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WM8726GEV 参数 Datasheet PDF下载

WM8726GEV图片预览
型号: WM8726GEV
PDF下载: 下载PDF文件 查看货源
内容描述: 24位192kHz的立体声DAC [24-bit 192kHz Stereo DAC]
分类和应用:
文件页数/大小: 20 页 / 222 K
品牌: WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
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WM8726  
Production Data  
DEVICE DESCRIPTION  
GENERAL INTRODUCTION  
The WM8726 is a high performance DAC designed for digital consumer audio applications. The  
range of features make it ideally suited for use in DVD players, AV receivers and other consumer  
audio equipment.  
The WM8726 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. It is fully compatible and an ideal partner for a range of industry  
standard microprocessors, controllers and DSPs. A novel multi bit sigma-delta DAC design is  
used, utilising a 128x oversampling rate, to optimise signal to noise performance and offer  
increased clock jitter tolerance. (In ‘high-rate’ operation, the oversampling ratio is 64x for system  
clocks of 128fs or 192fs)  
Control of internal functionality of the device is provided by hardware control (pin programmed).  
Operation using master clocks of 256fs, 384fs, 512fs or 768fs is provided, selection between  
clock rates being automatically controlled. Sample rates (fs) from less than 8kHz to 96kHz are  
allowed, provided the appropriate system clock is input. Support is also provided for up to 192kHz  
using a master clock of 128fs or 192fs.  
The audio data interface supports 16-bit right justified or 16-24-bit I2S (Philips left justified, one bit  
delayed) interface formats. A DSP interface is also supported, enhancing the interface options for  
the user.  
A single 2.7-5.5V supply may be used, the output amplitude scaling with absolute supply level.  
Low supply voltage operation and low current consumption combined with the low pin count small  
package make the WM8726 attractive for many consumer applications.  
The device is packaged in a small 14-pin SOIC.  
DAC CIRCUIT DESCRIPTION  
The WM8726 DAC is designed to allow playback of 24-bit PCM audio or similar data with high  
resolution and low noise and distortion. Sample rates up to 192kHz may be used, with much lower  
sample rates acceptable provided that the ratio of sample rate (LRCIN) to master clock (MCLK) is  
maintained at one of the required rates.  
The two DACs on the WM8726 are implemented using sigma-delta oversampled conversion  
techniques. These require that the PCM samples are digitally filtered and interpolated to generate  
a set of samples at a much higher rate than the up to 192kHz input rate. This sample stream is  
then digitally modulated to generate a digital pulse stream that is then converted to analogue  
signals in a switched capacitor DAC. The advantage of this technique is that the DAC is linearised  
using noise shaping techniques, allowing the 24-bit resolution to be met using non-critical  
analogue components. A further advantage is that the high sample rate at the DAC output means  
that smoothing filters on the output of the DAC need only have fairly crude characteristics in order  
to remove the characteristic steps, or images on the output of the DAC. To ensure that generation  
of tones characteristic to sigma-delta convertors is not a problem, dithering is used in the digital  
modulator along with a higher order modulator. The multi-bit switched capacitor technique used in  
the DAC reduces sensitivity to clock jitter, and dramatically reduces out of band noise compared  
to switched current or single bit techniques used in other implementations.  
The voltage on the CAP pin is used as the reference for the DACs. Therefore the amplitude of the  
signals at the DAC outputs will scale with the amplitude of the voltage at the CAP pin. An external  
reference could be used to drive into the CAP pin if desired, with a value typically of about midrail  
ideal for optimum performance.  
The outputs of the 2 DACs are buffered out of the device by buffer amplifiers. These amplifiers  
will source load currents of several mA and sink current up to 1.5mA allowing significant loads to  
be driven. The output source is active and the sink is Class A, i.e. fixed value, so greater loads  
might be driven if an external ‘pull-down’ resistor is connected at the output.  
PD Rev 4.1 September 2005  
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