Siglent SDS1104X-E anomaly on what should be a simple task. - Page 1
Forum section: electronics / testgear

author: bdunham7
author_rank: Super Contributor
timestamp: February 06, 2021, 04:32:25 am
content: I recently hauled out a project I've been planning and that is making a replacement LED display for the Fluke 8842A. That's another story--in short a drop-in replacement is impractical--but I ran into what I think is a shortcoming of the Siglent scope. I haven't tried to reproduce it with other test signals, so I'll just show you what I have. What I'm doing is taking the segment and digit scan signals from the VFD drivers of the 8842A and using them to drive a set of 7-segment blue LED displays. The display has 8 'digits' and 11 'segments' total, so 8 lines x 11 lines. I'm just looking at 3 digits and the 7 segment lines for now. The VFD drivers put out a +30V signal on both the segment and digit lines and when both are on, the segment for that digit lights. This obviously won't work for an LED, so I'm using the segment scan lines to drive the segments of common cathode displays in parallel and the digit scan lines to drive a darlington array which then grounds each common cathode in sequence. I'm using dropping resistors at this point, but I'll need to use a lower voltage supply for the system to work. I needed to know the maximum voltage drop across the darlington array, which I decided to determine by connecting a scope between ground and the common cathode of one digit. The specs say about 1 volt, but I was considering using a 5 volt supply, so I needed to know fairly closely.I connected Mr. Siglent with one probe to the incoming digit line and triggered off of that, then the other probe to the common cathode connection. The signal is noisy when the array transistor is off because of cross-feeds from other digits, but when on it seems to go down near zero. So I started changing the V/div setting and at 2V/div, it indicated a half a division above ground. I changed nothing except I twisted the V knob 1 click, the scope went to 1V/div and I heard a relay click--but the signal in question was now 4 division above ground. I rechecked everything, thinking I had some strange ground loop or capacitive coupling or bad probe (the probe was the Siglent PP510 and it is falling apart), so I tried another probe, a different channel, moving the grounds. I also tried both 1X and 10X, nothing changed and the problem was repeatable.So, I tried some other scopes. The problem didn't occur on my Tek TPS2024 and even my ancient Scopemeter gave me the correct result. Well, both of those are isolated, so perhaps still a ground? Now this is not a fast signal, the scan lines stay on for ~1 millisecond, which makes it difficult to even see the signal with an analog CRO. But, I still have a Tek 2221, 60MHz 20MSa/s, and it is common ground just like the Siglent or any other scope. Even that worked properly.I think I know what the issue is now, thanks to a comment David Hess made a while back, and I'm sure Siglent will claim it is user error. However, what I'm doing is not an unusual use of a scope and if this is a limitation, it would be good to know about it.Photos are a rough sketch of what I'm doing (on an actual envelope), the Siglent at 4 different V/div settings and then the Scopemeter, Tek TPS and Tek 2221 on just the final screen.

author: masterx81
author_rank: Frequent Contributor
timestamp: February 06, 2021, 07:19:15 am
content: You are overdriving the input amplifier.A good read:https://www.evaluationengineering.com/instrumentation/oscilloscopes/article/13002369/overcoming-overdrive-recoveryEvery scope have it's characteristics.Common "problem" on dso scopes.

author: tautech
author_rank: Super Contributor
timestamp: February 06, 2021, 08:32:03 am
content: Quote from: masterx81 on February 06, 2021, 07:19:15 amCertainly overdriven in the last screenshot and the giveaway is the long vertical tails in this screenshot:For the first screenshot the complete waveform is entirely on the display so another explanation is needed and the possibilities are; the unmatched probes, channel crosstalk, probe capacitive loading, circuit PSU not up to the task or inadequate decoupling yet the blip on the wider pulse at minimum amplitude is likely to have any impact at all as it seems well removed from any threshold levels.It is my view the scope is correctly displayingsomethingand further investigation should discover what yet if it has no effect on the operation of the DUT why bother.

author: bdunham7
author_rank: Super Contributor
timestamp: February 06, 2021, 02:57:09 pm
content: Quote from: tautech on February 06, 2021, 08:32:03 amSorry if that wasn't clear, but the first screenshot is not a problem at all--nothing is wrong. I just put the arrow there to show the area that I was trying to measure. The messy waveform is just a side effect of how I set it up to measure that specific voltage drop. The only time the scope is properly connected is when the green trace is high and the driver is on, the rest of the time it is bleed-through into a disconnected high impedance circuit. So the entire waveform during the time the green trace is low is just garbage. Of course that garbage is what is overdriving the scope, so I can't ignore it.QuoteYou can't see it in a still photo, but all of those bits hanging by those tails were dancing up and down like marionettes (puppets on strings). I actually don't see a lot of evidence that the waveform was badly distorted and the area being measured has the appropriate shape--flat in the middle and low at the extremes--but it is offset upwards by 3 volts. So an entire millisecond goes by and there's no sign of any recovery.

author: bdunham7
author_rank: Super Contributor
timestamp: February 06, 2021, 03:26:49 pm
content: Quote from: masterx81 on February 06, 2021, 07:19:15 amYes I am, and while every scope has those characteristics, almost none seem to specify them. The only reference I could find that did was a statement from someone at Cleverscope stating that their recovery time was 1 sample, but no further specifics. The way I amplified my area of interest is not at all an uncommon way to do it, thus my initial confusion. I expected it to work because I've done things the same way with other scopes. As I showed, the other DSOs either didn't overload at that same level or they exhibited much faster recovery times, if that is exactly what is going on here.So according to Tektronix, they don't specify a recover time from an overdrive situation, they say that if you are concerned about it, you have to characterize the scope yourself. So it seems that the main characteristics would be 1) at what level the overdrive condition occurs and 2) how long it takes to recover. It seems to me that 'more than a millisecond' is a pretty long recovery time for a 200MHz scope.

author: Fungus
author_rank: Super Contributor
timestamp: February 06, 2021, 03:54:49 pm
content: Quote from: bdunham7 on February 06, 2021, 03:26:49 pmYou're operating the chip outside it's maximum rating. What happens next is unknown even to the chip manufacturers.

author: bdunham7
author_rank: Super Contributor
timestamp: February 06, 2021, 04:53:33 pm
content: Quote from: Fungus on February 06, 2021, 03:54:49 pmIt says "400Vpkright on the front of the scope. I surely haven't exceeded that!Anyway, this isn't a complaint post that needs a resolution. It is an issue any scope user should be aware of and this one caught me off guard because the characteristics of this scope seem a bit different than all the others I tried. Since expanding a particular area in the way I did is a useful measurement tool, I would think it would be worthwhile to determine what the limits are of this scope in using that technique.

author: tautech
author_rank: Super Contributor
timestamp: February 06, 2021, 07:54:28 pm
content: The specification you are exceeding is:Offset Range (Probe 1X)500uV~118mV: ±2V120mV~1.18V: ±20V1.2V~10V: ±200VDatasheet P8 Vertical Systemhttps://siglentna.com/wp-content/uploads/dlm_uploads/2020/02/SDS1000X-E_DataSheet_DS0101E-E04C.pdf

author: bdunham7
author_rank: Super Contributor
timestamp: February 06, 2021, 09:28:14 pm
content: Quote from: tautech on February 06, 2021, 07:54:28 pmThat appears to just be the maximum setting for the vertical position knob in various ranges--which I confirmed by trying it. I was interested in the 118/120 thresholds and those are the points that I hear a relay click. So I set up a test signal to see if and when overdriving appeared to happen. I used a 5 volt rectangular pulse of 100 milliseconds at 5 Hz with a superimposed 100mV 1ms 100Hz rectangular pulse. The goal would be examine the bottom trailing edge to see the step down and subsequent pulses in as much detail as possible. I found overdriving and recovery artifacts even within the offset specs you posted, although they became much more severe as the scope shifted down from 120mV/div to 118mV/div, as you might expect.The test signal:Expanded to 10 division, 6 of which are on-screen. You can see 8 or 9 milliseconds of distortion already.More distortion at 200mV/div, which according to your specs would be good for +20V offset.Now at the minimum 120mV/div before the range switches and the relay clicks. 15 ms of ringing.Fine adjustment one click down to 118mV/div, relay clicks, fairly extreme ringing for ~50 ms.Reducing the top of the large signal to 1.5V to stay within the offset spec. Obviously still 'ringing', at an absurdly low frequency.And now back up just over the threshold at 2.1 volts. It appears to matter a lot how much it is overdriven. But clearly I can't closely examine my falling edge this way with this scope.And here is the Tektronix expanded all the way to 20mV/div with a 5-volt top--that is 250 divisions of overdrive and it still recovers quickly enough so that I can see the step down and subsequent pulses just as they should be, without a hint of overshoot, ringing or distortion.This makes it pretty clear that you need to keep the signal on-screen with the Siglent scope to avoid distortion--and the 'recovery' takes a very long time as scopes go. I'm not sure what the technical reason is for this, but it is a limitation to know and understand, I guess.

author: tautech
author_rank: Super Contributor
timestamp: February 06, 2021, 09:37:49 pm
content: Quote from: bdunham7 on February 06, 2021, 09:28:14 pmKnow, understand and work with.AC input coupling sometimes can help.

author: bdunham7
author_rank: Super Contributor
timestamp: February 06, 2021, 09:43:19 pm
content: Quote from: tautech on February 06, 2021, 09:37:49 pmDefinitely not in this case.

author: bdunham7
author_rank: Super Contributor
timestamp: February 06, 2021, 09:46:41 pm
content: Nothing better than a Jim Williams application note on point:https://www.analog.com/media/en/technical-documentation/application-notes/an120f.pdfAppendix B is most pertinent, but the whole note is of interest.

author: tautech
author_rank: Super Contributor
timestamp: February 06, 2021, 09:53:24 pm
content: Quote from: bdunham7 on February 06, 2021, 09:43:19 pmIt should.The total waveform amplitude if using AC input coupling will be shifted with 50% above and below the channel 0V marker which will allow you to offset the signal further before exceeding the offset limitation.The attenuation of the probe used however can put you into a different offset spec but some quick mental sums can disclose if that might be a problem.

author: bdunham7
author_rank: Super Contributor
timestamp: February 06, 2021, 10:17:36 pm
content: Quote from: tautech on February 06, 2021, 09:53:24 pmI have a signal that never goes to zero, and I'm trying to measure the absolute difference between zero and one particular part of it. I don't see how AC coupling could ever accomplish that.And I see the forum has struck again with the photos not showing properly, at least for me. What gives?

author: tautech
author_rank: Super Contributor
timestamp: February 06, 2021, 10:34:39 pm
content: Quote from: bdunham7 on February 06, 2021, 10:17:36 pmWith Measurements or Cursors.QuoteForum bug. Insert pics the old way with links to your uploaded thumbnails inserted between [ img] flags.Use only the 2nd attachment (more attachments) to also get around the attachment bug.

author: bdunham7
author_rank: Super Contributor
timestamp: February 06, 2021, 10:44:51 pm
content: Quote from: tautech on February 06, 2021, 10:34:39 pmStill not seeing that it is possible. Let's try a simple example. I have a triangle wave of about 5 Vrmsriding on an approximately 10VDC signal. I don't know either value exactly. What I want to do is measure the voltage relative to ground of the signal at the lowest point of the triangle wave. How can AC coupling manage that?

author: tautech
author_rank: Super Contributor
timestamp: February 06, 2021, 10:51:04 pm
content: Quote from: bdunham7 on February 06, 2021, 10:44:51 pmLater I can arrange similar within the limits of an AWG and grab some screenshot examples. Poke me if I forget.

author: kcbrown
author_rank: Frequent Contributor
timestamp: February 06, 2021, 10:52:03 pm
content: Quote from: bdunham7 on February 06, 2021, 10:17:36 pmI've never seen it work properly.What you have to do is to attach them as you did, then post the message, then examine the result in your browser (call the result of this the "view" of the message), and then edit it in another window or tab (right click on "modify" and tell the browser to open in another window or another tab, at your discretion). Expand the images in the view of the message, and for each one:1. right click on the expanded image and tell it to copy the image location,2. paste it in the appropriate location (i.e., wherever in the text you want the image to appear) in the edit box, then3. select the resulting pasted URL in the edit box (via click and drag while holding the mouse button down) and4. click on the "image" icon, which will enclose the URL in "image" tags. The image icon is the leftmost icon in the second row of icons that appears right above the editing box. If you hover your mouse pointer over the image icon, it should say "Insert Image".Then save the message.With any luck, the above makes some sense.

author: bdunham7
author_rank: Super Contributor
timestamp: February 06, 2021, 11:08:25 pm
content: Quote from: kcbrown on February 06, 2021, 10:52:03 pmThanks! Got 'er done. That's a lot of extra work...

author: kcbrown
author_rank: Frequent Contributor
timestamp: February 06, 2021, 11:26:21 pm
content: Quote from: bdunham7 on February 06, 2021, 11:08:25 pmYeah, it's really annoying. I don't understand why the site operators can't fix it or get it fixed. It's not like it's an obscure feature that hardly anyone would use. It's a very common thing for people to want to do here.

author: tautech
author_rank: Super Contributor
timestamp: February 07, 2021, 04:20:16 pm
content: Quote from: bdunham7 on February 06, 2021, 10:44:51 pmSimple examples displaying the usefulness of AC coupling.Waveform details deliberately not stated as the displayed info is sufficient to understand what it is. DC coupling tells that story.Channels 2 and 4 show the same waveform and the offset value when DC coupled shows how much the waveform is above 0V. Measurements deliberately omitted as we have graticules.AC coupling removes that offset and allows us to examine parts of the waveform to the limits of the channel offset specification. Channel tabs and menus tell the story.Any part of a waveform can certainly be measured with cursors.

author: bdunham7
author_rank: Super Contributor
timestamp: February 07, 2021, 06:40:03 pm
content: I'm listening, but not convinced yet. That looks a bit messy and I think you may be overdriving your scope as well in that example, even with the AC coupling. Offset range and amplifier dynamic range are different and you are driving it 190 divisions off the top of the screen.Humor me--try the exact test signal I was using. I used the SDG2042X, with 0-5V volt rectangular pulse of 100 milliseconds at 5 Hz on CHQ and a 100mV 1ms 100Hz rectangular pulse on CH2 and then combined them in the output menu. I want to pretend that small pulse only exists on the trailing edge of the big one--the rest are just for comparison--and I'd like to see if you can use your technique to accurately measure and perhaps cleanly display that pulse as accurately as the Tek scope does in my last picture.

author: StillTrying
author_rank: Super Contributor
timestamp: February 07, 2021, 10:05:36 pm
content: Quote from: bdunham7 on February 07, 2021, 06:40:03 pmYep, everyone is confusing the Y offset voltage with the pk-pk dynamic range of the variable gain amp.There's some triangular waveforms distorting because of the amount off screen waveform here.https://www.eevblog.com/forum/testgear/siglent-sds1000x-series-oscilloscopes/msg1208426/#msg1208426

author: bdunham7
author_rank: Super Contributor
timestamp: February 07, 2021, 11:10:54 pm
content: The interesting thing--I see it mentioned in the other thread as well--is this is mostly a low-frequency phenomenon. I say 'mostly' because it causes a residual offset at higher frequencies too.I tried a different setup--a +/- 5 volt square wave with superimposed 10kHz 100mV pulses. I set the channel to 200mV/div with a +5V offset so that the lower portion of the wave should be right on the center grid line. Set it to 1 Hz, captured the trailing edge and then some of the flat section so that you can see that -5V section of the square wave does indeed eventually line up with the center grid. But the trailing edge shows many milliseconds of recovery from the overdrive. Then I increased the frequency to 1kHz, now you can see the bottoms of that are relatively flat, but offset upwards by 200mV. AC coupling made little difference. At 200Hz, you see a bit of recovery 'bounce', looking sort of like the one Tautech posted.

author: py-bb
author_rank: Regular Contributor
timestamp: November 05, 2022, 12:42:08 pm
content: You posted a link to this from one of my threads and I agree your situation is terrible, the pictures show a stark contrast.What do you think of a Rigol DS1052E?I'm after a digital one to capture things that don't repeat and I'm not asking for recommendations as such, I'm asking "is it afflicted by the same deal breaking problem?"Or was yours somehow defective? The probes perhaps?Thanks

author: 2N3055
author_rank: Super Contributor
timestamp: November 05, 2022, 01:15:42 pm
content: Quote from: py-bb on November 05, 2022, 12:42:08 pmThere is no problem. Whole signal should fit on a screen. If you have something going off the screen then your signal is out of dynamic range of that particular input settings.That means you're overdriving something and will be at mercy of overdrive recovery.To be honest, there will be a little area of the screen where it still works but it is not 5 screens high more like 10%.So simple rule that works all the time: your whole signal amplitude should fit vertically on screen.

author: bdunham7
author_rank: Super Contributor
timestamp: November 06, 2022, 05:43:36 am
content: Quote from: py-bb on November 05, 2022, 12:42:08 pmIt wasn't defective, it simply has a characteristic of having much, much slower overdrive recovery than the other scopes I compared it to. It has been stated by others that this is simply the nature of modern DSO input amplifiers, but I haven't taken the time to compare any others nor do I actually have access to many to try. AFAIK nobody has tried my fairly simple signal test on any fancier scopes. It is possible that older designs may not have this issue even in cheapo scopes, but I don't know.Yes, keeping the signal on the screen fixes the issue, or at least almost does (there was a thread about this same scope showing a small dip on a very slow square wave and I think that is probably also related to the damping of the input amplifier somehow) but keeping it on the screen also reduces the resolution of your view of the signal that you actually want to see.

author: 2N3055
author_rank: Super Contributor
timestamp: November 06, 2022, 10:37:34 am
content: I'm sorry I don't know the links of top of my head (and won't be searching for it), but modern DSO scopes have more limited dynamic range than old CRT scopes. Members here did find that some old Tek DSO had a bit better overdrive behaviour but not much.I tried with Keysight 3000T, people tried with R&S scopes and they all have overdrive recovery distortions (R&S RTB2000 and RTM3000 quite nasty ones too). Also I remember RTB2000 had squarewave droop on some timebases on some scopes, it was on here few weeks ago..Quote from: bdunham7 on November 06, 2022, 05:43:36 amWould you be so kind and remind me as to what test you mean? Thanks.

author: bdunham7
author_rank: Super Contributor
timestamp: November 06, 2022, 02:24:17 pm
content: Quote from: 2N3055 on November 06, 2022, 10:37:34 amThis one here:https://www.eevblog.com/forum/testgear/siglent-sds1104x-e-anomaly-on-what-should-be-a-simple-task/msg3451402/#msg3451402QuoteMy Tek 2221A CRO/DSO hybrid did fine, but my Tek TPS2024 also seems to recover quickly enough to not have issues with this test. Since the recent poster asked about the Rigol 1052E, I have to wonder if it might actually be OK here--it has the same analog trigger circuitry (well, not quite) and pitifully small memory as the TPS2024. Looking at the thread again and in light of the more recent discussion regarding the 'dip' on a 10Hz square wave, I think there is visible distortion even on the first screenshot with the signal fully on the screen. I think there is more than just overdrive recovery going on there.Edit: One additional data point--I just tried the SDS2104X+ on this test, it works fine down to 200mV/div, (15 divisions off the top of the screen) but fails below that.

author: 2N3055
author_rank: Super Contributor
timestamp: November 06, 2022, 04:17:39 pm
content: Quote from: bdunham7 on November 06, 2022, 02:24:17 pmThanks fo the link. Yes these kinds of tests were done, and I cannot remember where exactly I posted this (there were dozens of these discussions on same topic over years) but pretty much all modern scopes (designed in the last 10ish years) will have same problem. R&S RTB2000/RTM3000 has really bad response to overdrive, my Keysight 3000T also.There is a bit of range outside screen but maybe 10-20% (it will vary on input range , sometimes a bit more) and only way to do it right is to keep it on the screen. Inside signal path uses low voltage rails and if you apply 1 volt to input of amplifier with 20X gain that drives amp into clipping. Simple as that.Even old CRT scopes had same problem, but they had very high voltages inside and therefore large dynamic headroom. Also they have been optimized for such use because with analog scopes you had to look at signal differently...Vertical offset works to nullify large DC from signal that has large DC with some AC on top. In which case you subtract DC part and amplifier gets only the rest. You could do that with AC coupling, but DC coupling with offset retains absolute voltage values for correct measurements.Different scopes have different DC offset ranges. One thing I like about SDS2000X HD is extended offset in comparison to other scopes in class.. Useful for work on power circuits, well complemented with 12 bit, low noise and analysis package..

author: mawyatt
author_rank: Super Contributor
timestamp: November 06, 2022, 04:27:51 pm
content: Quote from: 2N3055 on November 06, 2022, 04:17:39 pmExactly!! The DC Offset is very beneficial when one doesn't want the low corner of the AC coupling to alter the signal of interest. The SDS2000X+ also has a nice wide DC Offset range that is stable and doesn't add noise!!Does the HD version have a wider DC Offset range than the X+ ?Best,

author: 2N3055
author_rank: Super Contributor
timestamp: November 06, 2022, 04:52:51 pm
content: Quote from: mawyatt on November 06, 2022, 04:27:51 pmHi Mike,it does, quite more:------------------------------------------SDS2000X+ :Offset range (probe 1X)500 μV/div ~ 100 mV/div: ± 2 V102 mV/div ~ 1 V/div: ± 20 V1.02 V/div ~ 10 V/div: ± 200 V------------------------------------------SDS2000X HDOffset range (probe 1X)1 MΩ:0.5 mV/div ~ 5 mV/div: ±1.6 V;5.1 mV/div ~ 10 mV/div: ±4 V;10.2 mV/div ~ 20 mV/div:±8 V;20.5 mV/div ~ 100 mV/div: ±16 V；102 mV/div ~ 200 mV/div: ±80 V;205 mV/div ~ 1 V/div: ±160 V;1.02 V/div ~ 10 V/div: ±400 V50 Ω:0.5 mV/div ~ 5 mV/div: ±1.6V;5.1 mV/div ~ 10 mV/div: ±4 V;10.2 mV/div ~ 20 mV/div:±8 V;20.5 mV/div ~ 1 V/div: ±10 VTake care!

author: mawyatt
author_rank: Super Contributor
timestamp: November 07, 2022, 02:45:08 pm
content: Quote from: 2N3055 on November 06, 2022, 04:52:51 pmI thought the SDS2000X+ had a very good DC Offset range, the HD version is indeed outstandingThanks for the quick reply, and the usual quality informationBest,

author: py-bb
author_rank: Regular Contributor
timestamp: December 27, 2022, 04:27:06 am
content: Quote from: bdunham7 on November 06, 2022, 05:43:36 amSOrry for the late reply, can you link me the tests you want to run? I can give them a go if I have the equipment.One issue I've found with the DSO scopes around me (whether it generalises I can't say) is that if you use a voltage offset they get bad.I am 99.9% sure that internally the ones around me amplify/attenuate/buffer the input so it is in the range -1v to +1v for the scale on the settings.When I apply an offset and get above 70% of the range I can offset the edge of a square wave becomes really curved, it doesn't undershoot, it's just much slower - I'll take some screenshots later if it'll help.What I'll try doing is adding a DC offset to a square wave that is in range and see if it persists.

author: tautech
author_rank: Super Contributor
timestamp: December 27, 2022, 06:45:19 am
content: Quote from: py-bb on December 27, 2022, 04:27:06 amSee Offset Range (Probe 1X) P8 in Datasheet:https://int.siglent.com/u_file/document/SDS1000X-E_DataSheet_EN04D.pdfYep show us some screenshots.

author: py-bb
author_rank: Regular Contributor
timestamp: December 27, 2022, 07:24:24 am
content: Quote from: tautech on December 27, 2022, 06:45:19 amI've literally just put that away. I've got an older LeCroy to hand I'll take screenshots in a bit. I've not tried the DC offset thing before, but I have tried adjusting the offset, the more extreme the offset the slower the rise time on the square wave is - this is just "panning" around on the calibrate hook.It's an extreme effect and I do wonder how it works to generate it, I imagined it'd generate a voltage and feed that into an op-amp, that's what makes me think saturation could be in play.

author: py-bb
author_rank: Regular Contributor
timestamp: December 27, 2022, 07:29:43 am
content: Quote from: tautech on December 27, 2022, 06:45:19 amOkay it wasn't with the calibration port. I was using a function generator (but not changing the output just "panning" the waveform) - will definitely do it just to figure out what it's called, but not now sorry. Either in the next hour or two or tomorrow.

author: Performa01
author_rank: Super Contributor
timestamp: December 27, 2022, 10:33:17 am
content: The topic of overload recovery pops up over and over again, and still doesn't seem to be understood by everyone (for instance it has nothing to do with semiconductor switching times or something like this) and it certainly can't be a deal breaker.I've tried to explain the issue several times, the last one was reply #41 here:https://www.eevblog.com/forum/testgear/rtb2004-still-worth-it-in-2021/msg3788153/#msg3788153What I would like to add: A higher input offset compensation range in these split path input buffers will also result in worse input overload recovery beaviour.

author: py-bb
author_rank: Regular Contributor
timestamp: December 28, 2022, 11:58:25 am
content: Okay I did the experiment.First up the full wave we're viewing. There is a 50 ohm terminator in play (as with the DC offset the scope kept overloading and tripping)As you can see not a bad square, the rise is pretty good.Okay now we view the top - hmm... that wasn't there before.In this picture I've added a positive DC offset which the square wave is on top of, as a result the square wave's amplitude is lower, as you can see - it's a lot less bad.It's a pretty bad artifact. According to the service manual it's just a DC bias into an op-amp.Great that those attachments didn't work when it did it that way.BTW this is an extreme example, I had it at 6.84v offset (maxes out at 10) so it's not "terribly far" and a frighteningly large artifactbut when viewing something riding on an offset that's nearby it's OK, so as long as the signal's "within view" it tends to be good.There's a person here saying "oh that's expected behaviour"https://www.eevblog.com/forum/testgear/siglent-sds1104x-e-anomaly-on-what-should-be-a-simple-task/?action=dlattach;attach=1167288;image- this image is not. That's terrible! I agree with OP here and is on screen!You need to trust the scope to reproduce a signal that fits in the range accurately, there's no excuse for that!

author: 2N3055
author_rank: Super Contributor
timestamp: December 28, 2022, 02:00:33 pm
content: Quote from: py-bb on December 28, 2022, 11:58:25 amDo you plan to actually read what people answered and explained to you?You are overloading scope input amplifiers by several order of magnitude. Distortion you see is caused by user insisting on doing what people are telling you is wrong.ALL of your signal has to be on screen. If you have 100 mV P-P riding on top of 10V DC offset, you can set scope to 20mv/div, set offset for 10V (if scope has that offset in that range) and nicely see signal on the screen.Because setting offset subtracted 10V DC component form the signal and you defacto have a 100mV P-P signal left for scope to analyse.If you put in 10V P-P into scope set to 20mv/div and use scope offset to look at top level of signal, you are shoveling 10V signal in preamp set for 800mV full range... You get overdrive....So in short, ifm when you are setting the scope, some part of signal goes under or over visible screen, you are doing it wrong.... signal has to enter the screen from the left, and exit to the right and never go outside top or bottom. It actually can, 10-20% more but that is it...Once you accept that, I am willing to explain why is it so. And yes, all current digital scopes,cheapest to very expensive, from all brands do this same very thing.

author: py-bb
author_rank: Regular Contributor
timestamp: December 28, 2022, 02:22:49 pm
content: Quote from: 2N3055 on December 28, 2022, 02:00:33 pmYour tone is somewhat twatish there and I must point out:Did you see the picture linked?it is entirely on the screen!As for my screenshots, I was asked to provide them and yes we already agreed it was saturation.Finally: there's one difference between OP and I - mine rises quickly *then drops* then rises back up.saying real world things are not ideal (no matter how twatty or twat-free the tone isn't helpful.

author: 2N3055
author_rank: Super Contributor
timestamp: December 28, 2022, 03:10:01 pm
content: Quote from: py-bb on December 28, 2022, 02:22:49 pmYes I'm a twat... Thank you... You are so kind. That comment definitely elevated this discussion.. Thank you.This image ?https://www.eevblog.com/forum/testgear/siglent-sds1104x-e-anomaly-on-what-should-be-a-simple-task/?action=dlattach;attach=1167288;imageWhat is wrong with it?

author: py-bb
author_rank: Regular Contributor
timestamp: December 28, 2022, 03:40:41 pm
content: Twatish is bad..... but OKYou see where it changes and is all over the place - that's what wrong with it. I can't believe you consider that OK.

author: 2N3055
author_rank: Super Contributor
timestamp: December 28, 2022, 03:58:53 pm
content: Quote from: py-bb on December 28, 2022, 03:40:41 pmThank you for being kind....As for signal, that is how source signal looks. ...

author: bdunham7
author_rank: Super Contributor
timestamp: December 28, 2022, 10:32:00 pm
content: Quote from: 2N3055 on December 28, 2022, 03:58:53 pmPretty much--this was intended to be the 'good' example, but there is a small bit of settling after the large transition even with that screenshot with all of the signal on the screen. I didn't think much of it at the time since it is so small, but there does appear to be a bit of damping/settling behavior at these slower timebases. Others have remarked on a small 'dip' in slow square waves on this scope as well.