WM8746
Production Data
MUTE MODES
Setting the MUTE register bit will apply a 'soft' mute to the input of the digital filters:
REGISTER ADDRESS
0000010
BIT
LABEL
DEFAULT
DESCRIPTION
Soft Mute select
0
MUTE
0
DAC Channel Control
0 : Normal Operation
1: Soft mute all channels
1.5
1
0.5
0
-0.5
-1
-1.5
-2
-2.5
0
0.001
0.002
0.003
0.004
0.005
0.006
Time(s)
Figure 10 Application and Release of Soft Mute
Figure 10 shows the application and release of MUTE whilst a full amplitude sinusoid is being played
at 48kHz sampling rate. When MUTE (lower trace) is asserted, the output (upper trace) begins to
decay exponentially from the DC level of the last input sample. The output will decay towards VCAP
with a time constant of approximately 64 input samples. If MUTE is applied for 1024 or more input
samples, the outputs will be connected directly to VCAP - this feature can be disabled using the IZD
(infinite zero detect) bit. When MUTE is de-asserted, the output will restart almost immediately from
the current input sample.
Note that all other means of muting the DAC channels: setting the PL[3:0] bits to 0, setting the
PWDN bit or setting attenuation to 0 will cause much more abrupt muting of the output.
Setting the IZD register bit will enable the infinite zero detect feature:
REGISTER ADDRESS
0000010
BIT
LABEL
DEFAULT
DESCRIPTION
Internal Analogue Mute Disable
0 : Disable Analogue Mute
1: Enable Analogue Mute
4
IZD
0
DAC Channel Control
With IZD=1, applying MUTE for 1024 consecutive input samples will cause all outputs to be
connected directly to VCAP. This also happens if 2048 consecutive zero input samples are applied to
all 6 channels, and IZD=0. It will be removed as soon as any channel receives a non-zero input.
The MUTE pin can be used as an input. In this case it performs the same function as the MUTE
register bit. Driving the MUTE pin high will apply a 'soft' mute. Driving it low again, will remove the
MUTE immediately. Note that this hardware mute feature doesn't require the MODE pin to be set
high.
March 2006, PD Rev 4.0
16
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
