wm8940gefl-v Wolfson Microelectronics plc, wm8940gefl-v Datasheet - Page 23

• Manufacturer Part Number: wm8940gefl-v
• Description: Mono Codec With Speaker Driver
• Manufacturer: Wolfson Microelectronics plc

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Production Data
ANALOGUE TO DIGITAL CONVERTER (ADC)
Table 9 Microphone Bias Enable
Table 10 Microphone Bias Voltage Control
ADC DIGITAL FILTERS
The internal MICBIAS circuitry is shown in Figure 9.
capability for MICBIAS is 3mA. The external biasing resistors therefore must be large enough to limit
the MICBIAS current to 3mA.
The WM8940 uses a multi-bit, over sampled sigma-delta ADC channel. The use of multi-bit
feedback and high over sampling 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
The ADC filters perform true 24 bit signal processing to convert the raw multi-bit over sampled 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 Microphone Bias Schematic
R1
Power
management 1
R44
Input Control
rms
REGISTER
REGISTER
ADDRESS
ADDRESS
VMID
. Any voltage greater than full scale may overload the ADC and cause distortion.
4
8
BIT
BIT
MICBEN
MBVSEL
LABEL
LABEL
internal
resistor
internal
resistor
0
0
DEFAULT
DEFAULT
AGND
Microphone Bias Enable
0 = OFF (high impedance output)
1 = ON
Microphone Bias Voltage Control
0 = 0.9 * AVDD
1 = 0.65 * AVDD
Note that the maximum source current
MB
DESCRIPTION
DESCRIPTION
MBVSEL=0
MICBIAS
= 1.8 x VMID
= 0.9 X AVDD
MBVSEL=1
MICBIAS
= 1.3 x VMID
= 0.65 X AVDD
PD, Rev 4.2, April 2008
WM8940
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