Inexpensive DIY 50ps Ultra Fast Pulse Generator  - Page 1
Forum section: electronics / testgear

author: starlino
author_rank: Newbie
timestamp: August 29, 2013, 07:05:47 pm
content: Inspired by "EEVblog #306 - Jim Williams Pulse Generator" I decided to build my own ultra fast pulse generator.I stumbled upon an interesting chip from Analog Devices ADCMP580 , it's basically a SiGe based comparator that delivers a very fast rise/fall time. It's advertised to be 37ps (20%-80%) so I prorated it to about 50ps (10%-90%). I did a test setup and confirmed my 500Mhz scope's bandwidth . However I have no way to confirm the actual 50ps rise time (I have no 8Ghz + scope !). Any ideas how I can do that? Do I need necessarily a faster scope or is there any clever indirect method to confirm that ... ?Is anyone with a fast scope able to do the same test and confirm the 37ps/50ps rise times ? If fully confirmed it would be an interesting tool for evaluating scopes' bandwidth and such ... The chip and the demo board I used is relatively inexpensive.You can find the build details on my blog:http://www.starlino.com/build-a-really-fast-pulse-generator-50ps-rise-time-using-an-ultra-fast-sige-comparator.htmlI took screenshots from my scope and photos of the build.Thanks !

author: Unknown
author_rank: Unknown
timestamp: August 30, 2013, 06:54:46 am
content: Quote from: starlino on August 29, 2013, 07:05:47 pmthe only indirect way i can think of, to measure clock jitter & rise time, is using a sound card.http://www.transaudiogroup.com/clock-comparison-fileshttp://blacklionaudio.com/product/micro-clock-mk2/http://www.grimmaudio.com/pro_masterclocks_cc1.htmhttp://antelopeaudio.com/en/products/category/master-clocksbut you need a much faster clock source.really nice 3-way loudspeakers.

author: BravoV
author_rank: Super Contributor
timestamp: August 30, 2013, 06:58:52 am
content: Quote from: JuanPC on August 30, 2013, 06:54:46 amHuh ?Are you sure you're not posting at the wrong thread ?

author: Unknown
author_rank: Unknown
timestamp: August 30, 2013, 07:00:51 am
content: Quote from: BravoV on August 30, 2013, 06:58:52 amhttp://www.antelopeaudio.com/blog/word-clock-sync-jitter/http://en.wikipedia.org/wiki/Analog-to-digital_converter#Jitter

author: Unknown
author_rank: Unknown
timestamp: August 30, 2013, 07:20:02 am
content: seriously this test board can become a Rise Time test reference, just like those form VoltageStandard.http://shop.voltagestandard.com/main.sc;jsessionid=82D4359A155BB6590CCBD3F5C5ED0E54.m1plqscsfapp06

author: Marco
author_rank: Super Contributor
timestamp: August 30, 2013, 10:45:53 am
content: Could you create a rectangular pulse with two different length traces to feed the comparator inputs?

author: Rerouter
author_rank: Super Contributor
timestamp: August 30, 2013, 10:53:07 am
content: if you just want fast rise times you can get clock buffer / divider / driver chips with very very fast rise times, i'm currently eying a SY89312V which has a max of 160pS, you can easily feed this with any old clock signal as long as you make it differential,

author: krenzo
author_rank: Regular Contributor
timestamp: August 30, 2013, 03:07:11 pm
content: I played around with the ADCMP580 a few years ago. I analyzed it with my Tektronix 11801B with the SD-22 12.5 GHz sampling head. Attached is the only picture I still have of its outputs. The timing offset between its two outputs was intentionally my doing.

author: free_electron
author_rank: Super Contributor
timestamp: September 04, 2013, 02:37:49 am
content: Sorry to burst the bubble but thing is slower than the jim williams pulse generator.You are doing 400 millivolts in 37 picoseconds. or 92.5 picoseconds per volt.The JW avalanche generator shoots over 12 volts in 400 picoseconds. that is 33 picoseconds per volts ... the JW pulser has an almost 3 faster risetime ...You need to compare apples with apples. So normalisation to picosecondes per volt is in order. to compare to your 400 millivolts : the JW generator climbs 400 millivolt in 13 picoseconds. much faster than that chip can do.While this chip is not bad it is not nowhere near the JW pulser. it costs more , needs a signal generator to drive it and is not self containd. the JW pulser is small box running from a coin cell. ready to run.

author: starlino
author_rank: Newbie
timestamp: September 17, 2013, 03:20:08 am
content: I was thinking it can be made self-contained with a little feedback. See for example here:w2aew is using an inverter shmitt trigger 74AC14 , I think a similar trick can be used with this comparator to get it oscillating.Thanks everyone for the great feedback.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 17, 2013, 03:34:56 am
content: Hi,I was able to obtain a risetime of 70ps, measured with a 20GHz scope, with my version of an avalanche pulse generator.The thread starts here:https://www.eevblog.com/forum/projects/transmission-line-avalanche-pulse-generator/I used a BFR505 transistor.Jay_Diddy_B

author: starlino
author_rank: Newbie
timestamp: September 17, 2013, 03:50:35 am
content: free_electron: JW avalanche generator is fantastic, and yes it will win the competition if you're talking about slew rate (V/s) .However I would argue that 50ps rise time @ 0.4Vpp is still better than 400ps @ 12V if we're talking about measuring bandwidth on the scope.Let me start by noting that there's nowhere in the bandwidth formula Bw = 0.4/Tr , that we find the slew rate or the absolute Vpp value. That's because the bandwidth (frequency) of a pulse signal is determined by how fast it goes from (low) flat to (high) flat, and not really from how low to how high it travels. In other words by increasing the amplitude of your signal to 12V you do not get a faster equivalent bandwidth or rise time ... If you amplify a signal that has a 1Mhz harmonic (equvalent harmonic of 400ps rise time is 0.4/400ps = 1Mhz) to 12v that harmonic will still be 1Mhz ...The equivalent bandwidth of 50ps is 0.4/50ps = 8Mhz, thus you could evalute scopes up to ~8Mhz/5 = 1.6Mhz with it , or use the more complex formula Bw = 0.4/SQRT(Tr^2 – 50ps^2) and measure even higher bandwidths, that takes into account the 50ps rise time of the test signal.Let me know what you think guys.

author: Unknown
author_rank: Unknown
timestamp: September 17, 2013, 04:00:31 am
content: Quote from: starlino on September 17, 2013, 03:50:35 amThe bandwidth and slew rate of a system are largely independent. Scopes are generally thought to be bandwidth limited rather than slew rate limited.Quote from: starlino on September 17, 2013, 03:50:35 amIn theory you can use that formula, but you'll find that for Tr(scope) << 50 us Tr(scope) will disappear in the noise. For example a 1 MHz scope (Tr(scope)=350 ns) will have a Tr of sqrt(50us^2 + 350ns^2) = 50.001 us. Do you have the resolution to distinguish a 50 us rise time from a 50.001 us rise time? This is assuming the rise time of your pulse gen was known down to the nanosecond to begin with.

author: Galaxyrise
author_rank: Frequent Contributor
timestamp: September 17, 2013, 05:05:11 pm
content: Quote from: starlino on September 17, 2013, 03:50:35 amDid you mean picoseconds there? Or was the initial post in error?

author: starlino
author_rank: Newbie
timestamp: September 19, 2013, 03:53:11 am
content: Galaxyrise: yes I ment ps not us. I corrected my post. Sorry , late night posting