Cirrus Logic CS4272 - Manual (Page 32)

CS4272
32 DS593F1
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.
AIN+
AIN-
VCOM
-
+
-
+
470 pF
C0G
470 pF
C0G
CS4272
634 Ω
91 Ω
634 Ω
91 Ω
2700 pF
C0G
10 µF
10 µF
10 k Ω
10 k Ω
0.01 µF
1 µF 0.1 µF
Figure 12. CS4272 Recommended Analog Input Buffer
AIN+
AIN-
CS4272
AIN+
AIN-
Full-Scale Input Level= (AIN+) - (AIN-)= 5.6 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