XWM8728EDS(2001) Ver la hoja de datos (PDF) - Wolfson Microelectronics plc

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XWM8728EDS
(Rev.:2001)

24-bit, 192kHz Stereo DAC with Volume Control and DSD Support

Wolfson Microelectronics plc 

WM8728

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DEVICE DESCRIPTION

INTRODUCTION

The WM8728 is a high performance DAC designed for digital consumer audio applications. Its

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

consumer audio equipment.

WM8728 is a complete 2-channel stereo audio digital-to-analogue converter, including digital

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

output smoothing filters. The WM8728 includes an on-chip digital volume control, configurable

digital audio interface and a 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.

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

software control (2 or 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. In which case control data will be re-synchronised to the audio processing internally.

Operation using a master clock 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 justified, left justified and I2S (Philips left justified, one bit

delayed) 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 (I2S or right justified), input word length (20 or 24 bit) and de-emphasis functions.

In DSD mode, a separate bitstream data input pin is required for each of the channels, plus a 64fs

dataclock MCLK. These signals are applied via pins DIN and LRCIN and the signals routed

internally into the DAC circuits, under control of the SCKDSD mode select pin (19) See Figure 3.

Additionally a Phase Modulation scheme is supported, whereby the audio data is transmitted as a

Manchester encoded bitstream. This has the advantage of removing the significant spectral audio

energy from the datastream, minimising digital signal corruption of the analogue outputs. In order

to simplify decoding of this Phase modulated data, a 2x speed clock (BCKIN) is used to sample

the incoming data. See Figure 4.

The device is packaged in a small 20-pin SSOP.

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

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

Note that on the WM8728, MCLK 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.

WM8728 always acts as a slave and requires clocks to be inputs.

WOLFSON MICROELECTRONICS LTD

PP Rev 1.2 April 2001

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