Datasheet

AD7873 Data Sheet
Rev. F | Page 12 of 28
Figure 23. AC PSRR vs. Supply Ripple Frequency
Figure 23 shows the power supply rejection ratio vs. V
DD
supply
frequency for the AD7873. 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 100 mV sine wave applied to the
ADC V
CC
supply of frequency f
S
PSSR (dB) = 10log(Pf/Pf
s
)
where:
Pf is power at frequency, f, in ADC output.
Pf
s
is power at frequency, f
s
, coupled onto the ADC V
CC
supply.
Here a 100 mV p-p sine wave is coupled onto the V
CC
supply.
Decoupling capacitors of 10 µF and 0.1 µF were used on the supply.
–120
–100
–80
–60
–40
–20
0
PSRR (dB)
0 10 20 30 40 50 60 70 80 90 100
V
CC
RIPPLE FREQUENCY (kHz)
V
CC
= 3V
100mV p-p SINE WAVE ON +V
CC
V
REF
= 2.5V EXT REFERENCE
f
SAMPLE
= 125kHz,
f
IN
= 20kHz
02164-023