AD7918_15 datasheet(13/28 Pages) AD

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Data Sheet

AD7908/AD7918/AD7928

Rev. E | Page 13 of 28

TYPICAL PERFORMANCE CHARACTERISTICS

PERFORMANCE CURVES

Figure 4 shows a typical FFT plot for the AD7928 at 1 MSPS

sample rate and 50 kHz input frequency. Figure 5 shows the

signal-to-(noise + distortion) ratio performance vs. input

frequency for various supply voltages while sampling at 1 MSPS

with an SCLK of 20 MHz.

Figure 6 shows the power supply rejection ratio vs. 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) = 10 log(Pf/Pfs)

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.

100

150

200

250

300

350

400

450

500

FREQUENCY (kHz)

–10

–30

–50

–70

–90

–110

4096 POINT FFT

AVDD = 5V

fSAMPLE = 1MSPS

fIN = 50kHz

SINAD = 71.147dB

THD = –87.229dB

SFDR = –90.744dB

Figure 4. AD7928 Dynamic Performance at 1 MSPS

100

1000

INPUT FREQUENCY (kHz)

fSAMPLE = 1MSPS

TA = 25°C

RANGE = 0V TO REFIN

AVDD = VDRIVE = 2.70V

AVDD = VDRIVE = 3.60V

AVDD = VDRIVE = 4.75V

AVDD = VDRIVE = 5.25V

Figure 5. AD7928 SINAD vs. Analog Input Frequency for

Various Supply Voltages at 1 MSPS

Figure 7 shows a graph of total harmonic distortion vs. analog

input frequency for various supply voltages, and Figure 8 shows a

graph of total harmonic distortion vs. analog input frequency

for various source impedances. See the Analog Input section.

Figure 9 and Figure 10 show typical INL and DNL plots for the

AD7928.

SUPPLY RIPPLE FREQUENCY (kHz)

1000

500

900

800

700

600

400

300

200

100

–40

–60

–80

–90

–20

–50

–70

–10

–30

AVDD = 5V

200mV p-p SINEWAVE ON AVDD

REFIN = 2.5V, 1µF CAPACITOR

TA = 25°C

Figure 6. AD7928 PSRR vs. Supply Ripple Frequency

–50

–65

–75

–85

–90

–60

–70

–80

–55

AVDD = VDRIVE = 4.75V

AVDD = VDRIVE = 3.60V

AVDD = VDRIVE = 2.70V

fSAMPLE = 1MSPS

TA = 25°C

RANGE = 0V TO REFIN

AVDD = VDRIVE = 5.25V

100

1000

INPUT FREQUENCY (kHz)

Figure 7. AD7928 THD vs. Analog Input Frequency for

Various Supply Voltages at 1 MSPS

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