CS42448 datasheet(53/64 Pages) CIRRUS

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DS648F2

CS42448

7. EXTERNAL FILTERS

7.1

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 26 and 27 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 28 and 29 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

4.7

μF

100k

10k

100k

0.1

μF

100

μF

470pF

C0G

634

2700pF

C0G

332

AINx+

AINx-

ADC1-3

Figure 26. Single to Differential Active Input Filter

470 pF

C0G

634

2700 pF

C0G

4.7

μF

100 k

4.7

μF

AIN1+,2+,3+,4+

AIN1-,2-,3-,4-

ADC1-2

ADC3

470 pF

C0G

634

2700 pF

C0G

4.7

μF

100 k

AIN5A,6A

470 pF

C0G

634

2700 pF

C0G

4.7

μF

100 k

AIN5B,6B

Figure 27. Single-Ended Active Input Filter

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