Datasheet

AD7908/AD7918/AD7928
Rev. D | Page 13 of 32
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 AV
DD
supply of
frequency f
S
PSRR(dB) = 10 log(Pf/Pfs)
Pf is equal to the power at frequency f in ADC output; Pf
S
is
equal to the power at frequency f
S
coupled onto the ADC AV
DD
supply. Here a 200 mV p-p sine wave is coupled onto the AV
DD
supply.
0 50 100 150 200 250 300 350 400 450 500
SNR (dB)
FREQUENCY (kHz)
–10
–30
–50
–70
–90
–110
4096 POINT FFT
AV
DD
= 5V
f
SAMPLE
= 1MSPS
f
IN
= 50kHz
SINAD = 71.147dB
THD = –87.229dB
SFDR = –90.744dB
03089-004
Figure 4. AD7928 Dynamic Performance at 1 MSPS
75
70
65
60
55
10 100 1000
SINAD (dB)
INPUT FREQUENCY (kHz)
f
SAMPLE
= 1MSPS
T
A
= 25°C
RANGE = 0V TO REF
IN
AV
DD
= V
DRIVE
= 2.70V
AV
DD
= V
DRIVE
= 3.60V
AV
DD
= V
DRIVE
= 4.75V
AV
DD
= V
DRIVE
= 5.25V
03089-005
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.
PSRR (dB)
SUPPLY RIPPLE FREQUENCY (kHz)
0 1000500 900800700600400300200100
–40
–60
–80
–90
–20
–50
–70
0
–10
–30
AV
DD
= 5V
200mV p-p SINEWAVE ON AV
DD
REF
IN
= 2.5V, 1µF CAPACITOR
T
A
= 25°C
03089-006
Figure 6. AD7928 PSRR vs. Supply Ripple Frequency
–
50
–65
–75
–85
–90
–60
–70
–80
–55
AV
DD
= V
DRIVE
= 4.75V
AV
DD
= V
DRIVE
= 3.60V
AV
DD
= V
DRIVE
= 2.70V
f
SAMPLE
= 1MSPS
T
A
= 25°C
RANGE = 0V TO REF
IN
AV
DD
= V
DRIVE
= 5.25V
10 100 1000
THD (dB)
INPUT FREQUENCY (kHz)
03089-007
Figure 7. AD7928 THD vs. Analog Input Frequency for
Various Supply Voltages at 1 MSPS