WM8951L_07 WOLFSON [Wolfson Microelectronics plc], WM8951L_07 Datasheet - Page 19

• Manufacturer Part Number: WM8951L_07
• Description: Stereo ADC with Microphone Input and Clock Generator
• Manufacturer: WOLFSON [Wolfson Microelectronics plc]

Production Data
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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
overload the ADC and cause distortion. Note that the full scale input tracks directly with AVDD1/2.
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.
ADC 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. Figure 15
illustrates the digital filter path.
Figure 15 ADC Digital Filter
The ADC digital filters contain a digital high pass filter, selectable via software control. The high-pass
filter response detailed in Digital Filter Characteristics. 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 changes, the stored and subtracted value will not
change unless the high-pass filter is enabled. The software control is shown in Table 5.
Table 5 ADC Software Control
There are several types of ADC filters, frequency and phase responses of these are shown in Digital
Filter Characteristics. The filter types are automatically configured depending on the sample rate
chosen. Refer to the sample rate section for more details.
0000100
Analogue
Audio Path
Control
0000101
Digital Audio
Path Control
REGISTER
ADDRESS
FROM ADC
REGISTER
ADDRESS
2
BIT
BIT
4
0
DECIMATOR
DIGITAL
INSEL
LABEL
ADCHPD
LABEL
HPOR
0
DEFAULT
DECIMATION
DIGITAL
FILTER
DEFAULT
0
0
Microphone/Line Input Select to ADC
1 = Microphone Input Select to ADC
0 = Line Input Select to ADC
ADC High Pass Filter Enable
(Digital)
1 = Disable High Pass Filter
0 = Enable High Pass Filter
Store dc offset when High Pass
Filter disabled
1 = store offset
0 = clear offset
HPFEN
DIGITAL
HPF
DESCRIPTION
DESCRIPTION
PD Rev 4.1 December 2007
INTERFACE
TO DIGITAL
AUDIO
WM8951
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