D/A Analog Low Pass Filter - Motorola DSP56156 Manual

ON-CHIP CODEC FREQUENCY RESPONSE AND GAIN ANALYSIS
6.5.2.3

D/A Analog Low Pass Filter

The analog low-pass filter is a three-pole, two zero switched capacitor filter. The purpose
of this filter is to attenuate the out-of-band quantization noise and the images created by
the up-sampling. This filter is clocked at the slow D/A clock rate. Eqn. 6-4 gives the filter
transfer function:
Eqn. 6-4 Analog Low-pass Filter Transfer Function
H z ( )
Figure 6-11 shows an example of the D/A analog low-pass filter log magnitude response
using a 512Khz master clock. This figure shows the filter frequency response in the bands
0- 256 KHz and 0-8 KHz.
6 - 24
(
0.004514
= ------------------------------------------------------------------------------------------------------------ -
( ) 1 1.9504z
1 –
1 0.9501z –
DSP56156 ON-CHIP SIGMA/DELTA CODEC
) 1 1.9532z ( )
1 – 2 –
z
– +
(
1 –
– + 0.9546z
)
2 –
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