Pre-Production
WM8940
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.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R45
7
6
INPPGAZC
0
Input PGA zero cross enable:
Input PGA
volume
control
0=Update gain when gain register changes
1=Update gain on 1st zero cross after gain
register write.
INPPGAMUTE
INPPGAVOL
1
Mute control for input PGA:
0=Input PGA not muted, normal operation
1=Input PGA muted (and disconnected from
the following input BOOST stage).
5:0
010000
Input PGA volume
000000 = -12dB
000001 = -11.25db
.
010000 = 0dB
.
111111 = 35.25dB
ALC function select:
R32
8
ALCSEL
0
ALC control 1
0=ALC off (PGA gain set by INPPGAVOL
register bits)
1=ALC on (ALC controls PGA gain)
Table 4 Input PGA Volume Control
AUXILLIARY INPUT
An auxiliary 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 Auxiliary Input Circuit
Pre-Production, Rev 3.0, February 2007
19
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
