WM8731 / WM8731L
Production Data
There are several types of ADC filters, frequency and phase responses of these are shown in Digital
Filter Characteristics. The filter types are automatically configured depending on the sample rate
chosen. Refer to the sample rate section for more details.
DAC FILTERS
The DAC filters perform true 24 bit signal processing to convert the incoming digital audio data from
the digital audio interface at the specified sample rate to multi-bit oversampled data for processing by
the analogue DAC. Figure 17 illustrates the DAC digital filter path.
FROM DIGITAL
DIGITAL
TO LINE
DIGITAL
MUTE
INTERPOLATION
AUDIO
INTERFACE
DE_EMPHASIS
OUTPUTS
FILTER
DEEMP
DACMU
Figure 17 DAC Filter Schematic
The DAC digital filter can apply digital de-emphasis under software control, as shown in Table 7.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
0000101
2:1
DEEMP[1:0]
00
De-emphasis Control
(Digital)
Digital
Audio Path
Control
11 = 48kHz
10 = 44.1kHz
01 = 32kHz
00 = Disable
3
DACMU
1
DAC Soft Mute Control
(Digital)
1 = Enable soft mute
0 = Disable soft mute
Table 7 DAC Software Control
Notes:
1. Not valid when SR[3:0] = 1111 or 0111.
2. To ensure correct DACMU operation at fs = 88.2kHz, set SR[3:0] = 1000.
3. To ensure correct DACMU operation at fs = 96kHz, set SR[3:0] = 0000.
DAC
The WM8731/L employs a multi-bit sigma delta oversampling digital to analogue converter. The
scheme for the converter is illustrated in Figure 18.
PD, Rev 4.8, April 2009
27
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
