Can your arb generator do this? - Page 1
Forum section: electronics / testgear

author: precaud
author_rank: Frequent Contributor
timestamp: June 24, 2018, 03:19:23 pm
content: It's actually a very simple thing but most can't do it. My Pragmatic/Tegam 2414A does it easily, and is mainly why I keep using it..Generate a single burst of an arb waveform, with:: variable clock rate (NOT mapping the waveform into a fixed-clock DAC): a separate sync pulse output coincident with the first point: at defined intervals adjustable from roughly 2 secs to 40m Secs (that's milliSec).The only other requirement would be at least a 12-bit DAC.If yours can do this, what is it, and how do you set it up?The reason I ask is, I have enquired directly to the manufacturers of a couple of current-model arb/function gens and they can not do it.

author: exe
author_rank: Unknown
timestamp: June 24, 2018, 04:17:09 pm
content: Quote from: precaud on June 24, 2018, 03:19:23 pmIt might worth listing manufacturers here, this may save time for somebody.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 24, 2018, 05:14:04 pm
content: Quote from: precaud on June 24, 2018, 03:19:23 pmBeyond just basic general requirement (memory depth, bandwidth, filters, clock rates, channels.....) could you provide more details about these specific requirements you have.: variable clock rate (NOT mapping the waveform into a fixed-clock DAC)Does this very while the waveform is being played back? If so, I assume that function is programmable as well and may not be just a simple linear or log sweep. Could you describe this? What is the range of clock frequency you are after?

author: precaud
author_rank: Frequent Contributor
timestamp: June 24, 2018, 06:47:44 pm
content: Quote from: exe on June 24, 2018, 04:17:09 pmOne was GW Instek MFG-2000 series. Even with its separate built-in pulse gen, it can not trigger its own arb gen.The other is pending confirmation from a tech to their CS.

author: jpb
author_rank: Super Contributor
timestamp: June 24, 2018, 06:58:48 pm
content: Most arbs are fixed clock rate. I have an Agilent/Keysight one which is theoretically variable but it decimates and interpolates (in a clever way).For true arbs you probably need something like a Tabor one where the clock rate does vary:-https://www.taborelec.com/but they are not cheap. I think that they used to (or still do) produce the more expensive Keysight arbs as OEMs.

author: precaud
author_rank: Frequent Contributor
timestamp: June 24, 2018, 07:00:14 pm
content: Quote from: joeqsmith on June 24, 2018, 05:14:04 pmThe basic requirements are easily met by any recent single-channel arb gen, except of course filter, because none except the the Keysights have programmable filters.QuoteIn my application, no.QuoteNothing outrageous - from say 30MHz down to maybe 5kHz, clock rate.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 24, 2018, 07:39:44 pm
content: So you run some number of sweeps of a wave form at some rate but between sweeps change the clock rate?Quote from: jpb on June 24, 2018, 06:58:48 pmStrange. I will at times I have had to sync the clock of the Arb to my circuits.I wonder for the Agilent if you are referring to the how they synthesize the clock from the DDS.

author: precaud
author_rank: Frequent Contributor
timestamp: June 24, 2018, 07:53:35 pm
content: Quote from: joeqsmith on June 24, 2018, 07:39:44 pmOne ensemble of averages (typically 64) is taken at one clock rate, one set at another (lower) rate, and their FFT's are "spliced" together in the computer.

author: DaJMasta
author_rank: Super Contributor
timestamp: June 24, 2018, 08:02:52 pm
content: It would take a fair amount of extra programming, I expect, but you could create your waveform, then write a script to expand or compress it to the right period and then load it into the arb memory for playback, so that your only requirement for your generator is a sample rate high enough to get you the fine gradations you need in adjusting frequency steps - and with a little bit of interpolation in your algorithm wouldn't make these requirements high. That way at least you don't need a variable sample rate on the output. If your variations are in a set pattern and aren't changing on the fly, then you could also just look for an arb with a lot of sample memory - then you can do that process making the variable frequencies into a single waveform and just play back the full test regimen.Sort of hacky ways of doing it, but it would let you use a pretty wide variety of generators.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 24, 2018, 08:11:16 pm
content: Seems simple enough. I'm not seeing the problem. Are the Arb's clocks just not stable enough? Not enough resolution? Too much phase noise? Could you use a stable RF generator to drive your Arbs sample clock if you need lower phase noise and better drift?Or are new low cost Arbs really so bad that you can't do much with them? I haven't looked.

author: precaud
author_rank: Frequent Contributor
timestamp: June 24, 2018, 08:34:02 pm
content: Quote from: joeqsmith on June 24, 2018, 08:11:16 pmThe clocks are stable enough, phase noise is not an issue. It just that, for fixed-clock-DACs, unless the clock rate needed (which is determined by the DSO) is an integer multiple of the arb's clock, then some interpolation will occur.QuoteI don't know if they're bad or good. I just enumerate the requirements and see if they'll do it. The point of this little exercise is to see if a more modern arb, with more bits and faster clock, can replace the Pragmatic. So far, nada. The Keysight 33522B is probably the most interesting and capable of 'em, but even it does not have a trigger rate generator and costs more than I'd like to spend...

author: precaud
author_rank: Frequent Contributor
timestamp: June 24, 2018, 08:43:10 pm
content: Quote from: DaJMasta on June 24, 2018, 08:02:52 pmYeah, I don't want to mess with interpolation. The waveforms are calculated for specific # of points and freq span combos.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 24, 2018, 10:16:30 pm
content: Quote from: precaud on June 24, 2018, 08:34:02 pmSo you need higher resolution DDS synthesizer, or want one with a different technology all together?Looking at what appears to be the manual for yours, the clock appears fixed which is why I am confused about what you are asking."3.4.4 Sample Clock and Output FrequencyOutput waveform frequency is a function of both the clock frequency and the number of samples. (Output f = Clock f/# Samples.) Since the default clock frequency is 10 MHz andthe standard waveform default memory allocation is 1000 samples, the default output frequency is 10 MHz/1000 = 10 kHz.Press the CLOCK/FREQ key. Either the clock frequency (SCLK) or the desired output frequency (FREQ) can be entered directly. Use the double-arrow key to move the selection to the top row of the display. Use the edit knob or keypad to set the desired value. (Any change in the number of waveform samples will also affect the output frequency, as discussed in Section 5.) "

author: precaud
author_rank: Frequent Contributor
timestamp: June 24, 2018, 10:45:48 pm
content: Quote from: joeqsmith on June 24, 2018, 10:16:30 pmOK, now you're forcing me to getreallyspecificIf the 2414A had output filters that tracked the clock rate (like the 33512B), I would be a happy camper and life would be good.The newer arbs have faster clocks and typically 14 bits. So I figgered, if I could add two bits to the DAC, double (or more) the clock rate, and double my waveform sample length, that would reduce the errors caused by the stairstepping by at least a factor of two, probably more. It would be a reasonable thing to try, as long as the cost was not excessive and other functionality was maintained.QuoteThe clock is not fixed, it is variable from 0.1Hz to 20MHz. In that paragraph they're only explaining why the unit powers up with a "default" output frequency of 10kHz for standard (i.e. built-in) waveforms.

author: precaud
author_rank: Frequent Contributor
timestamp: June 25, 2018, 02:31:19 am
content: OK, so noone has answered the question in the positive. Since modern arbs all appear to be fixed-clock designs, let's relax the requirements, and allow for them. So now the question is, can your arb gen:Generate a single burst of an arb waveform, with:: at least 30MHz clock and 12 bits resolution: a separate sync pulse output coincident with the first point (to trigger your DSO): at defined intervals adjustable from roughly 2 secs to 40m Secs (that's milliSec).The latter feature is called "Trigger Generator Delay" in the 2414A. Other units may call it something else. It's basically the time between internally-generated triggers in Continuous or Free-Run mode.The reason I first looked at the Instek MFG-2000's is that they all come with a separate pulse generator built-in. The pulse gencouldgenerate the sync pulses at the desired rate AND trigger the arb. But their tech support says it can not do the latter.

author: tautech
author_rank: Super Contributor
timestamp: June 25, 2018, 02:40:31 am
content: I'm thinking a SDG2042X can do this but I'd need to run some checks.I've asked the higher skilled users about your requirements in the SDG2042X thread so give a bit of time for those that have these units to respond.Anyways, one of these:https://www.siglentamerica.com/waveform-generators/sdg2000x-series-functionarbitrary-waveform-generators/

author: precaud
author_rank: Frequent Contributor
timestamp: June 25, 2018, 03:00:58 am
content: OK, thanks. BTW, it's not really an unusual use. If you're making stimulus-response measurements in an environment that is noisy and/or has a long settling time, such as with a transducer in a gas (like air) or liquid (like water), this is the exact sort of setup needed. Averages of single bursts with sufficient delay between them to allow for for settling before hitting it again. There are other uses too.BTW2, I examined the SDG1032X manual last week and found no "trigger generator delay" setting.

author: tautech
author_rank: Super Contributor
timestamp: June 25, 2018, 11:48:33 am
content: Quote from: precaud on June 25, 2018, 03:00:58 amFrom your specs 1032X won't cut the mustard for you, instead focus on 2042X for its 16 bit and 8mpts.The capabilities are varied, depending on waveform type like there is delay but only in Pulse that can't be swept. But you can sweep an arb waveform and most others.Anyways, a dumb example of an AM modulated arb Stair with 10us pulses that took my fancy while stuffing around dead tired.I'll come back to this tomorrow.

author: precaud
author_rank: Frequent Contributor
timestamp: June 25, 2018, 01:22:38 pm
content: Quote from: tautech on June 25, 2018, 11:48:33 amI appreciate your help, but let's keep things in perspective. 16 bits is not necessary, and 8Mpts is practically irrelevant for my needs. The 1032 may not "cut the mustard" but its not because of those things...QuoteThe 2042X is two-channel, I don't need that. And I don't need to sweep the arb, either...

author: jpb
author_rank: Super Contributor
timestamp: June 25, 2018, 05:32:57 pm
content: Quote from: joeqsmith on June 24, 2018, 07:39:44 pmI may be wrong on this - I'm referring to Keysight's True Form:https://about.keysight.com/en/newsroom/backgrounders/33500B/This is very different from a Tabor unit where the DDS clock itself is varied in rate (they have clock generators)eg ww2571a (picked at random)https://www.taborelec.com/ww2571aQuote

author: Marco
author_rank: Super Contributor
timestamp: June 25, 2018, 06:26:04 pm
content: A fixed clock for the same investment/sophistication is always going to be cleaner than a PLL generated one, so it makes some sense to interpolate the signal data rather than PLL generate the clock. Especially with the higher clocked DACs.How aboutTGA12100. Bit of a boat anchor, but Aim-TTi is still selling it.

author: nfmax
author_rank: Super Contributor
timestamp: June 25, 2018, 09:22:16 pm
content: I had a play with my shiny new Agilent 33522B, and it is possible to do what you want, using a single channel (so a 33511B would also work).Set up the ARB waveform with whatever sample rate you want, and select the preferred filter to give you smoothed signal output. Disable modulation & sweep, enable burst. Select burst on, N-cycle mode, #cycles to 1. On the trigger menu, set the source to 'timer', then on the 'trigger setup' menu set the time period to whatever you want. Back on the trigger menu, set Sync on, set the channel to whichever channel you are using. On the 'Sync setup' menu, choose normal or inverted as required. If you choose sync mode 'normal', you get a sync pulse that stays active for the duration of the ARB signal being bursted. If you choose the mode 'carrier', you can adjust the number of samples (at the ARB sample rate) for which the sync signal is active, down to a minimum of 4.In both cases, the sync pulse starts at the start of the ARB waveform. You can adjust the burst phase to shift this, if your ARB signal starts & ends with a 'guard band' of constant DC level.

author: tautech
author_rank: Super Contributor
timestamp: June 25, 2018, 10:33:08 pm
content: Quote from: precaud on June 25, 2018, 01:22:38 pmOK but to quote you:QuoteIs the reason why I'd point you to 2024X models rather than 1032X and without the need to use any filters.

author: precaud
author_rank: Frequent Contributor
timestamp: June 26, 2018, 12:32:36 am
content: Quote from: nfmax on June 25, 2018, 09:22:16 pmDarn... that series of arbs looks better and better... maybe I'll keep an eye out for a used one...Thanks for checking this.

author: precaud
author_rank: Frequent Contributor
timestamp: June 26, 2018, 12:40:52 am
content: Quote from: tautech on June 25, 2018, 10:33:08 pmMy experience with wave generation is, the stairstepping is not significantly reduced just by having more bits; it's either by filtering at/near the clock rate, or a balanced combination of more samples and more bits. I.e. at the same sample rater, more bits doesn't buy you a whole lot unless the starting point is wholly inadequate, ind in this case, it is not...

author: nfmax
author_rank: Super Contributor
timestamp: June 26, 2018, 07:06:55 am
content: Quote from: precaud on June 26, 2018, 12:32:36 amI got mine used for 1600 USD (which seemed unusually cheap). It was in perfect condition, too! I hadn't been specifically looking to upgrade my ARB, but when an opportunity arises...

author: Berni
author_rank: Super Contributor
timestamp: June 26, 2018, 07:59:04 am
content: I have been using my Tektronix AWG2041 signal generator to generate sonar pulses.It has what is essentially segmented memory where a set of waveforms is stitched together in a sequence. This lets me separate the active pulse area from the long silent area so that i don't need to fill the memory with silence (The silence is just a short segment of silence looped around 1000s of times). Requires no PC or software to set all of it up too.Additionally it has two marker outputs. I was using one of them to generate a Enable signal (High during burst) for my power amplifier and to trigger my scope. The DAC sample rate can also be set up to 1GHz with 5 digits of resolution. But its only 8 bit so i guess it won't meet your requirements.

author: nfmax
author_rank: Super Contributor
timestamp: June 26, 2018, 08:30:11 am
content: The 33522B has segments as well, but you don't need to use them for the OP's application.

author: precaud
author_rank: Frequent Contributor
timestamp: June 26, 2018, 01:53:30 pm
content: Correct, segments aren't needed in this app.Quote from: nfmax on June 26, 2018, 07:06:55 amBoy, you got a heckuva deal... used 11B's seem to go for that much. Is that an OLED display?So... thus far, the 33500B series is the only capable replacement for the Pragmatic.And the adaptive filtering puts them in a class by themself.Despite all that, I really don't want to spend that much on an arb gen.So unless/until another viable alternative arises, I'll keep using the 2414A.

author: nfmax
author_rank: Super Contributor
timestamp: June 26, 2018, 02:30:46 pm
content: The display is described as "4.3" Color TFT WQVGA (480x272) with LED backlight" so not OLED.The 16-bit DACs are nice, too. There are all sorts of other goodies, like variable bandwidth (pseudo-random) noise that can be used to modulate or add to an output. I've hardly started to explore it yet. This is an upgrade from an HP 33120A which was the first ever model of ARB I used, many years ago, to simulate a pulse-output transducer.I now have a collection of 33522B, 33120A, 3312A, & 3311A generators...

author: jpb
author_rank: Super Contributor
timestamp: June 26, 2018, 05:24:00 pm
content: Quote from: precaud on June 26, 2018, 01:53:30 pmMy 33522A cost around £1500 from Agilent/Keysight's ebay store but this was with 20% VAT so probably close to $1600 ex VAT. The Keysight ebay store do good deals from time to time and they accept offers but it all depends on what demo stock/trade-in stuff they have.They have one for $1780 asking but would probably take closer to $1600:https://www.ebay.com/itm/Keysight-Used-33522B-Waveform-Generator-30-MHz-2-Ch-w-Arb-Agilent-/172910474534?hash=item2842447526What I'd really like would be the 33622 but that is even more pricey!https://www.ebay.com/itm/Keysight-Used-33622A-33600A-Series-Waveform-Generator-120-MHz-2-Ch-Agilent-/173230335511?hash=item2855552617

author: nfmax
author_rank: Super Contributor
timestamp: June 26, 2018, 08:57:27 pm
content: Quote from: jpb on June 26, 2018, 05:24:00 pmThat one is fully optioned up too, so definitely a good deal even at the asking price.

author: precaud
author_rank: Frequent Contributor
timestamp: June 27, 2018, 03:27:12 pm
content: OK, the Instek MFG-2000 series appear to meet the criteria and are now back in play. Which is good because I like that they have isolated outputs, and they boast "true point-by-point arb" which I take to mean variable-clock, non-interpolated points in arb mode. It turns out that models with an "M" suffix (the Modulation option) have a parameter called "trigger delay" which sets the trigger frequency. So the one I'd be looking at is the MFG_2130M:https://www.gwinstek.com/en-global/products/Signal_Sources/Arbitrary_Function_Generators/MFG-2000One possible negative of this series is the lack of an output antialiasing filter. At least its not mentioned in their specs. Am asking their tech to confirm. Since I will not be operating at anywhere near the 200MHz clock freq, this may not be an issue. Your thoughts?A rant: All of these "2nd-tier" (compared to the big boys) test equipment companies really need to learn how to write good user manuals. Half of the instrument's features are mentioned by name but not functionally explained. The Instek manual is better than many I've seen, but unless you read the Remote Programming section, you won't know what many named features actually do. Even their tech support didn't know this feature existed until I prodded them and told them where to look.Interestingly, their tech told me that the MFG functionality "was benchmarked to the KS 33500 series".

author: precaud
author_rank: Frequent Contributor
timestamp: June 30, 2018, 04:27:16 am
content: Quote from: precaud on June 24, 2018, 10:45:48 pmYes, I know... quoting yourself is dangerous, but I thought, before throwing money at this, I'd better test my figgering, and see if sample rate X2 or X4 actually does result in reduced errors caused by the stairstepping between points. The time domain waveform looks a little better on the screen. But FFT'ing each at the original sample rate and comparing them, the results are much worse. Putting the arb clock pulses in between every sampled data pair generates noise in the FFT. The attached graphs tell the story for X2 and X4. AS you can see, increasing the arb sample rate only distributes the noise more evenly over the spectrum.So if you're FFT'ing the arb waveform (and that's about all I use an arb for), unless the waveform is filtered to remove the arb sample freq steps, "oversampling" the arb only makes things worse.And the KS 33500B-series is the only arb mentioned thus far that does that.