WM8721

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WOLFSON MICROELECTRONICS LTD

PP Rev 1.3 November 2000

11

The DAC digital filter can apply digital de-emphasis under software control, as shown in Table 2. 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.

REGISTER

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

2:1

DEEMP[1:0]

00

De-emphasis Control

(Digital)

11 = 48KHz

10 = 44.1KHz

01 = 32KHz

00 = Disable

0000101

Digital Audio

Path Control

3

DACMU

1

DAC Soft Mute Control

(Digital)

1 = Enable soft mute

0 = Disable soft mute

Table 2 DAC Software Control

DAC

The WM8721 employs a multi-bit sigma delta oversampling digital to analogue converter. The

scheme for the converter is illustrated Figure 7.

FROM DAC

DIGITAL

FILTERS

TO LINE OUTPUT

Figure 7 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 WM8721 provides two low impedance line outputs LLINEOUT and RLINEOUT, suitable for

driving typical line loads of impedance 10K and capacitance 50pF.

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 9. 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.