WM8940_11 Datasheet, PDF (86/91 Pages) Wolfson Microelectronics plc – Mono CODEC with Speaker Driver

WM8940
Production Data
NOTCH FILTERS AND LOW PASS FILTER
The WM8940 supports four programmable notch filters. The fourth notch filter can be configured as a
low pass filter. The following illustrates three digital notch filters, followed by a single low pass filter in
the ADC filter path. Both the centre frequency and -3dB bandwidth are programmable for the notch
filters. The cut off frequency is programmable for the low pass filter. The following graphs show the
responses of 1) a single notch filter at three chosen centre frequencies, with three bandwidths for
each, 2) the low pass filter at three chosen cut off frequencies and 3) the cascade of three notch
filters followed by the low pass filter, each with a different centre / cut off frequency with three
bandwidths for each.
+0
-5
-10
R
E
S
-15
P
O _-20
N
S
E ^-25
(dB) _-30
-35
-40
-45
-50
-55
-60
20
50
100
200
500
1k
2k
Frequency (Hz)
5k
10k
20k
Figure 46 ADC Notch Filter Responses (48kHz); fc=100Hz, 1kHz, 10kHz; fb = 100Hz, 600Hz, 2kHz
+0
-5
-10
R
E
S
-15
P
O ^-20
N
S _-25
E
(dB) ^-30
-35
-40
-45
-50
-55
-60
20
50
100
200
500
1k
2k
Frequency (Hz)
Figure 47 ADC Low Pass Filter Responses (48kHz); fc= 1kHz, 5kHz, 10kHz
T
5k
10k
20k
w
PD, Rev 4.3, November 2011
86