WM8978GEFLSLASHV datasheet(32/78 Pages) WOLFSON

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WM8978

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PP Rev 1.7 January 2005

Figure 12 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 WM8978 via the flexible audio interface and is then passed through a

variety of advanced digital filters as shown in Figure 12 to the hi-fi DACs. The DACs are enabled by

the DACENL/R register bits.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

DACENL

Left channel DAC enable

0 = DAC disabled

1 = DAC enabled

Power

Management 3

DACENR

Right channel DAC enable

0 = DAC disabled

1 = DAC enabled

Table 18 DAC Enable Control

The WM8978 also has a Soft Mute function, which gradually attenuates the volume of the digital

signal to zero. When removed, the gain will ramp back up to the digital gain setting.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

DACPOLL

Left DAC output polarity:

0 = non-inverted

1 = inverted (180 degrees phase shift)

DACPOLR

Right DAC output polarity:

0 = non-inverted

1 = inverted (180 degrees phase shift)

AMUTE

Automute enable

0 = Amute disabled

1 = Amute enabled

DACOSR

DAC oversampling rate:

0=64x (lowest power)

1=128x (best performance)

R10

DAC Control

SOFTMUTE

Softmute enable:

0=Disabled

1=Enabled

Table 19 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.

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