What is the difference between a signal, function and pulse generator? - Page 1
Forum section: electronics / beginners

author: Specmaster
author_rank: Super Contributor
timestamp: August 01, 2017, 05:20:43 pm
content: Please can someone explain the differences between signal generators, function generators and pulse generators? Can they all be used for the generation of frequencies for the alignment of equipment like radios and used to help calibrate oscilloscopes for example, assuming the frequency range is high enough of course?I keep seeing loads of them for sale on Ebay etc but never too sure as to what each one does apart from I have a signal generator with modulation that can used for AM radios, not too sure about FM though, doesn't that require a wobbulator? I have a function generator which will give me sine, square, sawtooth and ramp waveforms as standard plus the ability to create a waveform of my own and store up to 10 of them in memory but has no modulation so I suppose that sort of answers what the first 2 do? but what about the pulse generator, surely any waveform is like a pulse?

author: jpb
author_rank: Super Contributor
timestamp: August 01, 2017, 05:39:15 pm
content: My understanding is that a:Signal Generator typically generates just sine waves but with AM and FM and go to relatively high frequencies for radio work (can go to many GHz depending).Function Generators generate particular wave shapes such as square or saw-tooth as well as sine but are lower frequency typically a few tens of MHz.Arbitrary Wave Form generators are more versatile function generators allowing arbitrary wave shapes read from memory.Function and Arbitrary Waveform generators may be used to apply modulation to a high frequency sine wave generated by a signal generator.A pulse generator generates square pulses (or oblong I suppose) with varying mark space ratios and perhaps varying rise and fall times. There are also pattern generators which are more sophisticated versions allowing more complicated combinations for digital circuits.Note that function generators or arbitrary waveform generators are jacks-of-all-trades and typically can generate pulses as well as other wave shapes.

author: alm
author_rank: Super Contributor
timestamp: August 01, 2017, 05:43:59 pm
content: It depends on the context, but in the RF context an (RF) signal generator is usually a generator that will generate narrow bandwidth signals with a high stability over a fairly wide frequency range, starting around 1 MHz and going up to GHz in some cases. Output types are usually CW and various types of modulation. The output levels might go from +20 dBm down to well under -100 dBm (i.e. a wide range).A function generator is a jack of all trades. Frequency range is lower than an RF signal generator, from < 1 Hz up to a few MHz up to a few dozens of MHz (though you can get them up to higher frequencies). Stability (e.g. phase noise) will often be worse than a true RF signal generator. Signals can be at least sine (CW), triangle and square wave. Some have more like ramps and pulse trains, and some can even do arbitrary signals within their bandwidth / memory depth. Modulation, if available, is more limited than an RF signal generator. Power output might go from +20 dBm down to -20 dBm, a much smaller range.A pulse generator is specialized, like an RF signal generator, but more aimed at digital circuits. It can generate pulses with variable transition times (can go much faster than a function generator) and a wide range of duty cycles (wider than some function generators). The signal will likely be more stable (less jitter) than a function generator. Some can even generate variable pulse patterns to emulate digital signals.So in short, a function generator can do it all but less well and over a more limited range, and the other two instruments are both more specialized and do one particular job very well.

author: Specmaster
author_rank: Super Contributor
timestamp: August 01, 2017, 06:07:52 pm
content: Quote from: alm on August 01, 2017, 05:43:59 pmThats pretty much what I was thinking, I keep seeing all this high end stuff but old, on Ebay and I think to myself that its all on the big side and in many ways duplicates what I already have, an old low end signal rf gen and a new but again budget arena function gen but has no modulation built in and stops at 25Mhz and the sig gen goes to 130Mhz (fundamental) and 500Mhz (harmonics), So how could add modulation to the function gen then?

author: MrAl
author_rank: Super Contributor
timestamp: August 01, 2017, 06:24:57 pm
content: Hi,You can make your own AM with any sig or function generator. FM is harder to make because you'd have to modify the function generator. If you can get a schematic you can find out how they generate the frequency and maybe you can modify it a little.For AM you can use a small external circuit sometimes just one transistor.You can make lower frequency FM with an LM339 and some resistors and a capacitor, maybe up to 200kHz. That would be square wave output but still FM.So it partly depends what you need it for.

author: alm
author_rank: Super Contributor
timestamp: August 01, 2017, 07:32:14 pm
content: If the function generator has a VCO/VCF input, then you can use that for FM.

author: Specmaster
author_rank: Super Contributor
timestamp: August 01, 2017, 07:46:17 pm
content: Quote from: alm on August 01, 2017, 07:32:14 pmNo it has nothing like that, here is a link to one that I have but as it has a top range of 25Mhz it is no good for FM.http://www.ebay.co.uk/itm/Digital-DDS-Dual-channel-Signal-Generator-Source-Frequency-Meter-25MHz-UK-Stock-/282474292359?hash=item41c4c7a487:g:UlgAAOSwi7RZFXw3

author: danadak
author_rank: Super Contributor
timestamp: August 01, 2017, 09:47:32 pm
content: You can with code run that generator and control phase whichwould allow for FM, but modulating rate is limited by abilityto get data into the unit.Maybe someone has tried this......? I know there has been somework discussed on this site programming the unit, MHS-5200AI think.Regards, Dana.

author: tautech
author_rank: Super Contributor
timestamp: August 01, 2017, 10:20:09 pm
content: Quote from: Specmaster on August 01, 2017, 05:20:43 pmThink about duty cycle...........a square wave is 50% and anything that isn't, consider it a pulse.The parameters (all) of any waveform can be fully user defined with an AWG both in the UI and by scripts that makes them much more versatile than a sig or function gen and many are moving to AWG's so there will be more sig and function gens on the market in the future.Edit to add.An AWG can also easily be used as a makeshift mark space generator for CRO alignment and better ones allow an external 10 MHz reference so to produce better accuracy.

author: Specmaster
author_rank: Super Contributor
timestamp: August 01, 2017, 11:31:22 pm
content: Quote from: tautech on August 01, 2017, 10:20:09 pmOk, that makes sense, so my function generator also doubles as lower class of pulse generator then because it has the ability to alter the duty cycle so it is good up to about 10Mhz with square waves so I expect that same kind of restriction on its maximum frequency would also apply if I use it as a pulse generator since pulses will be more about square waves then anything else is that correct? I had noticed a few more sig gens on Ebay lately and I'm looking for something a little bit better then my current one so I can set up FM radios as well.

author: tautech
author_rank: Super Contributor
timestamp: August 01, 2017, 11:55:31 pm
content: Quote from: Specmaster on August 01, 2017, 11:31:22 pmEvery brand and model is different in this respect and it sometimes has to do with the waveform generation technology used. Looking for an AWG is much like buying a scope.........there are lots of features to balance out based on personal need.For some example check SDG1000X series against SDG2000X series and while they are very similar (2000X higher signal fidelity and Sa/s) the 1000X cleans up on square wave being able to produce them to the same frequency as sinewave, few AWG's do that.They've both got threads on the forum if you want to look deeper at the features current owners value.