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5990 Discussions

FFT Megafunction - bit reversed or not

Altera_Forum
Honored Contributor II
973 Views

Hi all, 

 

using the FFT megafunction (fixed,streaming architecture), I have been assuming the data is natural order (user guide could be clearer?) 

Am I wrong? 

 

My sim. output looks wrong - with simple sine input , output has two large (same amplitude) peaks per packet 

 

I have read the manual, honest! :confused:
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4 Replies
Altera_Forum
Honored Contributor II
86 Views

You're aware of the fact, that the frequency domain data will be mirrored around fs/2?

Altera_Forum
Honored Contributor II
86 Views

Ok, thanks very much, 

 

that would make sense.. 

 

back to school for me! 

 

thanks again,
Altera_Forum
Honored Contributor II
86 Views

If your input is real sine (imag of zero) then you will get two equal mirrored peaks. 

If your input is complex sine/cos (well balanced in amplitude and phase) then you get one peak only. If it is complex but unbalanced then the peaks become unequal. The real case is the extreme subset when imbalance is maximum (imag = 0)
Altera_Forum
Honored Contributor II
86 Views

Kaz, 

thanks so much for extra info, very helpful
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