WM8971L datasheet(22/61 Pages) WOLFSON

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WM8971L

Production Data

PD Rev 4.1 August 2005

ANALOGUE TO DIGITAL CONVERTER (ADC)

The WM8971L uses a multi-bit, oversampled sigma-delta ADC for each channel. The use of multi-bit

feedback and high oversampling rates reduces the effects of jitter and high frequency noise. The

ADC Full Scale input level is proportional to AVDD. With a 3.3V supply voltage, the full scale level is

1.0 Volts r.m.s. Any voltage greater than full scale may overload the ADC and cause distortion.

ADC DIGITAL FILTER

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. The digital

filter path is illustrated in Figure 10.

FROM ADC

DIGITAL

HPF

DIGITAL

FILTER

TO DIGITAL

AUDIO

INTERFACE

DIGITAL

DECIMATOR

ADCHPD

Figure 10 ADC Digital Filter

The ADC digital filters contain a digital high pass filter, selectable via software control. The high-pass

filter response is detailed in the Digital Filter Characteristics section. 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 is changed, the stored and

subtracted value will not change unless the high-pass filter is enabled. This feature can be used for

calibration purposes. In addition the high-pass filter may be enabled separately on the left and right

channels (see Table 9).

The output data format can be programmed by the user to accommodate stereo or monophonic

recording on both inputs.

The polarity of the output signal can also be changed under software

control. The software control is shown in Table 8.

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