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Ultrashort pulse generation

Discussion in 'Electronic Design' started by Dyan Ali, Oct 29, 2003.

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  1. Dyan Ali

    Dyan Ali Guest

    Hello,
    I'm trying to design an ultrafast pulse generator, one that operates
    at 3.4kV, has rise times and fall times ~1 nsec and a pulse width of
    about 5-6 nsec.I need the pulse rate to be 10Hz. I've got hold of a
    few papers by R.J.Baker (available at
    http://cmosedu.com/jbaker/papers.htm) but they provide info on
    designing broader pulses, maybe because the power MOSFETs he was
    working with were inherently slower. Is such a design possible? Could
    someone help me out?
    -Dyan
     
  2. John Larkin

    John Larkin Guest


    Fets are too slow for your risetimes.

    There are a few ways to do this:

    1. A stack of avalanche transistors, probably dumping a coaxial
    energy-storage line into your load. You'd need about 10-20 of them in
    series, depending, probably the Zetex SOT-23 (!) parts. There are
    papers around on how to do this.

    2. A triggered spark gap or a krytron tube. Very simple.

    3. A DSRD (drift step-recovery diode) or Grehkov avalanche diode.

    4. A coaxial reed relay, again dumping a storage line into your load.
    The relay can be inside a tube that *is* the coaxial system. Cheap,
    clean, *lots* of jitter if it matters, maybe reasonable life at 10 Hz.

    5. Maybe even a regular relay. This actually works sometimes, even at
    these speeds.

    6. Buy it from the Russians; they are very good at this sort of stuff.


    If any of these are interesting, let me know and I can find a few
    paper references at work tomorrow.

    Any of these would be a *serious* development project, except maybe 2)
    or 4) or 5), which wouldn't be as terrible.

    Measurement will be interesting.


    I currently make a 2KV thing that's sort of in the ball park...

    http://www.highlandtechnology.com/DSS/T220DS.html

    which used DSRDs, and we're working on other techniques for bigger
    stuff.


    What's your application? What's the load like?

    John
     
  3. Ian Buckner

    Ian Buckner Guest

    That was a delay generator, done with a ramp and comparator.
    Unfortunately,
    they used a very small ramp, so jitter and stability was poor.

    If that's what you want, On Semi do a gate delay based ECL part with
    similar resolution.

    Regads
    Ian
     
  4. Dyan Ali

    Dyan Ali Guest

    I'm actually trying to build my own driver for a KDP Q-Switch, so that
    translates to a capacitance of 5pF (at 1kHz). The thing is that we are
    trying to ubild one such device rather than buy it.
    Dyan
     
  5. John Larkin

    John Larkin Guest


    OK, cool. You only need half the voltage at the pulser if you use a
    longish coax feed and let the pulse voltage naturally double at the
    end. And I presume you can't tolerate much jitter, so relays are out.

    A krytron can give you jitter close to 1 ns, and avalanche transistors
    will be even better. There should be lots of journal papers on stuff
    like this (RSI, NIM, etc), and Zetex has some app notes.

    John
     
  6. John Larkin

    John Larkin Guest

    Yeah, but how well will it work with Vee = -3500 volts?

    John
     

  7. It is possible or at least close.
    There indeed appears to be one guru in publications, RJ Baker.
    And there is another one that actually sells the stuff, Behlke.

    http://www.behlke.de/

    You could go through building such a switch. You get bags full
    of semiconductors and burn them while getting the experience.
    Then you also need a second person to be always around, just
    in case you security measures weren't that thorough.
    Measuring the stuff itself is a problem of its own.
    You want to measure a 3kV/ns slope with a Giga Ohm probe ?
    Your Giga sample scope has 50 Ohms for fast signals.

    Rene
     
  8. I read in sci.electronics.design that John Larkin <[email protected]
    techTHISnologyPLEASE.com> wrote (in <[email protected]
    4ax.com>) about 'Ultrashort pulse generation', on Wed, 29 Oct 2003:
    Briefly. Very briefly.
     
  9. Ian Buckner

    Ian Buckner Guest

    Maybe only for a nsec?

    ;-)

    Regards
    Ian
     
  10. Dyan Ali

    Dyan Ali Guest

    Thanks, John... i'll see what i can find. Do u have the approx years
    in which these articels were published in RSI and NIM?
     
  11. Does 200ps, 100Kw sound interesting? <http://tinyurl.com/t3zo>.
    Tom McEwan is an amazing guy - see his other patents too.
     
  12. Robert Baer

    Robert Baer Guest

    Mercury whetted reed relays were used by Tektronics and HP in the good
    old daze.
    One might need 20pSec samplers to to get an idea how fast they really
    are....
    The reed is mounted coaxially to get a resonably uniform 50 ohm
    impedance, an open coax cable on one end is charged thru a high value
    resistor, and the other end goes to the load.
    If a hole is placed so one can see the contacts, and more than 23V is
    used, then a light pulse of the same width is emitted and can be used to
    characterize photomultipliers; this configuration is called a Huggins
    Lamp (if i remember correctly).
     
  13. Bill Sloman

    Bill Sloman Guest

    This sounds as if it depends on a pulse-sharpening technique that
    hasn't been mentioned elsewhere in this thread - exploiting the
    non-linear relationship between magnetising current and flux generated
    in ferrite core material driven into saturation. There is not a lot
    published on the subject, but what there is seems to concentrate on
    high voltage, high current pulses.

    IIRR - and I can't even find the copy of the one Russian paper that I
    have read - you make a coaxial transmission line with the central
    conductor threaded through a bunch of high-frequency ferrite rings,
    which are then, in turn, threaded through your outer conductor -
    probably a length of copper water pipe.

    You launch a relatively slow rise-time pulse into this transmission
    line, where the pulse propagates relatively slowly until the current
    gets high enough to saturate the ferrite, and a apparently what
    emerges at the far end has a much faster rise-time.

    Maybe John Larkin has heard about it.
     
  14. Jim Meyer

    Jim Meyer Guest

    Sounds like it may be related to soloton wave transmission.

    Jim
     
  15. Jim Meyer

    Jim Meyer Guest

    I mispeled "soloton". It should be "soliton".

    Anyway, check out this site:

    http://citeseer.nj.nec.com/cache/pa....eduzSz~singerzSzsol1.pdf/singer98circuit.pdf

    Cut and paste as necessary....

    The paper references Horowitz and Hill too!

    Jim
     
  16. I've come across numerous articles on them. Try searching "magnetic
    pulse compressor" in the (AIP) journals, even on the web. Allied
    Metglass is a better material than ferrite, giving you over 50%
    efficiency, rather than 20 or 30% with ferrite, IIRC.

    --
    Scott

    **********************************

    DIY Piezo-Gyro, PCB Drill Bot & More Soon!

    http://home.comcast.net/~scottxs/

    **********************************
     
  17. Dyan Ali

    Dyan Ali Guest

    Thanks guys, but what i'm trying to do is design a cheaper switch
    based on power electronic devices to give me these short pulses... no
    solitons involved :)
     
  18. John Larkin

    John Larkin Guest

    Something sorta like this should work. Connect both ends (braids) of
    the hunk-o to the avalanche trannies. A separate, grounded, long coax
    to the load can be included as required. The length of hunk-o
    determines pulse width. Hi-z load will see a -3KV rectangular pulse.



    +1500v-------r--------------+ long coax
    | to load
    ----------*--------- -----
    gnd----50r------| hunk-o-coax |-----| |-----+
    ----------*--------- *-----* |
    | gnd gnd load
    +----+ |
    | | gnd
    c | } ~~ 5
    +---b r } stacked
    | e | } zetex
    r | | } avalanche
    +----+----+ } transistors
    | |
    c |
    trig----r--------b r
    e |
    | |
    +----+
    |
    gnd


    Comments/corrections welcome.

    John
     
  19. John Larkin wrote...
    It may work with Vee = 3500mV.

    Thanks,
    - Win

    whill_at_picovolt-dot-com
     
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