High Performance ISM Band
OOK/FSK Transmitter IC
ADF7901
Rev. A
Information furnished by Analog Devices is believed to be accurate and reliable.
However, no responsibility is assumed by Analog Devices for its use, nor for any
infringements of patents or other rights of third parties that may result from its use.
Specifications subject to change without notice. No license is granted by implication
or otherwise under any patent or patent rights of Analog Devices. Trademarks and
registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700 www.analog.com
Fax: 781.461.3113 ©2006 Analog Devices, Inc. All rights reserved.
FEATURES
Single-chip, low power UHF transmitter
369.5 MHz to 395.9 MHz frequency operation using
fractional-N PLL and fully integrated VCO
3.0 V supply voltage
Data rates up to 50 kbps supported
Low current consumption
26 mA at 12 dBm output at 384 MHz
Power-down mode (<1 μA)
24-lead TSSOP
GENERAL DESCRIPTION
The ADF7901 is a low power OOK/FSK UHF transmitter
designed for use in RF remote control devices. It is capable of
frequency shift keying (FSK) modulation on eight different
channels, selectable by three external control lines. OOK
modulation is performed by modulating the PA control line.
The on-chip VCO operates at 2× the output frequency. The
division by 2 at the output of the VCO reduces the amount of
PA feedthrough. As a result, OOK modulation depths of greater
than 50 dB are easily achievable.
The FSK_ADJ and ASK_ADJ resistors can be adjusted in the
system to optimize output power for each modulation scheme.
An additional 1.5 dB of output power is provided for the lower
bank of channels to adjust for antenna performance. The CE
line allows the transmitter to be powered down completely.
In this mode, the leakage current is typically 0.1 μA.
FUNCTIONAL BLOCK DIAGRAM
R = 1
FSK
DV
DD
T
X
DATA
CE D
GND
FSK1 OOK_SEL
RF
OUT
RF
GND
V
DD
R
SET
OSC2 C
VCO
C
REG2
PA_EN
RSET_FSK RSET_OOK
OSC1
PA
C
REG2
C
REG1
LDO
REGULATOR
1
LDO
REGULATOR
2
PDF
CHARGE
PUMP
⎟ FRACTIONAL N
Σ-Δ
FSK2 FSK3
CHANNEL SELECT
VCO
05349-001
Figure 1.
ADF7901
Rev. A | Page 2 of 12
TABLE OF CONTENTS
Features .............................................................................................. 1
General Description ......................................................................... 1
Functional Block Diagram .............................................................. 1
Specifications..................................................................................... 3
Absolute Maximum Ratings............................................................ 5
ESD Caution.................................................................................. 5
Pin Configuration and Function Descriptions............................. 6
Typical Performance Characteristics ............................................. 8
Circuit Description........................................................................... 9
Loop Filter ..................................................................................... 9
Channel Frequencies.....................................................................9
Layout Guidelines....................................................................... 10
Decoupling.............................................................................. 10
Regulator Stability.................................................................. 10
Grounding............................................................................... 10
Supply ...................................................................................... 10
Digital Lines............................................................................ 10
Outline Dimensions ....................................................................... 11
Ordering Guide .......................................................................... 11
REVISION HISTORY
3/06—Rev. 0 to Rev. A
Added Crystal ESR Parameter........................................................ 4
Change to Figure 8 ......................................................................... 10
Updated Outline Dimensions....................................................... 11
Changes to Ordering Guide .......................................................... 11
3/05—Revision 0: Initial Version
ADF7901
Rev. A| Page 3 of 12
SPECIFICATIONS
VDD =3.0 V; GND = 0 V; TA = TMIN to TMAX, unless otherwise noted. Typical specifications, TA = 25°C.1
Table 1.
Parameter Min Typ Max Unit Comments/Conditions
RF CHARACTERISTICS
Output Frequency Ranges
Channel 1 369.5 MHz
Channel 2 371.1 MHz
Channel 3 375.3 MHz
Channel 4 376.9 MHz
Channel 5 384.0 MHz
Channel 6 388.3 MHz
Channel 7 391.5 MHz
Channel 8 394.3 MHz
Channel 9 395.9 MHz
Phase Frequency Detector Frequency 9.8304 MHz
TRANSMISSION PARAMETERS
Transmit Rate
FSK 50 kbps
OOK 50 kbps
Frequency Shift Keying
FSK Separation2 −34.8 kHz Data = 1
+34.8 kHz Data = 0
On/Off Keying
Modulation Depth3 83 dB Output power = 12 dBm
Output Power
Min/Max Range4 15 dBm
fOUT ≤ 384 MHz 10 12 dBm
fOUT > 384 MHz 7 10.5 dBm
Occupied 20 dB BW
OOK at 1 kbps ±28 ±461.9 kHz
FSK (PA Off/On) at10 Hz5 ±26 ±461.9 kHz
LOGIC INPUTS
VINH, Input High Voltage 2.124 V
VINL, Input Low Voltage 0.2 × VDD V
IINH/IINL, Input Current ±1 μA
CIN, Input Capacitance 10 pF
POWER SUPPLIES
Voltage Supply
DVDD 3.0 V
Transmit Current Consumption
369.5 MHz to 376.9 MHz at 12 dBm 26 mA
384 MHz at +12 dBm 26 mA
388.3 MHz to 395.9 MHz at 10.5 dBm 21 mA
384 MHz at 5 dBm 17 mA
Power-Down Mode
Low Power Sleep Mode6 0.2 1 μA
ADF7901
Rev. A | Page 4 of 12
Parameter Min Typ Max Unit Comments/Conditions
PHASE-LOCKED LOOP
VCO Gain 30 MHz/V At 384 MHz
Spurious3, 7 100 kHz loop BW
Integer Boundary –45 −23 dBc
Reference −70 −23 dBc
Harmonics3
Second Harmonic VDD = 3.0 V −24 −21 dBc
Third Harmonic VDD = 3.0 V −14 −11 dBc
All Other Harmonics −18 dBc
REFERENCE INPUT
Crystal Reference 9.8304 MHz
Crystal ESR8 80 Ω
POWER AMPLIFIER
PA Output Impedance 97 Ω + 6.4 pF At 384 MHz
TIMING INFORMATION
Crystal Oscillator to PLL Lock3 2 3 ms
PA Enable to PA Ready–PLL Settle9 100 250 μs
TEMPERATURE RANGE (TA) 0 50 °C
1 Operating temperature range is 0°C to 50°C.
2 Frequency Deviation = 58 × (9.8304 MHz)/214. Error in the crystal is reflected in variation in the desired deviation.
3 Not production tested; based on characterization.
4 The output power can be varied in both ASK/FSK mode by altering the relevant external resistor.
5 Measured using spectrum analyzer, 1 MHz span, 100 kHz RBW, maximum hold enabled.
6 Maximum power-down current specification applies for the OSC2 pin grounded.
7 Measured >461.9 kHz away from channel.
8 Maximum recommended crystal ESR. The crystal oscillator works with crystals with higher ESR, but this results in longer power-up times.
9 This specification refers to the time taken for the PLL to regain lock after the PA has been enabled. The PA is should only be enabled after the PLL has settled to the
correct frequency.
ADF7901
Rev. A| Page 5 of 12
ABSOLUTE MAXIMUM RATINGS
TA = 25°C, unless otherwise noted.1
Table 2.
Parameter Value
VDD to GND2 −0.3 V to +4.0 V
RFVDD to GND −0.3 V to +4.0 V
Digital I/O Voltage to GND −0.3 V to VDD + 0.3 V
Operating Temperature Range
Industrial (B Version) 0°C to 50°C
Storage Temperature Range −65°C to +125°C
Maximum Junction Temperature 125°C
TSSOP θJA Thermal Impedance 150.4°C/W
Lead Temperature, Soldering
Vapor Phase (60 sec) 235°C
Infrared (15 sec) 240°C
1 This device is a high performance, RF-integrated circuit with an ESD rating
of <1 kV. It is ESD sensitive. Take proper precautions for handling and
assembly.
2 GND = RFGND = DGND = 0 V.
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those listed in the operational sections
of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
ESD CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the
human body and test equipment and can discharge without detection. Although this product features
proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy
electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance
degradation or loss of functionality.
ADF7901
Rev. A | Page 6 of 12
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
TOPVIEW
(Not to Scale)
24
23
22
21
20
19
18
17
16
15
14
13
1
2
3
4
5
6
7
8
9
10
11
12
ADF7901
D
GND
NC
TxDATA
FSK3
R
SET
CP
OUT
FSK1
CE
OOK
_
SEL
OSC2
OSC1
RSET_OOK
C
REG1
C
VCO
VCO
IN
DV
DD
RF
GND
RF
OUT
FSK2
DV
DD
PA_EN
C
REG2
D
GND
RSET_FSK
05349-002
Figure 2. Pin Configuration
Table 3. Pin Function Descriptions
Pin No. Mnemonic Function
1 DVDD Positive Supply for the Digital Circuitry. This must be 3.0 V. Decoupling capacitors to the analog ground plane
should be placed as close as possible to this pin.
2 CREG1 A 2.2 μF capacitor should be added at CREG1 to reduce regulator noise and improve stability. A reduced capacitor
improves regulator power-on time but can cause higher spurious.
3 CPOUT Charge Pump Output. This output generates current pulses that are integrated in the loop filter. The integrated
current changes the control voltage on the input to the VCO.
4 TxDATA Digital FSK data to be transmitted is inputted on this pin.
5 DGND Ground for Digital Section.
6 NC No Connect.
7 DGND Ground for Digital Section.
8 OSC1 The reference crystal should be connected between this pin and the OSC2 pin. The necessary crystal load
capacitor should be tied between this pin and ground.
9 OSC2 The reference crystal should be connected between this pin and the OSC1 pin. The necessary crystal load
capacitor should be tied between this pin and ground.
A TCXO or external square wave can also be connected to this pin, with OSC1 left floating. A DC-blocking
capacitor (4.7 nF is adequate) should be placed between the TCXO output and OSC2 pin.
When not using an external regulator, a 1 MΩ resistor can be tied between the OSC2 pin and ground to meet the
power-down current specification of 1 μA.
10 OOK_SEL A high on this pin selects operation in OOK mode at 384 MHz when CE is high.
11 FSK1 FSK Channel Select Pin. This represents the LSB of the channel select pins.
12 FSK2 FSK Channel Select Pin.
13 FSK3 FSK Channel Select Pin.
14 CE Bringing CE low puts the ADF7901 into power-down, drawing <1 μA of current.
15 RSET_OOK The value of this resistor sets the output power for data = 1 in OOK mode. A resistor of 3.6 kΩ provides the
maximum output power. Increasing the resistor reduces the power and the current consumption. A lower resistor
value than 3.6 kΩ can be used to increase the power to a maximum of 14 dBm. The PA does not operate efficiently
in this mode.
16 RSET_FSK The value of this resistor sets the output power in FSK mode. A resistor of 3.6 kΩ provides maximum output
power. Increasing the resistor reduces the power and the current consumption. A resistor value lower than 3.6 kΩ
can be used to increase the power to a maximum of 14 dBm. The PA does not operate efficiently in this mode.
17 CVCO A 22 nF capacitor should be tied between the CVCO and CREG2 pins. This line should run underneath the ADF7901.
The capacitor is necessary to ensure stable VCO operation.
18 VCOIN The tuning voltage on this pin determines the output frequency of the voltage controlled oscillator (VCO).
The higher the tuning voltage the higher the output frequency. The output of the loop filter is connected here.
19 RFGND Ground for Output Stage of Transmitter.
20 RFOUT The modulated signal is available at this pin. Output power levels are from –5 dBm to +12 dBm. The output
should be impedance matched using suitable components to the desired load.
ADF7901
Rev. A| Page 7 of 12
Pin No. Mnemonic Function
21 DVDD Voltage Supply for VCO and PA Section. It should be supplied with 3.0 V. Decoupling capacitors to the ground
plane should be placed as close as possible to this pin.
22 PA_EN This pin is used to enable the power amplifier. It should be modulated with the OOK data in OOK mode. In
FSK mode, it should be enabled when the PLL is locked.
23 RSET External Resistor. Sets charge pump current and some internal bias currents. Use 3.6 kΩ as default.
24 CREG2 A 2.2 μF capacitor should be added at CREG2 to reduce regulator noise and improve stability. A reduced capacitor
improves regulator power-on time but can cause higher spurs.
ADF7901
Rev. A | Page 8 of 12
TYPICAL PERFORMANCE CHARACTERISTICS
RSET
OUTPUT POWER (dBm)
16
12
8
4
0
2
35 9710468
05349-004
Figure 3. Output Power vs. RSET FSK, Upper FSK Channels,
Measured into 50 Ω
OUTPUT POWER (dBm)
IDD (mA)
30
25
20
15
10
35
59710468
05349-005
Figure 4. Current Consumption vs. Output Power, Upper FSK Channels,
Measured into 50 Ω
Center 395.948 29MHz
#Res BW 300Hz VBW 300Hz Span 50kHz
Sweep 2.118 s (601 pts)
Mkr1 10.00kHz
Noise –89.55dB/HzRef 15dBm
Avg
Log
10
dB/
PAvg
W
1
S3
£(f):
f<50k
Swp
S2
FS
AA
Atten 30dB
RBW
300.0000000Hz
1R
1
05349-006
Figure 5. Phase Noise at Channel 9
Center 5.50GHz
#Res BW 1MHz VBW 1MHz Span 10.5GHz
Sweep 17.52 ms (601 pts)
Mkr4 1.59GHz
–21.30dBRef 15dBm
Peak
Log
10
dB/
LgAv
Atten 30dB
1
2
3
4
Marker
1
2
3
4
Trace
(1)
(1)
(1)
(1)
Type
Freq
Freq
Freq
Freq
X Axis
400MHz
800MHz
1.19GHz
1.59GHz
Amplitude
–25.56dB
–13.89dB
–34.53dB
–21.30dB
05349-007
4R
Figure 6. Harmonic Levels—Up to Fourth Harmonic,
Measured at Channel 9 into 50 Ω
ADF7901
Rev. A| Page 9 of 12
CIRCUIT DESCRIPTION
Table 4.
Frequency (MHz) FSK3 FSK2 FSK1 OOK_SEL
369.5 0 0 0 0
371.1 0 0 1 0
375.3 0 1 0 0
376.9 0 1 0 0
384.0 Don’t
care
Don’t
care
Don’t
care
1
388.3 1 0 0 0
391.5 1 0 1 0
394.3 1 1 0 0
395.9 1 1 1 0
LOOP FILTER
The loop filter integrates the current pulses from the charge
pump to form a voltage that tunes the output of the VCO to the
desired frequency. It also attenuates spurious levels generated by
the PLL. The recommended loop filter design for this circuit is
297 kHz. This is based on the trade-off between attenuation of
beat note spurs and the need to minimize chirp when the PA is
turned on.
CHARGE
PUMP OUT VCO
05349-008
R2 = 6.2k
Ω
C3 = 10pFC1 = 33pF C2 = 390pF
R1 = 3k
Ω
Figure 7.
Improved spurious performance in FSK mode can be achieved
by using a narrower loop bandwidth. For a data rate of 20 kbps,
a loop bandwidth of roughly 50 kHz would be suitable. The
following components give a loop bandwidth of 51.1 kHz:
C1 = 680 pF
C2 = 15 nF
C3 = 180 pF
R1 = 510 Ω
R2 = 6.2 kΩ
ADIsimPLL is a free software tool offered by Analog Devices
for assistance in designing with ADI’s frequency synthesizers
and ISM band transmitters. To select the correct loop filter
components for use with the ADF7901, open a project for the
ADF7012 device. Then, enter the desired output carrier
frequency and loop bandwidth, and use the 870 μA charge
pump current setting.
ADIsimPLL can be downloaded from www.analog.com.
CHANNEL FREQUENCIES
The nine channel frequencies listed in Table 4 are obtainable
from a single 9.8304 MHz crystal reference by changing the
value of the N and F numbers in the fractional PLL, using
control lines FSK1, FSK2, and FSK3. The channel frequency is
given by
FCHANNEL = FREF × (N + F)
However, the VCO is tuned to operate over a frequency range
of 344 MHz to 401 MHz (typically). Therefore, any channel
frequency within this range can be obtained if the required
reference frequency is used. The N and F numbers for each
channel are listed in Table 5, together with the corresponding
channel frequencies for 9.8304 MHz and, for example purposes,
frequencies for 10 MHz. With the 10 MHz reference, the two
largest N settings give channel frequencies above the maximum
VCO output frequency and are therefore invalid.
Frequency deviation is also dependent on reference frequency.
The relationship is given by
FDEV = 58 × (9.8304 MHz)/214
Therefore, the frequency deviation is 34.8 kHz when the
9.8304 MHz reference is used and 35.4 kHz when the 10 MHz
reference is used.
Table 5.
Channel Frequency (MHz)
N F 9.8304 MHz Ref 10 MHz Ref
37 2406/4096 369.5 375.9
37 3073/4096 371.1 377.5
38 727/4096 375.3 381.8
38 1374/4096 376.9 383.4
39 256/4096 384.0 390.6
39 2048/4096 388.3 395
39 3381/4096 391.5 398.3
40 452/4096 394.3 N/A
40 1118/4096 395.9 N/A
ADF7901
Rev. A | Page 10 of 12
3pF 8pF
22nH
27nH
5.6pF
DV
DD
RF
OUT
R
SET
3.6kΩ
C
REG2
2.2μF
22nF
C
VCO
CP
OUT
VCOIN VCO
IN
FSK1
FSK2
FSK3
OOK_SEL
TxDATA
CE
9.8304MHz
33pF33pF
GND
OSC2
OSC1
ANTENNA
ADF7901
PA_EN
RSET_FSK
RSET_OOK 3.6kΩ
3.6kΩ
C
REG1
2.2μF
3pF
1.5pF
22nH
36nH
MATCHING 50Ω
TO ANTENNA
5TH-ORDER, LOW-PASS FILTER
MATCHING RF
OUT
TO 50Ω
05349-003
NOTES
1. DECOUPLING CAPACITORS HAVE
BEEN OMITTED FOR CLARITY.
Figure 8. Applications Diagram for the ADF7901 in a Remote Control System
LAYOUT GUIDELINES
The layout of the board is crucial to ensuring low levels of
spurious and harmonics.
Decoupling
Decoupling capacitors (high frequency 22 pF, low frequency
100 nF) should be placed as close as possible to the supply pins
on the part. Low size 0402 and 0603 components are recom-
mended for the high frequency rejection on the supply.
Regulator Stability
A minimum of 1 μF is needed on both CREG1 and CREG2 to ensure
stability. An additional 22 pF capacitor can be added to reject
higher frequency noise. Because many of the internal blocks
run off the regulator, it is critical to reduce its noise. Low size
0402 and 0603 components are recommended for the high
frequency rejection on the supply.
Grounding
Emphasis should be placed on grounding once the decoupling
capacitors have been added. The PA stage switches currents of
15 mA in maximum power mode. This causes changes in the
ground resulting in large return currents that can radiate to
other parts of the board. The shortest and least obstructed
ground from RFGND back to the ground of the battery should be
ensured. A 4-layer board helps, as well as flooding the top layer.
The ground paths should not have any vias and should be wide
tracks.
Supply
The supply tracks can be routed through vias, because they act
as free inductors and make layout easier on a 2-layer board
(see the Decoupling section). Tracks should be wide.
Digital Lines
Digital lines should contain a large resistor in series. This
impedance blocks signals of many frequencies, including
harmonics and the carrier frequency. Long control lines can
act as antennae. It can be useful to add capacitance to ground.
There is some capacitance to ground provided by the lines and
at the input of the digital pins.
ADF7901
Rev. A| Page 11 of 12
OUTLINE DIMENSIONS
24 13
121
6.40 BSC
4.50
4.40
4.30
PIN 1
7.90
7.80
7.70
0.15
0.05
0.30
0.19
0.65
BSC 1.20
MAX
0.20
0.09
0.75
0.60
0.45
8°
0°
SEATING
PLANE
0.10 COPLANARITY
COMPLIANT TO JEDEC STANDARDS MO-153AD
Figure 9. 24-Lead Thin Shrink Small Outline Package [TSSOP]
(RU-24)
Dimensions shown in millimeters
ORDERING GUIDE
Model Temperature Range Package Description Package Option
ADF7901BRU 0°C to 50°C 24-Lead Thin Shrink Small Outline Package (TSSOP) RU-24
ADF7901BRU-REEL 0°C to 50°C 24-Lead Thin Shrink Small Outline Package (TSSOP) RU-24
ADF7901BRU-REEL7 0°C to 50°C 24-Lead Thin Shrink Small Outline Package (TSSOP) RU-24
ADF7901BRUZ1 0°C to 50°C 24-Lead Thin Shrink Small Outline Package (TSSOP) RU-24
ADF7901BRUZ-RL1 0°C to 50°C 24-Lead Thin Shrink Small Outline Package (TSSOP) RU-24
ADF7901BRUZ-RL71 0°C to 50°C 24-Lead Thin Shrink Small Outline Package (TSSOP) RU-24
EVAL-ADF7901EB Evaluation Board
1 Z = Pb-free part.
ADF7901
Rev. A | Page 12 of 12
NOTES
©2006 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D05349-0-3/06(A)
