CS42438 Datasheet, PDF (51/64 Pages) Cirrus Logic – 108 dB, 192 kHz 6-in, 8-out TDM CODEC

8 APPENDIX A: EXTERNAL FILTERS
8.1 ADC Input Filter
The analog modulator samples the input at 6.144 MHz (internal MCLK=12.288 MHz). The digital filter will
reject signals within the stopband of the filter. However, there is no rejection for input signals which are
multiples of the digital passband frequency (n × 6.144 MHz), where n=0,1,2,... Refer to Figures 20 and 21
for a recommended analog input filter that will attenuate any noise energy at 6.144 MHz, in addition to
providing the optimum source impedance for the modulators. Refer to Figures 22 and 23 for low cost, low
component count passive input filters. The use of capacitors which have a large voltage coefficient (such
as general-purpose ceramics) must be avoided since these can degrade signal linearity.
100k Ω
634 Ω
4.7 µF
470 pF
C0G
-
+
VA
100k Ω
10k Ω
91 Ω
634 Ω
100k Ω
0.1 µF
100 µF ^{332 Ω}
634 Ω
470 pF
C0G
-
+
91 Ω
2700 pF
C0G
ADC1-3
AINx+
AINx-
Figure 20. Single to Differential Active Input Filter
100 kΩ
VA
100 kΩ
4.7 µF
100 kΩ
470 pF
634 Ω
C0G
-
91 Ω
+
2700 pF
C0G
ADC1-2
AIN1+,2+,3+,4+
4.7 µF
AIN1-,2-,3-,4-
100 kΩ
VA
100 kΩ
4.7 µF
100 kΩ
100 kΩ
VA
100 kΩ
4.7 µF
100 kΩ
470 pF
634 Ω
C0G
-
91 Ω
+
470 pF
634 Ω
C0G
-
91 Ω
+
2700 pF
C0G
2700 pF
C0G
Figure 21. Single-Ended Active Input Filter
ADC3
AIN5A,6A
AIN5B,6B
DS646PP2
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