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Visitor
Visitor
807 Views
Registered: ‎01-27-2015

FFT ip core not generating the correct results

I am using the FFT ipcore from Xilinx ISE. Ipcore specifications are as follows:

 

transform length is 8,

target clock frequency is 250

Pipelined architecture

fixed point

both input data width and phase phactor width  are 8

unscaled,Trunction,Natural order

input data timing : No offset , Block Ram, and uses 3 multiplier structure,

 

The output generated is not the same as the result from the matlab.

 

The following is the input sequence i have given for calculating the fft: [ 1 2 0 0 0 0 0 0]

 

the simulated output obtained is :

 

3, 0

1 , 0

-2, -1

-2, 1

0, -3

0, -1

-1,1

1,3

 

 

Though the output from the matlab is as follows:

3,0

2.414,-1.414

1,-2.00

-0.414,-1.414

-1.00,0.00

-0.414,1.414

1.00,2.00

2.414,1.414

 

 please suggest how to solve this problem?

 

 

 

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4 Replies
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Teacher
Teacher
761 Views
Registered: ‎07-09-2009

Re: FFT ip core not generating the correct results

so which do you think is "wrong" ?

 

how have you accounted for truncation , rounding , and decimal to binary transformation ? 

    

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Visitor
Visitor
748 Views
Registered: ‎01-27-2015

Re: FFT ip core not generating the correct results

I am not aware of what should be done with the simulation results to match the MATLAB results.

 

Could you please explain how to account for truncation and rounding?

 

Thanks in advance!

 

 

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Teacher
Teacher
740 Views
Registered: ‎07-09-2009

Re: FFT ip core not generating the correct results

You ask about truncation and rounding .

 

what do you know about rounding and truncation effects in fixed point maths ?

 

try this as a start

 

https://sestevenson.wordpress.com/2009/08/19/rounding-in-fixed-point-number-conversions/

 

<== If this was helpful, please feel free to give Kudos, and close if it answers your question ==>
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Visitor
Visitor
731 Views
Registered: ‎01-27-2015

Re: FFT ip core not generating the correct results

Thank you! I will go through it!!

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