Production Data
WM8945
ADC HIGH PASS FILTER
A digital high-pass filter can be applied by default to the ADC path to remove DC offsets. This filter
can also be programmed to remove low frequency noise in handheld applications (e.g. wind noise,
handling noise or mechanical vibration). This filter is controlled using the ADC_HPF and
ADC_HPF_CUT register bits (see Table 10).
Note that the ADC HPF is NOT enabled by default but must be used if DRC_ENA is enabled in
register R29(1Dh) bit 7. The DRC will not function correctly unless this filter is enabled.
When ADC_HPF_CUT=00, the high pass filter is optimised for hi-fi audio modes; the filter is designed
to remove DC offsets without degrading the bass response and has a cut-off frequency of 3.7Hz at
fs=44.1kHz.
In the other ADC_HPF_CUT modes. The high pass filter is optimised for voice communication
modes. It is recommended to select a cut-off frequency below 300Hz; the preferred setting may vary
according to the voice communication sample rate. (e.g. ADC_HPF_CUT=11 at fs=8kHz or
ADC_HPF_CUT=10 at fs=16kHz).
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R26 (1Ah)
ADC_HPF_CUT
[1:0]
High pass filter configuration.
00 = 1st order HPF
2:1
00
ADC Control 2
(fc=4Hz at fs=48kHz)
01 = 2nd order HPF
(fc=122Hz at fs=48kHz)
10 = 2nd order HPF
(fc=153Hz at fs=48kHz)
11 = 2nd order HPF
(fc=196Hz at fs=48kHz)
(See Table 11 for cut-off
frequencies at all supported sample
rates)
ADC_HPF
ADC Digital High Pass Filter Enable
0 = Disabled
0
0
1 = Enabled
Table 10 ADC High-pass Filter Control Registers
Value of ADC_HPF_CUT bits
01 10
Cut-off frequency (Hz)
00
11
Sample Rate
(kHz)
8.000
11.025
16.000
22.050
24.000
32.000
44.100
48.000
0.7
0.9
1.3
1.9
2.0
2.7
3.7
4.0
20
28
26
36
33
45
41
51
66
56
71
90
61
77
98
81
102
141
153
131
180
196
112
122
Table 11 ADC High-pass Filter Cut-off Frequencies
Filter response plots for the ADC high-pass filter are shown in “Digital Filter Characteristics”.
PD, May 2011, Rev 4.1
31
w
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
