WM8940 datasheet(20/85 Pages) WOLFSON

20 / 85 page

WM8940

Pre-Production

Pre-Production, Rev 3.0, February 2007

The AUXMODE register bit controls the auxiliary 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.

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

Auxiliary input buffer enable

0 = OFF

1 = ON

R44

Input control

AUXMODE

0 = inverting buffer

1 = mixer (on-chip input resistor bypassed)

Table 5 Auxiliary 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).

WM8940 Datasheet(PDF) 20 Page - Wolfson Microelectronics plc