ns pulse detection

Discussion in 'General Electronics Chat' started by abad109, Mar 14, 2011.

  1. abad109

    Thread Starter New Member

    Mar 14, 2011
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    I have a device that produces current pulses that are 5 ns wide and occur every 10Hz.
    Could you suggest an amplifier IC chip fast enough to detect such pulses?

    Thanks
     
  2. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    What voltage pulse...5V? How detected...stretched pulse width?

    Ken
     
  3. abad109

    Thread Starter New Member

    Mar 14, 2011
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    Thanks for your response.

    Its a current pulse, microamps to nanoamps range.

    I was thinking of a transimpedance amplifier with GHz bandwidth to do so.
     
  4. russ_hensel

    Well-Known Member

    Jan 11, 2009
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    Really every 10 Hz. One pulse per 10 waves?
     
  5. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    ... detect it,


    Sorry, I mis-read that you wanted to create the pulses? or need to detect the pulses?


    more info would help. How are you coupling the signal to your input? Coax, tranformer, opto coupled?
     
    Last edited: Mar 14, 2011
  6. abad109

    Thread Starter New Member

    Mar 14, 2011
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    i want to detect ns wide pulses
    the signal from a photodiode, which produces the current pulses may be connected through a BNC coax to the amplifier
     
  7. beenthere

    Retired Moderator

    Apr 20, 2004
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    Coax is a long capacitor. The length of the coax will have a marked effect of both pulse height and width. Your results would almost certainly be better with a buffer amp driving the coax.

    Have you ever looked at a TAOS light-to-voltage converter? - http://www.taosinc.com/
     
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  8. abad109

    Thread Starter New Member

    Mar 14, 2011
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    Thank you for suggesting alternative to coax.
    i certainly want to minimize RC delays.
     
  9. abad109

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    Mar 14, 2011
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  10. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Coax does not look capacitive if it is terminated in its characteristic impedance. However, it still won't carry a 5nS pulse very far without degradation in transition times.
    Also, microamps into 50 ohms, or 75 ohms, won't leave much voltage to work with.:(
    Any kind of voltage buffer will be problematic. For example, a one microamp 5ns pulse into any realistic capacitance will have a 1mV/nS slew rate.
    You might be able to use a transresistance amplifier, but that is probably not something a novice could handle, and it probably couldn't be designed on one side of a forum and debugged on the other.
    Sorry to be so negative, but this is not a simple problem.
     
  11. beenthere

    Retired Moderator

    Apr 20, 2004
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    Agreed, but the drive is coming from a photodiode -
     
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  12. abad109

    Thread Starter New Member

    Mar 14, 2011
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    Thanks anyway for your suggestions. I will try my best.
     
  13. ifixit

    Distinguished Member

    Nov 20, 2008
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    Hi abad109,

    I agree, you need to use a transimpedance amplifier with a bandwidth of at least 1GHz. Mount it within millimeters of the photodiode. From there you can buffer again if required to drive a coax transmission line (50Ω).

    Regards,
    Ifixit
     
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  14. abad109

    Thread Starter New Member

    Mar 14, 2011
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    thanks, i will build and see, if there is some improvement .:)
     
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