WM8731 datasheet(29/56 Pages) WOLFSON

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WM8731

Advanced Information

WOLFSON MICROELECTRONICS LTD

AI Rev 2.0 February 2001

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.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

0000100

Analogue

Audio Path

Control

BYPASS

Bypass Switch (Analogue)

1 = Enable Bypass

0 = Disable Bypass

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.

VMID

HPOUT

50k

10k

VMID

MICIN

VMID

10dB GAIN BOOST

VMID

FROM

LINE

INPUTS

LINEOUT

FROM

DAC

BYPASS (OFF)

DACSEL (OFF)

SIDETONE (ON)

Figure 23 Side Tone Mode Schematic

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

SIDETONE

Side Tone Switch (Analogue)

1 = Enable Side Tone

0 = Disable Side Tone

0000100

Analogue

Audio Path

Control

7:6

SIDEATT[1:0]

Side Tone Attenuation

11 = -15dB

10 = -12dB

01 = -9dB

00 = -6dB

Table 10 Side Tone Mode Table

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