK, RXCLK). The ADIO bus accepts input data-
words into the transmit path when the TXEN pin is high, the
RXEN pin is low, and a clock is present on the TXCLK pin, as
shown in Figure 49.
TXCLK
TXEN
ADIO[9:0]
RXEN
TX0 TX2 TX3 TX4TX1
tDIS
4493-0-007
t
DH
t
EN
t
DS
Figure 49. Transmit Data Input Timing Diagram
The Tx interpolation filter(s) following the ADIO port can be
flushed with zeros, if the clock signal into the TXCLK pin is
present for 33 clock cycles after TXEN goes low. Note that the
data on the ADIO bus is irrelevant over this interval.
The output from the receive path is driven onto the ADIO bus
when the RXEN pin is high, and a clock is present on the RXCLK
pin. While the output latch is enabled by RXEN, valid data
appears on the bus after a 6-clock-cycle delay due to the internal
FIFO delay. Note that Rx data is not latched back into the Tx
path, if TXEN is high during this interval with TXCLK present.
The ADIO bus becomes three-stated once the RXEN pin returns
low. Figure 50 shows the receive path output timing.
t
PZL
4493-0-008
RXEN
ADIO[9:0]
RXCLK
t
VT
t
PLZ
t
OD
RX0 RX1 RX2 RX3
Figure 50. Receive Data Output Timing Diagram
To add flexibility to the digital interface port, several program-
ming options are available in the SPI registers. These options
are listed in Table 14. The default Tx and Rx data input formats
are straight binary, but can be changed to twos complement.
The default TXEN and RXEN settings are active high, but can
be set to opposite polarities, thus allowing them to share the
same control. In this case, the ADIO port can still be placed
onto a shared bus by disabling its input latch via the control
signal, and disabling the output driver via the SPI register. The
clock timing can be independently changed on the transmit and
receive paths by selecting either the rising or falling clock edge
as the validating/sampling edge of the clock. Lastly, the output
driver’s strength can be reduced for lower data rate applications.
Table 14. SPI Registers for Half-Duplex Interface
Address (Hex)
Bit
Description
0x0C
(4) Invert TXEN
(1) TXCLK negative edge
(0) Twos complement
0x0D
(5) Rx port three-state
(4) Invert RXEN
(1) RXCLK negative edge
(0) Twos complement
0x0E
(7) Low digital drive strength
The half-duplex interface can be configured to act as a slave or a
master to the digital ASIC. An example of a slave configuration
is shown in Figure 51. In this example, the AD9865 accepts all
the clock and control signals from the digital ASIC. Because the
sampling clocks for the DAC and ADC are derived internally
from the OSCIN signal, the TXCLK and RXCLK signals must
be at exactly the same frequency as the OSCIN signal. The
phase relationships among the TXCLK, RXCLK, and OSCIN
signals can be arbitrary. If the digital ASIC cannot provide a low
jitter clock source to OSCIN, use the AD9865 to generate the
clock for its DAC and ADC, and to pass the desired clock signal
to the digital ASIC via CLKOUT1 or CLKOUT2.
AD9865 Data Sheet
Rev. B | Page 24 of 48
TO
Tx DIGITAL
FILTER
10
ADIO
[9:0]
OSCIN
RXEN
AD9865
FROM
Rx ADC
10
RXEN
TXEN
TXEN
TXCLK
RXCLK
DAC_CLK
ADC_CLK
CLKOUT
DIGITAL ASIC
4493-0-009
Tx/Rx
Data[9:0]
Figure 51. Example of a Half-Duplex Digital Interface
with AD9865 Serving as the Slave
Figure 52 shows a half-duplex interface with the AD9865 acting
as the master, generating all the required clocks. CLKOUT1
provides a clock equal to the bus data rate that is fed to the
ASIC as well as back to the TXCLK and RXCLK inputs. This
interface has the advantage of reducing the digital ASIC’s pin
count by three. The ASIC needs only to generate a bus control
signal that controls the data flow on the bidirectional bus.
TO
Tx DIGITAL
FILTER
10
ADIO
[9:0]
Tx/Rx
Data[9:0]
CLKOUT1
AD9865
FROM
Rx ADC
10
RXEN
TXEN
BUS_CTR
TXCLK
RXCLK
CLKIN
DIGITAL ASIC
4493-0-010
OSCIN
FROM
CRYSTAL
OR MASTER CLK
Figure 52. Example of a Half-Duplex Digital Interface
with AD9865 Serving as the Master
FULL-DUPLEX MODE
The full-duplex mode interface is selected when the MODE pin
is tied high. It can be used for full- or half-duplex applications.
The digital interface port is divided into two 6-bit ports called
Tx[5:0] and Rx[5:0], allowing simultaneous Tx and Rx opera-
tions for full-duplex applications. In half-duplex applications,
the Tx[5:0] port can also be used to provide a fast update of the
RxPGA (AD9875 backward-compatible) during an Rx opera-
tion. This feature is enabled by default and can be used to
reduce the required pin count of the ASIC (refer to RxPGA
Control section for details).
In either application, Tx and Rx data are transferred between
the ASIC and AD9865 in 6-bit (or 5-bit) nibbles at twice the
internal input/output word rates of the Tx interpolation filter
and ADC. Note that the TxDAC update rate must not be less
than the nibble rate. Therefore, the 2× or 4× interpolation filter
must be used with a full-duplex interface.
The AD9865 acts as the master, providing RXCLK as an output
clock that is used for the timing of both the Tx[5:0] and Rx[5:0]
ports. RXCLK always runs at the nibble rate and can be inverted
or disabled via an SPI register. Because RXCLK is derived from
the clock synthesizer, it remains active, provided that this func-
tional block remains powered on. A buffered version of the
signal appearing at OSCIN can also be directed to RXCLK by
setting Bit 2 of Register 0x05. This feature allows the AD9865 to
be completely powered down (including the clock synthesizer)
while serving as the master.
The Tx[5:0] port operates in the following manner with the SPI
register default settings. Two consecutive nibbles of the Tx data
are multiplexed together to form a 10-bit data-word in twos
complement format. The clock appearing on the RXCLK pin is
a buffered version of the internal clock used by the Tx[5:0]
port’s input latch with a frequency that is always twice the ADC
sample rate (2 × fADC). Data from the Tx[5:0] port is read on the
rising edge of this sampling clock, as illustrated in the timing
diagram shown in Figure 53. Note, TXQUIET must remain
high for the reconstructed Tx data to appear as an analog signal
at the output of the TxDAC or IAMP.
Tx2L
SB
Tx0LSB
t
SU
t
HD
t
DS
t
DH
RXCLK
TXSYNC
Tx[5:0]
4493-0-011
Tx1MSB Tx1LSB Tx2MSB Tx3LSB Tx3MSB
Figure 53. Tx[5:0] Port Full-Duplex Timing Diagram
The TXSYNC signal is used to indicate to which word a nibble
belongs. While TXSYNC is low, the first nibble of every word is
read as the most significant nibble. The second nibble of that
same word is read on the following TXSYNC high level as the
least significant nibble. If TXSYNC is low for more than one
clock cycle, the last transmit data is read continuously until
TXSYNC is brought high for the second nibble of a new trans-
mit word. This feature can be used to flush the interpolator
filters with zeros. Note that the GAIN signal must be kept low
during a Tx operation.
The Rx[5:0] port operates in the following manner with the SPI
register default settings. Two consecutive nibbles of the Rx data
are multiplexed together to form a 10-bit data-word in twos
complement format. The Rx data is valid on the rising edge of
RXCLK, as illustrated in the timing diagram shown in Figure 54.
The RXSYNC signal is used to indicate to which word a nibble
belongs. While RXSYNC is low, the first nibble of every word is
transmitted as the most significant nibble. The second nibble of
that same word is transmitted on the following RXSYNC high
level as the least significant nibble.
Data Sheet AD9865
Rev. B | Page 25 of 48
4493-0-012
RXCLK
RXSYNC
Rx[5:0]
Rx0LSB Rx1MSB Rx1LSB Rx2MSB Rx3LSB Rx3MSB
t
Dv
t
DH
Figure 54. Full-Duplex Rx Port Timing
To add flexibility to the full-duplex digital interface port, several
programming options are available in the SPI registers. These
options are listed in Table 15. The timing for the Tx[5:0] and/or
Rx[5:0] ports can be independently changed by selecting either
the rising or falling clock edge as the sampling/validating edge
of the clock. Inverting RXCLK (via Bit 1 or Register 0x05)
affects both the Rx and Tx interface, because they both use
RXCLK.
Table 15. SPI Registers for Full-Duplex Interface
Address (Hex) Bit Description
0x05
(2)
OSCIN to RXCLK
(1) Invert RXCLK
(0) Disable RXCLK
0x0B
(2) Rx gain on Tx port
0x0C (4) Invert TXSYNC
(3) Tx 5/5 nibble
(2) LS nibble first
(1) TXCLK negative edge
(0) Twos complement
0x0D
(5) Rx port three-state
(4) Invert RXSYNC
(3) Rx 5/5 nibble
(2) LS nibble first
(1)
RXCLK negative edge
(0) Twos complement
0x0E
(7) Low drive strength
The default Tx and Rx data input formats are twos complement,
but can be changed to straight binary. The default TXSYNC and
RXSYNC settings can be changed such that the first nibble of
the word appears while TXSYNC, RXSYNC, or both are high.
Also, the least significant nibble can be selected as the first
nibble of the word (LS nibble first). The output driver strength
can also be reduced for lower data rate applications.
For the AD9865, the most significant nibble defaults to 6 bits,
and the least significant nibble defaults to 4 bits. This can be
changed so that the least significant nibble and most significant
nibble have 5 bits each. To accomplish this, set the 5/5 nibble bit
in Register 0x0C and Register 0x0D and use data pins Tx[5:1]
and Rx[5:1].
Figure 55 shows a possible digital interface between an ASIC
and the AD9865. The AD9865 serves as the master generating
the required clocks for the ASIC. This interface requires that the
ASIC reserve 16 pins for the interface, assuming a 6-bit nibble
width and the use of the Tx port for RxPGA gain control. Note
that the ASIC pin allocation can be reduced by 3, if a 5-bit
nibble width is used and the gain (or gain strobe) of the RxPGA
is controlled via the SPI port.
TO
Tx DIGITAL
FILTER
10/12
AD9865/AD9866
FROM
RxADC
10/12
RXSYNC
TXSYNC
TX_SYNC
RXCLK
CLKOUT1
CLKOUT2
CLKIN
DIGITAL ASIC
4493-0-013
OSCIN
FROM
CRYSTAL
OR MASTER CLK
GAIN
OPTIONAL
Tx Data[5:0]
Rx Data[5:0] Rx[5:0]
RX_SYNC
MUX DEMUX
Tx[5:0]
6TO
RxPGA
Figure 55. Example of a Full-Duplex Digital Interface
with Optional RxPGA Gain Control via Tx[5:0]
RxPGA CONTROL
The AD9865 contains a digital PGA in the Rx path that is used
to extend the dynamic range. The RxPGA can be programmed
over −12 dB to +48 dB with 1 dB resolution using a 6-bit word,
and with a 0 dB setting corresponding to a 2 V p-p input signal.
The 6-bit word is fed into a LUT that is used to distribute the
desired gain over three amplification stages within the Rx path.
Upon power-up, the RxPGA gain register is set to its minimum
gain of −12 dB. The RxPGA gain mapping is shown in Figure 56.
Table 16 lists the SPI registers pertaining to the RxPGA.
AD9865 Data Sheet
Rev. B | Page 26 of 48
4493-0-014
6-BIT DIGITAL WORD-DECIMAL EQUIVALENT
GAIN (dB)
0
48
24 60 66
–12
–6
0
6
12
18
24
30
36
42
5442 4830 366 12 18
Figure 56. Digital Gain Mapping of RxPGA
Table 16. SPI Registers RxPGA Control
Address
(Hex)
Bit Description
0x09
(6)
Enable RxPGA update via SPI
(5:0) RxPGA gain code
0x0B
(6)
Select TxPGA via PGA[5:0]
(5)
Select RxPGA via PGA[5:0]
(3) Enable software GAIN strobe – Full-duplex
(2) Enable RxPGA update via Tx[5:0] – Full-duplex
(1) 3-bit RxPGA gain mapping – Half-duplex
The RxPGA gain register can be updated via the Tx[5:0] port,
the PGA[5:0] port, or the SPI port. The first two methods allow
fast updates of the RxPGA gain register and should be
considered for digital AGC functions requiring a fast closed-
loop response. The SPI port allows direct update and readback
of the RxPGA gain register via Register 0x09 with an update
rate limited to 1.6 MSPS (with SCLK = 32 MHz). Note that Bit 6
of Register 0x09 must be set for a read or write operation.
Updating the RxPGA via the Tx[5:0] port is an option only in
full-duplex mode1. In this case, a high level on the GAIN pin,2
with TXSYNC low, programs the PGA setting on either the
rising edge or falling edge of RXCLK, as shown in Figure 57.
The GAIN pin must be held high, TXSYNC must be held low,
and GAIN data must be stable for one or more clock cycles to
update the RxPGA gain setting.
A low level on the GAIN pin enables data to be fed to the digital
interpolation filter. This interface should be considered when
upgrading existing designs from the AD9875/AD9876 MxFE
products or half-duplex applications trying to minimize an
ASIC’s pin count.
t
SU
RXCLK
Tx SYNC
Tx [5:0]
t
HD
GAIN
GAIN
4493-0-015
Figure 57. Updating RxPGA via Tx[5:0] in Full-Duplex Mode
Updating the RxPGA (or TxPGA) via the PGA[5:0] port is an
option for both the half-duplex3 and full-duplex interface. The
PGA port consists of an input buffer that passes the 6-bit data
appearing at its input directly to the RxPGA (or TxPGA) gain
register with no gating signal required. Bit 5 or Bit 6 of
Register 0x0B is used to select whether the data updates the
RxPGA or TxPGA gain register. In applications that switch
between RxPGA and TxPGA gain control via PGA[5:0], be
careful that the RxPGA (or TxPGA) is not inadvertently loaded
with the wrong data during a transition. In the case of an
RxPGA to TxPGA transition, first deselect the RxPGA gain
register, update the PGA[5:0] port with the desired TxPGA gain
setting, and then select the TxPGA gain register.
The RxPGA also offers an alternative 3-bit word gain mapping
option4 that provides a −12 dB to +36 dB span in 8 dB increments
as shown in Table 17. The 3-bit word is directed to PGA[5:3]
with PGA[5] being the MSB. This feature is backward-compatible
with the AD9975 MxFE and allows direct interfacing to the
CX11647 or INT5130 HomePlug 1.0 PHYs.
Table 17. PGA Timing for AD9975 Backward-Compatible
Mode
Digital Gain Setting
PGA[5:3]
Decimal
Gain (dB)
000 0 −12
001
1
−12
010
2 −4
011
3 4
100
4 12
101 5 20
110 6 28
111 7 36
1 Default setting for full-duplex mode (MODE = 1).
2 The GAIN strobe can also be set in software via Reg. 0x0B, Bit 3 for
continuous updating. This eliminates the requirement for external GAIN
signal, reducing the ASIC pin count by 1.
3 Default setting for half-duplex mode (MODE = 0).
4 Default setting for MODE = 0 and CONFIG =1.
Data Sheet AD9865
Rev. B | Page 27 of 48
TXPGA CONTROL
The AD9865 also contains a digital PGA in the Tx path distri-
buted between the TxDAC and IAMP. The TxPGA is used to
control the peak current from the TxDAC and IAMP over a
7.5 dB and 19.5 dB span, respectively, with 0.5 dB resolution.
A 6-bit word is used to set the TxPGA attenuation according to
the mapping shown in Figure 58. The TxDAC gain mapping is
applicable only when Bit 0 of Register 0x0E is set, and only the
four LSBs of the 6-bit gain word are relevant.
04493-0-063
6-BIT DIGITAL CODE (Decimal Equivalent)
Tx ATTENUATION (dBFS)
0 8 16 24 32 40 48 56 64
0
–20
–16
–18
–14
–12
–10
–8
–6
–2
–4
–1
–17
–19
–15
–13
–11
–9
–7
–3
–5
TxDACs IOUTP OUTPUT
HAS 7.5dB RANGE
IAMPs IOUTN AND IOUTG
OUTPUTS HAS 19.5dB RANGE
Figure 58. Digital Gain Mapping of TxPGA
The TxPGA register can be updated via the PGA[5:0] port or
SPI port. The first method should be considered for fast updates
of the TxPGA register. Its operation is similar to the description
in the RxPGA Control section. The SPI port allows direct up-
date and readback of the TxPGA register via Register 0x0A with
an update rate limited to 1.6 MSPS (SCLK = 32 MHz). Bit 6 of
Register 0x0A must be set for a read or write operation.
Table 18 lists the SPI registers pertaining to the TxPGA. The
TxPGA control register default setting is for minimum
attenuation (0 dBFS) with the PGA[5:0] port disabled for Tx
gain control.
Table 18. SPI Registers TxPGA Control
Address (Hex)
Bit Description
0x0A
(6)
Enable TxPGA update via SPI
(5:0)
TxPGA gain code
0x0B
(6)
Select TxPGA via PGA[5:0]
(5)
Select RxPGA via PGA[5:0]
0x0E
(0)
TxDAC output (IAMP disabled)
AD9865 Data Sheet
Rev. B | Page 28 of 48
TRANSMIT PATH
The AD9865 (or AD9866) transmit path consists of a selectable
digital 2×/4× interpolation filter, a 10-bit or 12-bit TxDAC, and
a current-output amplifier (IAMP) as shown in Figure 59. Note
that the additional two bits of resolution offered by the AD9866
result in a 10 dB to 12 dB reduction in the pass-band noise
floor. The digital interpolation filter relaxes the Tx analog
filtering requirements by simultaneously reducing the images
from the DAC reconstruction process while increasing the
analog filter’s transition band. The digital interpolation filter
can also be bypassed, resulting in lower digital current
consumption.
10
AD9865/AD9866
0 TO –7.5dB
4493-0-017
0 TO –12dB
2-4X IOUT_G+
IOUT_N+
IOUT_N–
IOUT_G–
IAMP
IOUT_P+
IOUT_P–
TXCLK
TXEN/SYNC
ADIO[11:6]/
Tx[5:0]
ADIO[11:6]/
Rx[5:0]
TxDAC
Figure 59. Functional Block Diagram of Tx Path
DIGITAL INTERPOLATION FILTERS
The input data from the Tx port can be fed into a selectable
2×/4× interpolation filter or directly into the TxDAC (for a half-
duplex only). The interpolation factor for the digital filter is set
via SPI Register 0x0C with the settings shown in Table 19. The
maximum input word rate, fDATA, into the interpolation filter is
80 MSPS; the maximum DAC update rate is 200 MSPS. There-
fore, applications with input word rates at or below 50 MSPS
can benefit from 4× interpolation, while applications with input
word rates between 50 MSPS and 80 MSPS can benefit from
2× interpolation.
Table 19. Interpolation Factor Set via SPI Register 0x0C
Bits [7:6] Interpolation Factor
00
4
01 2
10 1 (half-duplex only)
11 Do not use
The interpolation filter consists of two cascaded half-band filter
stages with each stage providing 2× interpolation. The first
stage filter consists of 43 taps. The second stage filter, operating
at the higher data rate, consists of 11 taps. The normalized
wideband and pass-band filter responses (relative fDATA) for the
2× and 4× low-pass interpolation filters are shown in Figure 60
and Figure 61, respectively. These responses also include the
inherent sinc(x) from the TxDAC reconstruction process and
can be used to estimate any post analog filtering requirements.
The pipeline delays of the 2× and 4× filter responses are 21.5
and 24 clock cycles, respectively, relative to fDATA. The filter delay
is also taken into consideration for applications configured for a
half-duplex interface with the half-duplex power-down mode
enabled. This feature allows the user to set a programmable
delay that powers down the TxDAC and IAMP only after the
last Tx input sample has propagated through the digital filter.
See the Power Control and Dissipation section for more details.
4493-0-018
NORMALIZED FREQUENCY (Relative to
f
DATA
)
WIDE BAND RESPONSE (dB)
0
10
1.25 2.00
–90
–80
–70
–60
–50
–40
–30
–20
–10
0
1.750.75 1.00 1.50
WIDE BAND
0.500.25
PASS BAND RESPONSE (dB)
2.5
–2.5
–2.0
–1.5
–1.0
–0.5
0
0.5
1.0
1.5
2.0
PASS BAND
–1.0dB @ 0.441
f
DATA
Figure 60. Frequency Response of 2× Interpolation Filter
(Normalized to fDATA)
4493-0-019
NORMALIZED FREQUENCY (Relative to fDATA)
WIDE BAND RESPONSE (dB)
0
10
2.5 4.0
–90
–80
–70
–60
–50
–40
–30
–20
–10
0
3.51.5 2.0 3.0
WIDE BAND
1.00.5
PASS BAND RESPONSE (dB)
2.5
–2.5
–2.0
–1.5
–1.0
–0.5
0
0.5
1.0
1.5
2.0
PASS BAND
–1.0dB @ 0.45 fDATA
Figure 61. Frequency Response of 4× Interpolation Filter
(Normalized to fDATA)
TxDAC AND IAMP ARCHITECTURE
The Tx path contains a TxDAC with a current amplifier, IA M P.
The TxDAC reconstructs the output of the interpolation filter
and sources a differential current output that can be directed to
an external load or fed into the IAMP for further amplification.
The TxDAC’s and IAMPS’s peak current outputs are digitally
programmable over a 0 to −7.5 dB and 0 to −19.5 dB range,
respectively, in 0.5 dB increments. Note that this assumes
default register settings for Register 0x10 and Register 0x11.
Data Sheet AD9865
Rev. B | Page 29 of 48
Applications demanding the highest spectral performance
and/or lowest power consumption can use the TxDAC output
directly. The TxDAC is capable of delivering a peak signal
power-up to 10 dBm while maintaining respectable linearity
performance, as shown in Figure 27 through Figure 38. For
power-sensitive applications requiring the highest Tx power
efficiency, the TxDAC’s full-scale current output can be reduced
to as low as 2 mA, and its load resistors sized to provide a
suitable voltage swing that can be amplified by a low-power op-
amp-based driver.
Most applications requiring higher peak signal powers (up to
23 dBm) should consider using the IAMP. The IAMP can be
configured as a current source for loads having a well defined
impedance (50 Ω or 75 Ω systems), or a voltage source (with the
addition of a pair of npn transistors) for poorly defined loads
having varying impedance (such as power lines).
Figure 62 shows the equivalent schematic of the TxDAC and
IAMP. The TxDAC provides a differential current output
appearing at IOUTP+ and IOUTP−. It can be modeled as a
differential current source generating a signal-dependent ac
current, when ∆IS has a peak current of I along with two dc
current sources, sourcing a standing current equal to I. The full-
scale output current, IOUTFS, is equal to the sum of these
standing current sources (IOUTFS = 2 × I).
4493-0-020
N× (I+∆I)
N× (I–∆I)
G× (I+∆I)
G× (I–∆I)
IOUTN–
IOUTN+
IOUTG–
IOUTG+
±∆ISII
TxDAC
REFADJ
REFIO
IOUTP+
IOUTP–
I + ∆I
I – ∆I
IOFF1
RSET 0.1µF
IOFF1 IOFF2
xG xG
xN
xN
IOFF2
IAMP
Figure 62. Equivalent Schematic of TxDAC and IAMP
The value of I is determined by the RSET value at the REFADJ
pin along with the Tx path’s digital attenuation setting. With
0 dB attenuation, the value of I is
I = 16 × (1.23/RSET) (1)
For example, an RSET value of 1.96 kΩ results in I equal to
10.0 mA with IOUTFS equal to 20.0 mA. Note that the REFIO
pin provides a nominal band gap reference voltage of 1.23 V
and should be decoupled to analog ground via a 0.1 µF
capacitor.
The differential current output of the TxDAC is always con-
nected to the IOUTP pins, but can be directed to the IAMP by
clearing Bit 0 of Register 0x0E. As a result, the IOUTP pins
must remain completely open, if the IAMP is to be used. The
IAMP contains two sets of current mirrors that are used to
replicate the TxDAC’s current output with a selectable gain. The
first set of current mirrors is designated as the primary path,
providing a gain factor of N that is programmable from 0 to 4 in
steps of 1 via Bits 2:0 of Register 0x10 with a default setting of
N = 4. Bit 7 of this register must be set to overwrite the default
settings of this register. This differential path exhibits the best
linearity performance (see Figure 42) and is available at the
IOUTN+ and IOUTN− pins. The maximum peak current per
output is 100 mA and occurs when the TxDAC’s standing
current, I, is set for 12.5 mA (IOUTFS = 25 mA).
The second set of current mirrors is designated as the secon-
dary path providing a gain factor of G that is programmable
from 0 to 36 via Bits 6:4 of Register 0x10 and Bits 6:0 of Register
0x11 with a default setting of G = 12. This differential path is
intended to be used in the voltage mode configuration to bias
the external npn transistors, because it exhibits degraded
linearity performance (see Figure 43) relative to the primary
path. It is capable of sinking up to 180 mA of peak current into
either its IOUTG+ or IOUTG− pins. The secondary path
actually consists of three gain stages (G1, G2, and G3), which
are individually programmable as shown in
Table 20. While many permutations may exist to provide a fixed
gain of G, the linearity performance of a secondary path
remains relatively independent of the various individual gain
settings that are possible to achieve a particular overall gain
factor.
Both sets of mirrors sink current, because they originate from
NMOS devices. Therefore, each output pin requires a dc current
path to a positive supply. Although the voltage output of each
output pin can swing between 0.5 V and 7 V, optimum ac per-
formance is typically achieved by limiting the ac voltage swing
with a dc bias voltage set between 4 to 5 V. Lastly, both the
standing current, I, and the ac current, ∆IS, from the TxDAC are
amplified by the gain factor (N and G) with the total standing
current drawn from the positive supply being equal to
2 × (N = G) × I
Programmable current sources IOFF1 and IOFF2 via Register 0x12
can be used to improve the primary and secondary path
mirrors’ linearity performance under certain conditions by
increasing their signal-to-standing current ratio. This feature
provides a marginal improvement in distortion performance
under large signal conditions when the peak ac current of the
reconstructed waveform frequently approaches the dc standing
current within the TxDAC (0 to −1 dBFS sine wave) causing the
internal mirrors to turn off. However, the improvement in
distortion performance diminishes as the crest factor (peak-to-
rms ratio) of the ac signal increases. Most applications can
disable these current sources (set to 0 mA via Register 0x12) to
reduce the IAMP’s current consumption.
AD9865 Data Sheet
Rev. B | Page 30 of 48
Table 20. SPI Registers for TxDAC and IAMP
Address (Hex) Bit Description
0x0E (0) TxDAC output
0x10 (7) Enable current mirror gain settings
(6:4)
Secondary path first stage gain of 0
to 4 with ∆ = 1
(3) Not used
(2:0)
Primary path NMOS gain of 0 to 4
with ∆ = 1
0x11 (7) Don’t care
(6:4)
Secondary path second stage gain of
0 to 1.5 with ∆ = 0.25
(3) Not used
(2:0)
Secondary path third stage gain of 0
to 5 with ∆ = 1
0x12 (6:4) IOFF2, secondary path standing
current
(2:0) IOFF1, primary path standing current
Tx PROGRAMMABLE GAIN CONTROL
TxPGA functionality is also available to set the peak output
current from the TxDAC or IAMP. The TxDAC and IAMP are
digitally programmable via the PGA[5:0] port or SPI over a 0 dB
to −7.5 dB and 0 dB to −19.5 dB range, respectively, in 0.5 dB
increments.
The TxPGA can be considered as two cascaded attenuators with
the TxDAC providing 7.5 dB range in 0.5 dB increments, and
the IAMP providing 12 dB range in 6 dB increments. As a
result, the IAMP’s composite 19.5 dB span is valid only if
Register 0x10 remains at its default setting of 0x44. Modifying
this register setting corrupts the LUT and results in an invalid
gain mapping.
TxDAC OUTPUT OPERATION
The differential current output of the TxDAC is available at the
IOUTP+ and IOUTP− pins and the IAMP should be disabled
by setting Bit 0 of Register 0x0E. Any load connected to these
pins must be ground referenced to provide a dc path for the
current sources. Figure 63 shows the outputs of the TxDAC
driving a doubly terminated 1:1 transformer with its center-tap
tied to ground. The peak-to-peak voltage, V p-p, across RL (and
IOUT+ to IOUT−) is equal to 2 × I × (RL//RS). With I = 10 mA
and RL = RS = 50 Ω, V p-p is equal to 0.5 V with 1 dBm of peak
power being delivered to RL and 1 dBm being dissipated in RS.
4493-0-021
IOUTN–
IOUTN+
IOUTG–
IOUTG+
IOUT_P+
IOUT_P–
0 TO –7.5dB 0 TO –12dB
IAMP
REFIO
REFADJ
R
SET
0.1FR
S
1:1
R
L
TxDAC
Figure 63. TxDAC Output Directly via Center-Tap Transformer
The TxDAC is capable of delivering up to 10 dBm peak
power to a load, RL. To increase the peak power for a fixed
standing current, one must increase V p-p across IOUTP+
and IOUTP− by increasing one or more of the following
parameters: RS, RL (if possible), and/or the turns ratio, N, of
transformer. For example, the removal of RS and the use of
a 2:1 impedance ratio transformer in the previous example
results in 10 dBm of peak power capabilities to the load.
Note that increasing the power output capabilities of the
TxDAC reduces the distortion performance due to the
higher voltage swings seen at IOUTP+ and IOUTP−. See
Figure 27 through Figure 38 for performance plots on the
TxDAC’s ac performance. Optimum distortion
performance can typically be achieved by:
Limiting the peak positive VIOUTP+ and VIOUTP− to 0.8 V to
avoid onset of TxDAC’s output compression. (TxDAC’s
voltage compliance is around 1.2 V.)
Limiting V p-p seen at IOUTP+ and IOUTP− to less
than 1.6 V.
Applications demanding higher output voltage swings and
power drive capabilities can benefit from using the IAMP.
IAMP CURRENT-MODE OPERATION
The IAMP can be configured for the current-mode operation as
shown in Figure 64 for loads remaining relatively constant. In
this mode, the primary path mirrors should be used to deliver
the signal-dependent current to the load via a center-tapped
transformer, because it provides the best linearity performance.
Because the mirrors exhibit a high output impedance, they can
be easily back-terminated (if required).
For peak signal currents (IOUTPK up to 50 mA), only the
primary path mirror gain should be used for optimum
distortion performance and power efficiency. The primary
path’s gain should be set to 4, with the secondary path’s gain
stages set to 0 (Register 0x10 = 0x84). The TxDAC’s standing
current, I, can be set between 2.5 mA and 12.5 mA with the
IOUTP outputs left open. The IOUTN outputs should be
connected to the transformer, with the IOUTG (and IOUTP)
outputs left open for optimum linearity performance. The
Data Sheet AD9865
Rev. B | Page 31 of 48
transformer1 should be specified to handle the dc standing
current, IBIAS, drawn by the IAMP. Also, because IBIAS remains
signal independent, a series resistor (not shown) can be inserted
between AVDD and the transformer’s center-tap to reduce the
IAMP’s common-mode voltage, VCM, and reduce the power
dissipation on the IC. The VCM bias should not exceed 5.0 V and
the power dissipated in the IAMP alone is as follows:
PIAMP = 2 × (N + G) × I × VCM (2)
TxDAC
4493-0-022
IOUTN–
IOUTN+
IOUTG–
IOUTG+
IOUT_P+
IOUT_P–
0 TO –7.5dB 0 TO –12dB
IAMP
REFIO
REFADJ
R
SET
0.1µF
R
L
AVDD
0.1µFI
BIAS
= 2 × (N+G) × 1
IOUT
PK
T:1
IOUT
PK
= (N+G) × 1
P_OUT
PK
= (IOUT
PK
)
2
× T
2
× R
L
Figure 64. Current-Mode Operation
A step-down transformer1 with a turn ratio, T, can be used to
increase the output power, P_OUT, delivered to the load. This
causes the output load, RL, to be reflected back to the IAMP’s
differential output by T2, resulting in a larger differential voltage
swing seen at the IAMP’s output. For example, the IAMP can
deliver 24 dBm of peak power to a 50 Ω load, if a 1.41:1 step-
down transformer is used. This results in 5 V p-p voltage swings
appearing at IOUTN+ and IOUTN− pins. Figure 42 shows how
the third order intercept point, OIP3, of the IAMP varies as a
function of common-mode voltage over a 2.5 MHz to 20.0 MHz
span with a 2-tone signal having a peak power of approximately
24 dBm with IOUTPK = 50 mA.
For applications requiring an IOUTPK exceeding 50 mA, set the
secondary’s path to deliver the additional current to the load.
IOUTG+ and IOUTN+ should be shorted as well as IOUTG−
and IOUTN−. If IOUTPK represents the peak current to be
delivered to the load, then the current gain in the secondary
path, G, can be set by the following equation:
G = IOUTPK/12.5 − 4 (3)
The linearity performance becomes limited by the secondary
mirror path’s distortion.
1 The B6080 and BX6090 transformers from Pulse Engineering are worthy of
consideration for current and voltage modes.
IAMP VOLTAGE-MODE OPERATION
The voltage-mode configuration is shown in Figure 65. This
configuration is suited for applications having a poorly defined
load that can vary over a considerable range. A low impedance
voltage driver can be realized with the addition of two external
RF bipolar npn transistors (Phillips PBR951) and resistors. In
this configuration, the current mirrors in the primary path
(IOUTN outputs) feed into scaling resistors, R, generating a
differential voltage into the bases of the npn transistors. These
transistors are configured as source followers with the secon-
dary path current mirrors appearing at IOUTG+ and IOUTG−
providing a signal-dependent bias current. Note that the
IOUTP outputs must remain open for proper operation.
4493-0-023
IOUTN–
IOUTN+
IOUTG–
IOUTG+
IOUT_P+
IOUT_P–
0 TO –7.5dB 0 TO –12dB
REFIO
REFADJ
R
SET
0.1µF
TO LOAD
AVDD
IOUT
PK
RR
AVDD
R
S
0.1µF
R
S
0.1µF
DUAL NPN
PHILLIPS PBR951
IAMP
TxDAC
Figure 65. Voltage-Mode Operation
The peak differential voltage signal developed across the npn’s
bases is as follows:
VOUTPK = R × (N × I) (4)
where:
N is the gain setting of the primary mirror.
I is the standing current of the TxDAC defined in Equation 1.
The common-mode bias voltage seen at IOUTN+ and IOUTN−
is approximately AVDD − VOUTPK, while the common-mode
voltage seen at IOUTG+ and IOUTG− is approximately the
npn’s VBE drop below this level (AVDD − VOUTPK − 0.65). In
the voltage-mode configuration, the total power dissipated
within the IAMP is as follows :
PIAMP = 2 × I × {(AV DD − VOUTPK) × N
+ (AV DD − VOUTPK − 0.65) × G} (5)
The emitters of the npn transistors are ac-coupled to the trans-
former1 via a 0.1 µF blocking capacitor and series resistor of 1 Ω
to 2 Ω. Note that protection diodes are not shown for clarity
purposes, but should be considered if interfacing to a power or
phone line.
The amount of standing and signal-dependent current used to
bias the npn transistors depends on the peak current, IOUTPK,
required by the load. If the load is variable, determine the worst
case, IOUTPK, and add 3 mA of margin to ensure that the npn
transistors remain in the active region during peak load
currents. The gain of the secondary path, G, and the TxDAC’s
standing current, I, can be set using the following equation:
IOUTPK + 3 mA = G × I (6)
AD9865 Data Sheet
Rev. B | Page 32 of 48
The voltage output driver exhibits a high output impedance if
the bias currents for the npn transistors are removed. This
feature is advantageous in half-duplex applications (for
example, power lines) in which the Tx output driver must go
into a high impedance state while in Rx mode. If the AD9865 is
configured for the half-duplex mode (MODE = 0), the IAMP,
TxDAC, and interpolation filter are automatically powered
down after a Tx burst (via TXEN), thus placing the Tx driver
into a high impedance state while reducing its power
consumption.
IAMP CURRENT CONSUMPTION
CONSIDERATIONS
The Tx path’s analog current consumption is an important
consideration when determining its contribution to the overall
on-chip power dissipation. This is especially the case in full-
duplex applications, where the power dissipation can exceed the
maximum limit of 1.66 W, if the IAMP’s IOUTPK is set to high.
The analog current consumption includes the TxDAC’s analog
supply (Pin 43) along with the standing current from the IAMP’s
outputs. Equation 2 and Equation 5 can be used to calculate the
power dissipated in the IAMP for the current and voltage mode
configuration. Figure 66 shows the current consumption for the
TxDAC and IAMP as a function of the TxDAC’s standing current,
I, when only the IOUTN outputs are used. Figure 67 shows the
current consumption for the TxDAC and IAMP as a function of
the TxDAC’s standing current, I, when the IOUTN and IOUTG
outputs are used. Both figures are with the default current mirror
gain settings of N = 4 and G = 12.
04493-0-064
I (mA)
ISUPPLY (mA)
12345678910111213
100
10
20
30
40
50
60
70
80
90
IAMPN OUTPUT
TxDACs AVDD
Figure 66. Current Consumption of TxDAC and IAMP in Current-Mode
Operation with IOUTN Only (Default IAMP Settings)
04493-0-065
I (mA)
ISUPPLY (mA)
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0
100
110
120
130
140
150
10
20
30
40
50
60
70
80
90
IOUTN OUTPUT
IOUTG OUTPUT
TxDAC AVDD
Figure 67. Current Consumption of TxDAC and IAMP in Current-Mode
Operation with IOUTN Only (Default IAMP Settings)
Data Sheet AD9865
Rev. B | Page 33 of 48
RECEIVE PATH
The receive path block diagram for the AD9865 (or AD9866) is
shown in Figure 68. The receive signal path consists of a 3-stage
RxPGA, a 3-pole programmable LPF, and a 10-bit (or 12-bit)
ADC. Note that the additional two bits of resolution offered by
the AD9866 result in a 3 dB to 5 dB lower noise floor depending
on the RxPGA gain setting and LPF cutoff frequency. Also working
in conjunction with the receive path is an offset correction circuit.
These blocks are discussed in detail in the following sections.
Note that the power consumption of the RxPGA can be modified
via Register 0x13 as discussed in the Power Control and
Dissipation section.
0 TO 6dB
∆ = 1dB –6 TO 18dB
∆ = 6dB –6 TO 24dB
∆ = 6dB
XTAL
RX–
4
6
10/12
4493-0-024
REGISTER
CONTROL
CLK
SYN.
ADC
80MSPS
CLKOUT_1
CLKOUT_2
OSCIN
RX+
2
M
CLK
MULTIPLIER
2-POLE
LPF 1-POLE
LPF
SPORT
PGA[5:0]
RXCLK
RXEN/SYNC
ADIO[11:6]/
Tx[5:0]
ADIO[11:6]/
Rx[5:0]
GAIN
MAPPING
LUT
SPGA
AD9865/AD9866
Figure 68. Functional Block Diagram of Rx Path
RX PROGRAMMABLE GAIN AMPLIFIER
The RxPGA has a digitally programmable gain range from
−12 dB to +48 dB with 1 dB resolution via a 6-bit word. Its
purpose is to extend the dynamic range of the Rx path such that
the input of the ADC is presented with a signal that scales
within its fixed 2 V input span. There are multiple ways of
setting the RxPGA’s gain as discussed in the RxPGA Control
section, as well as an alternative 3-bit gain mapping having a
range of −12 dB to +36 dB with 8 dB resolution.
The RxPGA is comprised of two sections: a continuous time
PGA (CPGA) for course gain and a switched capacitor PGA
(SPGA) for fine gain resolution. The CPGA consists of two
cascaded gain stages providing a gain range from −12 dB to
+42 dB with 6 dB resolution. The first stage features a low noise
preamplifier (< 3.0 nV/rtHz), thereby eliminating the need for
an external preamplifier. The SPGA provides a gain range from
0 dB to 6 dB with 1 dB resolution. A look-up table (LUT) is
used to select the appropriate gain setting for each stage.
The nominal differential input impedance of the RxPGA input
appearing at the device RX+ and RX− input pins is 400 Ω//4 pF
(±20%) and remains relatively independent of gain setting. The
PGA input is self-biased at a 1.3 V common-mode level allowing
maximum input voltage swings of ±1.5 V at RX+ and RX−. AC
coupling the input signal to this stage via coupling capacitors
(0.1 µF) is recommended to ensure that any external dc offset
does not get amplified with high RxPGA gain settings,
potentially exceeding the ADC input range.
To limit the RxPGA’s self-induced input offset, an offset
cancellation loop is included. This cancellation loop is auto-
matically performed upon power-up and can also be initiated
via SPI. During calibration, the RxPGA’s first stage is internally
shorted, and each gain stage set to a high gain setting. A digital
servo loop slaves a calibration DAC, which forces the Rx input
offset to be within ±32 LSB for this particular high gain setting.
Although the offset varies for other gain settings, the offset is
typically limited to ±5% of the ADC’s 2 V input span. Note that
the offset cancellation circuitry is intended to reduce the voltage
offset attributed to only the RxPGA’s input stage, not any dc
offsets attributed to an external source.
The gain of the RxPGA should be set to minimize clipping of
the ADC while utilizing most of its dynamic range. The maxi-
mum peak-to-peak differential voltage that does not result in
clipping of the ADC is shown in Figure 69. While the graph
suggests that maximum input signal for a gain setting of −12 dB
is 8.0 V p-p, the maximum input voltage into the PGA should
be limited to less than 6 V p-p to prevent turning on ESD protec-
tion diodes. For applications having higher maximum input
signals, consider adding an external resistive attenuator network.
While the input sensitivity of the Rx path is degraded by the
amount of attenuation on a dB-to-dB basis, the low noise
characteristics of the RxPGA provide some design margin such
that the external line noise remains the dominant source.
04493-0-031
GAIN (dB)
FULL-SCALE PEAK-TO-PEAK INPUT SPAN (V)
–12 –6 0 6 12 18 24 30 36 42 48
8.0000
4.0000
2.0000
1.0000
0.5000
0.2500
0.1250
0.0625
0.0312
0.0156
0.0100
Figure 69. Maximum Peak-to-Peak Input vs. RxPGA Gain Setting
that Does Not Result in ADC Clipping
AD9865 Data Sheet
Rev. B | Page 34 of 48
LOW-PASS FILTER
The low-pass filter (LPF) provides a third order response with a
cutoff frequency that is typically programmable over a 15 MHz
to 35 MHz span. Figure 68 shows that the first real pole is im-
plemented within the first CPGA gain stage, and the complex
pole pair is implemented in the second CPGA gain stage.
Capacitor arrays are used to vary the different R-C time con-
stants within these two stages in a manner that changes the
cutoff frequency while preserving the normalized frequency
response. Because absolute resistor and capacitor values are
process-dependent, a calibration routine lasting less than 100 μs
automatically occurs each time the target cutoff frequency
register (Register 0x08) is updated, ensuring a repeatable cutoff
frequency from device to device.
Although the default setting specifies that the LPF be active, it
can also be bypassed providing a nominal f−3 dB of 55 MHz.
Table 21 shows the SPI registers pertaining to the LPF.
Table 21. SPI Registers for Rx Low-Pass Filter
Address (Hex) Bit Description
0x07 (0) Enable Rx LPF
0x08 (7:0) Target value
The normalized wideband gain response is shown in Figure 70.
The normalized pass-band gain and group delay responses are
shown in Figure 71. The normalized cutoff frequency, f−3 dB,
results in −3 dB attenuation. Also, the actual group delay time
(GDT) response can be calculated given a programmed cutoff
frequency using the following equation:
Actual GDT = Normalized GDT/(2.45 × f−3dB) (7)
4493-0-025
FREQUENCY
GAIN (dB)
0
5
1.0 3.0
–35
–30
–25
–20
–15
–10
–5
0
2.52.01.50.5
Figure 70. LPF’s Normalized Wideband Gain Response
4493-0-026
NORMALIZED FREQUENCY
GAIN (dB)
0 0.5 1.00.90.3 0.4 0.80.20.1
NORMALIZED GROUP DELAY
TIME RESPONSE (GDT)
1.30
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
1.05
1.10
1.15
1.20
1.25
0.25
–3.00
–2.75
–2.50
–2.25
–2.00
–1.75
–1.50
–1.25
–1.00
–0.75
–0.50
–0.25
0
0.6 0.7
NORMALIZED GROUP DELAY
NORMALIZED GAIN RESPONSE
Figure 71. LPF’s Normalized Pass-Band Gain and Group Delay Responses
The −3 dB cut-off frequency, f−3 dB, is programmable by writing
an 8-bit word, referred to as the target, to Register 0x08. The
cutoff frequency is a function of the ADC sample rate, fADC, and
to a lesser extent, the RxPGA gain setting (in dB). Figure 72
shows how the frequency response, f−3 dB, varies as a function of
the RxPGA gain setting.
4493-0-027
INPUT FREQUENCY (MHz)
FUNDAMENTAL (dB)
010 5030255
3
–18
–12
–6
0
15 20 35 40
–15
–9
–3
45
–6dB GAIN
0dB GAIN
+6dB GAIN
+18dB GAIN
+30dB GAIN
+42dB GAIN
Figure 72. Effects of RxPGA Gain on LPF Frequency Response
(f−3 dB = 32 MHz (@ 0 dB and fADC = 80 MSPS)
The following formula1 can be used to estimate f−3 dB for a
RxPGA gain setting of 0 dB:
f−3dB_0dB = (128/target) × (fADC/80) ×(fADC/30 + 23.83) f (8)
Figure 73 compares the measured and calculated f−3 dB using this
formula.
1 Empirically derived for a f−3 dB range of 15 MHz to 35 MHz and fADC of 40 MSPS
to 80 MSPS with an RxPGA = 0 dB.
Data Sheet AD9865
Rev. B | Page 35 of 48
4493-0-028
TARGET-DECIMAL EQUIVALENT
FREQUENCY (MHz)
48 128 224
19296 112 1768064
35
15
17
19
21
23
25
27
29
31
33
144 160 208
50 MSPS CALCULATED
80 MSPS CALCULATED
50 MSPS MEASURED
80 MSPS MEASURED
Figure 73. Measured and Calculated f−3 dB vs. Target Value
for fADC = 50 MSPS and 80 MSPS
The following scaling factor can be applied to the previous
formula to compensate for the RxPGA gain setting on f−3 dB:
Scale Factor = 1 − (RxPGA in dB)/382 (9)
This scaling factor reduces the calculated f−3 dB as the RxPGA is
increased. Applications that need to maintain a minimum cut-
off frequency, f−3 dB_MIN, for all RxPGA gain settings should first
determine the scaling factor for the highest RxPGA gain setting
to be used. Next, the f−3 dB_MIN should be divided by this scale
factor to normalize to the 0 dB RxPGA gain setting (f−3 dB_0 dB).
Equation 8 can then be used to calculate the target value.
The LPF frequency response shows a slight sensitivity to
temperature, as shown in Figure 74. Applications sensitive to
temperature drift can recalibrate the LPF by rewriting the target
value to Register 0x08.
4493-0-029
TARGET-DECIMAL EQUIVALENT
FREQUENCY (MHz)
96 128 240192176112
35
15
20
25
30
144 160 208
F
OUT
ACTUAL 80MHz AND –40°C
224
F
OUT
ACTUAL 80MHz AND +25°C
F
OUT
ACTUAL 80MHz AND +85°C
Figure 74. Temperature Drift of f−3 dB for fADC = 80 MSPS and RxPGA = 0 dB
ANALOG-TO-DIGITAL CONVERTER (ADC)
The AD9865 features a 10-bit analog-to-digital converter
(ADC) capable of up to 80 MSPS. Referring to Figure 68, the
ADC is driven by the SPGA stage, which performs both the
sample-and-hold and the fine gain adjust functions. A buffer
amplifier (not shown) isolates the last CPGA gain stage from
the dynamic load presented by the SPGA stage. The full-scale
input span of the ADC is 2 V p-p, and depending on the PGA
gain setting, the full-scale input span into the SPGA is
adjustable from 1 V to 2 V in 1 dB increments.
A pipelined multistage ADC architecture is used to achieve high
sample rates while consuming low power. The ADC distributes
the conversion over several smaller A/D subblocks, refining the
conversion with progressively higher accuracy as it passes the
results from stage to stage on each clock edge. The ADC typi-
cally performs best when driven internally by a 50% duty cycle
clock. This is especially the case when operating the ADC at
high sample rate (55 MSPS to 80 MSPS) and/or lower internal
bias levels, which adversely affect interstage settling time
requirements.
The ADC sampling clock path also includes a duty cycle
restorer circuit, which ensures that the ADC gets a near 50%
duty cycle clock even when presented with a clock source with
poor symmetry (35/65). This circuit should be enabled if the
ADC sampling clock is a buffered version of the reference signal
appearing at OSCIN (see the Clock Synthesizer section), and if
this reference signal is derived from an oscillator or crystal
whose specified symmetry cannot be guaranteed to be within
45/55 (or 55/45). This circuit can remain disabled if the ADC
sampling clock is derived from a divided down version of the
clock synthesizer’s VCO, because this clock is near 50%.
The ADC’s power consumption can be reduced by 25 mA, with
minimal effect on its performance, by setting Bit 4 of Register
0x07. Alternative power bias settings are also available via
Register 0x13, as discussed in the Power Control and
Dissipation section. Lastly, the ADC can be completely powered
down for half-duplex operation, further reducing the AD9865’s
peak power consumption.
AD9865 Data Sheet
Rev. B | Page 36 of 48
04493-0-066
1.0V
TO
ADCs
REFT
REFB
C1
0.1µFC2
10µF
C3
0.1µF
C4
0.1µF
C1
C4
C2
C3
TOP
VIEW
Figure 75. ADC Reference and Decoupling
The ADC has an internal voltage reference and reference ampli-
fier as shown in Figure 75. The internal band gap reference
generates a stable 1 V reference level that is converted to a dif-
ferential 1 V reference centered about mid-supply (AVDD/2).
The outputs of the differential reference amplifier are available
at the REFT and REFB pins and must be properly decoupled for
optimum performance. The REFT and REFB pins are conven-
iently situated at the corners of the CSP package such that C1
(0603 type) can be placed directly across its pins. C3 and C4 can
be placed underneath C1, and C2 (10 µF tantalum) can be
placed furthest from the package.
Table 22. SPI Registers for Rx ADC
Address (Hex) Bit Description
0x04 (5) Duty cycle restore circuit
(4) ADC clock from PLL
0x07 (4) ADC low power mode
0x13 (2:0) ADC power bias adjust
AGC TIMING CONSIDERATIONS
When implementing a digital AGC timing loop, it is important
to consider the Rx path latency and settling time of the Rx path
in response to a change in gain setting. Figure 21 and Figure 24
show the RxPGA’s settling response to a 60 dB and 5 dB change
in gain setting when using the Tx[5:0] or PGA[5:0] port. While
the RxPGA settling time may also show a slight dependency on
the LPF ’s cut-off frequency, the ADC’s pipeline delay along with
the ADIO bus interface presents a more significant delay. The
amount of delay or latency is dependent on whether a half-or
full-duplex is selected. An impulse response at the RxPGA’s
input can be observed after 10.0 ADC clock cycles (1/fADC) in
the case of a half-duplex interface, and 10.5 ADC clock cycles in
the case of a full-duplex interface. This latency, along with the
RxPGA settling time, should be considered to ensure stability of
the AGC loop.
Data Sheet AD9865
Rev. B | Page 37 of 48
CLOCK SYNTHESIZER
The AD9865 generates all its internal sampling clocks, as well as
two user-programmable clock outputs appearing at CLKOUT1
and CLKOUT2, from a single reference source as shown in
Figure 76. The reference source can be either a fundamental
frequency or an overtone quartz crystal connected between
OSCIN and XTAL with the parallel resonant load components
as specified by the crystal manufacturer. It can also be a TTL-
level clock applied to OSCIN with XTAL left unconnected.
The data rate, fDATA, for the Tx and Rx data paths must always be
equal. Therefore, the ADC’s sample rate, fADC, is always equal to
fDATA while the TxDAC update rate is a factor of 1, 2, or 4 of
fDATA, depending on the interpolation factor selected. The data
rate refers to the word rate and should not be confused with the
nibble rate in full-duplex interface.
÷2N
XTAL
C1
÷
2
L
÷
2
R
2M CLK
MULTIPLIER
C2
XTAL
OSCIN
CLKOUT2
CLKOUT1
TOADC
TO TxDAC
04493-0-030
Figure 76. Clock Oscillator and Synthesizer
The 2M CLK multiplier contains a PLL (with integrated loop
filter) and VCO capable of generating an output frequency that
is a multiple of 1, 2, 4, or 8 of its input reference frequency,
fOSCIN, appearing at OSCIN. The input frequency range of fOSCIN
is between 20 MHz and 80 MHz, while the VCO can operate
over a 40 MHz to 200 MHz span. For the best phase noise/jitter
characteristics, it is advisable to operate the VCO with a fre-
quency between 100 MHz and 200 MHz. The VCO output
drives the TxDAC directly such that its update rate, fDAC, is
related to fOSCIN by the following equation:
fDAC = 2M × fOSCIN (10)
where M = 0, 1, 2, or 3.
M is the PLL’s multiplication factor set in Register 0x04. The
value of M is determined by the Tx path’s word rate, fDATA, and
digital interpolation factor, F, as shown in the following
equation:
M = log2 (F × fDATA/fOSCIN) (11)
Note: if the reference frequency appearing at OSCIN is chosen
to be equal to the AD9865’s Tx and Rx path’s word rate, then M
is simply equal to log2(F).
The clock source for the ADC can be selected in Register 0x04
as a buffered version of the reference frequency appearing at
OSCIN (default setting) or a divided version of the VCO output
(fDAC). The first option is the default setting and most desirable
if fOSCIN is equal to the ADC sample rate, fADC. This option
typically results in the best jitter/phase noise performance for
the ADC sampling clock. The second option is suitable in cases
where fOSCIN is a factor of 2 or 4 less than the fADC. In this case,
the divider ratio, N, is chosen such that the divided down VCO
output is equal to the ADC sample rate, as shown in the
following equation:
fADC = fDAC/2N (12)
where N = 0, 1, or 2.
Figure 77 shows the degradation in phase noise performance
imparted onto the ADC’s sampling clock for different VCO
output frequencies. In this case, a 25 MHz, 1 V p-p sine wave
was used to drive OSCIN, and the PLL’s M and N factors were
selected to provide an fADC of 50 MHz for VCO operating
frequencies of 50, 100, and 200 MHz. The RxPGA input was
driven with a near full-scale, 12.5 MHz input signal with a gain
setting of 0 dB. Operating the VCO at the highest possible
frequency results in the best narrow and wideband phase noise
characteristics. For comparison purposes, the clock source for
the ADC was taken directly from OSCIN when driven by a
50 MHz square wave.
04493-0-067
FREQUENCY (MHz)
dBFS
2.5 4.5 6.5 8.5 10.5 12.5 14.5 16.5 18.5 20.5 22.5
0
–110
–100
–90
–80
–70
–60
–50
–40
–30
–20
–10 DIRECT
VCO = 50MHz
VCO = 100MHz
VCO = 200MHz
Figure 77. Comparison of Phase Noise Performance when ADC Clock Source
is Derived from Different VCO Output Frequencies
The CLK synthesizer also has two clock outputs appearing at
CLKOUT1 and CLKOUT2. They are programmable via
Register 0x06. Both outputs can be inverted or disabled. The
voltage levels appearing at these outputs are relative to DRVDD
and remain active during a hardware or software reset. Table 23
shows the SPI registers pertaining to the clock synthesizer.
CLKOUT1 is a divided version of the VCO output and can be
set to be a submultiple integer of fDAC (fDAC/2R, where R = 0, 1, 2,
or 3). Because this clock is actually derived from the same set of
dividers used within the PLL core, it is phase-locked to them
such that its phase relationship relative to the signal appearing
at OSCIN (or RXCLK) can be determined upon power up. Also,
this clock has near 50% duty cycle, because it is derived from
the VCO. As a result, CLKOUT1 should be selected before
CLKOUT2 as the primary source for system clock distribution.
AD9865 Data Sheet
Rev. B | Page 38 of 48
CLKOUT2 is a divided version of the reference frequency, fOSCIN,
and can be set to be a submultiple integer of fOSCIN (fOSCIN/2L,
where L = 0, 1, or 2). With L set to 0, the output of CLKOUT2 is
a delayed version of the signal appearing at OSCIN, exhibiting
the same duty cycle characteristics. With L set to 1 or 2, the
output of CLKOUT2 is a divided version of the OSCIN signal,
exhibiting a near 50% duty cycle, but without having a determi-
nistic phase relationship relative to CLKOUT1 (or RXCLK).
Table 23. SPI Registers for CLK Synthesizer
Address (Hex) Bit Description
0x04 (4) ADC CLK from PLL
(3:2) PLL divide factor (P)
(1:0) PLL multiplication factor (M)
0x06 (7:6) CLKOUT2 divide number
(5) CLKOUT2 invert
(4)
CLKOUT2 disable
(3:2) CLKOUT1 divide number
(1) CLKOUT1 invert
(0) CLKOUT1 disable
Data Sheet AD9865
Rev. B | Page 39 of 48
POWER CONTROL AND DISSIPATION
POWER-DOWN
The AD9865 provides the ability to control the power-on state
of various functional blocks. The state of the PWRDWN pin
along with the contents of Register 0x01 and Register 0x02
allow two user-defined power settings that are pin selectable.
The default settings1 are such that Register 0x01 has all blocks
powered on (all bits 0), while Register 0x02 has all blocks
powered down excluding the PLL such that the clock signal
remains available at CLKOUT1 and CLKOUT2. When the
PWRDWN pin is low, the functional blocks corresponding to
the bits in Register 0x01 are powered down. When the
PWRDWN is high, the functional blocks corresponding to the
bits in Register 0x02 are powered down. PWRDWN
immediately affects the designated functional blocks with
minimum digital delay.
Table 24. SPI Registers Associated with Power-Down and
Half-Duplex Power Savings
Address (Hex)
Bit
Description
Comments
0x01
(7) PLL
PWRDWN = 0.
Default setting is all
functional blocks
powered on.
(6) TxDAC/IAMP
(5) TX Digital
(4) REF
(3) ADC CML
(2) ADC
(1) PGA BIAS
(0) RxPGA
0x02
(7) PLL
PWRDWN = 1.
Default setting is all
functional blocks
powered off
excluding PLL.
(6) TxDAC/IAMP
(5) TX Digital
(4) REF
(3) ADC CML
(2) ADC
(1) PGA BIAS
(0) RxPGA
0x03
(7:3)
Tx OFF Delay
Half-duplex power
savings.
(2) Rx PWRDWN
via TXEN
(1) Enable Tx
PWRDWN
(0) Enable Rx
PWRDWN
1 With MODE = 1 and CONFIG =1, Reg. 0x02 default settings are with all blocks
powered off, with RXCLK providing a buffered version of the signal
appearing at OSCIN. This setting results in the lowest power consumption
upon power-up, while still allowing AD9865 to generate the system clock via
a crystal.
HALF-DUPLEX POWER SAVINGS
Significant power savings can be realized in applications having
a half-duplex protocol allowing only the Rx or Tx path to be
operational at any instance. The power savings method depends
on whether the AD9865 is configured for a full- or half-duplex
interface. Functional blocks having fast power on/off times for
the Tx and Rx path are controlled by the following bits:
TxDAC/IAMP, TX Digital, ADC, and RxPGA.
In the case of a full-duplex digital interface (MODE = 1), one
can set Register 0x01 to 0x60 and Register 0x02 to Register 0x05
(or vice versa) such that the AD9865’s Tx and Rx path are never
powered on simultaneously. The PWRDWN pin can then be
used to control which path is powered on, depending on the
burst type. During a Tx burst, the Rx path’s PGA and ADC
blocks can typically be powered down within 100 ns, while the
Tx paths DAC, IAMP, and digital filter blocks are powered up
within 0.5 µs. For an Rx burst, the Tx path’s can be powered
down within 100 ns, while the Rx circuitry is powered up
within 2 µs.
Setting the TXQUIET pin low allows it to be used with the full-
duplex interface to quickly power down the IAMP and disable
the interpolation filter. This is meant to maintain backward
compatibility with the AD9875/AD9876 MxFEs with the excep-
tion that the TxDAC remains powered, if its IOUTP outputs are
used. In most applications, the interpolation filter needs to be
flushed with 0s before or after being powered down. This
ensures that upon power-up, the TxDAC (and IAMP) have a
negligible differential dc offset, thus preventing spectral splatter
due to an impulse transient.
Applications using a half-duplex interface (MODE = 0) can
benefit from an additional power savings feature made available
in Register 0x03. This register is effective only for a half-duplex
interface. Besides providing power savings for half-duplex
applications, this feature allows the AD9865 to be used in
applications that need only its Rx (or Tx) path functionality
through pin-strapping, making a serial port interface (SPI)
optional. This feature also allows the PWRDWN pin to retain
its default function as a master power control, as defined in
Table 11.
The default settings for Register 0x03 provide fast power control
of the functional blocks in the Tx and Rx signal paths (outlined
above) using the TXEN pin. The TxDAC still remains powered
on in this mode, while the IAMP is powered down. Significant
current savings are typically realized when the IAMP is
powered down.
For a Tx burst, the falling edge of TXEN is used to generate an
internal delayed signal for powering down the Tx circuitry.
Upon receipt of this signal, power-down of the Tx circuitry
occurs within 100 ns. The user-programmable delay for the Tx
path power-down is meant to match the pipeline delay of the
AD9865 Data Sheet
Rev. B | Page 40 of 48
last Tx burst sample such that power-down of the TxDAC and
IAMP does not impact its transmission. A 5-bit field in Register 0x03
sets the delay from 0 to 31 TXCLK clock cycles, with the default
being 31 (0.62 μs with fTXCLK = 50 MSPS). The digital interpolation
filter is automatically flushed with midscale samples prior to
power-down, if the clock signal into the TXCLK pin is present
for 33 additional clock cycles after TXEN returns low. For an Rx
burst, the rising edge of TXEN is used to generate an internal
signal (with no delay) that powers up the Tx circuitry within 0.5 μs.
The Rx path power-on/power-off can be controlled by either
TXEN or RXEN by setting Bit 2 of Register 0x03. In the default
setting, the falling edge of TXEN powers up the Rx circuitry
within 2 μs, while the rising edge of TXEN powers down the Rx
circuitry within 0.5 μs. If RXEN is selected as the control signal,
then its rising edge powers up the Rx circuitry and the falling
edge powers it down. To disable the fast power-down of the Tx
and/or Rx circuitry, set Bit 1 and/or Bit 0 to 0.
POWER REDUCTION OPTIONS
The power consumption of the AD9865 can be significantly
reduced from its default setting by optimizing the power
consumption versus performance of the various functional
blocks in the Tx and Rx signal path. On the Tx path, minimum
power consumption is realized when the TxDAC output is used
directly and its standing current, I, is reduced to as low as 1 mA.
Although a slight degradation in THD performance results at
reduced standing currents, it often remains adequate for most
applications, because the op amp driver typically limits the
overall linearity performance of the Tx path. The load resistors
used at the TxDAC outputs (IOUTP+ and IOUTP−) can be
increased to generate an adequate differential voltage that can
be further amplified via a power efficient op-amp-based driver
solution. Figure 78 shows how the supply current for the
TxDAC (Pin 43) is reduced from 55 mA to 14 mA as the
standing current is reduced from 12.5mA to 1.25 mA. Further
Tx power savings can be achieved by bypassing or reducing the
interpolation factor of the digital filter as shown in Figure 79.
04493-0-068
ISTANDING (mA)
IAVDDTxDAC (mA)
012345678910111213
55
10
15
20
25
30
35
40
45
50
Figure 78. Reduction in TxDAC’s Supply Current vs. Standing Current
04493-0-069
INPUT DATA RATE (MSPS)
I
DVDD
(mA)
20 30 40 50 60 70 80
55
60
65
15
20
25
30
35
40
45
50
2
INTERPOLATION
4
INTERPOLATION
1
(HALF-DUPLEX ONLY)
Figure 79. Digital Supply Current Consumption vs. Input Data Rate
(DVDD = DRVDD =3.3 V and fOUT = fDATA/10)
Power consumption on the Rx path can be achieved by reduc-
ing the bias levels of the various amplifiers contained within the
RxPGA and ADC. As previously noted, the RxPGA consists of
two CPGA amplifiers and one SPGA amplifier. The bias levels
of each of these amplifiers along with the ADC can be con-
trolled via Register 0x13, as shown in Table 25. The default
setting for 0x13 is 0x00.
Table 25. SPI Register for RxPGA and ADC Biasing
Address (Hex) Bit Description
0x07 (4) ADC low power
0x13 (7:5) CPGA bias adjust
(4:3) SPGA bias adjust
(2:0) ADC power bias adjust
Data Sheet AD9865
Rev. B | Page 41 of 48
Because the CPGA processes signals in the continuous time
domain, its performance vs. bias setting remains mostly
independent of the sample rate. Table 26 shows how the typical
current consumption seen at AVDD (Pins 35 and 40) varies as a
function of Bits (7:5), while the remaining bits are maintained at
their default settings of 0. Only four of the possible settings
result in any reduction in current consumption relative to the
default setting. Reducing the bias level typically results in a
degradation in the THD vs. frequency performance as shown in
Figure 80. This is due to a reduction of the amplifier’s unity gain
bandwidth, while the SNR performance remains relatively
unaffected.
Table 26. Analog Supply Current vs. CPGA Bias Settings at
fADC = 65 MSPS
Bit 7 Bit 6 Bit 5 ∆mA
0 0 0 0
0 0 1 −27
0 1 0 −42
0 1 1 −51
1 0 0 −55
1 0 1 27
1 1 0 69
1 1 1 27
04493-0-091
CPGA BIAS SETTING-BITS (7:5)
SNR (dBFS)
THD (dBc)
000 100010 011001
65.0
40.0
–20
–70
–65
–60
–55
–50
–45
–40
–35
–30
–25
42.5
45.0
47.5
50.0
52.5
55.0
57.5
60.0
62.5 SNR_RxPGA = 0dB
SNR_RxPGA = 36dB
THD_RxPGA = 0dB
THD_RxPGA = 36dB
Figure 80. THD vs. fIN Performance and RxPGA Bias Settings
(000,001,010,100 with RxPGA = 0 and +36 dB and AIN = −1 dBFS,
LPF set to 26 MHz, and fADC = 50 MSPS)
The SPGA is implemented as a switched capacitor amplifier;
therefore, its performance vs. bias level is mostly dependent on
the sample rate. Figure 81 shows how the typical current
consumption seen at AVDD (Pin 35 and Pin 40) varies as a
function of Bits (4:3) and sample rate, while the remaining bits
are maintained at the default setting of 0. Figure 82 shows how
the SNR and THD performance is affected for a 10 MHz sine
wave input as the ADC sample rate is swept from 20 MHz to 80
MHz. The SNR and THD performance remains relatively stable,
suggesting that the SPGA bias can often be reduced from its de-
fault setting without impacting the device’s overall performance.
04493-0-070
ADC SAMPLE RATE (MSPS)
I
AVDD
(mA)
20 30 40 50 60 70 80
210
170
175
180
185
190
195
200
205
01
00
10
11
Figure 81. AVDD Current vs. SPGA Bias Setting and Sample Rate
04493-0-092
SAMPLE RATE (MSPS)
SNR (dBc)
THD (dBc)
20 8060 7030 40 50
61
51
–54
–74
–72
–70
–68
–66
–64
–62
–60
–58
–56
52
53
54
55
56
57
58
59
60
SNR-00
SNR-01
SNR-10
SNR-11
THD-00
THD-01
THD-10
THD-11
Figure 82. SNR and THD Performance vs. fADC and SPGA Bias Setting with
RxPGA = 0 dB, fIN = 10 MHz, LPF set to 26 MHz, and AIN = −1 dBFS
The ADC is based on a pipeline architecture with each stage
consisting of a switched capacitor amplifier. Therefore, its per-
formance vs. bias level is mostly dependent on the sample rate.
Figure 83 shows how the typical current consumption seen at
AVDD (Pins 35 and 40) varies as a function of Bits (2:0) and
sample rate, while the remaining bits are maintained at the
default setting of 0. Setting Bit 4 or Register 0x07 corresponds
to the 011 setting, and the settings of 101 and 111 result in
higher current consumption. Figure 84 shows how the SNR and
THD performance are affected for a 10 MHz sine wave input
for the lower power settings as the ADC sample rate is swept
from 20 MHz to 80 MHz.
AD9865 Data Sheet
Rev. B | Page 42 of 48
04493-0-071
SAMPLE RATE (MSPS)
I
AVDD
(mA)
20 30 40 50 60 70 80
220
120
130
140
150
160
170
180
190
200
210
000
001
010
011
100 101
101 OR 111
Figure 83. AVDD Current vs. ADC Bias Setting and Sample Rate
04493-0-092
SAMPLE RATE (MSPS)
SNR (dBc)
THD (dBc)
20 8060 7030 40 50
61
51
–54
–74
–72
–70
–68
–66
–64
–62
–60
–58
–56
52
53
54
55
56
57
58
59
60
THD-000
THD-001
THD-010
THD-011
THD-100
THD-101
SNR-000
SNR-001
SNR-010
SNR-011
SNR-100
SNR-101
Figure 84. SNR and THD Performance vs. fADC and ADC Bias Setting with
RxPGA = 0 dB, fIN = 10 MHz, and AIN = −1 dBFS
A sine wave input is a standard and convenient method of
analyzing the performance of a system. However, the amount of
power reduction that is possible is application dependent, based
on the nature of the input waveform (such as frequency content,
peak-to-rms ratio), the minimum ADC sample, and the mini-
mum acceptable level of performance. Thus, it is advisable that
power-sensitive applications optimize the power bias setting of
the Rx path using an input waveform that is representative of
the application.
POWER DISSIPATION
The power dissipation of the AD9865 can become quite high in
full-duplex applications in which the Tx and Rx paths are si-
multaneously operating with nominal power bias settings. In
fact, some applications that use the IAMP may need to either
reduce its peak power capabilities or reduce the power con-
sumption of the Rx path, so that the device’s maximum
allowable power consumption, PMAX, is not exceeded.
PMAX is specified at 1.66 W to ensure that the die temperature
does not exceed 125oC at an ambient temperature of 85oC. This
specification is based on the 64-pin LFSCP having a thermal
resistance, θJA, of 24oC/W with its heat slug soldered. (The θJA is
30.8oC/W, if the heat slug remains unsoldered.) If a particular
application’s maximum ambient temperature, TA, falls below
85oC, the maximum allowable power dissipation can be deter-
mined by the following equation:
PMAX = 1.66 + (85 − TA)/24 (13)
Assuming the IAMP’s common-mode bias voltage is operating
off the same analog supply as the AD9865, the following equa-
tion can be used to calculate the maximum total current
consumption, IMAX, of the IC:
IMAX = (PMAX − PIAMP)/3.47 (14)
With an ambient temperature of up to 85°C, IMAX is 478 mA.
If the IAMP is operating off a different supply or in the voltage
mode configuration, first calculate the power dissipated in the
IA M P, P IAMP, using Equation 2 or Equation 5, and then
recalculate IMAX, using Equation 14.
Figure 78, Figure 79, Figure 81, and Figure 83 can be used to
calculate the current consumption of the Rx and Tx paths for a
given setting.
MODE SELECT UPON POWER-UP AND RESET
The AD9865 power-up state is determined by the logic levels
appearing at the MODE and CONFIG pins. The MODE pin is
used to select a half- or full-duplex interface by pin strapping it
low or high, respectively. The CONFIG pin is used in conjunc-
tion with the MODE pin to determine the default settings for
the SPI registers as outlined in Table 11.
The intent of these particular default settings is to allow some
applications to avoid using the SPI (disabled by pin-strapping
SEN high), thereby reducing implementation costs. For
example, setting MODE low and CONFIG high configures the
AD9865 to be backward compatible with the AD9975, while
setting MODE high and CONFIG low makes it backward
compatible with the AD9875. Other applications must use the
SPI to configure the device.
A hardware (RESET pin) or software (Bit 5 of Register 0x00)
reset can be used to place the AD9865 into a known state of
operation as determined by the state of the MODE and
CONFIG pins. A dc offset calibration and filter tuning routine
is also initiated upon a hardware reset, but not with a software
reset. Neither reset method flushes the digital interpolation
filters in the Tx path. Refer to the Half-Duplex Mode and Full-
Duplex Mode sections for information on flushing the digital
filters.
A hardware reset can be triggered by pulsing the RESET pin low
for a minimum of 50 ns. The SPI registers are instantly reset to
their default settings upon RESET going low, while the dc offset
calibration and filter tuning routine is initiated upon RESET
returning high. To ensure sufficient power-on time of the
various functional blocks, RESET returning high should occur
no less than 10 ms upon power-up. If a digital reset signal from
a microprocessor reset circuit (such as ADM1818) is not
Data Sheet AD9865
Rev. B | Page 43 of 48
available, a simple R-C network referenced to DVDD can be
used to hold RESET low for approximately 10 ms upon power-
up.
ANALOG AND DIGITAL LOOP-BACK TEST MODES
The AD9865 features analog and digital loop-back capabilities
that can assist in system debug and final test. Analog loop-back
routes the digital output of the ADC back into the Tx data path
prior to the interpolation filters such that the Rx input signal
can be monitored at the output of the TxDAC or IAMP. As a
result, the analog loop-back feature can be used for a half- or
full-duplex interface, to allow testing of the functionality of the
entire IC (excluding the digital data interface).
For example, the user can configure the AD9865 with similar
settings as the target system, inject an input signal (sinusoidal
waveform) into the Rx input, and monitor the quality of the
reconstructed output from the TxDAC or IAMP to ensure a
minimum level of performance. In this test, the user can
exercise the RxPGA as well as validate the attenuation char-
acteristics of the RxLPF. Note that the RxPGA gain setting
should be selected such that the input does not result in clipping
of the ADC.
Digital loop-back can be used to test the full-duplex digital
interface of the AD9865. In this test, data appearing on the
Tx[5:0] port is routed back to the Rx[5:0] port, thereby
confirming proper bus operation. The Rx port can also be
three-stated for half- and full-duplex interfaces.
Table 27. SPI Registers for Test Modes
Address (Hex) Bit Description
0x0D
(7)
Analog loop-back
(6) Digital loop-back
(5) Rx port three-state
AD9865 Data Sheet
Rev. B | Page 44 of 48
PCB DESIGN CONSIDERATIONS
Although the AD9865 is a mixed-signal device, the part should
be treated as an analog component. The on-chip digital circuitry
has been specially designed to minimize the impact of its digital
switching noise on the MxFE’s analog performance.
To achieve the best performance, the power, grounding, and
layout recommendations in this section should be followed.
Assembly instructions for the micro-lead frame package can be
found in an application note from Amkor at:
http://www.amkor.com/products/notes_papers/MLF_AppNote
_0902.pdf.
COMPONENT PLACEMENT
If the three following guidelines of component placement are
followed, chances for getting the best performance from the
MxFE are greatly increased. First, manage the path of return
currents flowing in the ground plane so that high frequency
switching currents from the digital circuits do not flow on the
ground plane under the MxFE or analog circuits. Second, keep
noisy digital signal paths and sensitive receive signal paths as
short as possible. Third, keep digital (noise generating) and
analog (noise susceptible) circuits as far away from each other
as possible.
To best manage the return currents, pure digital circuits that
generate high switching currents should be closest to the power
supply entry. This keeps the highest frequency return current
paths short and prevents them from traveling over the sensitive
MxFE and analog portions of the ground plane. Also, these
circuits should be generously bypassed at each device, which
further reduces the high frequency ground currents. The MxFE
should be placed adjacent to the digital circuits, such that the
ground return currents from the digital sections do not flow in
the ground plane under the MxFE.
The AD9865 has several pins that are used to decouple sensitive
internal nodes. These pins are REFIO, REFB, and REFT. The
decoupling capacitors connected to these points should have
low ESR and ESL. These capacitors should be placed as close to
the MxFE as possible (see Figure 75) and be connected directly
to the analog ground plane. The resistor connected to the
REFADJ pin should also be placed close to the device and
connected directly to the analog ground plane.
POWER PLANES AND DECOUPLING
While the AD9865 evaluation board demonstrates a very good
power supply distribution and decoupling strategy, it can be
further simplified for many applications. The board has four
layers: two signal layers, one ground plane, and one power
plane. While the power plane on the evaluation board is split
into multiple analog and digital subsections, a permissible
alternative would be to have AVDD and CLKVDD share the
same analog 3.3 V power plane. A separate analog plane/supply
may be allocated to the IAMP, if its supply voltage differs from
the 3.3 V required by AVDD and CLKVDD. On the digital side,
DVDD and DRVDD can share the same 3.3 V digital power
plane. This digital power plane brings the current used to power
the digital portion of the MxFE and its output drivers. This
digital plane should be kept from going underneath the analog
components.
The analog and digital power planes allocated to the MxFE may
be fed from the same low noise voltage source; however, they
should be decoupled from each other to prevent the noise
generated in the digital portion of the MxFE from corrupting
the AVDD supply. This can be done by using ferrite beads be-
tween the voltage source and the respective analog and digital
power planes with a low ESR, bulk decoupling capacitor on the
MxFE side of the ferrite. Each of the MxFE’s supply pins
(AVDD, CLKVDD, DVDD, and DRVDD) should also have
dedicated low ESR, ESL decoupling capacitors. The decoupling
capacitors should be placed as close to the MxFE supply pins as
possible.
GROUND PLANES
The AD9865 evaluation board uses a single serrated ground
plane to help prevent any high frequency digital ground
currents from coupling over to the analog portion of the ground
plane. The digital currents affiliated with the high speed data
bus interface (Pin 1 to Pin 16) have the highest potential of
generating problematic high frequency noise. A ground
serration that contains these currents should reduce the effects
of this potential noise source.
The ground plane directly underneath the MxFE should be
continuous and uniform. The 64-lead LFCSP package is
designed to provide excellent thermal conductivity. This is
partly achieved by incorporating an exposed die paddle on the
bottom surface of the package. However, to take full advantage
of this feature, the PCB must have features to effectively
conduct heat away from the package. This can be achieved by
incorporating thermal pad and thermal vias on the PCB. While
a thermal pad provides a solderable surface on the top surface
of the PCB (to solder the package die paddle on the board),
thermal vias are needed to provide a thermal path to inner
and/or bottom layers of the PCB to remove the heat.
Lastly, all ground connections should be made as short as
possible. This results in the lowest impedance return paths and
the quietest ground connections.
SIGNAL ROUTING
The digital Rx and Tx signal paths should be kept as short as
possible. Also, the impedance of these traces should have a
controlled characteristic impedance of about 50 Ω. This
prevents poor signal integrity and the high currents that can
occur during undershoot or overshoot caused by ringing. If the
signal traces cannot be kept shorter than about 1.5 inches, series
termination resistors (33 Ω to 47 Ω) should be placed close to
all digital signal sources. It is a good idea to series-terminate all
Data Sheet AD9865
Rev. B | Page 45 of 48
clock signals at their source, regardless of trace length.
The receive RX+ and RX− signals are the most sensitive signals
on the entire board. Careful routing of these signals is essential
for good receive path performance. The RX+ and RX− signals
form a differential pair and should be routed together as a pair.
By keeping the traces adjacent to each other, noise coupled onto
the signals appears as common mode and is largely rejected by
the MxFE receive input. Keeping the driving point impedance
of the receive signal low and placing any low-pass filtering of
the signals close to the MxFE further reduces the possibility of
noise corrupting these signals.
AD9865 Data Sheet
Rev. B | Page 46 of 48
EVALUATION BOARD
An evaluation board is available for the AD9865 and AD9866.
The digital interface to the evaluation board can be configured
for a half- or full-duplex interface. Two 40-pin and one 26-pin
male right angle headers (0.100 inches) provide easy interfacing
to test equipment such as digital data capture boards, pattern
generators, or custom digital evaluation boards (FPGA, DSP, or
ASIC). The reference clock source can originate from an exter-
nal generator, crystal oscillator, or crystal. Software and an
interface cable are included to allow for programming of the SPI
registers via a PC.
The analog interface on the evaluation board provides a full
analog front-end reference design for power line applications. It
includes a power line socket, line transformer, protection diodes,
and passive filtering components. An auxiliary path allows
independent monitoring of the ac power line. The evaluation
board allows complete optimization of power line reference
designs based around the AD9865 or AD9866.
Alternatively, the evaluation board allows independent evalua-
tion of the TxDAC, IAMP, and Rx paths via SMA connectors.
The IAMP can be easily configured for a voltage or current
mode interface via jumper settings. The TxDAC’s performance
can be evaluated directly or via an optional dual op amp driver
stage. The Rx path includes a transformer and termination
resistor allowing a calibrated differential input signal to be
injected into its front end.
The Analog Devices, Inc. website offers more information on
the AD9865/AD9866 evaluation board.
Data Sheet AD9865
Rev. B | Page 47 of 48
OUTLINE DIMENSIONS
COMP LI ANT T O JEDE C S TANDARDS M O-220- V M M D- 4
0.25 MIN
1
64
16
17
49
48
32
33
0.50
0.40
0.30
0.50
BSC
0.20 REF
12° M AX 0.80 MAX
0.65 NO M
1.00
0.85
0.80
7.50 REF
0.05 MAX
0.02 NO M
SEATING
PLANE
PIN 1
INDICATOR
7.25
7.10 SQ
6.95
PIN 1
INDICATOR
0.30
0.23
0.18
FO R P ROPE R CONNECTI ON O F
THE EXPOSED PAD, REFER TO
THE P IN CO NFI GURAT IO N AND
FUNCT IO N DE S CRIPTI ONS
SECTION OF THIS DATA SHEET.
TOP VIEW
EXPOSED
PAD
BOTTOM VIEW
9.10
9.00 SQ
8.90
8.85
8.75 SQ
8.65
01-22-2015-D
0.60
0.42
0.24
0.60
0.42
0.24
PKG-001152
Figure 85. 64-Lead Lead Frame Chip Scale Package (LFCSP)
9 mm × 9 mm and 0.85 mm Package Height
[CP-64-3]
Dimensions shown in millimeters
ORDERING GUIDE
Model1 Temperature Range Package Description Package Option
AD9865BCPZ
−40°C to +85°C
64-Lead LFCSP
CP-64-3
AD9865BCPZRL −40°C to +85°C 64-Lead LFCSP CP-64-3
1 Z = RoHS Compliant Part
