CS42438-DMZ datasheet(52/61 Pages) CIRRUS

52 / 61 page

DS646F2

CS42438

8.1.2

Passive Input Filter w/Attenuation

Some applications may require signal attenuation prior to the ADC. The full-scale input voltage will scale

with the analog power supply voltage. For VA = 5.0 V, the full-scale input voltage is approximately

2.8 Vpp, or 1 Vrms (most consumer audio line-level outputs range from 1.5 to 2 Vrms).

Figure 23 shows a passive input filter with 6 dB of signal attenuation. Due to the relatively high input im-

pedance on the analog inputs, the full distortion performance cannot be realized. Also, the resistor divider

circuit will determine the input impedance into the input filter. In the circuit shown in Figure 23, the input

impedance is approximately 5 k

Ω. By doubling the resistor values, the input impedance will increase to

10 k

Ω. However, in this case the distortion performance will drop due to the increase in series resistance

on the analog inputs.

2700 pF

C0G

μF

2.5 k

AIN1+,2+,3+,4+

AIN1-,2-,3-,4-

ADC1-2

4.7

μF

2700 pF

C0G

μF

2.5 k

AIN5A,6A

AIN5B,6B

ADC3

2700 pF

C0G

μF

2.5 k

Figure 23. Passive Input Filter w/Attenuation

CS42438-DMZ Datasheet(PDF) 52 Page - Cirrus Logic