WM8944BECSSLASHR datasheet(48/165 Pages) CIRRUS

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WM8944B

Rev 4.3

DIGITAL-TO-ANALOGUE CONVERTER (DAC)

The WM8944B DAC receives digital input data from the digital audio interface. (Note that, depending

on the DSP Configuration mode, the digital input may first be processed and filtered in the DSP Core.)

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

interpolation filter. The bit-stream data enters the multi-bit, sigma-delta DAC, which converts it to high

quality analogue audio.

The analogue output from the DAC can then be mixed with other analogue inputs before being sent to

the analogue output pins (see “Output Signal Path”).

The DAC is enabled by the DAC_ENA register bit.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R3 (03h)

Power

Management

DAC_ENA

DAC Enable

0 = Disabled

1 = Enabled

DAC_ENA must be set to 1 when

processing data from the DAC or

Digital Beep Generator.

Table 25 DAC Enable Control

DAC DIGITAL VOLUME CONTROL

The output of the DAC can be digitally amplified or attenuated over a range from -71.625dB to

+23.625dB in 0.375dB steps. The volume can be controlled using DAC_VOL. The DAC Volume is part

of the DAC Digital Filters block. The gain for a given eight-bit code X is given by:

0.375

 (X-192) dB for 1  X  255;

MUTE for X = 0

The output of the DAC can be digitally muted using the DAC_MUTE bit.

A digital soft-mute feature is provided in order to avoid sudden glitches in the analogue signal. When

DAC_VOL_RAMP is enabled, then all mute, un-mute or volume change commands are implemented

as a gradual volume change in the digital domain. The rate at which the volume ramps up is half of

the sample freq (fs/2). The DAC_VOL_RAMP register field is described in Table 26.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R22 (16h)

DAC Control 2

DAC_VOL_RAMP

DAC Volume Ramp control

0 = Disabled

1 = Enabled

R23 (17h)

DAC Digital

Vol

DAC_MUTE

DAC Digital Mute

0 = Disable Mute

1 = Enable Mute

7:0

DAC_VOL [7:0]

1100_0000

(0dB)

DAC Digital Volume

0000_0000 = mute

0000_0001 = -71.625dB

0000_0010 = -71.250dB

…

1100_0000 = 0dB

...

1111_1111 = +23.625dB

(See Table 27 for volume range)

Table 26 DAC Digital Volume Control

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