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Altera_Forum's avatar
Altera_Forum
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14 years ago

FFT Megafunction - bit reversed or not

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:

4 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

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

  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    Ok, thanks very much,

    that would make sense..

    back to school for me!

    thanks again,
  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    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)