WM8903 datasheet(45/178 Pages) WOLFSON

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Production Data

WM8903

PD, Rev 4.5, June 2012

HIGH-PASS FILTER (HPF)

A digital high-pass filter is 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_ENA and

ADC_HPF_CUT register bits (see Table 13).

In hi-fi mode the high pass filter is optimised for removing DC offsets without degrading the bass

response and has a cut-off frequency of 3.7Hz at fs=44.1kHz.

In voice mode the high pass filter is optimised for voice communication and it is recommended to

program the cut-off frequency below 300Hz (e.g. ADC_HPF_CUT=11 at fs=8kHz or

ADC_HPF_CUT=10 at fs=16kHz).

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R38 (26h)

ADC Digital 0

6:5

ADC_HPF_CUT

[1:0]

ADC Digital High Pass Filter Cut-Off

Frequency (fc)

00 = hi-fi mode (fc=4Hz at

fs=48kHz)

01 = Voice mode 1 (fc=127Hz at

fs=16kHz)

10 = Voice mode 2 (fc=130Hz at

fs=8kHz)

11 = Voice mode 3 (fc=267Hz at

fs=8kHz)

(Note: fc scales with sample rate fs.

See Table 14 for cut-off frequencies

at all supported sample rates)

ADC_HPF_ENA

ADC Digital High Pass Filter Enable

0 = disabled

1 = enabled

Table 13 ADC High-pass Filter Control Registers

Sample

Rate (kHz)

Value of ADC_HPF_CUT bits

Cut-off frequency (Hz)

8.000

0.7

130

267

11.025

0.9

178

367

16.000

1.3

127

258

532

22.050

1.9

175

354

733

24.000

2.0

190

386

798

32.000

2.7

253

514

1063

44.100

3.7

348

707

1464

48.000

4.0

379

770

1594

88.200

7.4

696

1414

2928

96.000

8.0

758

1540

3188

Table 14 ADC High-pass Filter Cut-off Frequencies

The high pass filter characteristics are shown in “Digital Filter Characteristics” section.

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