WM8940
Pre-Production
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.
REGISTER
ADDRESS
BIT
LABEL
AUXEN
DEFAULT
DESCRIPTION
R1
6
3
0
Auxiliary input buffer enable
0 = OFF
Power
management 1
1 = ON
R44
AUXMODE
0
0 = inverting buffer
Input control
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
8.
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).
Pre-Production, Rev 3.0, February 2007
20
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
