Production Data
WM8750JL
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.
REGISTER
ADDRESS
BIT
LABEL
LIVU
DEFAULT
DESCRIPTION
R0 (00h)
Left Channel
PGA
0
Left Volume Update
8
0 = Store LINVOL in intermediate
latch (no gain change)
1 = Update left and right channel
gains (left = LINVOL, right =
intermediate latch)
LINMUTE
LZCEN
1
0
Left Channel Input Analogue Mute
1 = Enable Mute
7
6
0 = Disable Mute
Note: LIVU must be set to un-mute.
Left Channel Zero Cross Detector
1 = Change gain on zero cross only
0 = Change gain immediately
Left Channel Input Volume Control
111111 = +30dB
LINVOL
[5:0]
010111
( 0dB )
5:0
111110 = +29.25dB
. . 0.75dB steps down to
000000 = -17.25dB
R1 (01h)
Right Channel
PGA
8
RIVU
0
Right Volume Update
0 = Store RINVOL in intermediate
latch (no gain change)
1 = Update left and right channel
gains (right = RINVOL, left =
intermediate latch)
7
RINMUTE
RZCEN
1
0
Right Channel Input Analogue Mute
1 = Enable Mute
0 = Disable Mute
Note: RIVU must be set to un-mute.
Right Channel Zero Cross Detector
1 = Change gain on zero cross only
0 = Change gain immediately
Right Channel Input Volume Control
111111 = +30dB
6
5:0
RINVOL
[5:0]
010111
( 0dB )
111110 = +29.25dB
. . 0.75dB steps down to
000000 = -17.25dB
R23 (17h)
0
TOEN
0
Timeout Enable
Additional
Control (1)
0 : Timeout Disabled
1 : Timeout Enabled
Table 9 Input PGA Software Control
PD, April 2012, Rev 4.1
19
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
