FPGA : Open core FFT

Started by bijoy September 19, 2006
Hi all,

Does any one used Open core FFT.

I am trying to use it, but what my simulation results shows is that the performance
of the FFT does not match with the other FFT cores available from other vendors(eg.
xilinx).

The magnitude of the result seems matching except the attenuation of the side lobs
is not so good.

But what i am afraid is that the phase response of the FFT result is very bad
compared to FFT result from matlab or from other vendors.

Can anybody help me if you have used open core FFT .

Thanks in advance

rgds bijoy
xilinx's coregen can generate FFT modules..






bijoy wrote:
> Hi all, > > Does any one used Open core FFT. > > I am trying to use it, but what my simulation results shows is that the
performance of the FFT does not match with the other FFT cores available from other vendors(eg. xilinx).
> > The magnitude of the result seems matching except the attenuation of the side lobs
is not so good.
> > But what i am afraid is that the phase response of the FFT result is very bad
compared to FFT result from matlab or from other vendors.
> > Can anybody help me if you have used open core FFT . > > Thanks in advance > > rgds bijoy
we use this fft from opencores:

-- Title       : cfft64X12
-- Design      : cfft
-- Author      : ZHAO Ming

it seems ok to us other than it generates a lot of waring in simulation
due to uninitialized signels.
Plus XST8.2.2 synthesis is wrong where the keyword "signed" is used.
Other synthesisers like Synplify Pro do it ok.


bijoy ha scritto:

> Hi all, > > Does any one used Open core FFT. > > I am trying to use it, but what my simulation results shows is that the
performance of the FFT does not match with the other FFT cores available from other vendors(eg. xilinx).
> > The magnitude of the result seems matching except the attenuation of the side lobs
is not so good.
> > But what i am afraid is that the phase response of the FFT result is very bad
compared to FFT result from matlab or from other vendors.
> > Can anybody help me if you have used open core FFT . > > Thanks in advance > > rgds bijoy
Hiello ZHAO Ming

Thank you for your mail.

I have taken the fft core from open cores website

 <http://www.opencores.org/cvsweb.shtml/cfft/>

and then i configured it for 1024 point and 16-bit width. i modified the test-bench
to and send my input signal ( a sine wave). but what i observe is i am getting a
magnitude peak at the correct bin but there are significant peaks in nearby bins
also. and the phase response shows 180 degree change for some bins compared to the
matlab values.

could you please send the exact files that you have used.

rgds bijoy