WM8945ECSSLASHR datasheet(31/169 Pages) WOLFSON

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Production Data

WM8945

PD, May 2011, Rev 4.1

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

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).

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R26 (1Ah)

ADC Control 2

2:1

ADC_HPF_CUT

[1:0]

High pass filter configuration.

00 = 1

st order HPF

(fc=4Hz at fs=48kHz)

01 = 2

nd order HPF

(fc=122Hz at fs=48kHz)

10 = 2

nd order HPF

(fc=153Hz at fs=48kHz)

11 = 2

nd 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

1 = Enabled

Table 10 ADC High-pass Filter Control Registers

Sample Rate

(kHz)

Value of ADC_HPF_CUT bits

Cut-off frequency (Hz)

8.000

0.7

11.025

0.9

16.000

1.3

22.050

1.9

24.000

2.0

32.000

2.7

102

131

44.100

3.7

112

141

180

48.000

4.0

122

153

196

Table 11 ADC High-pass Filter Cut-off Frequencies

Filter response plots for the ADC high-pass filter are shown in “Digital Filter Characteristics”.

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