Forum Discussion

Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
8 years ago

ALtera FFT Outputs in SignalTapII

Hello,

I'm using an Alter 1024-point FFT IP (burst) and after implementing it I used SignalTapII for the FFT outputs acquisition. Now, I want to plot these output values using MATLAB but I'm a little confused about the format of these outputs. For testing I used 32-bit real input, all ones, and the imaginary is fixed to zero.

How are the real and exponent outputs represented; are they just decimal, signed or two's complement signed? How can I correctly plot these outputs?

Thanks

1 Reply

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor

    --- Quote Start ---

    Hello,

    I'm using an Alter 1024-point FFT IP (burst) and after implementing it I used SignalTapII for the FFT outputs acquisition. Now, I want to plot these output values using MATLAB but I'm a little confused about the format of these outputs. For testing I used 32-bit real input, all ones, and the imaginary is fixed to zero.

    How are the real and exponent outputs represented; are they just decimal, signed or two's complement signed? How can I correctly plot these outputs?

    Thanks

    --- Quote End ---

    altera fftcore if set to block floating point then output = fft_output * 2^(-exponent)

    Re/im data & exponent are all signed.

    signed = decimal = 2's complement...usually