CS42432 datasheet(49/62 Pages) CIRRUS

49 / 62 page

DS673PP2

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 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 which have a large voltage coefficient (such

as general-purpose ceramics) must be avoided since these can degrade signal linearity.

4.7

µF

100 k

Ω

10 k

Ω

100 k

Ω

100 k

Ω

0.1

µF

100

µF

470 pF

C0G

634

Ω

634

Ω

634

Ω

2700 pF

C0G

332

Ω

AINx+

AINx-

ADC1-2

Figure 19. Single to Differential Active Input Filter

470 pF

C0G

634

Ω

2700 pF

C0G

4.7

µF

100 k

Ω

100 k

Ω

100 k

Ω

4.7

µF

AIN1+,2+,3+,4+

AIN1-,2-,3-,4-

ADC1-2

Figure 20. Single-Ended Active Input Filter

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