Jim William's avalanche pulse generator - help needed - Page 1
Forum section: electronics / general

author: e-pirate
author_rank: Regular Contributor
timestamp: April 01, 2013, 04:01:40 pm
content: Hi folks!I've decided to make a well known Jim William's avalanche pulse generator to test my scopes. Basically, it's a LT1073 based DC-DC converter with diode voltage multiplier and 2N2369 transistor in avalanche mode. The board itself designed to fit in a small aluminum case with a single AAA battery holder, switch and all the components. As I have never designed and routed any of hi-freq stuff before, I need help in routing ground and ground polygons.JP1 and JP2 are external switch attachment, X1 is an BNC connector.P.S. The board is going to be a double sided, so ground polygons are possible on both sides, the question is in shape and joint point as there are two "parts" of scheme: DC-DC converter and an output.

author: AlfBaz
author_rank: Super Contributor
timestamp: April 01, 2013, 04:15:53 pm
content: You might get some ideas herehttps://www.eevblog.com/forum/blog/eevblog-306-jim-williams-pulse-generator/

author: free_electron
author_rank: Super Contributor
timestamp: April 01, 2013, 08:17:55 pm
content: lots of things ..The black magic part :BNC' dont have the bandwidth for these fast pulses... especially not those cheap AMP with all the white plastic.htose are intendend fro 10 megabnit ethernet.... not for instrumentation.get an edge-launch connector.If you read JW's appnote he recommned building the avalanche section dead-bug style to reduce all stray capacitance and leakage everywhere. capacitance slows down the edge ....so putting the transisor on the pcb is a bad idea. via's add inductance , planes around everything add inductance.That's why , in my version i mounted the transistor upside down. the case is the collector. it needs capacitance there. the emitter is where you don;t want stray capacitance. same around the base... by using this upside down method i am as far as mechanically possible from any 'bad influence'.You may want to carefully select the resistances. you don't want any spiral or meander cut resistances as these add inductance in their pathway... surface mount is the way to go.A stripline helps as reservoir capacitor and gives you a nice flat-top. may want to think about that one.As for the boost section : nothing critical. just use fast diodes and high voltage caps.

author: e-pirate
author_rank: Regular Contributor
timestamp: April 01, 2013, 08:36:52 pm
content: Well, my original idea was to connect transistor emitter directly to the BNC central pad and solder 50 ohm resistor in between emitter and ground, while connecting base and collector to the board. Seems, my idea was correct. So, I will redesign, keeping in mind this.What is the 'edge-launch' connector, could you please link some pictures.What about grounds and ground polygons and joint points?

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: April 01, 2013, 08:49:02 pm
content: Hi,Have a look at this thread:https://www.eevblog.com/forum/projects/transmission-line-avalanche-pulse-generator/msg188515/#msg188515You can see how edge mounted a SMA connector.I built my pulse generator on double sided FR4.Jay_Diddy_B

author: e-pirate
author_rank: Regular Contributor
timestamp: April 04, 2013, 07:48:49 pm
content: Should I separate booster and avalanche generator grounds or making a single polygon is fine?

author: free_electron
author_rank: Super Contributor
timestamp: April 04, 2013, 09:06:59 pm
content: single polygon is fine . go take a look at my layout in the topic mentioned above. there is tons of information in that topic. i have leftover boards too as well as kits...