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Altera_Forum
Honored Contributor I
1,513 Views

FFT Megacore sourceexponent

Hallo  

I use the the FFT-Megacore from Altera and it works fine. But i´m not shure about the output exponent. For example in my Simultion the peak in my frequency spectrum was half the magnitude i expected. On the other hand the Output of the sourceexponent[5],[4],[3]and [1] from the sourceexponent[5..0] were set '1'. Is there anybody well versed in this topic? 

Kind Regards
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7 Replies
Altera_Forum
Honored Contributor I
37 Views

have you taken a look at the FFT User Guide and the Application Note AN404? the exponent output is explained in these documents

Altera_Forum
Honored Contributor I
37 Views

i having problem in simulating fft in modelsim.as stated in the user manual i have added .vho file and compiled and simulated the file.But i am not getting any result only straight lines .Please guide me through this problem.

Altera_Forum
Honored Contributor I
37 Views

Yes i read the explenation in the userguide but it doesn´t work this way. I have a sine-wave with a magnitude from 256 while the output from the FFT Meagcore gives me a value of 128 for the according frequency. Additional it shows an exponent from -6 Bit (Bit 1, 3,4,5 is set, bit 0 and 2 not). That would be a factor of 2^6=64 which i would multiply with the value 128. 

128*64 = 8192. That doesn´t fit or did i use a wrong way to calculate this?
Altera_Forum
Honored Contributor I
37 Views

basically i am not getting any response i have no idea how to get the response from fft core .i read manual there is only stated that just compile .vho file.but i am not able to give input . i also simulated _tb.vhd file but same was the result. 

plz i give me a solution
Altera_Forum
Honored Contributor I
37 Views

I only simulated in Quartus not in modelsim, sorry

Altera_Forum
Honored Contributor I
37 Views

i also performed the simulation successfully but i could not give input properly . 

how did u give input . it will greatful if u attach image of ur response so i could have some reference.thanks for responding to my threat
Altera_Forum
Honored Contributor I
37 Views

Hi, 

 

I am a newbie to FPGA designs. I have few questions related to FFT mega core usage. 

 

1. I am trying to implement FFT mega core with variable length at run time. I expect the data( number of samples) and number of points in FFT as an input. So with this input, FFT core needs to be dynamically configured. The size of FFT varies between (256 - 65536) points.Is this feasible?? IF yes please suggest me. 

 

2. The input to FFT mega core is expected to be in some txt files and the data is in binary fixed point format. How do I now interface the input in files to FFT mega core?? Kindly suggest. 

 

Regards, 

Ramya
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