Wolfson WM8978, Manual, Page: 110 / 119

WM8978
Production Data
w
PD, Rev 4.5, October 2011
110
HIGHPASS FILTER
The WM8978 has a selectable digital highpass filter in the ADC filter path. This filter has two modes,
audio and applications. In audio mode the filter is a 1
st
order IIR with a cut-off of around 3.7Hz. In
applications mode the filter is a 2
nd
order high pass filter with a selectable cut-off frequency.
-40
-35
-30
-25
-20
-15
-10
-5
0
5
0 5 10 15 20 25 30 35 40 45
Frequency (Hz)
R
es
pons
e (
dB
)
Figure 54 ADC Highpass Filter Response, HPFAPP=0
-60
-50
-40
-30
-20
-10
0
10
0 200 400 600 800 1000 1200
Frequency (Hz)
R
e
spons
e (
d
B
)
-80
-70
-60
-50
-40
-30
-20
-10
0
10
0 200 400 600 800 1000 1200
Frequency (Hz)
Res
pons
e (
dB
)
Figure 55 ADC Highpass Filter Responses (48kHz),
HPFAPP=1, all cut-off settings shown.
Figure 56 ADC Highpass Filter Responses (24kHz),
HPFAPP=1, all cut-off settings shown.
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
10
0 200 400 600 800 1000 1200
Frequency (Hz)
R
esp
on
se
(
dB
)
Figure 57 ADC Highpass Filter Responses (12kHz),
HPFAPP=1, all cut-off settings shown.