Advanced Information
WM8753L
PGA CONTROL
The PGA matches the input signal level to the ADC input range. The PGA gain is logarithmically
adjustable from –17.25dB to +30dB 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. However, by setting the
LRINBOTH or RLINBOTH bits whilst programming the PGA gain, both channels are simultaneously
updated. This reduces the required number of software writes required. 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 R18 (12h).
The inputs can also be muted in the analogue domain under software control. The software control
registers are shown in Table 16
REGISTER
ADDRESS
BIT
LABEL
LIVU
DEFAULT
DESCRIPTION
R49 (31h)
Left Channel
PGA
0
Left Volume Update
0 = Store LINVOL in intermediate
latch (no gain change)
8
1 = Update left and right channel
gains (left
=
LINVOL, right
=
intermediate latch)
LINMUTE
LZCEN
1
0
Left Channel Input Analogue Mute
1 = Enable Mute
0 = Disable Mute
7
6
Note: LIVU must be set to un-mute.
Left Channel Zero Cross Detector
1 = Change gain on zero cross only
0 = Change gain immediately
5:0
8
LINVOL
[5:0]
010111
( 0dB )
Left Channel Input Volume Control
111111 = +30dB
111110 = +29.25dB
. . 0.75dB steps down to
000000 = -17.25dB
R50 (32h)
Right Channel
PGA
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.
6
Right Channel Zero Cross Detector
1 = Change gain on zero cross only
0 = Change gain immediately
5:0
RINVOL
[5:0]
010111
( 0dB )
Right Channel Input Volume Control
111111 = +30dB
111110 = +29.25dB
. . 0.75dB steps down to
000000 = -17.25dB
R18 (12h)
Additional
Control
0
TOEN
0
Timeout Enable
0 : Timeout Disabled
1 : Timeout Enabled
Table 16 Input PGA Software Control
AI Rev 3.1 June 2004
28
w
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
