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    Simple Pulse Stretcher out of one Flip-Flop

    Hi,

    I searched for a similar topic, but all I could find were some unanswered threads and because I don't necessarily want to hijack someone's topic and I also have an approach, I started my own.

    But now to my problem. I have to stretch an UWB pulse with some hundred ps up to at least 2.5ns (my TDC has this minimum input pulse width). The amplitude of the pulse can be easily adjusted, so no problem there.

    Well I thought, perhaps I can abuse the propagation delay of a flip flop to stretch my incoming pulse to a much wider one.
    My idea is to feed the outgoing signal back to the reset pin of the flip flop which has a propagation delay of about 3.5ns.

    This would be this one: sn74lvc112ad by Texas Instruments. The Data Sheet can be easily found over Google (I'm sorry, but I cannot post links yet and don't want to be banned because of cheating this link into the post by removing the protocoll prefix).

    But honestly I'm a little unsure about the minimum pulse width mentioned in the data sheet which would be 3.3ns. On the other hand I have read that this only concerns the clock and not the actual input pulse.

    I don't have much experience in flip flops, so perhaps could someone tell me if this would even work or otherwise help me obtaining my goal

    Best,
    Fiech
    Last edited by FIech; 9th November 2010 at 21:10. Reason: Grammar Issues

    •   Alt9th November 2010, 20:52

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    Re: Simple Pulse Stretcher out of one Flip-Flop

    How about this: I beleive this is a part of another problem. Why don't explain the original problem and there may be other solution than make an "pulse extender".

    I think this problem is possible to solve just using regular logic gates, But I cannot come up with something smart right now.

    I hava another very simple circuit that generates very short spikes. But it won't be longer than initial pulse so that idea won't help much I'm afraid.



    •   Alt10th November 2010, 01:38

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  3. #3
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    Re: Simple Pulse Stretcher out of one Flip-Flop

    First of all, thank you for your reply.

    Unfortunately there is no way around a pulse stretcher because this is for a project at my university. Also it's not my own project, so I can't just change parameters as I like.

    You see, I have some fix parameters: For one there is the initial pulse width of some hundred ps and also the minimum pulse width my TDC can handle which is as above 2.5ns
    Inbetween those two there is however a comparator to sort out multipath propagation and so on.
    And this I found out shortly after my post could also be a possible solution:

    The comparator which is an ADCMP572, an ADCMP573 or an ADCMP582, all made by Analog Devices (and again no links, but this time I will double post to get you the links), has the ability to latch the output, which means it will stay on the last output for as long as the latch is active.

    This I can use as described in the link (which will be in the upcoming post) to stretch the pulse to a varible length.

    Perhaps you or someone else could help me with this approach instead. These are the two ways I imagine how I could solve my problem.

    Best,
    Fiech

    ---------- Post added at 03:09 ---------- Previous post was at 03:01 ----------

    Ok, here now the links:
    This are the three Comparators by Analog Devices:
    Page for ADCMP572 with datasheets for ADCMP572 and ADCMP573
    and here
    Page and datasheet for ADCMP582

    Also here the approach over the latch:
    Fast, simple one-shot pulse stretcher detects nanosecond events

    But perhaps I should begin a new topic for this approach...

    Best,
    Fiech


    PS: I think, I should also say what my problem with the latch thingy is:
    I actually don't know if this would work with the AD comparators because of the different way to switch on/off the latch, but I will think some more over it.
    Last edited by FIech; 10th November 2010 at 02:16.



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