WM8976
Pre-Production
Figure 18 DAC Digital Filter Path
The analogue outputs from the DACs can then be mixed with the aux analogue inputs and the ADC
analogue inputs. The mix is fed to the output drivers for headphone (LOUT1/ROUT1), speaker
(LOUT2/ROUT2) or line (OUT3/OUT4). OUT3 and OUT4 have additional mixers which allow them
to output different signals to the headphone and speaker outputs.
DIGITAL PLAYBACK (DAC) PATH
Digital data is passed to the WM8976 via the flexible audio interface and is then passed through a
variety of advanced digital filters (as shown in Figure 18) to the hi-fi DACs. The DACs are enabled
by the DACENL/R register bits.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R3
0
DACENL
0
Left channel DAC enable
0 = DAC disabled
Power
Management 3
1 = DAC enabled
1
DACENR
0
Right channel DAC enable
0 = DAC disabled
1 = DAC enabled
Table 26 DAC Enable Control
The WM8976 also has a Soft Mute function, which, when enabled, gradually attenuates the volume
of the digital signal to zero. When disabled, the gain will ramp back up to the digital gain setting. This
function is enabled by default. To play back an audio signal, this function must first be disabled by
setting the SOFTMUTE bit to zero.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R10
DAC Control
0
DACPOLL
0
Left DAC output polarity:
0 = non-inverted
1 = inverted (180 degrees phase shift)
Right DAC output polarity:
0 = non-inverted
1
2
3
6
DACPOLR
AMUTE
0
0
0
0
1 = inverted (180 degrees phase shift)
Automute enable
0 = Amute disabled
1 = Amute enabled
DACOSR
SOFTMUTE
DAC oversampling rate:
0=64x (lowest power)
1=128x (best performance)
Softmute enable:
0=Enabled
1=Disabled
Table 27 DAC Control Register
The digital audio data is converted to oversampled bit streams in the on-chip, true 24-bit digital
interpolation filters. The bitstream data enters the multi-bit, sigma-delta DACs, which convert it to a
high quality analogue audio signal. The multi-bit DAC architecture reduces high frequency noise and
sensitivity to clock jitter. It also uses a Dynamic Element Matching technique for high linearity and
low distortion.
PP Rev 3.0 April 2006
42
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
