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Working with an FPGA to Count Coidncident Pulses

  1. Jun 17, 2011 #1
    I am currently trying to program an FPGA to mimic a coincidence counting module. What I basically need it to do is a modified AND operation. The inputs are square, 5V pulses from photon counters. Because I am working with two photon counters (that are the same model) but due to imperfections in the wiring and their internal circuits, pulses that are emitted from both from the same event might not be arriving at my FPGA at the same exact time.

    What I was wondering was if anyone knew create a time window so that the programmable AND logic will count any two pulses that occur within a set time window as the same? I know that if the pulses are a long enough, that any AND gate will return true if the pulses are overlapping at any point, but some of the pulses are as short as a few nano seconds so I want to make sure my design doesn't miss those.

    Thanks for the help, oh and if it matters I am using a Basys2 FPGA and I am programming it using VHDL in Xilinx
  2. jcsd
  3. Jun 17, 2011 #2


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    Science Advisor

    I'd just use monostables to stretch the pulses to whatever is your desired "non overlap window" and then and them together.
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