ADC08B200EB - National Semiconductor

June 2008

ADC08B200

8-Bit, 200 MSPS A/D Converter with Capture Buffer

General Description

The ADC08B200 is a high speed analog-to-digital converter

(ADC) with an integrated capture buffer. The 8-bit, 200 MSPS

A/D core is based upon the proven ADC08200 with integrated

track-and-hold and is optimized for low power consumption.

This device contains a selectable size capture buffer of up to

1,024 bytes that allows fast capture of an input signal with a

slower readout rate. An on-chip clock PLL circuit provides the

option of on-chip clock rate multiplication to provide the high

speed sampling clock.

The ADC08B200 is resistant to latch-up and the outputs are

short-circuit proof. The top and bottom of the ADC08B200's

reference ladder are available for connections, enabling a

wide range of input possibilities. The digital outputs are TTL/

CMOS compatible with a separate output power supply pin to

support interfacing with 2.7V to 3.3V logic. The digital inputs

and outputs are low voltage TTL/CMOS compatible and the

output data format is straight binary.

The ADC08B200 is offered in a 48-pin plastic package

(TQFP) and is specified over the extended industrial temper-

ature range of −40°C to +105°C. An evaluation board is

available to assist in the easy evaluation of the ADC08B200.

Features

■Single-ended input

■Selectable capture buffer size

■PLL for clock multiplication

■Reference Ladder Top and Bottom accessible

■Linear power scaling with sample rate

■FPGA training pattern

■Power-down feature

Key Specifications

(PLL Bypassed)

■Resolution 8 Bits

■Maximum sampling frequency 200 MSPS (min)

■DNL ±0.4 LSB (typ)

■ENOB (fIN= 49 MHz) 7.2 bits (typ)

■THD (fIN= 49 MHz) −53 dBc (typ)

■Power Consumption

—Operating, 50 MHz Input 2 mW / Msps (typ)

—Power Down 2.15 mW (typ)

Applications

■Laser Ranging

■RADAR

■Pulse Capturings

Pin Configuration

20214701

ADC08B200 8-Bit, 200 MSPS A/D Converter with Capture Buffer

Ordering Information

Order Number Temperature Range Package

ADC08B200CIVS −40°C ≤ TA ≤ +105°C TQFP

ADC08B200EB Evaluation Board

Block Diagram

20214702

Pin Descriptions and Equivalent Circuits

Pin No. Symbol Equivalent Circuit Description

6VIN Analog signal input. Conversion range is VRB to VRT.

3VRT

Analog Input that is the high (top) side of the reference ladder

of the ADC. Voltage on VRT and VRB inputs define the VIN

conversion range. VRT should be more positive than VRB.

Bypass well.

9VRM

Analog input that is the mid-point of the reference ladder.

This pin should be bypassed to a quiet point in the ground

plane with a 0.1 µF capacitor. DO NOT LOAD this pin.

10 VRB

Analog Input that is the low side (bottom) of the reference

ladder of the ADC. The voltages on VRT and VRB inputs

define the VIN conversion range. Bypass well.

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ADC08B200

Pin No. Symbol Equivalent Circuit Description

13 PD

Chip Power Down input. When this pin is high, the entire chip

is in the Power Down mode. Any data in the capture buffer

is lost and the output pins hold the last byte that was output.

41 PDADC

ADC Power Down Input. When this pin is high, the ADC is

powered down. The capture buffer is active and the data

within it may be clocked out.

46 CLK

CMOS/TTL compatible digital clock Input. When the PLL is

bypassed, the clock signal at this pin is the ADC sampling

clock and VIN is sampled on the rising edge of this clock input.

When the PLL is enabled, the signal at this input is the

reference clock, which is multiplied to provide a higher

frequency sample clock.

19 RCLK

Buffer Read Clock input. When the capture buffer is enabled,

this input signal is used to read the data from the internal

buffer. The data output and the buffer empty flag (EF)

transition with the rise of this clock.

17 WEN

Write Enable input. A high level at this input causes a byte

of data to be written into the capture buffer with the rise of

each sample clock.

20 REN

Read Enable input. A high level at this input causes a byte

of data to be read from the capture buffer with the rise of each

RCLK input. This rise of the REN input should be

synchronous with the RCLK input and should not be high

while the WEN input is high.

22 RESET Device Reset Input. A high level at this input resets all control

logic on the chip.

37 OE

Output Enable input. A high level at this input enables the

output buffers. A low level at this input puts the digital data

output pins into a high impedance state.

14 OEDGE/TEN

Output Edge Select or Test Mode Enable input. If this input

is high, the data outputs transition with the rising edge of the

DRDY output. If this input is low, the data outputs transition

with the falling edge of the DRDY output. Forcing a potential

of VA/2 at this input enables the Test Mode.

18 WENSYNC

Synchronized WEN output. The WEN control input is

synchronized on-chip with the internal sample clock and is

provided at this output.

31 DRDY

Data Ready output. This signal transitions with the transition

of the digital data outputs and indicates that the output data

is ready.

26 thru 29

and

33 thru 36

D0–D7 Digital data digital Outputs. D0 is the LSB, D7 is the MSB.

16 FF Buffer Full Flag. This output is high when the capture buffer

is full.

15 EF Buffer Empty Flag. This output is high when the capture

buffer is empty.

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ADC08B200

Pin No. Symbol Equivalent Circuit Description

25 ASW

Auto-Stop Write input. This pin has a dual function. With the

buffer enabled, this pin acts as the ASW input. When this

input is high, writing to the buffer is halted when the capture

buffer is full (FF high). When the buffer is disabled, this pin

is ignored. When the device is in Test Mode, this pin acts as

the Output Edge Select signal, functioning in accordance

with the description of the OEDGE/TEN pin.

23,24 BSIZE(1:0) Buffer Size input. These inputs determine the size of the

buffer, as described in the Functional Description.

38, 39 MULT(1:0) Clock Multiply Factor input. These inputs determine the

internal clock PLL's multiplication factor.

1, 4, 12 VA Positive analog supply pin. Connect to a voltage source of

+3.3V.

43, 44, 48 VP PLL supply pin. Connect to a voltage source of +3.3V.

40 VD Digital core supply pin. Connect to a voltage source of +3.3V.

32 VDR Power supply for the output drivers. Connect to a voltage

source of 2.7V to VD.

2, 5, 8, 11, 21,

42, 45, 47 GND The ground return for the chip core.

7 SIG GND Analog input signal ground.

30 DR GND The ground return for the output drivers.

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ADC08B200

Absolute Maximum Ratings

(Notes 1, 2)

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

Supply Voltage (VA, VP, VD, VDR)-0.3V to 3.8V

Driver Supply Voltage (VDR)-0.3V to VA +0.3V

Voltage on Any Input or Output Pin −0.3V to VA

Reference Voltage (VRT, VRB) GND to VA

Input Current, Data Outputs ±1 mA

Input Current all other pins (Note 3) ±25 mA

Package Input Current (Note 3) ±50 mA

Power Dissipation at TA = 25°C See (Note 4)

ESD Susceptibility (Note 5)

Human Body Model

Machine Model

Charged Device Model

2500V

200V

1000V

Soldering Temperature, Infrared,

10 seconds (Note 6) 235°C

Storage Temperature −65°C to +150°C

Operating Ratings (Notes 1, 2)

Operating Temperature Range −40°C ≤ TA ≤ +105°C

Supply Voltage (VA)+3.0V to +3.6V

Driver Supply Voltage (VDR)+2.7V to (VA + 0.3V)

Maximum Supply Voltage

VD, VPVA + 0.3V

CLK Frequency

PLL Bypassed

PLL used

1 to 210 MHz

15 to 105 MHz

RCLK Frequency (Note 12) 2 - 210 MHz

RCLK Duty Cycle 35% to 65%

Ground Difference |GND - DR GND| 0V to 300 mV

Upper Reference Voltage (VRT) 0.5V to (VA − 0.3V)

Lower Reference Voltage (VRB) 0V to (VRT − 0.5V)

Reference Delta (VRT − VRB)0.5V to 2.3V

VIN Voltage Range VRB to VRT

Package Thermal Resistance

Package θJA

48-Lead TQFP 76 °C/W

Converter Electrical Characteristics

The following specifications apply for VA = VD = VP = VDR = +3.3VDC, VRT = +1.9V, VRB = 0.3V, CL = 10 pF, fCLK = 200 MHz at 50%

duty cycle, OEDGE/TEN = 1, Buffer and PLL bypassed. Boldface limits apply for TJ = TMIN to TMAX: all other limits TJ = 25°C

(Notes 7, 8)

Symbol Parameter Conditions Typical

(Note 9)

Limits

(Note 9)

Units

(Limits)

DC ACCURACY

INL Integral Non-Linearity ±0.55 ±1.3 LSB (max)

DNL Differential Non-Linearity ±0.40 ±0.9 LSB (max)

Missing Codes 0(max)

FSE Full Scale Error −39 −80

mV (min)

mV (max)

VOFF Zero Scale Offset Error 55 70 mV (max)

ANALOG INPUT AND REFERENCE CHARACTERISTICS

VIN Input Voltage 1.6 VRB V (min)

VRT V (max)

CIN VIN Input Capacitance VIN = 0.75V +0.5 Vrms (CLK LOW) 3 pF

(CLK HIGH) 4 pF

RIN Analog Input Resistance >1 MΩ

FPBW Full Power Bandwidth 500 MHz

VRT Top Reference Voltage 1.9 VAV (max)

0.5 V (min)

VRB Bottom Reference Voltage 0.3 VRT − 0.5 V (max)

0V (min)

VRT - VRB Reference Voltage Delta 1.6 0.5 V (min)

2.3 V (max)

RREF Reference Ladder Resistance VRT to VRB 160 145 Ω (min)

200 Ω (max)

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ADC08B200

Symbol Parameter Conditions Typical

(Note 9)

Limits

(Note 9)

Units

(Limits)

DIGITAL INPUT CHARACTERISTICS

VIH Logic High Input Voltage OEDGE/TEN 2.2 2.7 V (min)

Others 1.6 2.1 V (min)

VIL Logic Low Input Voltage OEDGE/TEN 0.9 0.5 V (max)

Others 1.3 0.7 V (max)

IIH Logic High Input Current VIH = VDR = VA = 3.6V

OEDGE/TEN

Operational

Test Mode

µA

Others 10 nA

IIL Logic Low Input Current VIL = 0V, VDR = VA = 3.0V

OEDGE/TEN

Operational

Test Mode

−10

−600

µA

Others −50 nA

CIN Logic Input Capacitance 3 pF

DIGITAL OUTPUT CHARACTERISTICS

VOH High Level Output Voltage VA = VDR = 3.0V, IOH = −5 mA 3.0 2.4 V (min)

VOL Low Level Output Voltage VA = VDR = 3.0V, IOL = 5 mA 0.25 0.5 V (max)

COUT Digital Output Capacitance 2 pF

DYNAMIC PERFORMANCE

ENOB Effective Number of Bits

fIN = 10 MHz, VIN = FS − 0.25 dB 7.4 Bits

fIN = 49 MHz, VIN = FS − 0.25 dB 7.2 6.8 Bits (min)

fIN = 49 MHz, VIN = FS − 0.25 dB, PLL x8 7.2 Bits

fIN = 100 MHz, VIN = FS − 0.25 dB 7.0 Bits

fIN = 100 MHz, VIN = FS − 0.25 dB, PLL x4 6.9 Bits

SINAD Signal-to-Noise & Distortion

fIN = 10 MHz, VIN = FS − 0.25 dB 46 dBc

fIN = 49 MHz, VIN = FS − 0.25 dB 45 42.7 dBc (min)

fIN = 49 MHz, VIN = FS − 0.25 dB, PLL x8 45 dBc

fIN = 100 MHz, VIN = FS − 0.25 dB 44 dBc

fIN = 100 MHz, VIN = FS − 0.25 dB, PLL x4 43.4 dBc

SNR Signal-to-Noise Ratio

fIN = 10 MHz, VIN = FS − 0.25 dB 47 dBc

fIN = 49 MHz, VIN = FS − 0.25 dB 46.3 43.7 dBc (min)

fIN = 49 MHz, VIN = FS − 0.25 dB, PLL x8 45.8 dBc

fIN = 100 MHz, VIN = FS − 0.25 dB 45.6 dBc

fIN = 100 MHz, VIN = FS − 0.25 dB, PLL x4 45.6 \dBc

SFDR Spurious Free Dynamic Range

fIN = 10 MHz, VIN = FS − 0.25 dB 56 dBc

fIN = 49 MHz, VIN = FS − 0.25 dB 56 dBc

fIN = 49 MHz, VIN = FS − 0.25 dB, PLL x8 56 dBc

fIN = 100 MHz, VIN = FS − 0.25 dB 50 dBc

fIN = 100 MHz, VIN = FS − 0.25 dB, PLL x4 49.7 dBc

THD Total Harmonic Distortion

fIN = 10 MHz, VIN = FS − 0.25 dB −55 dBc

fIN = 49 MHz, VIN = FS − 0.25 dB −53 dBc

fIN = 49 MHz, VIN = FS − 0.25 dB, PLL x8 −53 dBc

fIN = 100 MHz, VIN = FS − 0.25 dB −49 dBc

fIN = 100 MHz, VIN = FS − 0.25 dB, PLL x4 -47.5 dBc

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ADC08B200

Symbol Parameter Conditions Typical

(Note 9)

Limits

(Note 9)

Units

(Limits)

HD2 2nd Harmonic Distortion

fIN = 10 MHz, VIN = FS − 0.25 dB −57 dBc

fIN = 49 MHz, VIN = FS − 0.25 dB −55 dBc

fIN = 49 MHz, VIN = FS − 0.25 dB, PLL x8 −55 dBc

fIN = 100 MHz, VIN = FS − 0.25 dB −50 dBc

fIN = 100 MHz, VIN = FS − 0.25 dB, PLL x4 −49.9 dBc

HD3 3rd Harmonic Distortion

fIN = 10 MHz, VIN = FS − 0.25 dB −62 dBc

fIN = 49 MHz, VIN = FS − 0.25 dB −63 dBc

fIN = 49 MHz, VIN = FS − 0.25 dB, PLL x8 −62 dBc

fIN = 100 MHz, VIN = FS − 0.25 dB −56 dBc

fIN = 100 MHz, VIN = FS − 0.25 dB, PLL x4 −54.6 dBc

IMD Intermodulation Distortion f1 = 11 MHz, VIN = FS − 6.25 dB

f2 = 12 MHz, VIN = FS − 6.25 dB -50 dBc

POWER SUPPLY CHARACTERISTICS

IAAnalog Supply Current

DC Input 72.5 mA

fIN = 50 MHz 76.8 88.3 mA (max)

PD High 0.3 mA

IDDigital Core Supply Current

DC Input, Buffer bypassed 1.2 mA

fIN = 50 MHz, Buffer bypassed 1.6 2.1 mA (max)

fIN = 50 MHz, 1k writing to Buffer (Note 10) 38 42.4 mA

PDADC High, reading Buffer (Note 10) 1.1 mA

PD High 0.3 mA

IPPLL Supply Current

PLL x2 8.8 10.1 mA (max)

PLL disabled 3.6 4.3 mA (max)

PD High 20 mA

IDR Output Driver Supply Current

DC Input 7 mA

fIN = 50 MHz 41 57 mA (max)

PD High 25 µA

IA + ID +

IP + IDR

Total Operating Current

DC Input, Buffer bypassed, PLL x2

(Note 10) 97.5 mA

50 MHz Input, writing to Buffer, PLL X2

(Note 10) 164.6 198 mA (max)

PDADC = Hi, reading Buffer,

RCLK = 200 MHz, D.C. input 20 mA

PD High 0.65 mA

PC Power Consumption

DC Input, Buffer & PLL bypassed 306 mW

50 MHz Input, writing to Buffer, PLL X2

(Note 10) 543 653 mW (max)

PDADC High, reading Buffer, PLL disabled

(Note 10) 66 mW

PD High 2.15 mW

PSRR1D.C. Power Supply Rejection Ratio FSE change with 3.0V to 3.6V change in VA48 dB

PSRR2A.C. Power Supply Rejection Ratio SNR reduction with 200 mV at 10MHz on

supply TBD dB

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ADC08B200

Converter Timing Characteristics

The following specifications apply for VA = VDR = +3.3VDC, VRT = +1.9V, VRB = 0.3V, CL = 50 pF, fCLK = 200 MHz at 50% duty cycle,

OEDGE/TEN = 1, Buffer and PLL bypassed. Boldface limits apply for TJ = TMIN to TMAX: all other limits TJ = 25°C (Notes 7, 8)

Symbol Parameter Conditions Typical

(Note 9)

Limits

(Note 9)

Units

(Limits)

fC1 Maximum Input Clock Rate PLL Disabled 210 200 MHz (min)

Using PLL 15 105 MHz (min)

fC2 Minimum Input Clock Rate PLL Disabled 1 MHz

Using PLL 15 MHz

tCL Minimum CLK Low Time (Note 11) 1.7 ns (min)

tCH Minimum CLK High Time (Note 11) 1.7 ns (min)

fRC1 Maximum RCLK Rate (Note 12) 210 200 MHz (min)

fRC2 Minimum RCLK Rate (Note 12) 2 MHz

tRCL Minimum RCLK Low Time (Note 11) 2.0 ns (min)

tRCH Minimum RCLK High Time (Note 11) 2.0 ns (min)

ΔDC DRDY to RCLK Duty Cycle Delta 0.3 ±3 %

tSU REN to RCLK Set-Up Time −0.4 −0.8

4.0

ns (min)

ns (max)

tRR RCLK Rising to DRDY Rising 3.8 2.4

5.9

ns (min)

ns (max)

tRF RCLK Falling to DRDY Falling 3.5 ns

tSKDR DRDY Rising to DATA Skew 160 ps

tSKR RCLK Falling to DATA Skew 2.3 1.8

7.4

ns (min)

ns (max)

tSKEF DRDY Rising to EF Skew 36 ps

tCFF CLK rise to FF Delay 4.2 ns

tFFW FF to WENSYNC Delay ASW pin high 4.2 ns

tCW CLK to WENSYNC Delay PLL Disabled 3.5 2.4

5.5

ns (min)

ns (max)

tRST RESET Pulse Width (Note 11) 4Write Clock

Cycles (min)

Output Data Rise Time

(0.4V to 2.5V)

CL = 10 pF 0.9 ns

CL = 20 pF 2 ns

Output Data Fall Time

(2.4V to 0.4V)

CL = 10 pF 1.4 ns

CL = 20 pF 3.2 ns

tODF

RCLK Rise to Output Fall to 0.4V

Output

Reading Buffer 7.0 4.0

11.7

ns (min)

ns (max)

Buffer bypassed, PLL disabled 5.5 ns

tODR

RCLK Rise to Output Rise to 2.5V

Output

Reading Buffer 6.5 2.3

13.1

ns (min)

ns (max)

Buffer bypassed, PLL disabled 5.5 ns

tOHF

Data High to Fall Hold to 2.5V

Output Reading Buffer 3.8 2.4

5.5

ns (min)

ns (max)

tOHR

Data Low to Rise Hold to 0.4V

Output Reading Buffer 4.5 2.6

6.9

ns (min)

ns (max)

tSLEW Output Slew Rate Output Falling (2.4V to 0.4V) 1.5 V / ns

Output Rising (0.4V to 2.5V) 2.3 V / ns

tDRDY1 PD Low to Device Active PLL Enabled 20 µs

PLL Bypassed 2 µs

tDRDY2 PDADC Low to Device Active 2 µs

Pipeline Delay (Latency) 6 Clock Cycles

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ADC08B200

Symbol Parameter Conditions Typical

(Note 9)

Limits

(Note 9)

Units

(Limits)

tAD Sampling (Aperture) Delay CLK Rise to

Acquisition of Data

PLL on 3.4 ns

PLL off 3.9 ns

tAJ Aperture Jitter PLL Bypassed 2 ps rms

PLL Enabled in x8 mode (Note 13) 7 ps rms

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is

functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The guaranteed

specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test

conditions.

Note 2: All voltages are measured with respect to GND = DR GND = 0V, unless otherwise specified.

Note 3: When the input voltage at any pin exceeds the power supplies (that is, less than GND or DR GND, or greater than VA, VP, VD or VDR), the current at that

pin should be limited to 25 mA. The 50 mA maximum package input current rating limits the number of pins that can safely exceed the power supplies with an

input current of 25 mA to two.

Note 4: The absolute maximum junction temperature (TJmax) for this device is 150°C. The maximum allowable power dissipation is dictated by TJmax, the

junction-to-ambient thermal resistance (θJA), and the ambient temperature (TA), and can be calculated using the formula PDMAX = (TJmax − TA) / θJA.

Note 5: Human body model is 100 pF capacitor discharged through a 1.5 kΩ resistor. Machine model is 220 pF discharged through ZERO Ohms.

Note 6: See AN-450, “Surface Mounting Methods and Their Effect on Product Reliability”.

Note 7: The analog inputs are protected as shown below. Input voltage magnitudes up to VA + 300 mV or to 300 mV below GND will not damage this device.

However, errors in the A/D conversion can occur if the input goes above VA or below GND by more than 100 mV. For example, if VA is 3.3VDC the input voltage

must be ≤3.4VDC to ensure accurate conversions.

20214707

Note 8: To guarantee accuracy, it is required that VA, VD, VP and VDR be well bypassed. Each supply pin should be decoupled with separate bypass capacitors.

Note 9: Typical figures are at TJ = 25°C, and represent most likely parametric norms. Test limits are guaranteed to National's AOQL (Average Outgoing Quality

Level).

Note 10: This current or power is used only during the short time that the buffer is being written to or read from, depending upon the specification.

Note 11: This parameter is guaranteed by design and/or characterization and is not production tested.

Note 12: RCLK should be stopped with the buffer is not being read.

Note 13: Jitter with the PLL enabled is measured with 32k samples and the PLL in the x8 multiplication mode.

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ADC08B200

Specification Definitions

APERTURE (SAMPLING) DELAY is that time delay after the

rise of the sample clock until the input signal is sampled within

the ADC.

APERTURE JITTER is the variation in aperture delay from

sample to sample. Aperture jitter shows up as input noise.

CLOCK DUTY CYCLE is the ratio of the time that the clock

waveform is at a logic high to the total time of one clock period.

DIFFERENTIAL NON-LINEARITY (DNL) is the measure of

the maximum deviation from the ideal step size of 1 LSB.

Measured at 200 MSPS with a ramp input.

EFFECTIVE NUMBER OF BITS (ENOB, or EFFECTIVE

BITS) is another method of specifying Signal-to-Noise and

Distortion Ratio, or SINAD. ENOB is defined as (SINAD –

1.76) / 6.02 and says that the converter is equivalent to a per-

fect ADC of this (ENOB) number of bits.

FULL POWER BANDWIDTH is a measure of the frequency

at which the reconstructed output fundamental drops 3 dB

below its low frequency value for a full scale input.

FULL-SCALE ERROR is a measure of how far the last code

transition is from the ideal 1½ LSB below VRT and is defined

as:

FSE = Vmax + 1.5 LSB – VRT

where Vmax is the voltage at which the transition to the maxi-

mum (full scale) code occurs.

INTEGRAL NON-LINEARITY (INL) is a measure of the de-

viation of each individual code from a line drawn from zero

scale (½ LSB below the first code transition) through positive

full scale (½ LSB above the last code transition). The devia-

tion of any given code from this straight line is measured from

the center of that code value. The end point test method is

used. Measured at 200 MSPS with a ramp input.

INTERMODULATION DISTORTION (IMD) is the creation of

additional spectral components as a result of two sinusoidal

frequencies being applied to the ADC input at the same time.

it is defined as the ratio of the power in the second and third

order intermodulation products to the power in one of the

original frequencies. IMD is usually expressed in dBFS.

MISSING CODES are those output codes that are skipped

and will never appear at the ADC outputs. These codes can-

not be reached with any input value.

OFFSET ERROR is the error in the input voltage required to

cause the first code transition. It is defined as the difference

between the voltage required to cause the first code transition

and the ideal voltage (1/2 LSB) to cause that transition.

VOFF = VZT − 1/2 LSB = VZT - (VRT − VRB) / 512

where VZT is the first code transition input voltage.

OUTPUT DELAY is the time delay after the rising edge of the

RCLK input before the data update is present at the output

pins.

OUTPUT HOLD TIME is the length of time that the output data

is valid after the rise of CLK or RCLK output.

PIPELINE DELAY (LATENCY) is the number of clock cycles

between initiation of conversion and when that data is pre-

sented to the output driver stage. New data is available at

every clock cycle, but the data lags the conversion by the

Pipeline Delay plus the Output Delay.

POWER SUPPLY REJECTION RATIO (PSRR) is a measure

of how well the ADC rejects a change in the power supply

voltage. For the ADC08B200, PSRR1 is the ratio of the

change in Full-Scale Error that results from a change in the

DC power supply voltage, expressed in dB. PSRR2 is a mea-

sure of how well an a.c. signal riding upon the power supply

is rejected at the output.

SIGNAL TO NOISE RATIO (SNR) is the ratio, expressed in

dB, of the rms value of the input signal at the output to the rms

value of the sum of all other spectral components below one-

half the sampling frequency, not including harmonics or d.c.

SIGNAL TO NOISE PLUS DISTORTION (S/(N+D) or

SINAD) is the ratio, expressed in dB, of the rms value of the

input signal at the output to the rms value of all of the other

spectral components below half the clock frequency, includ-

ing harmonics but excluding d.c.

SPURIOUS FREE DYNAMIC RANGE (SFDR) is the differ-

ence, expressed in dB, between the rms values of the input

signal at the output and the peak spurious signal, where a

spurious signal is any signal present in the output spectrum

that is not present at the input.

TOTAL HARMONIC DISTORTION (THD) is the ratio ex-

pressed in dB, of the rms total of the first nine harmonic levels

at the output to the level of the fundamental at the output. THD

is calculated as

where Af1 is the RMS power of the fundamental (output) fre-

quency and Af2 through Af10 are the RMS power of the first 9

harmonic frequencies in the output spectrum

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ADC08B200

Timing Diagrams (PLL Bypassed)

20214757

ADC08B200 Data Capture and Read Operation

20214731

ADC08B200 Capture and Write Enable Timing

20214754

ADC08B200 Buffer Write Timing

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ADC08B200

20214755

ADC08B200 Buffer Read Timing (OEDGE/TEN = 1)

20214758

ADC08B200 Buffer Read Timing (OEDGE/TEN = 0)

20214756

ADC08B200 Buffer Bypassed Timing

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ADC08B200

Typical Performance Characteristics

VA = VD = VP = VDR = 3.3V, fCLK = 200 MHz, fIN = 50 MHz, PLL & Buffer bypassed, TA = 25°C, unless otherwise stated

INL

20214708

INL vs. Supply Voltage

20214715

INL vs. Temperature

20214714

INL vs. Sample Rate

20214710

DNL

20214709

DNL vs. Supply Voltage

20214718

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ADC08B200

DNL vs. Temperature

20214717

DNL vs. Sample Rate

20214711

Offset Error vs. Temperature

20214761

Full Scale Error vs. Temperature

20214762

SNR vs. Supply Voltage

20214721

SNR vs. Input Frequency

20214723

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ADC08B200

SNR vs. Temperature

20214720

SNR vs. Sample Rate

20214712

SNR vs. Clock Duty Cycle

20214724

Distortion vs. Supply Voltage

20214726

Distortion vs. Input Frequency

20214728

Distortion vs. Temperature

20214725

15 www.national.com

ADC08B200

Distortion vs. Sample Rate

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Distortion vs. Clock Duty Cycle

20214729

SINAD vs. Supply Voltage

20214738

SINAD vs. Input Frequency

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SINAD vs. Temperature

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SINAD vs. Sample Rate

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ADC08B200

SINAD vs. CLK Duty Cycle

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SFDR vs. Supply Voltage

20214727

SFDR vs. Input Frequency

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SFDR vs. Temperature

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SFDR vs. Sample Rate

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SFDR vs. Clock Duty Cycle

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ADC08B200

Power Consumption vs. Sample Rate

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Power Consumption vs. Temperature

20214760

Spectral Response @ fIN = 49 MHz

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Spectral Response @ fIN = 76 MHz

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Spectral Response @ fIN = 99 MHz

20214748

Intermodulation Distortion

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www.national.com 18

ADC08B200

Functional Description

The ADC08B200 integrates an 8-bit, high speed ADC and a

configurable capture buffer of up to 1 kilobyte, allowing the

sampling and processing tasks to be independent of each

other. This functionality is intended for those applications that

need to sample an input signal at a high rate and then read

the collected samples at a slower rate. The Timing Diagrams

illustrate the operation of the ADC08B200.

The analog input signal that is within the voltage range set by

VRT and VRB is digitized to eight bits. Input voltages below

VRB will cause the output word to consist of all zeroes. Input

voltages above VRT will cause the output word to consist of

all ones.

The ADC08B200 exhibits a power consumption that is pro-

portional to frequency, limiting power consumption to what is

needed at the clock rate that is used. This, its excellent per-

formance over a wide range of clock frequencies and the

incorporation of a capture buffer make ADC08B200 an ideal

choice for many 8-bit ADC applications.

Data is acquired at the rising edge of the sample clock and,

in the buffer bypass mode, the digital equivalent of that data

is available at the digital outputs 6 clock cycles plus tOD later.

When the Buffer is enabled, the converted data is written to

the buffer with each internal conversion clock cycle and can

be read out with the RCLK signal. The ADC08B200 will con-

vert as long as a CLK signal is present, but when using the

buffer no writing to the buffer will occur when that buffer is full.

The output coding is straight binary.

The entire device is in the active state when the Power Down

pin (PD) is low. When the PD pin is high, the entire device is

in the power down mode, consuming very little power. Holding

the clock input low after raising the Power Down pin will further

reduce the power consumption in the power down mode.

When the PDADC pin is high, only the A/D converter itself is

in the power down mode. The rest of the chip is left powered

up so that the capture buffer may be read. If both the PD and

PDADC pins are high, the PD pin dominates and the entire

device is powered down.

The A/D converter sample clock can be either the clock signal

at the CLK input pin or a multiplied version of that clock. The

clock multiplier can be 2, 4 or 8. In any case, the sample clock

is also used to write the converter data into the capture buffer

when that buffer is used.

As long as the chip is not in a power down state and there is

a clock signal present, the A/D converter is converting the in-

put signal. However, the data is stored into the capture buffer,

when the buffer is used, only while the Write Enable (WEN)

input is high. The data is read from the capture buffer with the

RCLK signal, which can be a free running clock, while the

Read Enable (REN) signal is high.

Note that the capture buffer on this chip must be entirely filled

to its configured size before reading its contents can begin. It

is not possible to write to and read from the buffer at the same

time and the WEN and REN inputs should not be high at the

same time. If they are high at the same time, the REN input

is ignored. This is true even if the REN input is high first and

a read operation is progressing normally when the WEN input

goes high. Asserting the WEN input while REN is high will

cause the read operation to be aborted and the capture op-

eration to begin. Although this device is intended for fast

capture and slower read out applications, it is possible for the

RCLK to operate at the same rate or faster than the sample

clock.

Two status flags are provided to manage the capture buffer.

As the name suggests, the Full Flag (FF) goes high when the

buffer is full. The next sample clock rise after the assertion of

FF will begin writing over the oldest data because the write

pointer will "wrap around". This is called an "over run" condi-

tion. Similarly, the Empty Flag (EF) indicates that the last of

the data has been read and the buffer is empty. When EF

goes high, the DRDY and Data outputs stop switching and

both DRDY and the Data lines remain low if OEDGE=1. Both

remain high if OEDGE=0.

The user has the option to stop writing to the buffer automat-

ically upon a buffer full condition with the use of the ASW

(Auto Stop Write) input. If the ASW input is low, the buffer will

be continually written to, resulting in the possibility of the write

pointer "wrapping around" and the data continually being

overwritten as long as there is a clock and the WEN input is

high. If the ASW input is high, the write operation stops upon

reaching the "full" condition.

FF goes low upon device reset and when the "full" condition

is removed by starting a transfer operation with the assertion

of REN. The EF output goes low when the "empty" condition

is removed by starting a capture operation with the raising of

WEN. The EF output goes high upon device reset because

resetting empties the buffer.

The RESET signal resets the read and write pointers and the

EF and FF flags. The RESET signal also stops the read op-

eration early (before the EF flag goes high). Consequently,

only a partial read is performed if the RESET input goes high

while a buffer read out is under way. This allows the buffer

pointers to be reset so a new capture operation can begin.

The RESET signal has no effect upon the A/D converter,

which has its own internal Power-On Reset circuit.

Note that the RCLK input does not need to be as noise (jitter)

free as does the CLK signal. The reason for this is that RCLK

is only used to read the Capture Buffer, while the CLK signal

is either the ADC sample clock or is the reference for the in-

ternal PLL that generates the sample clock for the ADC.

Consequently, CLK jitter directly affects the ADC's SNR per-

formance. There is no requirement for the RCLK to have any

fixed relationship with CLK in terms of phase or frequency.

Applications Information

1.0 REFERENCE INPUTS

The reference inputs VRT and VRB are the top and bottom of

the reference ladder, respectively. Input signals between

these two voltages will be digitized to 8 bits. External voltages

applied to the reference input pins should be within the range

specified in the Operating Ratings and the Electrical Charac-

teristics table. Any device used to drive the reference pins

should be able to source sufficient current into the VRT pin and

sink sufficient current from the VRB pin to maintain the desired

voltages.

19 www.national.com

ADC08B200

20214732

FIGURE 1. Simple, low component count reference biasing. Because of the ladder and external resistor tolerances, the

reference voltage of this circuit can vary too much for some applications.

The reference bias circuit of Figure 1 is very simple and the

performance is adequate for many applications. However,

circuit tolerances will lead to a wide reference voltage range.

Better reference tolerance can be achieved by driving the ref-

erence pins with low impedance sources.

The circuit of Figure 2 will allow a more accurate setting of the

reference voltages, with upper and lower reference accura-

cies of about 16 mV, or about 2 1/2 LSB. The upper amplifier

must be able to source the reference current as determined

by the value of the reference resistor and the value of (VRT −

VRB). The lower amplifier must be able to sink this reference

current. Both amplifiers should be stable with a capacitive

load.

The LM8272 was chosen because of its rail-to-rail input and

output capability, its high output current capability and its abil-

ity to drive large capacitive loads.

The divider resistors at the inputs to the amplifiers could be

changed to suit the application reference voltage needs, or

the divider can be replaced with potentiometers or DACs for

precise settings. The bottom of the ladder (VRB) may be re-

turned to ground if the minimum input signal excursion is 0V.

VRT should always be at least 0.5V more positive than VRB.

While VRT may be as high as the VA supply voltage and VRB

may be as low as ground, the difference between these two

voltages (VRT − VRB should not exceed 2.3V to prevent a slight

waveform distortion.

The VRM pin is the center of the reference ladder and should

be bypassed to a quiet point in the ground plane with a 0.1 µF

capacitor. DO NOT leave this pin open and DO NOT load this

pin with more than 10µA.

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ADC08B200

20214733

FIGURE 2. Driving the reference to force desired values requires driving with a low impedance source.

2.0 THE ANALOG INPUT

The analog input of the ADC08B200 is a switch followed by

an integrator. The input capacitance changes with the clock

level, appearing as 3 pF when the clock is low, and 4 pF when

the clock is high. The sampling nature of the analog input

causes current spikes at the input that result in voltage spikes

there. These spikes are normal and need not be eliminated.

However, any amplifier used to drive the analog input must

be able to settle within the clock high time. Using a single pole

RC filter between the amplifier and the ADC input will mini-

mize the effects of these transients on the driving amplifier.

The cutoff frequency of this filter should be approximately the

same as the ADC sample rate for Nyquist applications.

Choose a capacitor value of 33 pF to 51 pF and a resistor

value according to the formula

where fS is the converter sample rate. The added 6 pF in the

formula above allows for the ADC input capacitance and a

small board capacitance. For undersampling applications,

eliminate the capacitor and chose a pole frequency of about

2 to 3 times the maximum input frequency, using the ADC

input capacitance when the the clock is high, plus trace ca-

pacitance, for the filter capacitor. The optimum time constant

for this circuit depends not only upon the amplifier and ADC,

but also upon the circuit layout and board material. The

LMH6702 and the LMH6628 have been found to be good

amplifiers to drive the ADC08B200.

Figure 3 shows an example of an input circuit using the

LMH6702 at the ADC08B200 input. The input amplifier should

incorporate some gain as most operational amplifiers exhibit

better phase margin and transient response with gains above

2 or 3 than with unity gain. If an overall gain of less than 3 is

required, attenuate the input and operate the amplifier at a

higher gain, as indicated in Figure 3.

This will provide optimum SNR performance for Nyquist ap-

plications. Best THD performance is realized when the ca-

pacitor and resistor values are both zero, but this would

compromise SNR and SINAD performance. Generally, the

capacitor should not be added for undersampling applica-

tions.

The circuit of Figure 3 has both gain and offset adjustments.

If you eliminate these adjustments normal circuit tolerances

may result in signal clipping unless care is exercised in the

worst case analysis of component tolerances and the input

signal excursion is appropriately limited to account for the

worst case conditions.

Full scale and offset adjustments may also be made by ad-

justing VRT and VRB, perhaps with the aid of a pair of a DACs

or a dual DAC.

21 www.national.com

ADC08B200

20214734

FIGURE 3. The input amplifier should incorporate some gain for best performance (see text).

3.0 POWER SUPPLY CONSIDERATIONS

A/D converters draw sufficient transient current to corrupt

their own power supplies if not adequately bypassed. Gener-

ally, a 10 µF tantalum or aluminum electrolytic capacitor

should be provided for each of the four supplies and a 0.1 µF

ceramic chip capacitor placed within one centimeter of each

converter power supply pin.

To further lower the inductance in series with the capacitors,

mount the 0.1 µF capacitors on the same side of the board as

the ADC and use 2 to 4 closely spaced through holes to con-

nect the ground side of the capacitors to the ground plane.

The through holes used to ground one side of these capaci-

tors should not be used to connect anything else to ground.

Leadless chip capacitors are preferred because they have

low lead inductance.

While a single voltage source is recommended for the VA,

VD and VP supplies of the ADC08B200, the VA supply pins

should be well isolated from the other supply pins to prevent

any digital noise from being coupled into the analog portions

of the ADC. A choke is recommended between the VDR supply

pin and the other supply pins with adequate bypass capaci-

tors close to each supply pin, as shown in Figure 1, Figure 2

and Figure 3.

As is the case with all high speed converters, the ADC08B200

should be assumed to have little power supply rejection. None

of the supplies for the converter should be the supply that is

used for other digital circuitry in any system with a lot of digital

power being consumed. The ADC supplies should be the

same supply used for other analog circuitry.

No pin should ever have a voltage on it that is in excess of the

supply voltage or below ground by more than 300 mV, not

even on a transient basis. This can be a problem upon appli-

cation of power and power shut-down. Be sure that the sup-

plies to circuits driving any of the input pins, analog or digital,

do not come up any faster than does the voltage at the

ADC08B200 power pins.

4.0 THE DIGITAL INPUT PINS

The ADC08B200 has 14 digital input pins, 6 of which are used

for buffer control and 2 of which are used for PLL control.

4.1 The PD Pin

The Power Down (PD) pin, when high, puts the ADC08B200

into a low power mode where power consumption is signifi-

cantly reduced below its operating power. Stopping the clock

after raising the PD input will reduce power consumption even

more. The ADC is active and will perform normally about 2

microseconds after the PD pin is brought low. However, the

PLL, if used, requires 20 microseconds to stabilize after the

PD pin is brought low.

The digital output pins retain the last conversion output code

when either the clock is stopped or the PD pin is high. The

buffer contents are lost when PD is brought high.

4.2 The PDADC Pin

When the PDADC pin is high the ADC is powered down. The

capture buffer is active and the data within it may be clocked

out.

This is helpful for reduction of average power consumption as

the ADC can be powered down while data is being read from

the buffer. As with the PD pin, the ADC is active and will per-

form normally about 2 microseconds after the PDADC pin is

www.national.com 22

ADC08B200

brought low. Again the PLL, if used, requires 20 microseconds

to stabilize after the PD pin is brought low.

The PLL remains active when the PDADC input is high to al-

low for faster initiation of data capture after PDADC is low-

ered. Stopping the input clock when PDADC is invoked can

result in a loss of PLL lock and a longer than normal recovery

time from PDADC.

4.3 The Master CLK Pin

Although the ADC08B200 is tested and its performance is

guaranteed with a 200 MHz clock, it typically will function well

with clock frequencies as indicated in the Electrical Charac-

teristics table.

The low and high times of the clock signal can affect the per-

formance of any A/D Converter. Because achieving a precise

duty cycle is difficult, the ADC08B200 is designed to maintain

performance over a range of duty cycles. While it is specified

and performance is guaranteed with a 50% clock duty cycle

and 200 Msps, ADC08B200 performance is typically main-

tained with clock high and low times and a clock frequency

range as indicated in the electrical table. Note that clock min-

imum low and high times may not be simultaneously imposed.

The ADC Clock input line should be series terminated at the

clock source in the characteristic impedance of that line if the

clock line is longer than

where tr is the clock rise time and tprop is the propagation rate

of the signal along the trace. Typical tprop is about 150 ps/inch

(59 ps/cm) on FR-4 board material.

It is always best and advisable that one clock source pin drive

a single destination pin for best signal integrity. However, if

the clock source is used to drive more than just one destina-

tion, the CLK pin should be a.c. terminated with a series RC

to ground such that the resistor value is equal to the charac-

teristic impedance of the clock line and the capacitor value is

where tPROP is the signal propagation rate down the clock line,

"L" is the line length and ZO is the characteristic impedance

of the clock line. The units of "L" must be compatible with the

units of tPROP. This termination should be located as close as

possible to, but within one centimeter of, the ADC08B200

clock pin. Furthermore, this termination should be beyond the

receiving pin as seen from the clock source. For FR-4 board

material, the value of C becomes

Where L is the length of the clock line in inches.

4.4 The RESET Pin

A high level at this Reset input resets all control logic on the

chip, including the buffer's read and write counters. The FF

output is reset low and the EF flag is reset high upon a device

reset. Invoking a reset during the WRITE phase can cause

buffer data to be corrupted. A reset during the READ phase

will stop the READ phase before it is completed.

The RESET signal is asynchronous and should be at least 4

sample clock cycles wide. If no RESET is provided, the chip

generates its own internal reset signal at the beginning of the

buffer write phase.

4.5 The OEDGE/TEN Pin

If this Output Edge Select input is high, the data outputs tran-

sition with the rising edge of the DRDY output. If this input is

low, the data outputs transition with the falling edge of the

DRDY. Forcing a potential of VA/2 at this input enables the

Test Mode. There is an on-chip pull-up resistor at this pin, so

the device interprets a floating input at this pin to be a logic

high. See Section 10.0 TEST PATTERN OUTPUT for the

output test pattern.

4.6 The OE Pin

A high level at this Output Enable input enables the output

buffers. A low level at this input puts the digital data output

pins, including the DRDY output, into a high impedance state.

Caution: Although this device has a TRI-STATE output, main-

taining optimum noise performance requires keeping the ca-

pacitance on the data output pins as low as possible.

Therefore, it is never a good idea to connect the output pins

to a bus. Each output pin should be connected to a single

input with lines as short as possible.

4.7 Buffer-Associated Pins

The on-chip buffer is 1 kilobyte (1,024 bytes) in size and is

controlled through six (6) TTL-CMOS compatible digital input

pins.

4.7.1 THE RCLK PIN

When the capture buffer is enabled, the RCLK input is used

to read the data from the buffer. The data output and the EF

flag transition with the rise of RCLK.

It is best to halt the RCLK when not reading the buffer to min-

imize its impact upon noise performance. RCLK may be

stopped in either the high or the low state.

4.7.2 THE WEN PIN

A high level at this Write Enable input causes data to be writ-

ten into the capture buffer. One byte is written with the rise of

each sample clock. This input may go high asynchronously.

4.7.3 THE REN PIN

A high level at this Read Enable input causes data to be read

from the capture buffer. One byte is read with the rise of each

RCLK input. This signal should go high synchronous with the

RCLK input and should not be high while the WEN input is

high. If this input is high while the WEN input is high, the WEN

input has priority and the REN input is ignored, regardless of

which of these two inputs is high first. It is not possible to read

from the buffer while a write to the buffer is in progress.

4.7.4 THE ASW PIN

This Auto-Stop Write input has a dual function. With writing to

the buffer enabled and this ASW high, this pin acts as the

ASW (Auto-Stop Write) input, which causes writing to the

buffer to halt once the buffer is full (FF high). This prevents

write "wrap around" and the over-writing of older data. When

writing to the buffer is disabled, this pin is ignored. When the

device is in Test Mode, this pin acts as the Output Edge Select

input and functions as described for the OEDGE/TEN input.

4.7.5 THE BSIZE PINS

The two Buffer Size input pins (BSIZE0 and BSIZE1) are used

to select the required buffer size for the application or to by-

23 www.national.com

ADC08B200

pass the buffer altogether. Refer to Section 8.0 USING THE

DATA BUFFER for use of these pins

5.0 PLL CONTROL: THE MULT PINS

The two MULT input pins (MULT0 and MULT1) are used to

select the CLK Multiplier for the internal PLL, or to bypass the

PLL. Refer to Section 7.0 CLOCK OPTIONS for more infor-

mation.

6.0 DIGITAL OUTPUT PINS

The ADC08B200 has 12 digital output pins: 8 Digital Data

Output pins, DRDY, WENSYNC, EF and FF

6.1 Digital Data Outputs

This 8-bit bus is LVTTL/LVCMOS compatible, with a Straight

Binary output format. Data is clocked out on this bus in one

of two ways. When the internal buffer is bypassed, data is

clocked out at the sample clock rate. When the internal buffer

is used, data is clocked out at the RCLK rate. In either case,

data is clocked out on the rising edge of the appropriate clock.

Refer to Section 7.0 CLOCK OPTIONS for information on

sample rate determination.

When the Capture Buffer is bypassed, data is read directly

from the converter at the sample clock rate.

When the capture buffer is used, data is read from the capture

buffer and presented at these pins when the REN input is

high. If OEDGE/TEN is high, the digital data output and DRDY

are held low when no valid data is being sent out. If OEDGE/

TEN is low, the digital data and DRDY are held high when no

valid data is being sent out. These pins source data at the

converter sample rate when the buffer is disabled.

Whether the buffer is enabled or not, the output data is pro-

vided synchronous with DRDY. That is, the data transition

occurs with the edge of DRDY defined by OEDGE/TEN such

that the data transitions on the rise of DRDY if OEDGE/TEN

is high or on the fall of DRDY if OEDGE/TEN is low.

The data output drivers are capable of sourcing and sinking

a relatively high current to enable rapid charging and dis-

charging of the output capacitance, thereby allowing fast

output rise and fall times. The data outputs should be as lightly

loaded as possible to minimize on-chip noise and the resulting

loss of SNR performance. Note the specified load capaci-

tance at the heading of the Electrical Characteristics Table.

6.2 The DRDY Pin

This output is intended for use to latch output data into a re-

ceiving device and transitions with the transition of the digital

data outputs. The synchronizing edge of the DRDY signal can

be selected with the OEDGE input. When the buffer is not

used, DRDY is active as long as the ADC is functioning. When

the buffer is enabled, DRDY is active only while data is being

sent out. When no valid data is being sent out, the DRDY

output sense is the opposite of the OEDGE input. As long as

PD is low, this signal is always active (not high impedance)

whether or not the buffer is enabled.

The DRDY output should be have a load that is identical to

the load of the digital data outputs to ensure that one DRDY

output edge transitions at the same time as does the data.

6.3 The WENSYNC Pin

This output is synchronous with the internal sample clock and

is provided as an indication as to when sampling takes place.

The actual point in time when sampling takes place is as in-

dicated in the "Capture and Write Enable" Timing Diagram.

6.4 The EF Pin

This Empty Flag goes high, synchronous with the internal

sample clock, when the Capture Buffer is empty, either by the

buffer having been completely read or upon RESET of the

device. This output goes low when one or more bytes is writ-

ten to the buffer. When EF goes high, the DRDY and Data

outputs stop switching and both DRDY and the Data lines re-

main low if OEDGE=1, or high if OEDGE=0.

6.5 The FF Pin

The Full Flag output indicates that the buffer is full and goes

high, synchronous with the internal sample clock, when the

capture buffer is full. If the WEN input remains high, the rise

of the next sample clock after the FF output goes high will

cause the buffer pointer to "wrap around" and start writing

over the previous data unless the ASW input is high. The FF

signal goes low when the REN signal goes high and the full

condition no longer exists. This signal also goes low upon a

RESET of the device.

7.0 CLOCK OPTIONS

The ADC08B200 incorporates a PLL to facilitate clocking.

The PLL, like any PLL or DLL, can add phase noise to the

clock signal and so to the conversion process. The effect of

this phase noise increases with higher analog signal input

frequencies. If a stable clock source at the desired sample

rate is available, it is preferable to use that clock as the sample

clock for the ADC08B200, bypassing the PLL. If such a source

is not available, the internal PLL may be used to multiply the

input clock frequency by 2, 4 or 8 to obtain the desired sample

rate from a lower frequency clock source.

Bypassing the PLL or setting the CLK frequency multiplier is

accomplished through the use of the two MULT pins as indi-

cated in Table 1. Expected noise performance with and with-

out the use of the PLL is indicated in the Typical Performance

Characteristics of this data sheet.

TABLE 1. MULT Pin Function

MULT1 MULT0

CLK

Frequency

Multiplier

CLK Freq.

Range (MHz)

0 0 1 1 - 210

0 1 2 15 - 105

1 0 4 15 - 50

1 1 8 15 - 25

The internal sampling clock frequency is the input clock fre-

quency at the CLK pin multiplied by the multiplier in Table 1.

When the PLL is bypassed, the input clock at the CLK pin is

used as the sample clock and the PLL is disabled.

8.0 USING THE DATA BUFFER

The Data Buffer has read and write pointers and the first word

written to it is the first word read from it. The Data Buffer is

configurable to 256-, 512-, or 1024- bytes, and must be com-

pletely filled to the configured number of bytes before it can

be read. The "FF" flag goes high once the configured number

of bytes is in the buffer are read. Once the data buffer contents

are completely read, indicated by the "EF" flag going high, the

same data cannot be read again. It is possible to read back

only part of the contents, after which a RESET must be is-

sued, clearing the remaining data stored in the data buffer,

before the buffer may be written to again.

The WEN (Write Enable) input is used to enable writing to the

buffer, while the REN (Read Enable) input is used to enable

reading from the buffer. If both of these are high, the WEN

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ADC08B200

input dominates and the REN input is ineffective until WEN

goes low. If the WEN pin remains high after the buffer is full,

the previous contents are over-written. The ASW (Auto-Stop

Write) pin may be used to automatically stop writing to the

buffer when it is full to the configured number of bytes. See

Sections 4.7.2 THE WEN PIN, 4.7.3 THE REN PIN and 4.7.4

THE ASW PIN for information on these inputs.

The BSIZE inputs are used to configure the Data Buffer size

(described in Table 2). The user has a choice of using the

buffer or bypassing it.

When the buffer is used and its contents have been read, the

DRDY and the Data Outputs maintain the opposite sense of

the OEDGE input. When the buffer is bypassed, it is not used

and the data is presented at the ADC data output pins at the

same rate as the sample clock. Table 2 indicates the choices

available and the BSIZE pin settings to achieve each.

When the buffer is bypassed (both BSIZE pins low), the ADC

output is sent directly to the output port at the sample clock

rate without going through the buffer. In this mode all buffer

control inputs (WEN, REN, ASW and RCLK) are ignored and

the EF and FF outputs are held low. The DRDY output may

be used to capture the data at the output port.

TABLE 2. BSIZE Pin Function

BSIZE1 BSIZE0 Buffer Size

0 0 Buffer is bypassed

0 1 256 bytes

1 0 512 bytes

1 1 1024 bytes

9.0 MODES OF OPERATION

The ADC08B200 has several modes of operation. These

modes are detailed in Table 3.

The buffer function is controlled by the BSIZE pins, BSIZE0

and BSIZE1, as indicated in Table 4. The buffer can be by-

passed and data read directly from the ADC by setting both

of the BSIZE pins low.

TABLE 3. Modes of Operation

PD PDADC WEN REN Power State Operational State

1 x x x Shutdown Shutdown, non-operational

0 1 0 0 Buffer Active, ADC

Shutdown ADC powered down, no data can be captured. Buffer may be read.

0 x 0 1 Active Data is being read from buffer with RCLK

0 0 0 0 Active If buffer is bypassed, data is present at output bus. If buffer is used,

the chip is ready to capture data to the buffer.

0 0 1 x Active The ADC's digital output is being captured to the buffer. The REN input

is ignored.

0 1 1 x Buffer Active, ADC

Shutdown PROHIBITED. WEN input is ignored.

TABLE 4. Buffer Write/Read

BSIZE1 BSIZE0 WEN REN Buffer Function

0 0 x x Buffer bypassed

0 1 1 x Write to 256 byte buffer

1 0 1 x Write to 512 byte buffer

1 1 1 x Write to 1k byte buffer

0 1 0 1 Read from 256 byte buffer

1 0 0 1 Read from 512 byte buffer

1 1 0 1 Read from 1k byte buffer

10.0 TEST PATTERN OUTPUT

The ADC08B200 has a test mode whereby the data outputs

have a test pattern which may be used to "train" a receiving

device, such as a PLD. The Test Mode is invoked by forcing

a potential of VA/2 at the OEDGE/TEN input. There is an on-

chip pull-up resistor at this pin, so the device interprets a

floating input at this pin to be a logic high. This pattern is used

to test the integrity of the buffer, so the RCLK (Read Clock)

input must be used to get the output pattern.

The test pattern that is put out is a continuously repeated pat-

tern of output codes 00h - FFh - 00h - FFh - 00h. Note that

this pattern repeats as long as the test mode is invoked and

RCLK is running, so that every second time a logic low ap-

pears it will be present for two bit times.

11.0 APPLICATION EXAMPLE

Figure 4 shows an example of a typical application. The ana-

log input and reference circuits are as described in Figure 2

and Figure 3, except the input amplifier is shown without any

gain and offset adjustments. The overall nominal gain of the

input amplifier circuit is 1.98 and the nominal −3 dB input

bandwidth is about 195 MHz. Note that this circuit does not

show an anti-aliasing filter.

A 50 MHz clock oscillator is used for the input clock source.

The MULT0 input grounded and the MULT1 input high means

(from Table 1) that this 50 MHz input clock is multiplied by the

internal PLL by 4 to provide a 200 Msps capture rate.

Since the BSIZE0 and BSIZE1 pins are both high, the internal

capture buffer size is set to 1,024 bytes (see Table 2). Data

writing to the internal buffer will automatically stop when the

buffer is full because the ASW input is high. The FF (Full Flag)

will go high when the buffer is full and data is ready to be read.

The OEDGE pin is high, meaning the output data will transi-

tion at the rise of the DRDY output. Since the PD pin is

grounded and the OE pin is high, the device will never be

completely powered down and the outputs are always en-

abled. Since the PDADC pin is driven from the controlling

device, the ADC may be powered down, leaving the output

buffer active, when the device buffer is being read, or when

the device is not in use.

The digital lines between the ADC08B200 and the receiving

device have 33 Ohms at the signal source end as source ter-

minators, assuming output impedances of about 20 Ohms

and 50-Ohm lines. The RESET and PDADC lines are not ter-

minated because these are basically d.c. lines and it is as-

sumed that they do not toggle frequently.

25 www.national.com

ADC08B200

20214736

FIGURE 4. Example of a Typical Application.

The average power consumption of the ADC08B200 (assum-

ing a new capture is taken as soon as the buffer contents is

read) may be calculated by taking power consumed while

capturing and writing to the buffer and multiplying it by the

capture time divided by the throughput time (interval between

the successive rises of the WEN signal), added to the power

while reading the buffer with PDADC high (assuming the

PDADC input is taken high whenever data is not being cap-

tured) multiplied by the time that PDADC is high (Buffer read

time plus any idle time) divided by the throughput rate.

Assuming a Capture Power of 543 mW, a 200 Msps capture

rate and a 66mW Read Power with PDADC high, a 50 MHz

data read rate and no completely idle time, the average power

consumption would be 161.4 mW.

12.0 POWER SUPPLY CONSIDERATIONS

It is important to note that capacitors have an equivalent se-

ries inductance associated with them such that, beyond a

certain frequency, the capacitor behaves more like an induc-

tance than a capacitance and adequate bypassing may be

infective, resulting in the power distribution system having a

high impedance, which could further result in excessive noise

on the power supply. The frequency beyond which adequate

bypassing may be effective depends primarily upon the

chemistry of the capacitor dielectric, but can also vary a little

from one manufacturer to another. Even so, this frequency is

in the hundreds of Megahertz. Note, however, that a 200 MHz

clock will have significant harmonic energy far beyond this.

The result could be high frequency noise on the supply lines

that could effect the SNR performance of the converter.

The use of adjacent power and ground planes will go a long

way toward reducing the impedance of the power distribution

system and is encouraged. Furthermore, we suggest placing

the lowest value of bypass capacitor close to the supply pin

on the same side of the board as the ADC and connect the

ground end of the bypass capacitor to the ground plane with

at least two through holes. The through holes have an induc-

tance associated with them and using two or more such holes

puts these inductances in parallel, lowering the effective in-

ductance to ground.

www.national.com 26

ADC08B200

12.1 Supply Voltages

The ADC8D200 will perform well with power supply voltages

in the range specified in the Operating Ratings, just before the

Electrical Table. Many individual devices may perform well

down to supply voltages of 2.7V, but this should not be relied

upon because part of the product distribution, depending up-

on normal fabrication process tolerances, could result in the

majority of some production runs not functioning well below

3.0V.

While all supplies may be of the same voltage, the digital

supply (VD), the PLL supply (VP) and the output driver supply

(VDR) ADC08B200 should never be higher than 300 mV

above the analog supply (VA). Furthermore, the output driver

supply, VDR may be as low as 2.7V only when using the buffer

and when the buffer read clock (RCLK) frequency is no higher

than 50 MHz because the output slew rate decreases at low

VDR voltages and the output eye may not be open enough to

allow reliable data capture.

13.0 LAYOUT AND GROUNDING

Proper grounding and proper routing of all signals are essen-

tial to ensure accurate conversion. A single, unified ground

plane should be used. Do not split the ground plane.

Coupling between the typically noisy digital circuitry and the

sensitive analog circuitry can lead to poor performance that

may seem impossible to isolate and remedy. The solution is

to keep all lines separated from each other by at least six

times the height above the reference plane, and to keep the

analog circuitry well separated from the digital circuitry.

The DR GND connection to the ground plane should not use

the same through holes used by other ground connections.

High power digital components should not be located near

any analog components.

Generally, analog and digital lines should cross each other at

90° to avoid getting digital noise into the analog path. In high

frequency systems, however, avoid crossing analog and dig-

ital lines altogether. Clock lines should be isolated from ALL

other lines, analog AND digital. Even the generally accepted

90° crossing should be avoided as even a little coupling can

cause problems at high frequencies. Best performance at

high frequencies is obtained with a straight signal path.

The reference and analog inputs should be isolated from

noisy signal traces to avoid coupling of spurious signals into

the input. Any external component (e.g., a filter capacitor)

connected between the converter's input and ground should

be connected to a very clean point in the ground plane and

preferably with 2 to 4 closely spaced through holes.

14.0 DYNAMIC PERFORMANCE

The ADC08B200 is a.c. tested and its dynamic performance

is guaranteed. To meet the published specifications, the clock

source driving the CLK input must exhibit as little jitter as pos-

sible. For best a.c. performance, each clock destination

should be driven by a separate source, such as with a clock

distribution chip or with a clock tree such as seen

in Figure 5.

20214737

FIGURE 5. Isolating the ADC Clock from Digital Circuitry

It is good practice to keep the ADC clock line as short as pos-

sible and to keep it well away from other signals, which can

introduce jitter into the clock signal. The clock signal can also

introduce noise into a nearby signal path.

15.0 COMMON APPLICATION PITFALLS

Driving the inputs (analog or digital) beyond the power

supply rails. For proper operation, all inputs should not go

more than 300 mV below the ground pins or 300 mV above

the supply pins. Exceeding these limits on even a transient

basis may cause faulty or erratic operation. It is not uncom-

mon for high speed digital circuits (e.g., 74F and 74AC de-

vices) to exhibit undershoot that goes more than a volt below

ground. A 47Ω resistor in series with the offending digital in-

put, close to the driving source, will usually eliminate the

problem.

Care should be taken not to overdrive the inputs of the

ADC08B200. Such practice may lead to conversion inaccu-

racies and even to device damage.

Attempting to drive a high capacitance digital data bus.

The more capacitance the output drivers must charge for

each conversion, the more instantaneous digital current is re-

quired from VDR and DR GND. These large charging current

spikes can couple into the analog section, degrading dynamic

performance. Buffering the digital data outputs may be nec-

essary if the data bus capacitance exceeds 10 pF. Dynamic

performance can also be improved by adding 12Ω to 27Ω se-

ries resistors at each digital output, reducing the energy cou-

pled back into the converter input pins.

Using an inadequate amplifier to drive the analog input.

As explained in Section 2.0 THE ANALOG INPUT, there are

voltage spikes at the ADC analog input. These voltage spikes

can cause instability in a feedback type amplifier used to drive

the analog input. These spikes need not be filtered out, but

should settle quickly. The amplifier should be fast enough to

handle the frequencies presented to it, but not so fast that it

would readily oscillate. A single-pole RC filter, as explained

in Section 2.0 THE ANALOG INPUT will help ensure amplifier

stability and accurate data capture.

Driving the VRT pin or the VRB pin with devices that can

not source or sink the current required by the ladder. As

mentioned in Section 1.0 REFERENCE INPUTS, care should

be taken to see that any driving devices can source sufficient

current into the VRT pin and sink sufficient current from the

VRB pin. If these pins are not driven with devices than can

handle the required current, these reference pins will not be

stable, resulting in a reduction of dynamic performance.

Using a clock source with excessive jitter, using an ex-

cessively long clock signal trace, or having other signals

coupled to the clock signal trace. This will cause the sam-

pling interval to vary, causing excessive output noise and a

27 www.national.com

ADC08B200

reduction in SNR performance. The use of simple gates with

RC timing is generally inadequate as a clock source.

Busing the data outputs. SNR performance of all ADCs,

especially high speed ADCs, is sensitive to the amount of ca-

pacitance at the data outputs because the currents required

of the ADC data outputs to charge and discharge these ca-

pacitances cause voltage spikes (noise) on the die. Minimiz-

ing the output capacitance will help maintain noise perfor-

mance of the converter. Busing the outputs adds undesired

capacitive loading to the ADC. Similarly, it is important to keep

trace capacitance to a minimum by using short traces at the

ADC outputs.

www.national.com 28

ADC08B200

Physical Dimensions inches (millimeters) unless otherwise noted

NOTES: UNLESS OTHERWISE SPECIFIED

REFERENCE JEDEC REGISTRATION mo-153, VARIATION AD, DATED 7/93.

48-Lead Package BC

Order Number ADC08B200CIVS

NS Package Number VBC48A

29 www.national.com

ADC08B200

Notes

ADC08B200 8-Bit, 200 MSPS A/D Converter with Capture Buffer

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