Hi Sean,

I'm not sure why a phase shift would deform the DDS's output. What frequency is the DDS clock and what max frequency is your desired output? The DDS output spectrum should look like a pure sine wave, plus some phase noise, and then a whole bunch of stuff which is all at higher than half the DDS clock. So, if you want 100kHz max freq output and you have a 10MHz DDS clock, then you would set your Fc for, say, 1MHz, and all the junk at 5MHz and above would be taken out and you would be left with a pure sine wave plus some fairly low noise. Even if your filter has a significant phase shift below Fc, a phase shift doesn't change the shape of a sine wave.

Sean




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