WM8731 Wolfson Microelectronics Ltd., WM8731 Datasheet - Page 23

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

WM8731
Figure 13 Microphone Bias Schematic
ADC
The WM8731 uses a multi-bit oversampled sigma-delta ADC. A single channel of the ADC is
illustrated in the Figure 14.
Figure 14 Multi-Bit Oversampling Sigma Delta ADC Schematic
The use of multi-bit feedback and high oversampling rates reduces the effects of jitter and high
frequency noise.
The ADC Full Scale input is 1.0V rms at AVDD = 3.3 volts. Any voltage greater than full scale will
possibly overload the ADC and cause distortion. Note that the full scale input tracks directly with
AVDD.
The device employs a pair of ADCs. The input can be selected from either the Line Inputs or the
Microphone input under software control. The two channels cannot be selected independently. The
control is shown in Table 4.
Table 4 ADC Software Control
The digital data from the ADC is fed for signal processing to the ADC Filters.
0000100
Analogue
Audio Path
Control
REGISTER
ADDRESS
FROM MICROPHONE
FROM LINE INPUT
VMID
INPUT
2
BIT
INSEL
INSEL
LABEL
0
DEFAULT
INTEGRATOR
ANALOG
AGND
Microphone/Line Input Select to ADC
1 = Microphone Input Select to ADC
0 = Line Input Select to ADC
MULTI
BITS
DESCRIPTION
AI Rev 2.3 August 2001
TO ADC DIGITAL FILTERS
MICBIAS
Advanced Information
23