WM8973 Wolfson Microelectronics Ltd., WM8973 Datasheet - Page 21

• Manufacturer Part Number: WM8973
• Description: The WM8976 is a low power, high quality stereo codec designed for portable applications such as Digital still camera or Digital Camcorde
• Manufacturer: Wolfson Microelectronics Ltd.

Production Data
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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.
Table 9 Input PGA Software Control
R0 (00h)
Left Channel
PGA
R1 (01h)
Right Channel
PGA
R23 (17h)
Additional
Control (1)
REGISTER
ADDRESS
8
7
6
5:0
8
7
6
5:0
0
BIT
LIVU
LINMUTE
LZCEN
LINVOL
[5:0]
RIVU
RINMUTE
RZCEN
RINVOL
[5:0]
TOEN
LABEL
0
1
0
010111
( 0dB )
0
1
0
010111
( 0dB )
0
DEFAULT
Left Volume Update
0 = Store LINVOL in intermediate
latch (no gain change)
1 = Update left and right channel
gains (left = LINVOL, right =
intermediate latch)
Left Channel Input Analogue Mute
1 = Enable Mute
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
111110 = +29.25dB
. . 0.75dB steps down to
000000 = -17.25dB
Right Volume Update
0 = Store RINVOL in intermediate
latch (no gain change)
1 = Update left and right channel
gains (right = RINVOL, left =
intermediate latch)
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
111110 = +29.25dB
. . 0.75dB steps down to
000000 = -17.25dB
Timeout Enable
0 : Timeout Disabled
1 : Timeout Enabled
PD Rev 4.2 September 2005
DESCRIPTION
WM8973L
21