WM8737L
Production Data
PGA CONTROL
The Left and Right PGAs match the input signal levels to the ADC input ranges. The PGA gain is
logarithmically adjustable from –97dB to +30dB in 0.5dB steps. Each PGA can be controlled either by
the user or by the ALC function (see “Automatic Level Control” section). When ALC is enabled for one
or both channels then writing to the corresponding PGA gain control register has no effect. The gain
is independently adjustable on both Right and Left Line Inputs. By setting the LVU or RVU bits whilst
programming the PGA gain, both channels can be simultaneously updated. The inputs can also be
muted under software control. The PGA control register maps are shown in Table 7.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R0 (00h)
LINVOL[7:0]
C3h
( 0dB )
Left Channel Input Volume Control
00000000: MUTE
00000001: -97dB
00000010: -96.5dB
…
7:0
Left Channel
PGA
11000011: 0dB
…
11111111: +30dB
Left PGA volume update
LVU
0
8
0: Store LINVOL in left intermediate
latch but do not update left gain.
1: Update both PGA gains
simultaneously (left gain = LINVOL,
right gain = right intermediate latch).
R1 (01h)
Right Channel
PGA
RINVOL[7:0]
RVU
C3h
( 0dB )
0
Right Channel Input Volume Control.
Same as LINVOL.
7:0
8
Right PGA volume update
0: Store RINVOL in right
intermediate latch but do not update
right gain.
1: Update both PGA gains
simultaneously (right gain =
RINVOL, left gain = left intermediate
latch).
Table 7 PGA Software Control
ZERO-CROSS DETECTION
To avoid zipper or click noises, it is preferable to change the microphone preamplifier and PGA gains
only when the input signal is at zero. The WM8737L has built-in zero-cross detectors to achieve this.
This function is enabled by setting the LMZC, LPZC, RMZC and RPZC bits. The zero-cross detection
feature includes a programmable time-out, selected by writing to LZCTO[1:0] and RZCTO[1:0]. If no
zero crossing occurs within the time-out period then the WM8737L changes the PGA or microphone
preamplifier gains when the time-out elapses.
PD, Rev 4.4, January 2012
18
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
