You could use two FIR filters in SigmaStudio, where the coefficients are calculated with a constant phase shift of 90°.
A good program to do this is SCOPEFIR5; with this program, the phase changes, but the phase difference is constant to the chosen value, ie. 90°.
It deprends also if your frequency is fixed or if you process speech, for instance.
1) if your frequency is fixed, or slowly variable, with constant amplitude, you can generate at 4 times the frequency and divide by two and again by two, thus giving you signals at 90° difference, taking the right taps.
2) if you process speech, with variable amplitude and frequency, you can use two low-pass or band-pass FIR filters covering the same frequency range, that may have a varying phase, graphically going down, thus going up in phase, towards 180° or more, but -and this is important- with a phase DIFFERENCE of 90°. This gives you the celebrated I and Q signals.
I hope to be clear; you may have to dig into the theory.
If others can explain this in a more pedagogic manner, please step in.
Ready to help again
I want to be with ADAU1701 to handle speech signal. The speech signal do 90 ° / 180 ° / 270 ° / 360 ° such a treatment, what a pity, English is not my native language, I can't very good understanding...
You need to goole for "hilbert transform filter", it is a FIR filter that gives you a 90 deg. shifted signal.
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