Antialiasing And Sync-Compensation Filter

Posted on Oct 10, 2012

Two dual-biquad filter chips and some external components form a multipurpose filter to reconstru

Antialiasing And Sync-Compensation Filter
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ct 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(7rx)()—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 attenuation. 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 (/„ + 2). To achieve 70-dB stopband rejection with this eighth-order filter requires a transition ratio (/stopband -K/passband) 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 corner frequency.

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