WM8988 datasheet(26/56 Pages) WOLFSON

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WM8988

Production Data

PD, Rev 4.0, October 2008

OUTPUT SIGNAL PATH

The WM8988 output signal paths consist of digital filters, DACs, analogue mixers and output drivers.

The digital filters and DACs are enabled when the WM8988 is in ‘playback only’ or ‘record and

playback’ mode. The mixers and output drivers can be separately enabled by individual control bits

(see Analogue Outputs). Thus it is possible to utilise the analogue mixing and amplification provided

by the WM8988, irrespective of whether the DACs are running or not.

The WM8988 receives digital input data on the DACDAT pin. The digital filter block processes the

data to provide the following functions:

•

Digital volume control

•

Graphic equaliser and Dynamic Bass Boost

•

Sigma-Delta Modulation

Two high performance sigma-delta audio DACs convert the digital data into two analogue signals (left

and right). These can then be mixed with analogue signals from the LINPUT1/2 and RINPUT1/2 pins,

and the mix is fed to the output drivers, LOUT1/ROUT1 and LOUT2/ROUT2.

•

LOUT1/ROUT1: can drive a 16

Ω or 32Ω stereo headphone or stereo line output.

•

LOUT2/ROUT2: can drive a 16

Ω or 32Ω stereo headphone or stereo line output

DIGITAL DAC VOLUME CONTROL

The signal volume from each DAC can be controlled digitally, in the same way as the ADC volume

(see Digital ADC Volume Control). 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

The LDVU and RDVU control bits control the loading of digital volume control data. When LDVU or

RDVU are set to 0, the LDACVOL or RDACVOL control data is loaded into an intermediate register,

but the actual gain does not change. Both left and right gain settings are updated simultaneously

when either LDVU or RDVU are set to 1.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

LDVU

Left DAC Volume Update

0 = Store LDACVOL in intermediate

latch (no gain change)

1 = Update left and right channel

gains (left = LDACVOL, right =

intermediate latch)

R10 (0Ah)

Left Channel

Digital Volume

7:0

LDACVOL

[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

RDVU

Right DAC Volume Update

0 = Store RDACVOL in intermediate

latch (no gain change)

1 = Update left and right channel

gains (left = intermediate latch, right

= RDACVOL)

R11 (0Bh)

Right Channel

Digital Volume

7:0

RDACVOL

[7:0]

11111111

( 0dB )

Right DAC Digital Volume Control

similar to LDACVOL

Table 17 Digital Volume Control

WM8988 Datasheet(PDF) 26 Page - Wolfson Microelectronics plc

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