Hi!

I have a designg for a digitally controlable sign wave generator, using one
of Analog Devices AD9834 DDS's and am looking for a way to turn it's output
signal into a sine-wave that looks near-perfect on an old analog scope. I
had the idea to use a Sallen-Key filter with a butterworth configuration
(2nd order), to filter my DDS's output, but after numerous simulation it
seems that the filter starts deforming the DDS's output because of it's
fase-shift  characteristic of the filter. Taking this into concideration
that the deformations start well before my 'Fc', I would never be able to
output a perfect looking sine at the desired Fc of about 25Khz, unless I
would filter at a far higher frequency - my view anyway.

My options are either using a variable bandpass filter - How do I make one
that is controllable by a pic? Switched capacitor filters? - or building the
circuit and hoping that the sun and moon are in a right setting for it to
work.

Help?

Sean.
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