CS5364
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.
634 Ω
AIN+
100 kΩ
10 uF
AIN-
100 kΩ
10 uF
470 pF
COG
-
+
10 k Ω
VQ
10 k Ω
+
-
470 pF
COG
91 Ω
91 Ω
ADC AIN+
COG
2700 pF
ADC AIN-
634 Ω
Figure 15. Recommended Analog Input Buffer
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DS625F2