Cirrus Logic CS5368 - Manual (Page 28)

28 DS624F5
CS5368
4.10 Analog Connections
The analog modulator samples the input at half of the internal Master Clock frequency, or 6.144 MHz nom-
inally. The digital filter will reject signals within the stopband of the filter. However, there is no rejection of
input signals that are at (N X 6.144 MHz) the digital passband frequency, where n=0,1,2.... Refer to
Figure 15 , which shows the suggested filter that will attenuate any noise energy at 6.144 MHz in addition to
providing the optimum source impedance for the modulators. The use of capacitors that have a large volt-
age coefficient (such as general-purpose ceramics) must be avoided since these can degrade signal linear-
ity. COG capacitors are recommended for this application. For additional configurations, refer to Cirrus
Application Note AN241.
Figure 15. Recommended Analog Input Buffer
VQ
+
634 
634 
91 
91  +
-
-
2700 pF
470 pF
470 pF
COG
COG
10 uF
10 uF
ADC AIN+
ADC AIN-
AIN+
AIN-
COG
100k
10 k 
10 k 
100k