SDG1025 - Lengthening SYNC OUT pulse, fastest way... - Page 1
Forum section: electronics / testgear

author: blindsight
author_rank: Newbie
timestamp: June 18, 2016, 09:44:43 am
content: Hi Everyone,I have an SDG1025, which I mostly use to pass low frequency test signals to biosignal amplifiers, we are talking Hz and not MHz here. However, one thing I need is a trigger pulse from the SDG that is phase synchronous with the output signal and that can be recorded as a TTL trigger event by my biosignal amps, along with the test signals, to be used for later offline analysis.Sadly, the minimum pulse length my biosig amps can detect is 10us and with the SYNC OUT on the SDG1025 being ~56ns, this obviously does not work. I therefore need to extend the SDG1025 SYNC OUT pulse to at least 20us, but more reasonably even to a couple of ms.Of course there are numerous ways of doing this, but with e.g. an LMC555 monostable having a trigger output propagation delay of ~100ns and an output rise time of another 15ns I am also delaying the SDG's SYNC by those 115ns.While this is pretty much deterministic and then not problematic for my specific purposes, I would nonetheless like to avoid this as much as possible, so I though I'd ask the gurus around here what would be the best way of extending the SYNC OUT signal to at least 20us with the lowest possible trigger to output propagation delay?

author: tautech
author_rank: Super Contributor
timestamp: June 18, 2016, 11:18:14 am
content: Welcome to the forum.I've not got my SDG1010 (same series as yours) handy I think this is simple to accomplish.Tee your output and link the signal to the trigger input at the rear and have that trigger the second output at TTL level for the duration you require.Have a play with that idea and let us know your outcome.

author: blindsight
author_rank: Newbie
timestamp: July 09, 2016, 09:20:49 am
content: Hi tautech,thank you for your reply and sorry about the long answer delay. I was out of the office travelling incessantly until yesterday, not the nicest aspect of my job...I tried your suggestion and linking SyncOut to GateIn and then gating a 5ms pulse with it works beautfully, thanks for the ultra quick and extremely helpful answer! - This is going to be of great help especially where I need to test timing synchrony between analog and digital channel reading in my biosignal amplifiers.However, the one and only drawback of your solution is that I was hoping to use BOTH channels for generating test signals while your solution means that one SDG channel is now used to create the lengthened version of the SyncOut signal. Therefore, if you or anyone else would have another suggestion for a fast and low delay way of externally extending the SyncOut pulse, I would really appreciate hearing about it.Kind regards,Ingmar

author: tautech
author_rank: Super Contributor
timestamp: July 09, 2016, 09:51:54 am
content: Do both channels need be the same, you can use CHCopy in the Output setup menu.Then by way of using Sync and TrigOut rear BNC connectors and the functionality described in the manual on pages 54 and 69 you should be able to accomplish it. Hint: Burst set to Infinite.Note, the manual has been updated from many that were shipped with units so ensure you have the latest one.http://www.siglentamerica.com/USA_website_2014/Documents/UserManual/SDG1000_UserManual_UM02010-E07B.pdf

author: blindsight
author_rank: Newbie
timestamp: July 09, 2016, 09:57:05 am
content: I was actually hoping to use two channels with separate content, so your suggestion will not work here. However, it sounds like I have a lot to learn about my SDG and its capabilities and I will therefore try your suggestion anyway, even if only for "educational" purposes...

author: tautech
author_rank: Super Contributor
timestamp: July 09, 2016, 10:23:49 am
content: Quote from: blindsight on July 09, 2016, 09:57:05 amThere's a lot of tricks you can do with the Trig in/out, Sync and Teeing outputs along with the many features that are included/hidden in menus, it's really down to one's imagination and creativity.(and #'s of spare BNC cables of course)Bit like the old glue logic in many ways.

author: blindsight
author_rank: Newbie
timestamp: September 16, 2016, 04:31:14 pm
content: @tautech: Thanks again for helping me with the Sync/Trigger question. I have been using this for testing of my biosignal equipment and it works great. However, whenever I pull the two channels apart on my scope (SDS1102CML) I am seeing something weird that I wanted to ask your advice on.As a reminder, I am bridging the SyncOut signal generated for channel 2 to the Gate input and am using this signal to trigger a 5ms pulse on channel 1. The attached figure shows this. Triggering is on channel 1 and thus on my generated 5ms trigger pulse (yellow).However, with persistent mode on I see that channel 2 (cyan), which carries the actual signal to be output to my biosignal equipment, shows a pretty wide range of lead times on the trigger signal. That the trigger lags the actual signal is clear or at least understandable, but a) why minimally by a whopping 169 us and b) why with a range of about 160 us?Do you have any idea/hint why this may be and if this is ok?

author: tautech
author_rank: Super Contributor
timestamp: September 17, 2016, 11:36:41 pm
content: After having a good fiddle with a similar configuration I am of the opinion that it is internal clock jitter. Should you set your scope to trigger on the other channel you again see this jitter but now on the other channel. I do not have a 10 MHz reference to use instead of the internal clock to check if the jitter is reduced with an external reference. Owners do either upgrade the internal clock or provide a better ext clock ref and you can read about this more in the SDG1000 thread.Showing CH 1 as a 5ms pulse generated as an infinite burst from CH 2 10 Hz square wave and the Sync pulse on CH 3. Triggered from CH 3

author: Performa01
author_rank: Super Contributor
timestamp: September 18, 2016, 03:26:22 am
content: @tautechEven the cheapest and crappiest clock oscillator would not explain a jitter in the microsecond range. Of course I cannot know what’s wrong here, but assuming that the sync pulse has a very short and fixed delay to the edge of the related waveform, I have a proposal…@blindsightYou could try the following circuit:It’s old style, with two digital ICs. Use 74HCT74 and 47HC14, and of course V1 and R14 just simulates the original sync output from the generator and R1 simulates some external load.VCC should be +5V obviously.This circuit will convert every rising edge on the input into an ~10µs wide negative pulse at the output. You can always fine-tune the pulse width by varying R3. If you want a positive output pulse, just connect the output drivers U3 … U7 to QN instead Q of U1.