WM8721

Product Preview

WOLFSON MICROELECTRONICS LTD

PP Rev 1.3 November 2000

10

DEVICE DESCRIPTION

INTRODUCTION

The WM8721 is a low power audio DAC designed specifically for portable audio products. It’s

features, performance and low power consumption make it ideal for portable MP3, CD and mini-disc

players.

The WM8721 includes line and headphone outputs from the on-board DAC, configurable digital audio

interface and a choice of 2 or 3 wire MPU control interface. It is fully compatible and an ideal partner

for a range of industry standard microprocessors, controllers and DSPs.

The on-board digital to analogue converter (DAC) accepts digital audio from the digital audio

interface. Digital filter de-emphasis at 32kHz, 44.1kHz and 48kHz can be applied to the digital data

under software control. The DAC employs a high quality multi-bit high-order oversampling

architecture to again deliver optimum performance with low power consumption.

The DAC outputs are available both at line level and through a headphone amplifier capable of

efficiently driving low impedance headphones. The headphone output volume is adjustable in the

analogue domain over a range of +6dB to –73dB and can be muted.

The design of the WM8721 minimises power consumption without compromising performance. It

includes the ability to power off selective parts of the circuitry under software control, thus conserving

power. Separate power save modes can be configured under software control including a standby

and power off mode.

Special techniques allow the audio to be muted and the device safely placed into standby, sections

of the device powered off, volume levels adjusted without any audible clicks, pops or zipper noises.

Therefore standby and power off modes maybe used dynamically under software control, whenever

playback is not required.

The device caters for a number of different sampling rates including industry standard 8kHz, 32kHz,

44.1kHz, 48kHz, 88.2kHz and 96kHz. The WM8721 has two schemes to support the programmable

sample rates: Normal industry standard 256/384 fs sampling mode may be used. A special USB

mode is included, where all audio sampling rates can be generated from a 12.00MHZ USB clock.

The digital filters used for playback are optimised for each sampling rate used.

The digital audio interface can support a range of audio data formats including I2S, DSP Mode (a

burst mode in which frame sync plus 2 data packed words are transmitted), MSB-First, left justified

and MSB-First, right justified. The digital audio interface can operate in both master or slave modes.

The software control uses either a 2 or 3-wire MPU interface.

AUDIO SIGNAL PATH

DAC FILTERS

The DAC filters perform true 24 bit signal processing to convert the incoming digital audio data from

the digital audio interface at the specified sample rate to multi-bit oversampled data for processing by

the analogue DAC. Figure 6 illustrates the DAC digital filter path.

FROM DIGITAL

AUDIO

INTERFACE

MUTE

DIGITAL

INTERPOLATION

FILTER

TO LINE

OUTPUTS

DIGITAL

DE_EMPHASIS

DEEMP

DACMU

Figure 6 DAC Filter Schematic