To all FFT guru's (2048 point FFT on Virtex 2 pro)

Discussion in 'VHDL' started by aj, Nov 23, 2005.

  1. aj

    aj Guest

    Hello FFT guru's

    I am implementing 2048 point FFT on Virtex as a part of my small
    project at uni. i want to put couple of questions.. please help me to
    your best as i am a starter...:)

    I have gone through couple of IEEE papers and i have found that i
    should use (Mixed Radix alg).i.e. like Radix4 and Radix2 butterflies to
    implement this algorithm. i have an understanding to use total of 6
    stages...i.e. 5 stages of Radix-4 and 1 stage of Radix-2 operations.

    Question 1. Is the aforementioned technique the best in terms of speed
    and area that operation will acquire.?

    Ans---->

    Question 2. I am very much confused about the Which ARCHITECTURE that i
    should use...??(any web links would be great) ??
    what would be the input to 2048 point fft... ??l know it has to be
    streaming data..
    where will that input come from....my understanding says that i have to
    feed x(n) n=0....2047 with data... but its kind of confusing me ... i
    am checking this site for
    reference...http://www.xilinx.com/ipcenter/catalog/logicore/docs/xfft.pdf

    Answer---->

    Quetion 3.----> my tutor also asked me to start my project with mapping
    "one kernel element of FFT to virtex-II board"...So what is the kernel
    element of FFT ??
    ..---->is this the Twiddle factor(e to the power of (-j*n*k*2*pi/N))
    that is multiplied with the inputs...

    Ans------->

    Question 4....----> (Most important for me)----------------> can i know
    the exact steps that i should follow to implement 2048 point FFT on
    Virtex2 pro.this answere will solve all my problems....
    Ans--------->

    Question 5....Can any one tell me any website for getting source code
    for FFT in VHDL(for my reference) because i am using windows machine
    and the code from opencores(cf_fft) can be downloaded as .tz
    format...which i am not able to untar... and it is in verilog as
    well...

    Answer ----->

    Aj
    aj, Nov 23, 2005
    #1
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  2. Mike Treseler, Nov 23, 2005
    #2
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  3. aj

    Dal Guest

    aj wrote:
    > Hello FFT guru's
    >
    > I am implementing 2048 point FFT on Virtex as a part of my small
    > project at uni. i want to put couple of questions.. please help me to
    > your best as i am a starter...:)
    >
    > I have gone through couple of IEEE papers and i have found that i
    > should use (Mixed Radix alg).i.e. like Radix4 and Radix2 butterflies to
    > implement this algorithm. i have an understanding to use total of 6
    > stages...i.e. 5 stages of Radix-4 and 1 stage of Radix-2 operations.
    >
    > Question 1. Is the aforementioned technique the best in terms of speed
    > and area that operation will acquire.?
    >
    > Ans---->
    >


    Why not start with the simplest approach?

    First, understand what a Radix-2 butterfly does, and how it is used to
    make a larger FFT. You can use one butterfly, or many, depending on how
    you want to structure your design.

    Work out the sequence of data input to each pass, and the coefficient
    sequence. You need 11 radix-2 passes for 2048 points, and the algorithm
    has a very regular structure in this case.

    Once you understand the basic operation, work out where the input data
    comes from, and how you might buffer it for each pass, and how the data
    will be output. Understand the difference between Decimation-in-Time and
    Decimation-in-Frequency, and how you can use a single buffer and
    in-place storage between passes.

    Then design the FPGA. That will be a lot easier when you understand what
    you are trying to do.

    You can worry about radix-4 and mixed-radix later, if you need to. More
    complicated architectures may give you higher performance, but you will
    find them harder to design, especially if you do not understand the basics.

    Read some application notes for DSP processor implementations of radix-2
    FFT algorithms, they will help you understand the basic operations required.
    Dal, Nov 23, 2005
    #3
  4. aj wrote:
    > Hello FFT guru's
    >
    > <"do-my-homework" part snipped>


    Would you like us to also write the project report for you ? :)
    ----> Answer

    How did people manage to design anything before there were Google,
    newsgroups etc.. ? I guess we have some old farts here that have
    actually read some printed manuals and datasheets to get their HW
    working :-o

    Sorry for the off-topic post, but I think the "give me exact steps how
    to complete my homework" was a bit too much...

    Anyway, it's good that you have done also some research yourself
    already. As I'm not an "FFT guru", here is just a general tip: Try
    installing Cygwin on your Windows machine, you'll be able to untar
    zipped packages and do also lots of other neat stuff...

    -jv-
    Jaakko Varteva, Nov 24, 2005
    #4
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