WM8731 datasheet(24/56 Pages) WOLFSON

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WM8731

Advanced Information

WOLFSON MICROELECTRONICS LTD

AI Rev 2.0 February 2001

The DAC digital filter can apply digital de-emphasis under software control, as shown in Table 6.The

DAC can also perform a soft mute where the audio data is digitally brought to a mute level. This

removes any abrupt step changes in the audio that might otherwise result in audible clicks in the

audio outputs.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

2:1

DEEMP[1:0]

De-emphasis Control

(Digital)

11 = 48kHz

10 = 44.1kHz

01 = 32kHz

00 = Disable

0000101

Digital

Audio Path

Control

DACMU

DAC Soft Mute Control

(Digital)

1 = Enable soft mute

0 = Disable soft mute

Table 6 DAC Software Control

DAC

The WM8731 employs a multi-bit sigma delta oversampling digital to analogue converter. The

scheme for the converter is illustrated in Figure 17.

FROM DAC

DIGITAL

FILTERS

TO LINE OUTPUT

Figure 17 Multi-Bit Oversampling Sigma Delta Schematic

The DAC converts the multi-level digital audio data stream from the DAC digital filters into high

quality analogue audio.

LINE OUTPUTS

The WM8731 provides two low impedance line outputs LLINEOUT and RLINEOUT, suitable for

driving typical line loads of impedance 10K and capacitance 50pF. The line output is used to

selectively sum the outputs from the DAC or/and the Line inputs in bypass mode.

The LLINEOUT and RLINEOUT outputs are only available at a line output level and are not level

adjustable in the analogue domain, having a fixed gain of 0dB. The level is fixed such that at the DAC

full scale level the output level is Vrms at AVDD = 3.3 volts. Note that the DAC full scale level tracks

directly with AVDD. The scheme is shown in Figure 18. The line output includes a low order audio

low pass filter for removing out-of band components from the sigma-delta DAC. Therefore no further

external filtering is required in most applications.

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