0.35

µµµµm 16-BIT 44.1KHZ SIGMA-DELTA STEREO DAC

BW0405XA

11

FUNCTIONAL DESCRIPTION

Compensation Filter

&

De-emphasis/

FIR Filter

Sinc Filter

&

Σ∆

Modulator

4bit DAC

&

SC-Postfilter

Anti-Image

Filter

SDATA

BCK

LRCK

AoutL

4Fs/8Fs

16bits

64Fs

1bit

DEEM

DN

1Fs/2Fs

16bits

S/P Converter

&

Attenuator

MCLK

MDATA

MLD

AoutR

MUTEL

Figure 4. Funtional Block Diagram

Fig4 is the 1bit 4th order sigma-delta DAC block daigram. S/P Converter converts serial 16bit input data to parallel

16bit data. Digital input data is attenuated by MICOM interface pin control. Compensation Filter compensates gain

droop in Passband by Sinc Filter and Sigma-Dellta Modulator Signal Transfer Function. De-emphasis Block de-

emphasizes pre-emphasised input data to emphssize high frequency in audible band. FIR Filter perfroms 4X

interpolation. And it outputs 4Fs(DN='Low') rate data or 8Fs(DN='High') rate data by variabled input data rate. It

also removes the images of the input signal that are present at multiples of the input sample frequency. And Sinc

filter makes the constant 64Fs rate data by 16 times or 8 times upsampling FIR Filter output data according to

DN(Double/Normal Mode) Pin Selection. This operation intorduces a sinc function responce on the resulting

frequency spectrum, which greatly attenuates the energy of images at the multifules of 4Fs(or 8Fs).

Digital sigma-delta modulator of bit-stream type has the IFL (Inverse-Follower-Leader) topology, and it performs a

noise-shaping function. The modulator shapes the quantization noise by suppressing its in-band component and

pushes the noise energy of outside the band-of-interest without deteriorating the audio input signal. The 64 times

oversampled 1-bit PDM outputs from the modulator drives a analog postfilter.

The analog postfilter comprises SC-postfilter, anti-imaging filter. The SC-postfilter removes the quantization noise

shaped to out-of-band by digital sigma-delta modulator. This analog filter has the good clock jitter characteristc and

very linear characteristic. And following the CTF(continuous time filter) removes the sampling images and makes

the high resolution analog output.