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Altera_Forum
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16 years ago

Altera FFT - output scaling. How to do this correctly?

Hi, I do not get correct scaled results if I do everything the FFT user guide recommends. I have instantiated a 1024 points FFT, with single output and burst architecture. The data width...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
16 years ago

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I am not sure about the 9 bits shift but here is my suspicion:

If your fft output bitwidth is 25 bits while your input bitwidth is 16 bits then I guess the IP may introduce 2^9 scaling to fill up all output bits. Thus you need to divide back by 2^9. You can just take the 16 MSBs instead of shifting right then taking lower 16 bits.

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My output is not 25bits wide. It is 16bits + a maximum of 15bits. So chosing the MSBs only is not a good idea