WM8973_05 Datasheet, PDF (22/61 Pages) Wolfson Microelectronics plc – Stereo CODEC for Portable Audio Applications

WM8973L
Production Data
ANALOGUE TO DIGITAL CONVERTER (ADC)
The WM8973L 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 9.
FROM ADC
DIGITAL
DECIMATOR
DIGITAL
FILTER
DIGITAL
HPF
TO DIGITAL
AUDIO
INTERFACE
ADCHPD
Figure 9 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 highpass filter may be enabled separately on the left and right
channels (see Table 11).
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 10.
w
PD Rev 4.2 September 2005
22