WM8974 datasheet(27/63 Pages) WOLFSON

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WM8974

PP Rev 1.1 September 2004

Figure 13 DAC Digital Filter Path

The analogue output from the DAC can then be mixed with the AUX analogue input and the ADC

analogue input. The mix is fed to the output drivers, SPKROUTP/N, and MONOOUT.

MONOOUT: can drive a 16

Ω or 32Ω headphone or line output or can be a buffered version of VMID

(When MONOMUTE=1).

SPKROUTP/N: can drive a 16

Ω or 32Ω stereo headphone or stereo line output, or an 8Ω BTL mono

speaker.

DIGITAL HI-FI DAC VOLUME CONTROL

The signal volume from each Hi-Fi DAC can be controlled digitally. The gain and attenuation range

is –127dB to 0dB in 0.5dB steps. The level of attenuation for an eight-bit code X is given by:

0.5

× (X-255) dB for 1 ≤ X ≤ 255;

MUTE for X = 0

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R11

DAC Digital

Volume

7:0

DACVOL

[7:0]

11111111

( 0dB )

Left DAC Digital Volume Control

0000 0000 = Digital Mute

0000 0001 = -127dB

0000 0010 = -126.5dB

... 0.5dB steps up to

1111 1111 = 0dB

HI-FI DIGITAL TO ANALOGUE CONVERTER (DAC)

After passing through the graphic equaliser 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 DAC is enabled by the DACEN register bit..

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

Power

Management 3

DACEN

DAC enable

0 = DAC disabled

1 = DAC enabled

The WM8974 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. This function is

enabled by default. To play back an audio signal, it must first be disabled by setting the DACMU bit

to zero.

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