WM8731 Wolfson Microelectronics Ltd., WM8731 Datasheet - Page 24

• Manufacturer Part Number: WM8731
• Description: WM8731 : Low Power Audio Codec With Integrated Headphone Driver
• Manufacturer: Wolfson Microelectronics Ltd.

WM8731
ADC FILTERS
The ADC filters perform true 24 bit signal processing to convert the raw multi-bit oversampled data
from the ADC to the correct sampling frequency to be output on the digital audio interface. Figure 15
illustrates the digital filter path.
Figure 15 ADC Digital Filter
The ADC digital filters contain a digital high pass filter, selectable via software control. The high-pass
filter response detailed in Digital Filter Characteristics. When the high-pass filter is enabled the dc
offset is continuously calculated and subtracted from the input signal. By setting HPOR the last
calculated dc offset value is stored when the high-pass filter is disabled and will continue to be
subtracted from the input signal. If the dc offset changes, the stored and subtracted value will not
change unless the high-pass filter is enabled. The software control is shown in Table 5.
Table 5 ADC Software Control
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 16 illustrates the DAC digital filter path.
0000101
Digital Audio
Path Control
FROM ADC
REGISTER
ADDRESS
BIT
4
0
DECIMATOR
DIGITAL
ADCHPD
LABEL
HPOR
DECIMATION
DIGITAL
FILTER
DEFAULT
0
0
ADC High Pass Filter Enable
(Digital)
1 = Disable High Pass Filter
0 = Enable High Pass Filter
Store dc offset when High Pass
Filter disabled
1 = store offset
0 = clear offset
HPFEN
DIGITAL
HPF
DESCRIPTION
AI Rev 2.3 August 2001
INTERFACE
TO DIGITAL
Advanced Information
AUDIO
24