WM8959
Pre-Production
OUTPUT SIGNAL PATH VOLUME CONTROL
The output drivers LOPGA, ROPGA, LOUT and ROUT can be independently controlled as shown in
Table 27 and Table 28.
To minimise pop noise it is recommended that only the LOPGAVOL, ROPGAVOL, LOUTVOL and
ROUTVOL are modified while the output signal path is active. Other gain controls are provided in the
output signal path to provide appropriate relative scaling of signals from different sources, and to
prevent clipping when multiple signals are mixed. To prevent pop noise, only the gain controls noted
above should be modified while playback is active.
To prevent "zipper noise", a zero-cross function is provided on these output paths, so that when
enabled, volume updates will not take place until a zero-crossing is detected. In the event of a long
period without zero-crossings, a timeout function is available. When this function is enabled (using
the TOCLK_ENA register bit), the volume will update after the timeout period if no earlier zero-cross
has occurred. The timeout period is set by TOCLK_RATE. See “Clocking and Sample Rates” for
more information on these fields.
The OPVU bit controls the loading of the output driver volume data. When OPVU is set to 0, the
volume control data will be loaded into the respective control register, but will not actually change the
gain setting. The LOPGA, ROPGA, LOUT and ROUT volume settings are all updated when a 1 is
written to OPVU. This makes it possible to update the gain of all output paths simultaneously.
Note that the headphone outputs LOUT and ROUT have dedicated volume controls. As a result, the
output PGAs LOPGA and ROPGA do not need to be enabled to provide volume control for the LOUT
and ROUT outputs.
REGISTER
ADDRESS
BIT
LABEL
OPVU[2]
DEFAULT
DESCRIPTION
R32 (20h)
R33 (21h)
R28 (1Ch)
8
N/A
Output PGA Volume Update
Writing a 1 to this bit will update
LOPGA, ROPGA, LOUTVOL and
ROUTVOL volumes simultaneously.
7
LOPGAZC
0b
LOPGA Zero Cross Enable
0 = Zero cross disabled
1 = Zero cross enabled
LOPGA Volume
6:0
8
LOPGAVOL
[6:0]
79h
(0dB)
(See Table 28 for output PGA volume
control range)
OPVU[3]
N/A
0b
Output PGA Volume Update
Writing a 1 to this bit will update
LOPGA, ROPGA, LOUTVOL and
ROUTVOL volumes simultaneously.
7
ROPGAZC
ROPGA Zero Cross Enable
0 = Zero cross disabled
1 = Zero cross enabled
ROPGA Volume
6:0
8
ROPGAVOL
[6:0]
79h
(0dB)
(See Table 28 for output PGA volume
control range)
OPVU[0]
N/A
0b
Output PGA Volume Update
Writing a 1 to this bit will update
LOPGA, ROPGA, LOUTVOL and
ROUTVOL volumes simultaneously.
7
LOZC
LOUT (Left Headphone Output) Zero
Cross Enable
0 = Zero cross disabled
1 = Zero cross enabled
6:0
LOUTVOL
[6:0]
00h
LOUT (Left Headphone Output)
Volume
(mute)
(See Table 28 for output PGA volume
control range)
PP, May 2008, Rev 3.1
60
w
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
