WM8731_09 Datasheet, PDF (33/64 Pages) Wolfson Microelectronics plc – Portable Internet Audio CODEC with Headphone Driver and Programmable Sample Rates

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 BIT
ADDRESS
LABEL
0000100
3
BYPASS
1
Analogue
Audio Path
Control
Table 10 Bypass Mode Software Control
DEFAULT
DESCRIPTION
Bypass Switch (Analogue)
1 = Enable Bypass
0 = Disable Bypass
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
MICIN
10k
VMID
10dB GAIN BOOST
VMID
FROM
LINE
INPUTS
FROM
DAC
SIDETONE (ON)
BYPASS (OFF)
DACSEL (OFF)
VMID
LINEOUT
Figure 24 Side Tone Mode Schematic
REGISTER BIT
LABEL
DEFAULT
ADDRESS
0000100
5
SIDETONE
0
Analogue
Audio Path
Control
7:6 SIDEATT[1:0] 00
Table 11 Side Tone Mode Table
VMID
HPOUT
DESCRIPTION
Side Tone Switch (Analogue)
1 = Enable Side Tone
0 = Disable Side Tone
Side Tone Attenuation
11 = -15dB
10 = -12dB
01 = -9dB
00 = -6dB
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PD, Rev 4.8, April 2009
33