WM8731 Wolfson Microelectronics Ltd., WM8731 Datasheet - Page 30

• Manufacturer Part Number: WM8731
• Description: WM8731 : Low Power Audio Codec With Integrated Headphone Driver
• Manufacturer: Wolfson Microelectronics Ltd.

WM8731
Figure 23 Side Tone Mode Schematic
MICIN
10k
VMID
50k
The bypass mode is selected under software control using the BYPASS microphone bit as shown in
Table 9. 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.
Table 9 Bypass Mode Software Control
SIDETONE MODE
The WM8731 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 23.
The side tone mode allows the microphone input to be attenuated to the outputs for telephone and
headset applications.
Table 10 Side Tone Mode Table
0000100
Analogue
Audio Path
Control
0000100
Analogue
Audio Path
Control
REGISTER
REGISTER
ADDRESS
ADDRESS
10dB GAIN BOOST
VMID
3
5
7:6
BIT
BIT
INPUTS
FROM
FROM
BYPASS
SIDETONE
SIDEATT[1:0]
LINE
DAC
LABEL
LABEL
SIDETONE (ON)
BYPASS (OFF)
DACSEL (OFF)
1
0
00
VMID
DEFAULT
DEFAULT
Bypass Switch (Analogue)
1 = Enable Bypass
0 = Disable Bypass
Side Tone Switch (Analogue)
1 = Enable Side Tone
0 = Disable Side Tone
Side Tone Attenuation
11 = -15dB
10 = -12dB
01 = -9dB
00 = -6dB
LINEOUT
VMID
DESCRIPTION
DESCRIPTION
AI Rev 2.3 August 2001
Advanced Information
HPOUT
30