Simulink IIR Bandpass filter on DE2

Question

I made a filter with matlab simulink and used one of its tools to create vhdl code out of it. I implemented it on an FPGA and it gives me reasonable output except that the frequencies that it pass are not the frequency I designed it to pass. When testing in matlab, a FFT of the output from the filter gives a single peak at 82Hz, but the filter on the board passes 56Hz as well at 170Hz. Any idea what would cause this? Thanks for the help.

altera_forum · Answer

The question doesn't seem particularly related to Altera FPGA or tools, but did you set the correct clock frequency when creating the filter?

altera_forum · Answer

I'm sorry to have been vague. I am implementing this filter on a Cyclone II DE2. I'm feeding data in from the audio codec. I'm using the ADCLRC clock. Would that be correct or incorrect?

altera_forum · Answer

ADCLRC seems reasoanable as a filter sampling clock. The results seem to indicate, that the actual clock frequency is different from calculated value.

The said 170 Hz looks like a 3rd harmonic, either caused by a distorted signal source, ADC overload or filter truncation errors (You didn't tell about relative amplitudes or the filter word length).

altera_forum · Answer

Would my vhdl code be at all useful? It was created automatically by Matlab Simulink. I attached the .vhd file. I hope that works.

altera_forum · Answer

I wonder, which filter specification is represented by the VHDL code. The coefficients look strange.

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Simulink IIR Bandpass filter on DE2

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