3
\$\begingroup\$

I need to create a very short (<1 ns) pulse and control the pulse frequency between 1 MHz and 10 MHz. One method to create short pulse I came across is Jim Williams avalanche pulse generator. Before I build it, I wanted to try it in LTspice. Here at APPENDIX D there is the Jim Williams avalanche pulse generator:

enter image description here

I simulated this in LTspice with the same circuit and transistor:

enter image description here

The voltage amplitude is not 10 V but very low in 250 uV level. The repetition rate in my case is 19 kHz and the pulse width is more than 650 ns and the pulses stop after some ms. Here are the plots:

enter image description here

enter image description here

enter image description here

This shows the voltage at both node A and Vout. Close to 20 ms the node A becomes 90 V but the pulses stop:

enter image description here

Does this mean the transistor is not going into avalanche in simulation? Besides the simulation, if it would work as in the paper, would it be possible to control the pulse frequency?

Edit:

To make simulation quick I used a voltage source instead of boost converter. I followed some SPICE commands from the answer and had to increase the voltage upto minimum 120 V:

enter image description here

I get short pulse now around 800 ps with 2 pF and 1.3 ns with 4.7 pF:

enter image description here

But my problem is I need repetition rate from 1 MHz to 10 MHz and when I tweak the 1 Meg resistor I cannot achieve that. Is that possible in any way?

\$\endgroup\$
1
  • \$\begingroup\$ Comments are not for extended discussion; this conversation has been moved to chat. \$\endgroup\$
    – Voltage Spike
    Oct 18, 2022 at 19:37

1 Answer 1

4
\$\begingroup\$

Here is an example of an LTSpice file ...

  • Bordodynov\npnAvalanche\AvalancheMMBT2369\ExampleMMBT2369_v2.asc. Seems ok.
    Note the symbol of the transistor X1.
    Green curve is X1 collector.

For repetitive pulse, use a pre-charge cicuit and a pulse on "base" would be probably enough.

Sorry, don't know enough LTSpice changing colors ... :-(

enter image description here

enter image description here

enter image description here

To "help" (some sort of "synchronizing") a little with the "breakdown", I used this circuit.
But pulse is wider than needed :-( . However, the idea could help ...

enter image description here

Another circuit (2 ns pulse, 250ns recovery time). R1 must be greater than 5k.

enter image description here

I have tried this. Don't know if it is an "artefact" ...
Pusle has 400-500 ns wide.

enter image description here

\$\endgroup\$
3
  • \$\begingroup\$ I get pulses now in simulation but cannot adjust the pulse freq. more than 1MHz. I need a range of 1MHz to 10MHz. \$\endgroup\$
    – user16307
    Oct 18, 2022 at 13:39
  • 2
    \$\begingroup\$ @user16307 As I said, it's down to how well the models for each transistor is implemented. Relying on the .model, alone, will likely not work, unless it's the level=504(Mextram), which I haven't used; feel free to experiment. \$\endgroup\$ Oct 18, 2022 at 14:12
  • \$\begingroup\$ I need min 500ps which can have 1Meg to 10MegHz freq. There are chips that can generate 1ns but thats not enough for me. I cannot find a ready module sold besides super expensive drivers with LCDs. \$\endgroup\$
    – user16307
    Oct 18, 2022 at 17:25

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.