I would like to ask something regarding CICs (Cascaded Integrator-Comb filters) or more particular about the frequency response of it.
Assuming that I have as input IQ samples from a signal generator that are multiplied over a complex multiplier by another set of IQ samples; by changing the frequency of each of the IQ samples generators one can see a single spike on the spectrum analyser shifting left or right (exp()*exp()).
If I apply a CIC decimator in the output of that complex multiplier I would expect to see (according to some matlab code I have put together) that spike to be moved according to the decimation factor (forward in frequency by a factor of 2 if the decimation rate is 2).And that would occur if that spike “falls” within the CIC’s pass band.
That, I can confirm on matlab.
However, in an actual design by plotting on an actual Spectrum analyser (after DAC), the only think am getting in the output is the frequency response of the CIC.
Can you give some input on my thoughts?
G
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