CS4271 datasheet(32/53 Pages) CIRRUS

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CS4271

DS592F1

5.4

Analog Connections

5.4.1

Input Connections

The analog modulator samples the input at 6.144 MHz (MCLK=12.288 MHz). The digital filter will reject signals with-

in the stopband of the filter. However, there is no rejection for input signals which are (n

× 6.144 MHz) the digital

passband frequency, where n=0,1,2,... Refer to Figure 12 for a recommended analog input buffer 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 which have a large voltage coefficient (such as general purpose ceramics) must be avoided since

these can degrade signal linearity. Figure 13 shows the full-scale analog input levels.

AINA

VQ2

VQ1

470 pF

C0G

CS4271

634

Ω

2700 pF

C0G

µF

10 k

Ω

10 k

Ω

µF

0.1

µF

AINB

2700 pF

C0G

470 pF

C0G

Ω

634

Ω

VQ3

AINL

AINR

Figure 12. CS4271 Recommended Analog Input Buffer

CS4271

AINA

AINB

Full-Scale Input Level = 2.8 Vpp

3.9 V

2.5 V

1.1 V

3.9 V

2.5 V

1.1 V

Figure 13. Full-Scale Analog Input

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