µPD63210, 63210L
3.3 Digital Filter
The 8-times oversampling FIR digital filter is used to attenuate the image out of band noise component, thus
facilitating the analog filter designing.
The configuration of the digital filter is shown in Figure 3-5. The characteristics of the digital filter are shown
in Figures 3-6 and 3-7.
Figure 3-5. Configuration of Digital Filter
(Input)
fs
1st 127th FIR filter
2fs
2nd 23rd FIR filter
4fs
3rd 11th FIR filter
8fs
(Output)
Figure 3-6. Frequency Characteristics of Digital Filter
0
–40
–80
–120
0
1
2
3
4
5
6
7
8
Frequency (fS)
Figure 3-7. Intraband Ripple Characteristics of Digital Filter
0.005
0
–0.005
0 0.0625 0.125 0.1875 0.25 0.3125 0.375 0.4375 0.5
Frequency (fS)
10