Pre-Production
WM8940
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R45
6
8
INPPGAMUTE
1
Mute control for input PGA:
Input PGA gain
control
0=Input PGA not muted, normal operation
1=Input PGA muted (and disconnected from
the following input BOOST stage).
R47
PGABOOST
0
0 = PGA output has +0dB gain through
input BOOST stage.
Input BOOST
control
1 = PGA output has +20dB gain through
input BOOST stage.
Table 6 Input BOOST Stage Control
The Auxiliary 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.
The MICP path to the BOOST stage is controlled by the MICP2BOOSTVOL[2:0] register bits.
When MICP2BOOSTVOL=000 this input pin is completely disconnected from the BOOST stage.
Settings 001 through to 111 control the gain in 3dB steps from -12dB to +6dB.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R47
6:4 MICP2BOOSTVOL 000
Controls the MICP pin to the input boost
stage (NB, when using this path set
MICP2INPPGA=0):
Input BOOST
control
000=Path disabled (disconnected)
001=-12dB gain through boost stage
010=-9dB gain through boost stage
…
111=+6dB gain through boost stage
2:0 AUX2BOOSTVOL
000
Controls the auxiliary amplifier to the input
boost stage:
000=Path disabled (disconnected)
001=-12dB gain through boost stage
010=-9dB gain through boost stage
…
111=+6dB gain through boost stage
Table 7 Input BOOST Stage Control
The BOOST stage is enabled under control of the BOOSTEN register bit.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
Input BOOST enable
R2
4
BOOSTEN
0
Power
management 2
0 = Boost stage OFF
1 = Boost stage ON
Table 8 Input BOOST Enable Control
MICROPHONE BIASING CIRCUIT
The MICBIAS output provides a low noise reference voltage suitable for biasing electret type
microphones and the associated external resistor biasing network. Refer to the Applications
Information section for recommended external components. The MICBIAS voltage can be altered via
the MBVSEL register bit.
When MBVSEL=0, MICBIAS=0.9*AVDD and when MBVSEL=1,
MICBIAS=0.65*AVDD. The output can be enabled or disabled using the MICBEN control bit.
Pre-Production, Rev 3.0, February 2007
21
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
