WM8976 datasheet(29/83 Pages) WOLFSON

29 / 83 page

Preliminary Technical Data

WM8976

PTD Rev 2.0 February 2005

Figure 13 Microphone Bias Schematic

ANALOGUE TO DIGITAL CONVERTER (ADC)

The WM8976 uses a multi-bit, oversampled sigma-delta ADC. 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 1.0Vrms. Any

voltage greater than full scale may overload the ADC and cause distortion.

ADC DIGITAL 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. The

digital filter path for each ADC channel is illustrated in Figure 14.

Figure 14 ADC Digital Filter Path

The ADC is enabled by the ADCENL register bit.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

Power

management 2

ADCENL

Enable ADC:

0 = ADC disabled

1 = ADC enabled

Table 13 ADC Enable Control

AGND

MBVSEL=0

MICBIAS

= 1.8 x VMID

= 0.9 X AVDD

VMID

internal

resistor

internal

resistor

MBVSEL=1

MICBIAS

= 1.2 x VMID

= 0.6 X AVDD

WM8976 Datasheet(PDF) 29 Page - Wolfson Microelectronics plc