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Altera_Forum's avatar
Altera_Forum
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11 years ago

DC in the CIC-FIR filter result

Hi All, I have attached a figure showing my filter issue. Please subtract 28 MHz from the x axis values (it was a typo). It is apparent that there is a strong DC peak in the plot. My question i...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
11 years ago

You can check dc gain of CIC and FIR by injecting it with step input.

if you can't achieve unity by discarding LSBs then you can rescale FIR to any value compensate for overall gain.

Mixer will cause dc if there is power in a frequency that is shifted to dc at mixing. For example if your NCO is at 1MHz then any power in 1MHz (or its multiples) will move to dc (or alias to dc). You wiil then need LPF before mixing.