Function generator frequency sync with an optical pulse - Page 1
Forum section: electronics / projects

author: ash1204
author_rank: Newbie
timestamp: June 10, 2024, 12:35:13 pm
content: Hello everyone,I am quite new to using function generators. I am hoping someone can help me with this:I am looking to give an external trigger of a pulse operating at 30 KHz to my function generator (Agilent 33250A). I want the function generator to provide an output of the same frequency as the external trigger.So, I want the function generator's frequency to change automatically to match the input trigger's frequency.I have two of the Agilent 33250A function generators. The output of one is connected to the trigger of the second. So, if I were to change the frequency of the first, this should automatically change the frequency of the second, and that should reflect on the oscilloscope.Is this possible?I have attempted this on several occasions, but cannot find a way to do this.Can someone please help me with this?Best regards,Ash

author: DTJ
author_rank: Super Contributor
timestamp: June 10, 2024, 01:36:09 pm
content: Get a freq counter and read the signal freq out via '232 then instruct your sig gen to output that frequ using '232?

author: joeqsmith
author_rank: Super Contributor
timestamp: June 10, 2024, 01:46:46 pm
content: I have not looked at the specs for your generator but would think it would be simple. At 30kHz, I would set the generator for a single sweep (burst?) on the external trigger and output a 16.67us pulse. You don't care about the duty cycle, which would obviously change but the frequency would match.

author: ConKbot
author_rank: Super Contributor
timestamp: June 10, 2024, 03:15:51 pm
content: Set it up to do a "burst" of a single pulse, and trigger off the external trigger. Obviously this won't be a constant duty cycle, as the pulse width will be constant as the frequency varies, but if that's ok, it's all you need.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 10, 2024, 04:51:11 pm
content: Following an external function would be a kind of PLL function. This is not a functionality regularly found with function generators - more like an oddity. One may have a slight chance to find this with some old instruments, but not sure about that.One may be able to create that function with an external PLL and a function generator that allows for a VCO mode. The VCO function is found with some older analog FGens from the 1980-1990s.The external part would be a phase/frequency comparator (e.g. 74HC4046) and some loop filter.

author: 2N3055
author_rank: Super Contributor
timestamp: June 10, 2024, 06:11:31 pm
content: Let's also not forget that any trigger input on general purpose AWG will have certain time delay from trigger to pulse emit.Explaining better what is going on here would be useful.This is classical case of having a problem, devising a plan with theoretical components ("what I need is some kind of tool that can do that and that") and then asking for help to solve newly created problem of fitting the solution into way of thinking that might not be optimum way of doing things.Better way is to ask for help to solve the original problem by asking for help to devise solution to original problem itself.Brainstorming, if you will. It always amazes me how different people come with simple but great solutions sometimes, all while completely different than what I myself would do..So do you have optical pulses that you need to trigger a burst or a pattern of data from a signal source?What are you doing with such triggered signal?Those optical pulses repeat at roughly 30kHz. Optical pulses change repetition frequency, any you want to keep being locked to pulses. Do they change repetition interval from pulse to pulse and you want to follow the timing closely? Or optical pulses come at relatively steady 30kHz but you want to stay locked (synchronized) and what you really need is synchronised bursts but some continuous waveshape that is locked to source pulses?How fast pulses change timing? How much timing is changed?Etc etc...

author: Njk
author_rank: Frequent Contributor
timestamp: June 10, 2024, 10:14:59 pm
content: Quote from: Kleinstein on June 10, 2024, 04:51:11 pmAlthough Agilent 33250A is not that old, perhaps it uses DC coupling on external input for FM (not clear from the manual)

author: Lomax
author_rank: Frequent Contributor
timestamp: June 10, 2024, 10:51:26 pm
content: Quote from: 2N3055 on June 10, 2024, 06:11:31 pmI'm curious about this too.Quote from: ash1204 on June 10, 2024, 12:35:13 pmIt doesn't sound like you need a function generator at all, since you already have the signal. If, for example, you want to convert the waveform, say from a square wave to a sine wave, there are simpler ways to do this using basic filters. Using a comparator (op-amp) much more can be done, such as modifying the duty cycle. Or if you really must generate a completely new signal, look atPLL circuits. Also, since the signal is just 30 kHz you could easilysample the frequencywith a microcontroller which opens up a wealth of options.P.S. You've surely thought of my suggestions above already, or you wouldn't be using kit that costs several times more than my entire lab to do what £5 of parts could do...

author: PCB.Wiz
author_rank: Super Contributor
timestamp: June 11, 2024, 03:57:53 am
content: Quote from: ash1204 on June 10, 2024, 12:35:13 pmOver what range and to what precision ? What output waveform do you need ?Function generators/waveform generators expect to play back their memory at a certain defined speed.The trigger can start that playback, but it cannot easily stretch it to fit the trigger speed.An auto-stretch-to-fit feature would need a dedicated MCU design, or as someone hinted above, you could capture Fin, and then generate a new waveform dump on a PC host for each frequency change. That SW+ update would have a slew/tracking limit.

author: Henrik_V
author_rank: Regular Contributor
timestamp: June 13, 2024, 01:25:09 pm
content: Your two Agilent 33250A generators have the ability to sync.First choose one to be the master clock and use a 50 Ohm BNC cable from 10 MHz Ref out of your master to the 10 MHz Ref in of your slave.Now the clocks run synchronised so if you change the frequncy on both to the same value (by 488 or 232) and use the sync of one to trigger the second they generate synchronised.