Production Data
WM8945
MICROPHONE BIAS CONTROL
The WM8945 provides a low noise reference voltage suitable for biasing electret condenser (ECM)
type microphones via an external resistor. Refer to the “Applications Information” section for
recommended components. The MICBIAS voltage is enabled using the MICB_ENA register bit; the
voltage can be selected using the MICB_LVL bit, as described in Table 3.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R2 (02h)
MICB_ENA
Microphone Bias Enable
0 = Disabled
4
0
Power
Management 1
1 = Enabled
R39 (27h)
Input Ctrl
MICB_LVL
Microphone Bias Voltage control
0 = 0.9 x LDOVOUT
1 = 0.65 x LDOVOUT
6
0
Table 3 Microphone Bias Control
INPUT PGA GAIN CONTROL
The volume control gain for the PGA is adjusted using the PGAL_VOL register field as described in
Table 4. The gain range is -12dB to +35.25dB in 0.75dB steps. The gains on the inverting and non-
inverting inputs to the PGA are always equal. The input PGA can be muted using the PGAL_MUTE
mute bit.
The PGA_VU bit controls the loading of digital volume control data. The PGAL_VOL control data is
only loaded into the respective control register when PGA_VU = 1.
To prevent “zipper noise”, a zero-cross function is provided on the input PGA. When this feature is
enabled, volume updates will not take place until a zero-crossing is detected. In the case of a long
period without zero-crossings, a timeout function is provided. When the zero-cross function is
enabled, the volume will update after the timeout period if no earlier zero-cross has occurred. The
timeout clock is enabled using TOCLK_ENA. See “Clocking and Sample Rates” for the definition of
this bit. Note that the zero-cross function can be supported without TOCLK enabled, but the timeout
function will not be provided in this case.
The Input PGA volume control register fields are described in Table 4.
REGISTER
ADDRESS
BIT
LABEL
PGA_VU
DEFAULT
DESCRIPTION
R40 (28h)
Input PGA Volume Update
8
0
Left INP PGA
gain ctrl
Writing a 1 to this bit enables the
Left PGA volume to be updated
PGAL_ZC
Left Input PGA Zero Cross Detector
0 = Change gain immediately
1 = Change gain on zero cross only
Left Input PGA Mute
0 = Disable Mute
7
6
0
1
PGAL_MUTE
PGAL_VOL [5:0]
1 = Enable Mute
Left Input PGA Volume
00_0000 = -12dB
5:0
01_0000
(0dB)
00_0001 = -11.25dB
…
01_0000 = 0dB
...
11_1111 = +35.25
(See Table 5 for volume range)
Table 4 Input PGA Volume Control
PD, May 2011, Rev 4.1
25
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
