Advanced Information

WM8722

WOLFSON MICROELECTRONICS LTD

AI Rev 1.5 May 2000

17

REGISTER 0/1

DAC OUTPUT ATTENUATION

A digital attenuator is provided to allow the levels of DAC signals to be attenuated in the digital

domain.

Register 0 (A[1:0] = 00) is used to control left channel attenuation. Bits 0-7 (AL[7:0]) are used to

determine the attenuation level. The level of attenuation is given by:

Attenuation = [20.log10 (Attenuation_Data/255)] dB

Bit 8 in register 0 (LDL) is used to control the loading of attenuation data in B[7:0]. When LDL is set

to 0, attenuation data will be loaded into AL[7:0], but it will not affect the attenuation level until LDL is

set to 1. LDR in register 1 has the same function for right channel attenuation.

Attenuation levels are controlled by setting the register set AL[7:0] (left channel) or AR[7:0] (right

channel). Attenuation levels are given in Table 7.

AX[7:0]

ATTENUATION LEVEL

00h

-

∞ dB (Mute)

01h

-48.16 dB

::

::

::

FEh

-0.034 dB

FFh

0dB

Table 7. Attenuation Control Levels

Register 1 (A[1:0] = 01)is used to control right channel attenuation in a similar manner.

REGISTER 2

SOFT MUTE

Soft mute is controlled by setting bit 0 in register 2 (A[1:0]=10). A high level on bit 0 will cause the

DAC outputs to be muted, the effect of which is to ramp the signal down in the digital domain so that

there is no discernible click.

DIGITAL DE-EMPHASIS

Bit 1 (DE) in register 2 (A[1:0]=10) is used to control digital de-emphasis.

A low level on bit 1

disables de-emphasis whilst a high level enables de-emphasis.

POWER OFF CONTROL

Bit 2 (PWD) in register 2 is used for operation control. With PWD = low (default) the device functions

normally. With PWD = high the device is disabled and the outputs are held at midrail. Current

consumption of the digital section is minimised, but analogue bias sections remain active in order to

preserve DC levels.

INPUT WORD RESOLUTION

Bits 3 and 4 of register 2 (IW[1:0]) are used to determine the input word resolution. The WM8722

supports 16-bit, 18-bit, 20-bit and 24-bit word formats.

BIT 4 (IW1)

BIT 3 (IW0)

INPUT RESOLUTION

00

16-bit Data Word

01

20-bit Data Word

10

24-bit Data Word

11

18-bit Data Word

Table 8. Input Data Resolution