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  1. #1
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    Pulse generator circuit for pulses in sub-nanosecond region

    Hi All

    I have been working in building a pulse generator circuit, but I am failing to get the pulse in the sub nanosecond reigon (400ps). The lowest I get is around 5ns. Does anybody have a working circuit I can play with that has the capabilty to go to 400ps. I only have a suplly of 24V and need a pulse of 5-10V with a pulse with of less than 1ns.

    Thank you
    :D

    •   Alt8th September 2005, 15:06

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  2. #2
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    pulse generator 74ac

    may be 555 timers could solve your problem, and generate a pulse width of 1 ns, up on values of capacitors and resistors



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    74ac pulse generator

    Hello Gandalf007,
    What kind of circuit are you using?
    A posible starting point could be to use an avalanche mode pulse generator, but with only 24V it could be dificult.
    I have made an avalache mode pulse generator, I don't remember pulse with, but attempting to measure its rise time with a 500 Mhz scope (the best I could get in this time) gives me the scope's rise time.
    Hope this helps

    Best regards



  4. #4
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    pulse generator circuit fast rise time avalanche

    Hi,I have designed a pulse generator for sub nanosecond ,also used avalanche NPN transistors.I don't know what type of ciucuit you choose and what do you wanna know about it!



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    custom pulse circuit

    Will I be able to use a avalanche NPN with only 24V supply?



    •   Alt12th September 2005, 06:35

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    2n2369a +pulse generator

    It seems impossible,
    but with low votage you can use SRD



    •   Alt12th September 2005, 14:20

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    pulse generator circuit 24v

    Do you have a circuit for me that uses a SRD?



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    pulser

    here is a circuit about SRD pulse generator!



  9. #9
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    srd short pulse circuit

    the out waveform



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    74ac nanosecond pulse

    In years past, I built a number of different high-speed pulse generators; including several avalanche-xsistor based units.

    The #1 advantage of using avalanche pulsers is the ease of obtaining quite high output power.

    24v is very marginal for avalanche circuits....you might try some of the recent 8ghz fT small-signal xsistors, with the -lowest- Vcc-max rating you can find; and see if you can get consistent operation under 24v.

    I can pretty easily get 600ps transition times from a 2N2369A, but most of them require 50-60 volt supply for consistent operation.

    But since you left out a whole lot of necessary specification information; it's real hard to give specific advice.

    For example....

    You didn't specify whether you need high output power, or not.

    You say you need 5-10v pulse height, but you didn't specify the load resistance.

    You didn't specify what repetition-rate (frequency) you need.

    You didn't specify what waveform you needed; and whether or not waveshape quality was important or not.

    These things are important because, for example, if you need kilowatt peak power, a typical small-signal SRD isn't going to work; whereas an avalanche will easily make that kind of high-power pulse.

    But if you need 100ps edge-rates, an avalanche won't work; but an SRD will.

    Also, avalanche circuits are generally hard to build for a rep-rate much above 100-200 khz. The heating in the xsistor becomes a real issue as the freq rises. Higher F ckts can be made, but they're much trickier. A 10khz avalanche, on the other hand, is very very simple to make.

    Also, depending on what kind of shape you need for the low-frequency portion of the waveform, you can get your required 10v of signal -regardless- of the available power-supply voltage; simply by using a xformer at the output. This is true regardless of what device you use.

    If you only need single pulses, or at most a few hundred Hz, then you can get very fast pulses with nothing but a relay and a piece of coax. For 400ps, you really don't even need the coax.....a short microstrip trace on the PCB will work for the xmission line.

    To avoid contact-bounce and get a clean output pulse-train, you will have to use a mercury-wetted type of relay. Even at that, a 400ps overall-width will be very hard to achieve. Tek used to make a relay-type pulse-gen, which used their own custom relay, which was filled with high-pressure hydrogen to improve operation.

    However, I've acheived decent results from regular 'commercial' type merc-wetted relays. You need to look at the physical construction and choose one which is set up closest to good RF practice...i.e. straight-thru signal-path, short connections, etc..

    Bear in mind that a 400ps "pulse" implies edge-rates of 200ps, or even less; and that is a VERY high-frequency signal. No matter which "device" you design around, you will have to do a VERY VERY good job on the PHYSICAL design (layout, construction, choice of components and materials) to have any chance of achieving a usable result.

    best of luck with it....high-speed pulsers are an enjoyable fun challenge to work with.

    PS: the Tek 7904 scope with the right plug-ins is available pretty cheap (a couple hundred bucks) and is just barely capable of work in the 700ps and up arena.

    A Tek 7104 with the right plugins is probably around 700-1000 bucks, and is just barely capable of useful work in the 400ps arena you're talking about.

    Any Tek 7000 series storage scope, with the 7T11/7S11 sampling plugins, is fully capable of working down to the sub-200ps arena; and with the right front-end module for the 7S11, could probably be had for around 300-600 bucks.

    If you plan on doing a lot of fast-edge/fast-pulse work, the sampling-scope setup is probably worth the investment.

    You might be able to find an older sampling-type digital scope for similar money....like one of the old 54000 series HP units. Just make sure it's working (inputs not blown), because otherwise it's a useless piece of scrap....the repair parts are all custom and are big $$$$$.

    ps; you may be able to get close to the pulse you need with nothing more than a logic-IC from some very fast modern family....i.e. something like 74ACxxx logic, but a bit newer and faster. As I recall, 74AC has edge rates right around 1ns or even a bit faster...so presumably the next-newer series might get into the range you need.

    Differentiate the output-edge, and you might end up with a pretty short pulse....600-800ps or so...and to get the voltage you need, add a xformer at the output.



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    Pulse circuit

    Hi,dozer!
    You made an excellent job at pulser,I learnd more from your report above.Thanks!



  12. #12
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    Pulse circuit

    Just posted this for another high speed pulse generator, might be usefull to you as well

    http://www.hp.woodshot.com/hprfhelp/...elit/an918.pdf



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    Need of circuit

    I am developing a COMB GENERATOR. So please send me the circuits along with component values to generate a picosecond range pulses at 50 ohms output load (Antenna).



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