WM8955BLGECOSLASHV datasheet(19/44 Pages) WOLFSON

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WM8955BL

PD Rev 4.1 February 2007

DIGITAL TO ANALOGUE CONVERTER (DAC)

Treble and linear bass enhancement may produce signals that exceed full-scale. In order to avoid

limiting under these conditions, it is recommended to set the DAT bit to attenuate the digital input

signal by 6dB. The gain at the outputs should be increased by 6dB to compensate for the attenuation.

Cut-only tone adjustment and adaptive bass boost cannot produce signals above full-scale and

therefore do not require the DAT bit to be set.

After passing through the tone control filters, digital ‘de-emphasis’ can be applied to the audio data if

necessary (e.g. when the data comes from a CD with pre-emphasis used in the recording). De-

emphasis filtering is available for sample rates of 48kHz, 44.1kHz and 32kHz.

The WM8955BL also has a Soft Mute function, which gradually attenuates the volume of the digital

signal to zero. This function is enabled by default. To play back an audio signal, the WM8955BL must

first be unmuted by setting the DACMU bit to zero.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

DAT

DAC 6dB attenuate enable

0 = disabled (0dB)

1 = -6dB enabled

DACMU

Digital Soft Mute

1 = mute

0 = no mute (signal active)

R5 (05h)

DAC Control

2:1

DEEMPH

De-emphasis Control

11 = 48kHz sample rate

10 = 44.1kHz sample rate

01 = 32kHz sample rate

00 = No De-emphasis

Table 5 DAC Control

The digital audio data is converted to oversampled bit streams in the on-chip, true 24-bit digital

interpolation filters. The bitstream data enters two multi-bit, sigma-delta DACs, which convert them to

high quality analogue audio signals. 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.

In normal operation, the left and right channel digital audio data are converted to analogue in two

separate DACs. However, it is also possible to disable one channel, so that the same signal (left or

right) appears on both analogue output channels. Additionally, there is a mono-mix mode where the

two audio channels are mixed together digitally and then converted to analogue using only one DAC,

while the other DAC is switched off. The mono-mix signal can be selected to appear on both

analogue output channels (see Analogue Outputs).

The DAC output defaults to non-inverted. Setting DACINV will invert the DAC output phase on both

left and right channels.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

5:4

DMONOMIX[1:0]

DAC mono mix

00: stereo

01: mono ((L+R)/2) into DACL, ‘0’ into

DACR

10: mono ((L+R)/2) into DACR, ‘0’ into

DACL

11: mono ((L+R)/2) into DACL &

DACR

R23 (17h)

Additional (1)

DACINV

DAC phase invert

0: non-inverted

1: inverted

Table 6 DAC Mono Mix Select

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