Datasheet

AD7843
Rev. B | Page 10 of 20
–120
–100
–80
–60
–40
–20
0
PSRR (dB)
0 102030405060708090100
V
CC
RIPPLE FREQUENCY (kHz)
02144-B-016
V
CC
= 3V, V
REF
= 2.5V
100mV p-p SINEWAVE ON +V
CC
f
SAMPLE
= 125kHz, f
IN
= 20kHz
Figure 16. AC PSRR vs. Supply Ripple Frequency
Figure 16 shows the power supply rejection ratio versus V
CC
supply frequency for the AD7843. The power supply rejection
ratio is defined as the ratio of the power in the ADC output at
full-scale frequency f
S
to the power of a 100 mV sine wave
applied to the ADC V
CC
supply of frequency f
S
:
PSRR (dB) = 10 log (Pf/Pfs)
where:
Pf is the power at frequency f in ADC output.
Pfs is the 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.