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Help on picking a part to use

Discussion in 'Electronic Design' started by [email protected], Jan 17, 2009.

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  1. Guest

    I have outputs from 4 A/D's. Each output is 8 bits ( // output ) and
    will likely be sampled at 40MHz.

    I need to manipulate that data in some kind of device. This includes
    level shifting, multiplying the data against each other and possibly
    applying some FIR filtering to the data. The output will be three 8
    bit data streams running at the 40 MHz rate. Can anyone suggest a
    to consider using for an application such as this?


  2. Andrew Holme

    Andrew Holme Guest

    An FPGA e.g. Xilinx Spartan-3.
  3. linnix

    linnix Guest

    I would suggest a small high speed sram with it, since he is doing
    FIR. It should cut down on the gate counts, unless cost is no
  4. Guest

    Thanks everyone for the useful inputs
  5. linnix

    linnix Guest

    I think you should go with the xc3sd3400a. It costs around the same
    as the xc3s1500 ($70) but same number of MAC (104) as the xc3s5000
    ($120). As John said, you will likely be MAC bounded. For four
    inputs, you can do 25 TAPS FIR.
  6. linnix

    linnix Guest

    Or if you work for the government, perhaps they can spare $8000 for

    It gives you 176 MACs or 4 44 TAP FIR filters.
  7. linnix

    linnix Guest

    I believe they are single cycle MAC. Xilinx's are 18 bits and Altera
    can be down to 9 bits. But a partial serial (4 TAPs per clock) design
    would be far more complicated than either a parallel or serial design.
    The xc3sd3400a is going in the right direction, with more MACs and
    less gates. If only they can cut down the BGA pads (600+). I wish to
    have a thousand MACs in a 64 pins TQFP, less than $5 of course.
  8. linnix

    linnix Guest

    Yes, 1.27mm pitch DIP40. I'll see if I can fit the 464 BGA in it.
    Don't forget jtags as well.
  9. JosephKK

    JosephKK Guest

    I am not so sure about that if you have to off chip and back on, that
    takes a lot of cells also.
  10. linnix

    linnix Guest

    Yes, simple sram wouldn't do it. We need multi-port register cells.
    But even with the top end chip, we are MAC bounded (100 to 200). So,
    the OP might end up with multi-chips with external registers anyway.
    We really need more info about his spec before making educated
    guesses. For example, are the transfer functions linearly independent
    on inputs? What is the order of the FIR filter?

    The good news is that Spartan 3a dsp chips are surprisingly
    affordable. I though they were thousands of dollars before. Even a 5
    chips solution (4 inputs + 1 mixer) would not be too expensive for a
    45MHz dsp problem. We also need to know his budget limits, of course.
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