wm8988 Wolfson Microelectronics plc, wm8988 Datasheet - Page 18

• Manufacturer Part Number: wm8988
• Description: Stereo Codec For Portable Audio Applications
• Manufacturer: Wolfson Microelectronics plc

WM8988
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MONO MIXING
The stereo ADC can operate as a stereo or mono device, or the two channels can be mixed to mono,
either in the analogue domain (i.e. before the ADC) or in the digital domain (after the ADC).
MONOMIX selects the mode of operation. For analogue mono mix either the left or right channel
ADC can be used, allowing the unused ADC to be powered off or used for a dc measurement
conversion. The user also has the flexibility to select the data output from the audio interface using
DATSEL. The default is for left and right channel ADC data to be output, but the interface may also
be configured so that e.g. left channel ADC data is output as both left and right data for when an
analogue mono mix is selected.
Note:
If DC measurement is selected this overrides the MONOMIX selection.
Table 7 Mono Mixing
Table 8 ADC Data Output Configuration
PGA CONTROL
The PGA matches the input signal level to the ADC input range. The PGA gain is logarithmically
adjustable from +30dB to –17.25dB in 0.75dB steps. Each PGA can be controlled either by the user
or by the ALC function (see Automatic Level Control). When ALC is enabled for one or both
channels, then writing to the corresponding PGA control register has no effect.
The gain is independently adjustable on both Right and Left Line Inputs. Additionally, by controlling
the register bits LIVU and RIVU, the left and right gain settings can be simultaneously updated.
Setting the LZCEN and RZCEN bits enables a zero-cross detector which ensures that PGA gain
changes only occur when the signal is at zero, eliminating any zipper noise. If zero cross is enabled
a timeout is also available to update the gain if a zero cross does not occur. This function may be
enabled by setting TOEN in register R23 (17h).
The inputs can also be muted in the analogue domain under software control. The software control
registers are shown in Table 9. If zero crossing is enabled, it is necessary to enable zero cross
timeout to un-mute the input PGAs. This is because their outputs will not cross zero when muted.
Alternatively, zero cross can be disabled before sending the un-mute command.
R31 (1Fh)
ADC input
Mode
R23 (17h)
Additional
Control (1)
REGISTER
REGISTER
ADDRESS
ADDRESS
BIT
7:6
BIT
3:2
MONOMIX
[1:0]
DATSEL
[1:0]
LABEL
LABEL
DEFAULT
DEFAULT
00
00
00: left data=left ADC; right data =right ADC
01: left data =left ADC; right data = left ADC
10: left data = right ADC; right data =right
ADC
11: left data = right ADC; right data = left
ADC
00: Stereo
01: Analogue Mono Mix (using left ADC)
10: Analogue Mono Mix (using right ADC)
11: Digital Mono Mix
DESCRIPTION
DESCRIPTION
PD, Rev 4.0, October 2008
Production Data
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