WM8962B datasheet(135/295 Pages) WOLFSON

135 / 295 page

WM8962

Rev 4.3

135

DC SERVO ACTIVE MODES

The DC Servo Start-Up mode described above is suitable for initialising the DC offset correction circuit

on the input or output signal paths as part of a controlled start-up sequence which is executed before

the signal path is fully enabled. The WM8962 also supports DC offset measurement and correction on

the HP output paths whilst the signal path is active; this may be of benefit following a large change in

signal gain, which can lead to a change in DC offset level.

Writing a logic 1 to HP1L_DCS_SYNC initiates a series of DC offset measurements and applies the

necessary correction to the HPOUTL output. Writing a logic 1 to HP1R_DCS_SYNC initiates a series

of DC offset measurements and applies the necessary correction to the HPOUTR output.

The number of DC Servo operations performed is determined by HP1_DCS_SYNC_STEP. A

maximum of 127 operations may be selected, though a much lower value will be sufficient in most

applications. The DC Servo uses filtering to measure the DC offset in the presence of any audio that

may be present; this requires a longer time to perform the correction process than in the Start-Up

mode, and means that the DC Servo may be operating for several seconds after the process was

initiated.

The DC Servo Sync mode described above is supported on the HPOUT DC Servo channels;

individual register control is provided for each channel. It is recommended that the DC Servo Sync

mode is scheduled whenever a large change in signal gain (eg. >6dB) is applied in the output signal

path. Note that the DC Servo Sync mode is not required on the input signal paths as the DC offset in

these paths does not change with gain, and only the Start-Up correction is necessary.

The DC Servo control fields associated with Sync mode (suitable for use on a signal path that is in

active use) are described in Table 83.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R61 (3Dh)

DC Servo 1

HP1L_DCS_SYN

Writing 1 to this bit selects a series of

DC offset corrections for HPOUTL

HP1R_DCS_SYN

Writing 1 to this bit selects a series of

DC offset corrections for HPOUTR

R64 (40h)

DC Servo 4

13:7

HP1_DCS_SYNC

_STEP [6:0]

10h

Number of DC Servo updates to perform

in a series event (HPOUTL and

HPOUTR)

00h to 0Fh = Reserved

10h = 16 (default)

11h = 17

…

7Fh = 127

Table 83 DC Servo Active Modes

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