Cirrus Logic CS4271 - Manual (Page 32)

CS4271
32 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
91 Ω
2700 pF
C0G
10 µF
10 µF
10 k Ω
10 k Ω
1 µF 0.1 µF
AINB
2700 pF
C0G
-
+
470 pF
C0G
91 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