WM8974 datasheet(16/63 Pages) WOLFSON

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WM8974

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PP Rev 1.1 September 2004

INPUT PGA VOLUME CONTROL

The input microphone PGA has a gain range from -12dB to +35.25dB in 0.75dB steps. The gain

from the MICN input to the PGA output and from the AUX amplifier to the PGA output are always

common and controlled by the register bits INPPGAVOL[5:0]. These register bits also affect the

MICP pin when MICP2INPPGA=1.

When the Automatic Level Control (ALC) is enabled the input PGA gain is then controlled

automatically and the INPPGAVOL bits should not be used.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

5:0

INPPGAVOL

010000

Input PGA volume

000000 = -12dB

000001 = -11.25db

010000 = 0dB

111111 = 35.25dB

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).

R45

Input PGA

volume

control

INPPGAZC

Input PGA zero cross enable:

0=Update gain when gain register changes

1=Update gain on 1

st zero cross after gain

R32

ALC control 1

ALCSEL

ALC function select:

0=ALC off (PGA gain set by INPPGAVOL

1=ALC on (ALC controls PGA gain)

Table 1 Input PGA Volume Control

AUXILLIARY INPUT

An auxilliary input circuit (Figure 7) is provided which consists of an amplifier which can be

configured either as an inverting buffer for a single input signal or as a mixer/summer for multiple

inputs with the use of external resistors. The circuit is enabled by the register bit AUXEN.

Figure 7 Auxilliary Input Circuit

The AUXMODE register bit controls the auxillary input mode of operation:

In buffer mode (AUXMODE=0) the switch labelled AUXSW in Figure 7 is open and the signal at the

AUX pin will be buffered and inverted through the aux circuit using only the internal components.

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