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Altera_Forum
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17 years ago

Altera FFT Vs Matlab FFT. Strange Results

Hi, I’m testing some FFT Altera Core using those parameters: 1)Single Streaming or Burst 16K length FFT 2)12-14-16 bits input REAL data (pseudorandom code {-1,1}) 3)same bits for twiddle...
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Altera_Forum
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17 years ago

After plotting

>> plot(real(ifft(out_Altera)))

>> plot(imag(ifft(out_Altera)))

it is evident that the imaginary part of the IFFT (which should be zero everywhere) is considerably different from zero.

Also I tried to understand what kind of disturbance is imposed over the ideal result by:

>> plot(abs(out_Altera./out_Matlab))

or

>> plot(log10(abs(out_Altera))-log10(abs(out_Matlab)))

if you prefer the log diagram.

It is difficult to check the problem with this kind of pseudo-random signal, try to build a periodic signal (square wave, etc.) by using only +1 and -1 at the input and check the output. It should be easier to analyze.