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Active filter for DAC reconstruction

The Sallen-Key topology has no DC path from its input to ground, so if you have a current-output DAC it will not "play" into a Sallen-Key. A Multiple FeedBack (MFB) topology allows for DC current to flow. If your DAC is a voltage-output DAC, then the Sallen-Key will probably do OK -- just make sure it can drive capacitive loads.

As for the preferred characteristic type -- for audio, generally a Butterworth is used because people want that "flat" audio response. But, it all depends on your sampling rate, and the audio bandwidth. If your sampling rate is 44 kHz and you want that "20-20kHz" bandwidth, a Butterworth will require many poles (=many OpAmp stages). If you can't afford too many OpAmp stages, then you might consider a medium-ripple Chebychev characteristic.

Reply to
tlbs
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A while back someone posted that a Sallen-key active op amp filter might not be the best topology for preserving the SNR of a signal coming from a DAC.

What is the preferred filter type to get rid of alias products for an audio signal after a DAC?

Stephen

Reply to
Stephen Boulet

might

from

an

Apart from the other notes already here, the filter function should be considered. If you are reconstructing previously encoded analog signals, then a raised cosine filter is the most common solution. (That's because the encoding process induces a SinX/x Power distribution on the signal).

A good paper on this may be found at

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(Note : I have nothing whatever to do with the site)

Cheers

PeteS

Reply to
PeteS

I use the one recommended by the DAC maker !

Graham

Reply to
Pooh Bear

"total attenuation at thigh frequencies"

Skinny legs?

John

Reply to
John Larkin

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