AD7908 datasheet(12/24 Pages) AD

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AD7908/AD7918/AD7928–Typical Performance Characteristics

REV. A

PERFORMANCE CURVES

TPC 1 shows a typical FFT plot for the AD7928 at 1 MSPS

sample rate and 50 kHz input frequency. TPC 2 shows the

signal-to-(noise + distortion) ratio performance versus input

frequency for various supply voltages while sampling at 1 MSPS

with an SCLK of 20 MHz.

TPC 3 shows the power supply rejection ratio versus supply

ripple frequency for the AD7928 when no decoupling is used.

The power supply rejection ratio is defined as the ratio of the

power in the ADC output at full-scale frequency f, to the power

of a 200 mV p-p sine wave applied to the ADC AVDD supply of

frequency fS:

PSRR dB

Pfs

()

log(

)

= 10

Pf is equal to the power at frequency f in ADC output; PfS is

equal to the power at frequency fS coupled onto the ADC AVDD

supply. Here a 200 mV p-p sine wave is coupled onto the AVDD

supply.

TPC 4 shows a graph of total harmonic distortion versus analog

input frequency for various supply voltages, while TPC 5 shows

a graph of total harmonic distortion versus analog input frequency

for various source impedances. See the Analog Input section.

TPC 6 and TPC 7 show typical INL and DNL plots for the

AD7928.

FREQUENCY (kHz)

–10

100

200

300

400

500

–30

–50

–70

–90

–110

150

250

350

450

4096 POINT FFT

AVDD = 5V

fSAMPLE = 1MSPS

fIN = 50kHz

SINAD = 71.147dB

THD = –87.229dB

SFDR = –90.744dB

TPC 1. AD7928 Dynamic Performance at 1 MSPS

INPUT FREQUENCY (kHz)

1000

100

fSAMPLE = 1MSPS

TA = 25 C

RANGE = 0 TO REFIN

AVDD = V DRIVE = 2.7V

AVDD = V DRIVE = 3.6V

AVDD = V DRIVE = 4.75V

AVDD = V DRIVE = 5.25V

TPC 2. AD7928 SINAD vs. Analog Input Frequency for

Various Supply Voltages at 1 MSPS

SUPPLY RIPPLE FREQUENCY (kHz)

1000

–40

–60

–80

–90

500

–20

–50

–70

900

800

700

600

400

300

200

100

AVDD = 5V

200mV p-p SINE WAVE ON AVDD

REFIN = 2.5V, 1 F CAPACITOR

TA = 25 C

–10

–30

TPC 3. AD7928 PSRR vs. Supply Ripple Frequency

INPUT FREQUENCY (kHz)

–50

1000

–65

–75

–85

–90

–60

–70

–80

100

–55

AVDD = V DRIVE = 5.25V

AVDD = V DRIVE = 4.75V

AVDD = V DRIVE = 2.7V

fSAMPLE = 1MSPS

TA = 25 C

RANGE = 0 TO REFIN

AVDD = V DRIVE = 3.6V

TPC 4. AD7928 THD vs. Analog Input Frequency for

Various Supply Voltages at 1 MSPS

INPUT FREQUENCY (kHz)

–50

1000

–65

–75

–85

–90

–60

–70

–80

100

–55

fSAMPLE = 1MSPS

TA = 25 C

RANGE = 0 TO REFIN

AVDD = 5.25V

RIN = 1000

RIN = 10

RIN = 50

RIN = 100

TPC 5. AD7928 THD vs. Analog Input Frequency for

Various Source Impedances

–12–

AD7908 Datasheet(PDF) 12 Page - Analog Devices

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