CS42448-CQZR Cirrus Logic Inc, CS42448-CQZR Datasheet - Page 54

• Manufacturer Part Number: CS42448-CQZR
• Description: IC,Soundcard Circuits,CMOS,QFP,64PIN,PLASTIC
• Manufacturer: Cirrus Logic Inc

54
7.1.1
7.1.2
Passive Input Filter
The passive filter implementation shown in
will not provide optimum source impedance for the ADC modulators. Full analog performance will there-
fore not be realized using a passive filter.
In this topology the distortion performance is affected, but the dynamic range performance is not limited.
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 29
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
impedance is approximately 5 kΩ. By doubling the resistor values, the input impedance will increase to
10 kΩ. However, in this case the distortion performance will drop due to the increase in series resistance
on the analog inputs.
shows a passive input filter with 6 dB of signal attenuation. Due to the relatively high input im-
100 kΩ
100 kΩ
100 kΩ
Figure 28. Passive Input Filter
150 Ω
150 Ω
150 Ω
10 μF
10 μF
10 μF
Figure 28
Figure 28
4.7 μF
illustrates the unity gain, passive input filter solution.
2700 pF
2700 pF
2700 pF
C0G
C0G
C0G
will attenuate any noise energy at 6.144 MHz but
AIN1+,2+,3+,4+
AIN1-,2-,3-,4-
AIN5A,6A
AIN5B,6B
ADC1-2
ADC3
Figure
CS42448
29, the input
DS648F3