Siglent SDG2000X having much worse rise times than cheaper SDG1000X?  - Page 1
Forum section: electronics / testgear

author: RBBVNL9
author_rank: Frequent Contributor
timestamp: July 18, 2021, 08:29:15 pm
content: Hello, I recently wanted to upgrade my Siglent SDG1032X function generator to a SDG2042X. Among other things, I was hoping for higher signal fidelity. After all, the sample rate goes up from 150MSa/s to 1.2GSa/s.Doing some quick tests, however, it seems that a standard 10 MHz block wave output is much worse on the SDG2042X. Its rise time is 8.4 ns, whereas the SDG1032X has a 3.2 nS rise time. This is measured with identical settings on the signal generators (10MHz block, 4Vpp) and used 50 Ohms input termination on the scope. I synced the clocks of the devices to get them on the same screen, but the syncing does not affect rise times. It is measured on a 300 MHz scope, which I have certified to be able to measure rise times as short as 950ps.Checked theSDG1000X series product specifications: Lists 3.8ns rise time for 10% ~ 90%, 2.5 Vpp, 50 Ω load. And checked theSDG2000X series product specifications(sorry for the unusual link, the one of the Siglent website itself is broken :~|.Lists 9ns rise time for 10% ~ 90%, 1 Vpp, 50ΩLoad.So, yes, the product specs confirm that the more expensive model has like 2-3 times worse rise times than the cheaper mode… Still feel puzzled and a bit disappointed.

author: tautech
author_rank: Super Contributor
timestamp: July 18, 2021, 08:49:59 pm
content: Yes SDG2000X is an older product than SDG1000X that has better HW that also supports the same max frequency for both sine and square waves.Unfortunately to push past the limitations of these models the dearer SDG6000X series are the only existing solution until SDG7000 is released.As always the devil is in the data sheets.

author: bdunham7
author_rank: Super Contributor
timestamp: July 18, 2021, 08:52:38 pm
content: The SDG1032X has a special, specific square wave circuit that goes to 60MHz. The SDG2042X can be hacked to a 120MHz generator (and is a great value and very useful tool overall), but the square wave frequency is limited to 25MHz. Also, it really is a 300MSa/s AWG with a 4X oversampling output interpolation filter of some sort. I think it's a bit deceptive for Siglent to call it 1.2MSa/s unless I'm missing some aspect.

author: tautech
author_rank: Super Contributor
timestamp: July 18, 2021, 10:49:36 pm
content: Quote from: bdunham7 on July 18, 2021, 08:52:38 pmYou are.TrueArb or DDS mode.https://int.siglent.com/u_file/document/SDG2000X_DataSheet_DS0202X-E02E.pdf

author: bdunham7
author_rank: Super Contributor
timestamp: July 19, 2021, 12:14:24 am
content: Cryptic you are. I've not see anything indicating that the 1.2GSa/s is anything more than a 2-bit digital low pass filter. True Arb is 75MSa/s maximum and Easy Pulse jitter reduction is something different that doesn't depend on higher sample rates.From the datasheet:Sampling Rate: 1.2 GSa/s (4X Interpolation)The only thing we don't know is the exact interpolation strategy.

author: rf-loop
author_rank: Super Contributor
timestamp: July 19, 2021, 05:39:19 am
content: Signal is produced by 300MSa/s DDS. It goes to interpolator. Result goes to DAC what use 1.2GHz clock, derived using PLL from DDS 300MHz clock.Explained more in this Siglent app note.

author: RBBVNL9
author_rank: Frequent Contributor
timestamp: July 19, 2021, 05:44:53 am
content: Dear Tautech,QuoteYou are now raising a point of confusion. On the SDG1032X, when you go to "Waveform" and "Arb", you get a menu button where you can choose between DDS and TruArb. (See attached picture.). Moreover, onSiglent web page for the SDG1000X series, they write "The proprietary EasyPulse & TrueArb technique helps to solve the weaknesses inherent in traditional DDS generators when generating pulse waveforms".So I must assume thatboththe SDG1000X series and the SDG2000X series.

author: AaronLee
author_rank: Regular Contributor
timestamp: July 19, 2021, 06:06:16 am
content: Quote from: tautech on July 18, 2021, 08:49:59 pmAh, thanks for that information. I was planning to buy a SDG2000X series, blindly thinking it would be able to handle up to 100MHz square wave. In checking the datasheet, yep, max 25MHz. But for the SDG6032X which can do 100MHz, the price of $3400 is way beyond what I'm willing to spend. Hmm, now I need to rethink my purchase plans.

author: tv84
author_rank: Super Contributor
timestamp: July 19, 2021, 10:44:47 am
content: Quote from: AaronLee on July 19, 2021, 06:06:16 amThere are guys here that have upgraded their SDG6022X to SDG6052X...

author: RBBVNL9
author_rank: Frequent Contributor
timestamp: July 19, 2021, 12:32:55 pm
content: Thanks for the various replies.In theirmarketing communications, Siglent touted the SDG2000X series as much better as their 1000X series, but after looking at the signals it generates, and the comments above (commenting the 1000X has better hardware), it feels more like a downgrade to me. I did some further measurements, like on the harmonic distortion of a sine wave, but also there, the 2000X does not really improve upon the 1000X, at least not in the ways the plots in the marketing document show. The second and third largest harmonic tones are just as strong.I will consider sending this unit back and reconsider my options.Should I decide to buy an SDG6022X, is there anything I should know or be aware of before purchase?

author: AaronLee
author_rank: Regular Contributor
timestamp: July 19, 2021, 12:56:44 pm
content: Quote from: tv84 on July 19, 2021, 10:44:47 amThat's still $1,500 for that SDG6022X. I'll consider it, but maybe just settle for a much lower maximum square wave than what I was hoping for, and buy a SDG2000X series.

author: RBBVNL9
author_rank: Frequent Contributor
timestamp: July 19, 2021, 01:58:45 pm
content: @AaronLee,I don't know about your specific needs for square waves, but if the budget is lacking for an expensive general purpose frequency generator, then perhaps a separate specialist device for that square wave can meet your needs?Maybe a far stretch, but Leo Bodnar sells very affordably10MHz block wave generatorswith rise times as low as 30ps (!), reviewed in The Signal Path, episode 3138. It's based on the MAX3939, a chip often used as optical driver. I have one and its a handy device. There isanother designthat uses the ultra fast comparator ADCMP580 available from Analog Devices. Should create waves that are pretty squared. Of course, they do not have all the features and output settings of a regular function generator.I've been considering using either of these two chips to build a versatile circuit that can be driven by a (lower rise time) function generator, or a very accurate time source. Or maybe modify the Leo Bodnar pulse generator I have.

author: AaronLee
author_rank: Regular Contributor
timestamp: July 20, 2021, 01:24:21 am
content: Quote from: RBBVNL9 on July 19, 2021, 01:58:45 pmI'd already thought of that, and did some searching and found a cheap 160MHz square wave generator which will suit my purposes just fine. So I ordered that, and then I'll get a Siglent 2000X series for when I need non-square waves.

author: gf
author_rank: Super Contributor
timestamp: July 20, 2021, 02:30:05 pm
content: Quote from: bdunham7 on July 19, 2021, 12:14:24 amI wonder what EasyPulse actually does? Seems to me that it just reduces the bandwidth of the given waveform to < 150MHz (therefore the rise time degradation), in order that the waveform can be safely re-sampled by the DDS at 300MSa/s w/o violating the sampling theorem?[ The traditional one-clock-period-jitter for square waves is actually an aliasing artifact. It does not happen when a DDS resamples properly band-limited signals from waveform memory. Unfortunately, a square wave is not band-limited, and a "band-limited sqaure wave" is not square any more. ]The up-sampling to 1.2GSa/s (with a digital up-sampling filter) does of course not increase the DDS sampling rate, but it certainly makes life easier for the analog reconstruction filter, so that frequencies closer to Nyqist can be reproduced, eventually. Nyquist still remains 150MHz, though.

author: bdunham7
author_rank: Super Contributor
timestamp: July 20, 2021, 02:55:26 pm
content: Quote from: gf on July 20, 2021, 02:30:05 pmYou've got the idea. DDS square wave jitter occurs when calculated transition falls between two DDS samples and the square wave algorithm only allows for high and low samples. AFAIK, these schemes for reducing DDS jitter typically just adjust the amplitude of the closest sample, or perhaps two samples, according to how close they are to the transition--a sort of time-based interpolation if you will--and then blur the whole thing by reducing the bandwidth. In any case, the overall effect is more or less as you state--they change the targeted output waveform to a bandwidth-limited square wave and then the DDS sample rate is sufficient to reconstruct that.QuoteYes, the 4X thing is just an oversampling low pass filter that allows for a steeper cutoff. It's a good idea, but using it to claim 1.2GSa/s is a bit sketchy IMO. CD players used to use this method because the specified analog reconstruction filter for CD audio is hard to implement in pure analog. They didn't call it hi-rez audio or claim 176.4kSa/s.Making clean square waves requires a separate circuit. The SDG1032X has that, the SDG2042X does not--it's that simple.

author: RBBVNL9
author_rank: Frequent Contributor
timestamp: July 22, 2021, 08:27:22 am
content: QuoteThanks for mentioning this. When I was reading the Siglent app note posted by rf-loop above, I had the same impression, that this is a technology we have seen in CD players for many years. While the very earliest CD players, introduced in 1982, used 44.1kHz DAC followed by an analog low passfilter, a Philipspublication from 1984proposed the use of oversampling. Not before long, all major brands implemented oversampling in their commercial products. So in nothing new under the sun...

author: mawyatt
author_rank: Super Contributor
timestamp: July 22, 2021, 02:00:08 pm
content: Quote from: RBBVNL9 on July 22, 2021, 08:27:22 amThe 1st CD players from Sony had an elegant (and expensive) passive low pass filter, this was a very complex filter that achieved ~90dB attenuation from ~20KHz passband to ~22KHz stopband which was the alias frequency. Oversampling allowed the use of a much simpler and lower cost low pass filter, which significantly lowered the CD player cost. Remember studying that Sony filter in detail, and engineering work of art. Another elegant analog filter showed up in the 1st SRI function generator.Best,

author: richmit
author_rank: Contributor
timestamp: July 23, 2021, 09:05:58 pm
content: Quote from: RBBVNL9 on July 19, 2021, 01:58:45 pmI needed something similar, but not as fast (anything under 1ns would have done the job). I found a DC2767A board for the LTC6754 on ebay for $7US, and had very good luck getting ~700ps pulses out of them. I think the boards are about $25US new.

author: TurboTom
author_rank: Super Contributor
timestamp: July 23, 2021, 10:22:35 pm
content: Provided the output level suits your needs, you can use any AWG and feed its square output through a bunch of LVC gates to achieve sub-nanosecond rise & fall times. The tiny 74LVC2G04 (inverter) or 2G014 (Schmitt trigger inverter) are good candidates. I used them for pulse shaping in myLPRO101 reference clockwith very good results.

author: RBBVNL9
author_rank: Frequent Contributor
timestamp: July 24, 2021, 06:05:30 am
content: QuoteTurboTom, that is a nice design with inspiring parts. The output stages remind me of theFrequency Divider Design for a GPSDOby Dave Partridge (schematics). I build one of these as well (with thanks to Dave to share the Gerber files). It uses the 74AC541DW in the output stage and I measure a rise time of 1.9ns. Not as short as the sub-1ns times your 74LVC2G04 is providing, but still pretty good.PS. Should anyone be interested in building the Frequency Divider mentioned above, I still have a number of PCBs that I am happy to send you. Having a single PCB produced did not make economic sense...

author: RBBVNL9
author_rank: Frequent Contributor
timestamp: July 26, 2021, 07:07:04 am
content: Above in this threat, people have commented that the Siglent SDG1032X has special hardware for better square waves. Great, even if it is just a sufficiently fast port after the wave generator, if it works, it works.I thought I may validate that by comparing its square wave output with the output of the arbitrary (Arb) patterns with also have something resembling a square wave – assuming the Arb mode does not engage that special hardware. Indeed, my measurements (table below) confirm that the regular square wave produces results much shorter rise times. All good.A surprise comes, however, when measuring the Siglent SDG2042X. Here, I expected to find similar performance for square wave and Arb modes, as there is apparently no such special circuit. But the Arb pattern output is muchbetterthan the square wave output.This seems to suggest that of you need square waves from the SDG2042X, then not to use the square wave function, but ARB Square Duty50 instead. (At least up to the 6MHz that is supported for Arb).

author: blurpy
author_rank: Regular Contributor
timestamp: July 26, 2021, 11:22:13 am
content: Quote from: RBBVNL9 on July 26, 2021, 07:07:04 amThat's very interesting. I was able to reproduce. I set my SDG2042X to produce Duty50 Arb on channel 1, connected to my SDS1204X-E channel 2 (pink), and channel 2 on the SDG to produce a square wave, into channel 4 (green) on the SDS. Both terminated into 50ohm.It's clear that the arb square wave is much faster than the regular square wave.1MHz, showing the whole wave form:1MHz, showing just the rise:20MHz, showing the whole wave form:20MHz, showing just the rise:Wondering if it's different chips being used for generating arbitrary waveforms that makes this possible? Or could it be possible for Siglent to tweak their square wave code in the firmware to get similar rise times for the regular square wave too?

author: gf
author_rank: Super Contributor
timestamp: July 26, 2021, 12:22:15 pm
content: Quote from: blurpy on July 26, 2021, 11:22:13 amI guess so, but then the resulting waveform would no longer meet the specified maximum overshoot.It's a trade-off between rise time and ringing.

author: RBBVNL9
author_rank: Frequent Contributor
timestamp: July 26, 2021, 01:29:50 pm
content: @blurpy, thanks for validating the measurements. Your post made me realize I made a typo in my earlier post:This seems to suggest that if you need square waves from the SDG2042X, then not to use the square wave function, but ARB Square Duty50 instead. (At least up to the6MHz20 MHzthat is supported for Arb).From 20 MHz to 25 MHz, regular square waves are the only option.@GF:QuoteYes, that trade-off is a fair point. But they may actually use the opportunities offered by Arb patterns to find the best balance between both rise time and overshoot! Such an optimum might be frequency dependent, though...

author: mawyatt
author_rank: Super Contributor
timestamp: July 26, 2021, 01:52:02 pm
content: Thanks a lotThis is very useful indeedBest,

author: bdunham7
author_rank: Super Contributor
timestamp: July 26, 2021, 01:54:48 pm
content: Quote from: RBBVNL9 on July 26, 2021, 01:29:50 pmIf you want to use TrueARB at frequencies over a few kHz, you are going to have to generate your own ARB file. If you use the ARB waveform in DDS mode, it will have faster transitions, but unless your selected frequency is an exact submultiple of the DDS sample rate (300MSa/s) you will have the classic DDS jitter issue. To demonstrate that set your SDG2042X up for the SqD50, DDS mode, 20MHz and the scope at 5ns/div. You'll see a 20MHz square wave (or at least the first 5 harmonics worth) with a sub-5ns rise time. Then dial the SDG down to 19Mhz, 18Mhz, etc and you'll see the misplaced falling edges--that's the DDS jitter.

author: rf-loop
author_rank: Super Contributor
timestamp: July 26, 2021, 02:16:22 pm
content: Quote from: RBBVNL9 on July 26, 2021, 01:29:50 pmWhole one or cycle repeating max is 20MHz. Naturally your one Arb cycle can include for example two cycles of square wave or more of course. If two, you set the Arb freq to 10MHz and get out to 20MHz and so on. This is really an old trick and have used as long as arb generators have existed.With square wave no need tell duty is 50%. Square tells it. Other dyty % are rectangle waves, not square waves.With two cycle square in Arb you can try how high freq you can go so that you can still accept its "quality". Yes, you can see many weird effects but if find some useful for some purpose just go on.I have not here available my some old tests with SDG2042X.Just write .CSV file and let it go.

author: mawyatt
author_rank: Super Contributor
timestamp: July 26, 2021, 05:27:19 pm
content: RBBVNL9,Just looking at the edge, can confirm blurpy measurements. Getting ~8.1ns edge 10-90% from the Squarewave waveform, and ~4.3ns from the Arb DDS mode (~8ns with TrueArb mode). So indeed the Arb DDS edge speed is almost twice as fast as the SquarewaveThanks for discovering and pointed this outBest,Edit: here's the waveform, nice display of the Gibbs Phenomenon too

author: gf
author_rank: Super Contributor
timestamp: July 27, 2021, 01:54:32 pm
content: Quote from: mawyatt on July 26, 2021, 05:27:19 pmI wonder, whether the (non-trigger) edges of the square wave do jitter now (by one DDS clock cycle, i.e. 3.33ns), if you choose a frequency which is not an integral fraction of 150 Mhz (like e.g. 19MHz).A rise time of 4.3 ns should actually suffice in order not to exceed Nyquist (150MHz), but the question is whether the bandwidth of the provided ARB waveform happens to be limited by the generatorbeforebeing resampled by the DDS, or whether it is only limited by the reconstruction filter (i.e.afterDDS)?