Fast Fourier Transform

Hi,

At school we have a project and our subject is to make a simple spectrum
analyser. Now I want to know if it would be possible to perform a realtime
FFT with an FPGA/CPLD (if possible in Xilinx). And if it is possible, where
I can find/download the source and which chip is best to use.

Any help will be appreciated.

Thanks in advance,

Sander Odekerken

It is.  Real-time is a bit of a loose definition that depends on the
application.  A serial implementation might be considered real time for an
audio analyzer, while it would not be for FFT's performed for radar.  You need
to define the size of the FFT you wish to perform and the transform time
required before you can determine what approach (and therefore which chip) is
appropriate.  You can go from a bit serial iterative FFT in a very small FPGA +
external memory to an FFT that computes all the points in parallel in a much
larger device.  We offer an FFT core that is arguably the fastest single
threaded (one point at a time) FFT possible in an FPGA (it does one point per
clock and is limited by the minimum clock pulse width, not by routing delays),
however it is not free.  Both Xilinx and Altera offer FFT cores as part of
their core library, but you don't get any insight into the inside of the core,
as they don't make the source code available.  IIRC, there is also a free FFT
design on opencores.com which should have source with it.  Alternatively, you
can roll your own.  The math to do the fft is not difficult to code.  What is
difficult is making it an efficient design.

Sander Odekerken wrote:

> Hi,
>
> At school we have a project and our subject is to make a simple spectrum
> analyser. Now I want to know if it would be possible to perform a realtime
> FFT with an FPGA/CPLD (if possible in Xilinx). And if it is possible, where
> I can find/download the source and which chip is best to use.
>
> Any help will be appreciated.
>
> Thanks in advance,
>
> Sander Odekerken

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