Transmission Line Avalanche Pulse Generator

[daiguangming]

schematic?way fall is slower ?

[Insatman]

schematic?way fall is slower ?

The fall is almost always slower than the rise on chargeline pulsers.  You can usually reduce it by putting a resistor from the output of the transistor to ground.  The value of which depends on your particular circuit.  I've found for most 50 ohm circuits that something between 50 and 200 ohms usually works best to shape the falling edge.   I'm sure that better methods exist as well.

[ducus]

Good evening

Is there any chance of getting the PCB project? I made a variant with BFR93A built around an SMA plug. The results are satisfactory but not mechanically stable. That's why I would like to build a PCB-like version. Sorry but my English is not very good. I'll be back with photos.

Thanks!
Dan

[Jay_Diddy_B]

Hi,

I have the Gerber files and the original Orcad 9.2 Files.

There were changes made after the board was designed, especially in the output area:




Regards,
Jay_Diddy_B

[ducus]

Super. Can send me an email with both?

[ducus]

Ugly construction

[ducus]

Thanks Jay_Diddy_B.
I did the pcb and i have some results. Scoop is TDS745C hacked to 785C but not calibrated till 1GHz.

[Jay_Diddy_B]

Hi Ducus,

Are you in the Southern Hemisphere? Your scope is upside down 


Are you going to share pictures of your board?

Jay_Diddy_B

[ducus]

I removed attenuators from board because i have lots of ringing and i use my function generator to trigger the transistor. Like this BFR93A avalanche at aproximativ 40V. Without external trigger it will avalanche at 50V. Until now i'm satisfied with results. Next step to finish ground via on the transmision line and if is ok to do an new pcb more clean (this is made in harry with toner transfer).

Regards
Dan

[Jay_Diddy_B]

Hi,

Somebody asked me by private message for the Gerber files. Here they are. These are the last boards I ordered and if you follow the thread there was a lot of experimenting with the output section.

The .TXT is the drill data.

Jay_Diddy_B

 Jay_Diddy_B_avalanche_PG_gerbers .zip (56.08 kB - downloaded 83 times.)

[jonpaul]

We use the Leo Bodnar 40 pS pulser, very fine and tiny, designed to check scope RT and aberration. Much faster and better!

Cost L49 UK

http://www.leobodnar.com/shop/index.php?main_page=product_info&products_id=295

Jon

[Jay_Diddy_B]

Jon,
You are right the Leo Bodnar design is better. I shared the files in response to a request from a forum member.

History

The design presented here is around 9 years old. Starting in mid-2012 there was tremendous interest in the Jim Williams pulse generator. At the time people were upgrading the newly introduced Rigol scope and were looking for something cheap to demonstrate the increase in bandwidth. People were turning 50MHz 1052E into the 100MHz 1102E.

Dave produced a video:

https://www.eevblog.com/forum/blog/eevblog-306-jim-williams-pulse-generator/

and forum member, Free Electron, start what was to become a very popular project:



The Jim Williams pulse generator and the derivatives produced a pulse like this:



In order to measure the scope risetime, you need a flat topped waveform. I promoted the transmission line version at the time.

Free Electron added the transmission to MKII of the unit he designed:

https://www.eevblog.com/forum/blog/eevblog-306-jim-williams-pulse-generator/msg192189/#msg192189


I started with the 2N2369 transistor and achieved risetime in the 200 - 300 ps range.

I quickly changed to using an RF transistors (BFR505) and got into the 60ps region.


It is a neat circuit to play with. You can spend very little money and play around for hours ....

Best regards,
Jay_Diddy_B

[rodd]

Hi folks,
I found this old thread but decided to build the Jay Diddy version of the pulser.
In one of the replies he provided the Gerber files for the PCB.
There had been a lot of changes in the design, all documented in the thread, but one issue has been left open.
In the gerber files provided, U3 is actually a 555 timer, NOT a LTC1799CS5.
C7 and C8 are also missing in the all versions of the schemitics provided untill now.
I consulted Jay_Diddy (in another thread) which promptly provided the "old version" of the schematics used as reference for the Gerber files, which I decided to post here for reference, in case some other person decides to build this project.
Thanks again for Jay_Diddy. Transmission Line Avalanche Pulse - Nov 28 2013.pdf (28.83 kB - downloaded 66 times.)