WM8974 datasheet(17/63 Pages) WOLFSON

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WM8974

PP Rev 1.1 September 2004

In mixer mode (AUXMODE=1) the on-chip input resistor is bypassed, this allows the user to sum in

multiple inputs with the use of external resistors.

When used in this mode there will be gain

variations through this path from part to part due to the variation of the internal 20kΩ resistors

relative to the higher tolerance external resistors.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

Power

management 1

AUXEN

Auxilliary input buffer enable

0 = OFF

1 = ON

R44

Input control

AUXMODE

0 = inverting buffer

1 = mixer (on-chip input resistor bypassed)

Table 2 Auxilliary Input Buffer Control

INPUT BOOST

The input BOOST circuit has 3 selectable inputs: the input microphone PGA output, the AUX

amplifier output and the MICP input pin (when not using a differential microphone configuration).

These three inputs can be mixed together and have individual gain boost/adjust as shown in Figure

Figure 8 Input Boost Stage

The input PGA path can have a +20dB boost (PGABOOST=1) a 0dB pass through (PGABOOST=0)

or be completely isolated from the input boost circuit (INPPGAMUTE=1).

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R45

Input PGA gain

control

INPPGAMUTE

Mute control for input PGA:

0=Input PGA not muted, normal operation

1=Input PGA muted (and disconnected from

the following input BOOST stage).

R47

Input BOOST

control

PGABOOST

0 = PGA output has +0dB gain through

input BOOST stage.

1 = PGA output has +20dB gain through

input BOOST stage.

Table 3 Input BOOST Stage Control

The Auxilliary amplifier path to the BOOST stage is controlled by the AUX2BOOSTVOL[2:0] register

bits.

When AUX2BOOSTVOL=000 this path is completely disconnected from the BOOST stage.

Settings 001 through to 111 control the gain in 3dB steps from -12dB to +6dB.

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