WM8961 datasheet(30/116 Pages) WOLFSON

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WM8961

Pre-Production

PP, August 2009, Rev 3.1

ADC DIGITAL FILTERS

The ADC filters perform true 24-bit signal processing to convert the raw multi-bit over-sampled data

from the ADC to the correct sampling frequency to be output on the digital audio interface.

ADC HIGH PASS FILTER

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 voice applications (e.g. wind noise or mechanical

vibration).

This filter can be disabled using the ADCHPD register bit. The cut-off frequency of the filter is

controlled by ADC_HPF_CUT.

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

R5 (05h)

ADC and DAC

Control (1)

ADCHPD

ADC High Pass Filter Disable

0 = Enable high pass filter on left and

right channels

1 = Disable high pass filter on left and

right channels

R6 (06h)

ADC & DAC

Control 2

8:7

ADC_HPF_CUT[

1:0]

ADC High Pass Filter Cutoff

00: Hi-fi mode (fc=4Hz at fs=48kHz)

01: Voice mode 1 (fc=127 at

fs=16kHz)

10: Voice mode 2 (fc=130 at

fs=8kHz)

11: Voice mode 3 (fc=267Hz at

fs=8kHz)

(Note: fc scales with sample rate.

See Table 14 for cut-off frequencies

at all supported sample rates)

Table 13 ADC High Pass Filter

SAMPLE

FREQUENCY

(KHZ)

CUT-OFF FREQUENCY (HZ)

ADC_HPF_CUT

=00

ADC_HPF_CUT

=01

ADC_HPF_CUT

=10

ADC_HPF_CUT

=11

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

Table 14 ADC High Pass Filter Cut-Off Frequencies

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

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