WM8706

Product Preview

WOLFSON MICROELECTRONICS LTD

PP Rev 1.2 April 2001

9

DEVICE DESCRIPTION

INTRODUCTION

The WM8706 is a high performance DAC designed for digital consumer audio applications. Its

range of features make it ideally suited for use in DVD players, AV receivers and other high end

consumer audio equipment.

The WM8706 is a complete 2-channel stereo audio digital-to-analogue converter, including

digital interpolation filter, multi-bit sigma delta with dither, and switched capacitor multi-bit

stereo DAC and output smoothing filters. The WM8706 includes an on-board digital volume

control, configurable digital audio interface and a 3 wire MPU control interface. It is fully

compatible and an ideal partner for a range of industry standard microprocessors, controllers

and DSPs.

Control of internal functionality of the device is by either hardware control (pin programmed) or

software control (3-wire serial control interface). The MODE pin selects between hardware and

software control. The software control interface may be asynchronous to the audio data

interface. Control data will be re-synchronised to the audio processing internally.

Operation using master clocks of 256fs, 384fs, 512fs or 768fs is provided, selection between

clock rates being automatically controlled in hardware mode, or serial controlled when in

software mode. Sample rates (fs) from less than 8ks/s to 96ks/s are allowed, provided the

appropriate master clock is input. Support is also provided for up to 192ks/s using a master

clock of 128fs or 192fs.

The audio data interface supports right, left and I

interface formats along with a highly flexible DSP serial port interface. When in hardware mode,

the three serial interface pins become control pins to allow selection of input data format type

(I

The device is packaged in a small 28-pin SSOP and is a pin-compatible alternative to the

WM8716.

CLOCKING SCHEMES

In a typical digital audio system there is only one central clock source producing a reference

clock to which all audio data processing is synchronised. This clock is often referred to as the

audio system’s Master Clock. The external master system clock can be applied directly through

the XTI input pin with no software configuration necessary for sample rate selection.

Note that on the WM8706, XTI is used to derive clocks for the DAC path. The DAC path

consists of DAC sampling clock, DAC digital filter clock and DAC digital audio interface timing.

In a system where there are a number of possible sources for the reference clock it is

recommended that the clock source with the lowest jitter be used to optimise the performance

of the DAC.

DIGITAL AUDIO INTERFACE

Audio data is applied to the internal DAC filters via the Digital Audio Interface. 5 popular

interface formats are supported:

•

Left Justified mode

•

Right Justified mode

•

I

•

DSP Early mode

•

DSP Late mode

All 5 formats send the MSB first and support word lengths of 16, 20, 24 and 32 bits. The

exception is that 32 bit data is not supported in right justified mode. DIN and LRCIN are

sampled on the rising, or falling edge of BCKIN depending on the format selected.

In left justified, right justified and I

input. Audio Data is time multiplexed with LRCIN indicating whether the left or right channel is

present. LRCIN is also used as a timing reference to indicate the beginning or end of the data

words.