WM8731 datasheet(22/56 Pages) WOLFSON

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WM8731

Advanced Information

WOLFSON MICROELECTRONICS LTD

AI Rev 2.0 February 2001

VMID

MICBIAS

AGND

Figure 13 Microphone Bias Schematic

ADC

The WM8731 uses a multi-bit oversampled sigma-delta ADC. A single channel of the ADC is

illustrated in the Figure 14.

FROM MICROPHONE

INPUT

FROM LINE INPUT

ANALOG

INTEGRATOR

INSEL

MULTI

BITS

TO ADC DIGITAL FILTERS

Figure 14 Multi-Bit Oversampling Sigma Delta ADC Schematic

The use of multi-bit feedback and high oversampling rates reduces the effects of jitter and high

frequency noise.

The ADC Full Scale input is 1.0V rms at AVDD = 3.3 volts. Any voltage greater than full scale will

possibly overload the ADC and cause distortion. Note that the full scale input tracks directly with

AVDD.

The device employs a pair of ADCs. The input can be selected from either the Line Inputs or the

Microphone input under software control. The two channels cannot be selected independently. The

control is shown in Table 4.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

0000100

Analogue

Audio Path

Control

INSEL

Microphone/Line Input Select to ADC

1 = Microphone Input Select to ADC

0 = Line Input Select to ADC

Table 4 ADC Software Control

The digital data from the ADC is fed for signal processing to the ADC Filters.

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