WM8945
Production Data
5-NOTCH FILTER
The 5-notch filter is part of the SE1 block. This function allows up to 5 programmable frequency
bands to be attenuated. The frequency and width of each notch is configurable; the depth of the
attenuation may also be adjusted. The default setting is bypass (OFF). The notch filters are enabled
using the SE1_NOTCH_L_ENA register bit defined in Table 13. For the derivation of the other
associated registers, refer to the configuration tools supplied with the WM8945 Evaluation Kit.
Typical applications for the notch filters are filtering of fixed-frequency noise or resonances; these
might arise from a motor (e.g. DSC zoom lens motor) or from characteristics of the application
housing. Example plots of the Notch filter response are shown in Figure 15.
Notch Response - Slave Mode - fc=1kHz, fb=100, 500, 1k, 5k, 10kHz -
Depth=100%
Notch Response - Slave Mode - fc=1kHz, fb=1kHz Depth 0 to 100%
+0
+0
-10
T
-10
-20
-30
-40
-50
-60
-70
-80
-90
-20
-30
-40
-50
-60
-70
-80
-90
d
B
V
d
B
V
-100
-100
20
520 550 600 650 700 750 800 850 900
1k
1.2k
1.5k
50
100
200
500
1k
2k
5k
10k
20k
Hz
Hz
1kHz notch, 100% depth, bandwidth 100Hz, 500Hz, 1kHz, 5kHz, 10kHz
1kHz notch, bandwidth 1kHz, depth 0% to 100% in 20% steps
Notch Response - Slave Mode - fc=200, 500, 1k, 2k, 5k, 10kHz, fb=fc/2,
Depth 100%
+0
T
-10
-20
-30
-40
-50
-60
-70
-80
-90
d
B
V
-100
100
200
500
1k
2k
5k
10k
20k
Hz
5 notches, bandwidth Fcentre/2, depth 100%
Figure 15 Notch Filter Responses
PD, May 2011, Rev 4.1
34
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
