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Altera_Forum's avatar
Altera_Forum
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16 years ago

frequency spectrum

Hallo,

I worked with the Altera FFT Megafunction.At the output i have an imaginery and a real part. but the output (sourcereal and sourceim)in the simulator is time-dependent. How can i get the frequency-spectrum for the signal? and how can i analyse the output, if its right or wrong?

2 Replies

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    16 years ago

    The I/Q of fft is the frequency domain.

    so just plot the absolute value of output.

    IQ = I + jQ;

    power = 20* log10(abs(IQ)); %dB

    f = linspace(-.5*Fs,.5*Fs,fft_points) % if centered on dc else

    %f = linspace(0,1*Fs,fft_points);

    %Fs = fft clock frequency

    plot(f,power)
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    16 years ago

    So If i have a 1024 fft i take the last 1024 values of the real and imaginery part and set them as an array in i and q? What means "centered on dc"?