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Altera_Forum
Honored Contributor I
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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
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Altera_Forum
Honored Contributor I
61 Views

 

--- 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
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