CS42435_07 Datasheet, PDF (48/57 Pages) Cirrus Logic – 108 dB, 192 kHz 4-In, 8-Out TDM CODEC

8. EXTERNAL FILTERS
CS42435
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 mul-
tiples of the digital passband frequency (n × 6.144 MHz), where n=0,1,2,... Refer to Figures 19 and 20 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 21 and 22 for low-cost, low-component-
count passive input filters. The use of capacitors that have a large voltage coefficient (such as general-pur-
pose ceramics) must be avoided since these can degrade signal linearity
100 kΩ
634 Ω
4.7 μF
470 pF
C0G
-
+
VA
100 kΩ
10 kΩ
91 Ω
634 Ω
100 kΩ
0.1 μF
100 μF ^{332 Ω}
634 Ω
470 pF
C0G
-
+
91 Ω
2700 pF
C0G
Figure 19. Single-to-Differential Active Input Filter
100 kΩ
VA
100 kΩ
4.7 μF
100 kΩ
634 Ω
470 pF
C0G
-
91 Ω
+
2700 pF
C0G
ADC1-2
AIN1+,2+,3+,4+
ADC1-2
AINx+
AINx-
4.7 μF
AIN1-,2-,3-,4-
Figure 20. Single-Ended Active Input Filter
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DS685F2