WM8731 / WM8731L
Production Data
The bypass mode is selected under software control using the BYPASS microphone bit as shown in
Table 10. In true bypass mode, the output from the DAC (DACSEL) and (SIDETONE) should be de-
selected from the line output block. However this can also be used to sum the DAC output, Line
Inputs together and microphone inputs. The analogue line input and headphone output volume
controls and mutes are still operational in bypass mode. The 0dB gain setting is recommended for
the Line Input volume control to avoid distortion. The maximum signal at any point in the bypass path
must be no greater than 1.0V rms at AVDD = 3.3V, to avoid distortion. This amplitude tracks linearly
with AVDD. This means that if the DAC is producing a 1Vrms signal, and it is being summed with
1Vrms line BYPASS signal, the resulting LINEOP signal will be clipped.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
0000100
3
BYPASS
1
Bypass Switch (Analogue)
1 = Enable Bypass
Analogue
Audio Path
Control
0 = Disable Bypass
Table 10 Bypass Mode Software Control
SIDETONE MODE
The WM8731/L also includes a side tone mode where the microphone input is routed to line and
headphone outputs. The scheme for this is shown in Figure 24.
The side tone mode allows the microphone input to be attenuated to the outputs for telephone and
headset applications.
50k
10dB GAIN BOOST
MICIN
10k
VMID
SIDETONE (ON)
VMID
BYPASS (OFF)
FROM
LINE
INPUTS
DACSEL (OFF)
FROM
DAC
LINEOUT
VMID
HPOUT
VMID
Figure 24 Side Tone Mode Schematic
REGISTER
ADDRESS
0000100
BIT
LABEL
DEFAULT
DESCRIPTION
5
SIDETONE
0
Side Tone Switch (Analogue)
1 = Enable Side Tone
0 = Disable Side Tone
Side Tone Attenuation
11 = -15dB
Analogue
Audio Path
Control
7:6
SIDEATT[1:0]
00
10 = -12dB
01 = -9dB
00 = -6dB
Table 11 Side Tone Mode Table
PD, Rev 4.8, April 2009
33
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
