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ANTIALASING_AND_SYNC_COMPENSATION_FILTER

2017-02-19 23:37  
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ANTIALASING_AND_SYNC_COMPENSATION_FILTER
Two dual-biquad filter ciUps and some external components form a multipurpose filter to reconstruct D/A converter signals. Connected to a converter’s output, the filter provides antialiasing, reduces the D/A converter’s quantization noise, and compensates for sin(πx) ÷ (πx)-the sync function (attenuation). The circuit incorporates an inverse-sync function that operates to one-third of the converter’s sample rate. Beyond one-third, the filter’s response shifts to a stopband filter, which provides -70 dB attenua-tion. This attenuation conforms to the converter’s inherent signal-to-noise ratio and quantization error. To prevent aliasing, the stopband edge must be no higher than the Nyquist frequency (fsn÷2). To achieve 70-dB stopband rejection with this eighth-order filter requires a transition ratio (fSTOPgAND÷fPASSsAND) of 1.5, which sets the passband’s upper limit at fS÷3. Notice also that you can apply a simple divide-by-64 circuit to the 192-kHz clock frequency to set the necessary 3× ratio between the converter’s sample rate and the filter’s 1-kHz comer frequency. The V+, V-, and the FO through F5 connections program each filter chip for an fCLK/f0 ratio of 191.64.