Update:

I am currently looking into "All-Pass" filters to correct (counter) the
phase-shift that occurs in the pass-band. If anybody has any tips, tricks or
informative resources are, their more than welcome!

Thanks,

Sean.

p.s. Excuse my mixing up of dutch and english,   "fase" in the last email
was supposed to be "phase". Sorry.



On 2/10/06, Sean Schouten <dev.seantech@gmail.com> wrote:
>
> 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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