wm8941 Wolfson Microelectronics plc, wm8941 Datasheet - Page 24

• Manufacturer Part Number: wm8941
• Description: Mono Codec With Speaker Driver And Video Buffer
• Manufacturer: Wolfson Microelectronics plc

WM8941
Figure 10 ADC Digital Filter Path
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ANALOGUE TO DIGITAL CONVERTER (ADC)
ADC DIGITAL FILTERS
The internal MICBIAS circuitry is shown in Figure 9. Note that the maximum source current capability
for MICBIAS is 3mA. The external biasing resistors therefore must be large enough to limit the
MICBIAS current to 3mA.
The WM8941 uses a multi-bit, oversampled sigma-delta ADC 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 1.0V
Any voltage greater than full scale may overload the ADC and cause distortion.
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.
Figure 9 Microphone Bias Schematic
VMID
internal
resistor
internal
resistor
AGND
MB
PD, Rev 4.0, August 2008
MBVSEL=0
MICBIAS
= 1.8 x VMID
= 0.9 X AVDD
MBVSEL=1
MICBIAS
= 1.3 x VMID
= 0.65 X AVDD
Production Data
rms
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