WTB - Fast, Cost-effective (Jim Williams - type?) Pulse Generator - Page 1
Forum section: electronics / general

author: Electro Fan
author_rank: Super Contributor
timestamp: September 13, 2015, 09:11:59 pm
content: I'm looking to purchase a Pulse Generator that can produce fast (fewer the picoseconds the better) rise and fall times. Could be a Jim Williams type device or maybe something else. Ship to location is in the U.S. so probably most practical for a U.S. seller. Please PM me with any proposals. Thx

author: Electro Fan
author_rank: Super Contributor
timestamp: September 20, 2015, 09:04:13 pm
content: bump

author: tautech
author_rank: Super Contributor
timestamp: September 20, 2015, 09:27:45 pm
content: free_electronwas designing one in this thread:https://www.eevblog.com/forum/blog/eevblog-306-jim-williams-pulse-generator/msg127205/#msg127205Sorry I have no idea if they are still available. PM him and ask for an update.Please post your findings.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 20, 2015, 10:56:00 pm
content: I've got a one of those laying around, more or less. Can only tell that the risetime is less than 1ns, and not very flat. Needs 12VDC. I could slap it in a project box if you like?Tim

author: John_ITIC
author_rank: Frequent Contributor
timestamp: September 21, 2015, 04:02:11 am
content: If you need picosecond rise time then perhaps a TDR could work? I have an old Tektronix 11801 with SD-24 TDR head. This has a rise time of 17.5 ps. Mine is not for sale but available on Ebay for cheap...http://w140.com/tekwiki/wiki/SD-24

author: Electro Fan
author_rank: Super Contributor
timestamp: September 21, 2015, 04:34:01 am
content: Quote from: T3sl4co1l on September 20, 2015, 10:56:00 pmTim, Thanks. I appreciate the thought and the offer to put it in a project box but I'm holding out for something that measures as far into the picoseconds as possible/practical. BTW, I am a big fan of your posts - I always read them and take them seriously - your posts are very informative, enjoyable, and helpful. EF

author: Electro Fan
author_rank: Super Contributor
timestamp: September 21, 2015, 04:36:28 am
content: Quote from: John_ITIC on September 21, 2015, 04:02:11 amThanks for the suggestion. That looks good, and I'd be happy to have a Tektronix solution - but maybe it needs a Tek 11800 scope to go with it?

author: John_ITIC
author_rank: Frequent Contributor
timestamp: September 21, 2015, 04:52:20 am
content: Yes, you'll need a 11801A/B or C model scope. I have two 11801B scopes and a bunch of different sampling heads. A scope is under $1,000 and the SD-24 is $395.Here are a couple of current Ebay links:http://www.ebay.com/itm/Tektronix-SD24-SD-24-TDR-Sampling-Head-for-11801C-etc-Oscilloscope-S-N-B020880-/201397874656?hash=item2ee43fafe0http://www.ebay.com/itm/Tektronix-11801B-Digital-Sampling-Oscilloscope-DC-to-50-GHz-/361379632865?hash=item5423e796e1Make sure you agree via seller to be able to return if not working correctly. It has happened to me in the past that Ebay/Paypal did not honor the "14 day right of return" policy. The rules are fuzzy and often Ebay/Paypal rules in favor of the seller (since they make their commission that way)...Also make sure that both channels work on the SD-24. I once bought one head that had a bad negative channel. These sampling heads make it possible to do TDR differentially and sample up to 50 GHz (with the correct sampling head). Rock solid units but getting a bit aged...Note though that these scopes are not real-time scopes and that they need a clock to trigger on. They can therefore not be used to do eye diagram directly on all modern high-speed serial buses. For PCI Express (which has a separate 100 MHz reference clock) it is possible though (which is what I bought my scopes for).

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 21, 2015, 11:11:13 am
content: Quote from: Electro Fan on September 21, 2015, 04:34:01 amOh, thanks -- appreciate it.If you want serious thin picoseconds, then an avalanche device won't cut it, period. They bottom out in the 100ps range, as far as I know. ~10ps is in the realm of drift step recovery diodes and monolithic nonlinear shock lines. You'll be looking for special hardware, not something that can be built by hand. The SD-24 mentioned is probably one of the most common ones, if you don't mind buying a mainframe in the process.Tim

author: Electro Fan
author_rank: Super Contributor
timestamp: September 21, 2015, 07:52:24 pm
content: Quote from: T3sl4co1l on September 21, 2015, 11:11:13 amOk, I guess I'm forming my buying criteria (or you are forming it for me). I'm open to whatever is "cost-effective" in the 100ps to 999ps range. Any guess what the entry price is for something that gets to roughly 500ps range? (What does a Jim Williams device sell for?)- I followed your advice on the vitreous resistor for capacitor discharging

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 22, 2015, 12:13:47 am
content: No clue if those sorts of things (a crude box, that is) are usually available, and for how much at that. So easy to build, though.High speed digital logic is also in that range, and probably a fine price. 74LVC I think is around 1ns or just shy of it, so just meets your range; higher speed families are available, especially ECL, LVDS, CML, etc. small signal or differential families (if you don't mind that your pulse is smaller, that is). An RC oscillator with 74LVC14 and some buffering would be a fine start; following that with an LVDS transmitter should get reasonably well down in the 300ps or less range, I think.What's eBay say for vintage Tek/HP/etc. pulse generators?TIm

author: Paul Moir
author_rank: Frequent Contributor
timestamp: September 22, 2015, 12:29:30 am
content: I'm pretty ignorant about these things; for me 10MHz is fast. Can something like a SATA driver be used in this application? For example, the MAX4951 SATA redriver which quotes a typical risetime of 60ps.

author: MarkL
author_rank: Unknown
timestamp: September 22, 2015, 01:15:51 am
content: The Analog Devices ADCMP580 comparator has a very fast output rise and fall time of 37ps typ. (20% to 80%). You can drive it with a function generator. Cost is about US$20 in single quantities from Mouser, Digikey, etc.http://www.analog.com/en/products/linear-products/comparators/adcmp580.htmlThere's also a very well made eval board available for it, part #EVAL-ADCMP580BCPZ (also at the above link). Current price is about US$290.Last time I checked the board was $55. I don't know why the price suddenly got crazy.

author: Electro Fan
author_rank: Super Contributor
timestamp: September 23, 2015, 01:52:56 am
content: Quote from: MarkL on September 22, 2015, 01:15:51 amCan you say more about this? Beside the $20 part and a function generator, what else is needed? What speed function generator is needed to enable the comparator to produce 37ps rise and fall times?

author: tggzzz
author_rank: Super Contributor
timestamp: September 23, 2015, 08:39:50 am
content: Quote from: Electro Fan on September 23, 2015, 01:52:56 amWhich bits ofhttp://www.analog.com/media/en/technical-documentation/data-sheets/ADCMP580_581_582.pdfdon't you understand? As with any picosecond circuit, youwillneed to understand how to do a good layout and construction methods, using the appropriate components and materials.If an edge is sufficient, then I would second using several 74LVC1G14 devices in parallel. Myindirectmeasurements indicate edge rates of around 625ps.

author: acbern
author_rank: Frequent Contributor
timestamp: September 23, 2015, 11:02:25 am
content: Well, if you want to use this (designed by yourself), you also need to have it calibrated, in order to use it. Your design may make it slower than it can be, hence you need a test. otherwise this is of no use essentially.So you may also wish to check in parallel for a voltnut/timenut who has capability in the 20+ghz range to test it once designed.