Author Topic: DS1054Z distortion issue?  (Read 17253 times)

0 Members and 1 Guest are viewing this topic.

Offline alsetalokin4017

  • Super Contributor
  • ***
  • Posts: 1873
  • Country: us
Re: DS1054Z distortion issue?
« Reply #50 on: April 29, 2016, 02:38:30 pm »
Confidence.... RIGOL lol.....
 :-DD

It's a great scope -- on what other scope can you display 5 bugs simultaneously? (4 obvious and one not so obvious)   :clap:

The easiest person to fool is yourself. -- Richard Feynman
 

Offline Fungus

  • Super Contributor
  • ***
  • Posts: 9875
  • Country: 00
Re: DS1054Z distortion issue?
« Reply #51 on: April 29, 2016, 07:13:03 pm »
Why don't you tell us, Mr. self-appointed Rigol expert? The schematic is out there.
I've never claimed to be a Rigol expert.  I'm a USER of this model scope-- at least I try to use its features and functions, in spite of its many problems. My post points out that we may not be justified in having supreme confidence in the hardware design, bearing in mind the many software problems that plague this model scope.

The problem being discussed applies to many more oscilloscopes than Rigol but you came in here with your usual Rigol-bashing post.

(and not just oscilloscopes, it's a general problem with op-amps)
 

Offline Keysight DanielBogdanoff

  • Frequent Contributor
  • **
  • Posts: 680
  • Country: us
  • ALL THE SCOPES!
    • Keysight Scopes YouTube channel
Re: DS1054Z distortion issue?
« Reply #52 on: April 29, 2016, 08:15:21 pm »
Looking at the 1054Z schematics (and this is probably old news, but fresh for this thread), the signal is split at the input.

1st, there's resistive attenuation. Then the signal splits to an AC path and  DC path.  Those paths are massaged and combined at the input of the amplifier. Doing this helps avoid unwanted capacitive effects at the amp input.

The other way around this (used by Tek, some others) is to use specially designed, different (or multiple) amps.

Both of these will behave differently when saturating.
 

Offline tautech

  • Super Contributor
  • ***
  • Posts: 15688
  • Country: nz
  • Taupaki Technologies Ltd. NZ Siglent Distributor
    • Taupaki Technologies Ltd.
Re: DS1054Z distortion issue?
« Reply #53 on: April 29, 2016, 08:34:54 pm »
Why don't you tell us, Mr. self-appointed Rigol expert? The schematic is out there.
I've never claimed to be a Rigol expert.  I'm a USER of this model scope-- at least I try to use its features and functions, in spite of its many problems. My post points out that we may not be justified in having supreme confidence in the hardware design, bearing in mind the many software problems that plague this model scope.

The problem being discussed applies to many more oscilloscopes than Rigol but you came in here with your usual Rigol-bashing post.

(and not just oscilloscopes, it's a general problem with op-amps)
As alsetalokin4017 owns one, has found bugs in it, struggles with trust of it, has documented such,  he has more right than most to offer comment.
That you take it as personal is a surprise  :-// are you Rigol's knight in shining armour?


alsetalokin4017 like myself consider use of a DSO of any brand in this manner incorrect .  Period.
Avid Rabid Hobbyist
 

Offline hans

  • Super Contributor
  • ***
  • Posts: 1038
  • Country: nl
Re: DS1054Z distortion issue?
« Reply #54 on: April 29, 2016, 09:09:36 pm »
Reading some of the comments here make me almost cry inside because of it's ignorance.

In my post that was referenced earlier, I wanted to validate and match the pulse-length of a sleep-run-transmit waveform of a battery powered device. In that case the "run" current was minuscule compared to transmit current, creating a large dynamic range in the signal. In order to more accurately measure the length of the "run" current, I zoomed in and stumbled upon this issue.

It's obvious this not a valid way of using a scope, because the hardware cannot deliver accurate measurements in these circumstances. However basing the stance of "this is not how you use a oscilloscope" is IMHO the wrong way around. It seems based because this is how most oscilloscopes are like, not how I would like them to be. I can accept it's limitations as I suspected it is a clamping limitation - however expressed my disgust in the recovery time of the Rigol.

If still you think making measurements with periodically clamped signals is an invalid use-case of a oscilloscope, please explain a productive (not just functional) way to make said measurement without fiddling around the knobs half a dozen times every trigger attempt. Because in my experience these are user error prone and frustrating to do.

Scopes have horizontal zoom functions, why not vertical? Why not capture scope at 1V/div, and display it at say 100mV/div? It seems like the R&S scopes that Dave reviewed lately have a functionality just like that in order to utilize the 10-bit ADC in a bench model. Are most vendors embarrassed by the 8-bit resolution and probably even worse noise performance of their scope?

Ah well.. so much to wish for. Ultimately I expanded the capabilities of that "16-bit sampler board" referenced earlier in combination with digital inputs, to make these measurements (along a whole slew of other measurements that are the primary subjective) possible automatically.
« Last Edit: April 29, 2016, 09:28:17 pm by hans »
 

Offline nctnico

  • Super Contributor
  • ***
  • Posts: 17392
  • Country: nl
    • NCT Developments
Re: DS1054Z distortion issue?
« Reply #55 on: April 29, 2016, 09:15:54 pm »
Scopes have horizontal zoom functions, why not vertical? Why not capture scope at 1V/div, and display it at say 100mV/div?
My GW Instek 2000E and Agilent DSO7104A scope allow vertical zoom even when the signal is halted. Also the GDS2000E seems to be much better at doing the overdrive recovery compared to the tests in the first post.
« Last Edit: April 29, 2016, 09:26:19 pm by nctnico »
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline tggzzz

  • Super Contributor
  • ***
  • Posts: 9649
  • Country: gb
    • Having fun doing more, with less
Re: DS1054Z distortion issue?
« Reply #56 on: April 29, 2016, 09:23:50 pm »
If still you think making measurements with periodically clamped signals is an invalid use-case of a oscilloscope, please explain a productive (not just functional) way to make said measurement without fiddling around the knobs half a dozen times every trigger attempt. Because in my experience these are user error prone and frustrating to do.

You are not the first person to run into such problems.

Famously Jim Williams was very interested in equivalent problems, and developed ways to circumvent them. His writings are widely available on the web. Look out for his measurements of opamp's settling time.

You will note, and DSO proponents will rail against, his opinions of modern scope's performance in this respect.
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
 

Offline tautech

  • Super Contributor
  • ***
  • Posts: 15688
  • Country: nz
  • Taupaki Technologies Ltd. NZ Siglent Distributor
    • Taupaki Technologies Ltd.
Re: DS1054Z distortion issue?
« Reply #57 on: April 29, 2016, 09:31:46 pm »
Reading some of the comments here make me almost cry inside because of it's ignorance.


If still you think making measurements with periodically clamped signals is an invalid use-case of a oscilloscope, please explain a productive (not just functional) way to make said measurement without fiddling around the knobs half a dozen times every trigger attempt. Because in my experience these are user error prone and frustrating to do.

Scopes have horizontal zoom functions, why not vertical? Why not capture scope at 1V/div, and display it at say 100mV/div?
General DSO comments, all brands.

1 Know the limitations of your instrument.
2 Learn the capabilities of your instrument.
3 For accurate representation of waveforms keep them within the confines of the display at all times.(excepting captures)
4 The triggering suite in your scope is the most powerful tool you have, use it.
5 Before connection attempt to deduce the waveform you expect and set the scope accordingly.
6 If all this is above you use Autoset.

To get real info from any scope you must drive it, yes there are several knob adjustments required, learn them.



Edit
Added "DSO"
« Last Edit: April 29, 2016, 10:15:20 pm by tautech »
Avid Rabid Hobbyist
 

Offline hans

  • Super Contributor
  • ***
  • Posts: 1038
  • Country: nl
Re: DS1054Z distortion issue?
« Reply #58 on: April 29, 2016, 10:22:58 pm »
Reading some of the comments here make me almost cry inside because of it's ignorance.


If still you think making measurements with periodically clamped signals is an invalid use-case of a oscilloscope, please explain a productive (not just functional) way to make said measurement without fiddling around the knobs half a dozen times every trigger attempt. Because in my experience these are user error prone and frustrating to do.

Scopes have horizontal zoom functions, why not vertical? Why not capture scope at 1V/div, and display it at say 100mV/div?
General DSO comments, all brands.

1 Know the limitations of your instrument.
2 Learn the capabilities of your instrument.
3 For accurate representation of waveforms keep them within the confines of the display at all times.(excepting captures)
4 The triggering suite in your scope is the most powerful tool you have, use it.
5 Before connection attempt to deduce the waveform you expect and set the scope accordingly.
6 If all this is above you use Autoset.

To get real info from any scope you must drive it, yes there are several knob adjustments required, learn them.



Edit
Added "DSO"

I think you misunderstood the meaning of my post.

Having to fiddle 6 knobs to make 1 measurement, and then doing it all over again 2 minute later after a change is not productive. That is my view on it anyway - I'm fine turning all the knobs a hundred times on an oscilloscope to find, lock and explain the details I am looking for (I disgust auto set), but not when I'm measuring 1 quantity repeatably in a very limited changing environment while still needing to make adjustments back and forth for the scope to work. This level of interface is maybe acceptable for some, but not for me.

Like I said, a vertical zoom level would be most helpful. Unfortunately the Rigol does not have this feature (like nctnico explained) - changing vertical settings in "zoom" mode also changes vertical level of acquisition. In the test signal I referred to, the dynamic range of interest is only 1:25 or so (there are other current pulses swamped in the noise of the scope though). 1:25 is still measurable on a 8-bit ADC, but not good for eye fatigue if you want to make horizontal measurements on 1/5 of a division.

Unfortunately, my measurement shows the limitations of the oscilloscope very clearly. I can't have vertical acquisition zoom in, or it will cause overdrive and make any measurements post-overdrive impossible. If I don't zoom any, any horizontal measurements are hard to make (unless the turning-a-dozen-knobs-every-2-minutes story), and vertical are downright inaccurate to any satisfactory level (unless you want >10% error).
« Last Edit: April 29, 2016, 10:27:58 pm by hans »
 

Offline tom66

  • Super Contributor
  • ***
  • Posts: 3449
  • Country: gb
  • Electronic Engineer & Hobbyist
Re: DS1054Z distortion issue?
« Reply #59 on: April 29, 2016, 10:45:06 pm »
The 1054Z only has a single attenuator range, indicated by the relay click, which is why the distortion occurs only past a certain point.
 

Offline tautech

  • Super Contributor
  • ***
  • Posts: 15688
  • Country: nz
  • Taupaki Technologies Ltd. NZ Siglent Distributor
    • Taupaki Technologies Ltd.
Re: DS1054Z distortion issue?
« Reply #60 on: April 29, 2016, 10:59:49 pm »
I think you misunderstood the meaning of my post.
Maybe.
You mean this post?
https://www.eevblog.com/forum/testgear/new-rigol-ds1054z-oscilloscope/msg868911/#msg868911

Quote
Having to fiddle 6 knobs to make 1 measurement, and then doing it all over again 2 minute later after a change is not productive. That is my view on it anyway - I'm fine turning all the knobs a hundred times on an oscilloscope to find, lock and explain the details I am looking for (I disgust auto set), but not when I'm measuring 1 quantity repeatably in a very limited changing environment while still needing to make adjustments back and forth for the scope to work. This level of interface is maybe acceptable for some, but not for me.
Me too.

But there are other ways to make these measurements.
100:1 probes
Current probes.



Quote
Like I said, a vertical zoom level would be most helpful. Unfortunately the Rigol does not have this feature (like nctnico explained) - changing vertical settings in "zoom" mode also changes vertical level of acquisition. In the test signal I referred to, the dynamic range of interest is only 1:25 or so (there are other current pulses swamped in the noise of the scope though). 1:25 is still measurable on a 8-bit ADC, but not good for eye fatigue if you want to make horizontal measurements on 1/5 of a division.
Filters can be useful.

Quote
Unfortunately, my measurement shows the limitations of the oscilloscope very clearly. I can't have vertical acquisition zoom in, or it will cause overdrive and make any measurements post-overdrive impossible. If I don't zoom any, any horizontal measurements are hard to make (unless the turning-a-dozen-knobs-every-2-minutes story), and vertical are downright inaccurate to any satisfactory level (unless you want >10% error).
I disagree.

Not all instruments will easily deliver the measurements you need, when they don't/won't it's time for other solutions and they might include investment in other scope accessories.

Most measurement is easy, how you solve the trickier ones is partly experience, available tools and full use of the functionality within your scope.
Avid Rabid Hobbyist
 

Offline alsetalokin4017

  • Super Contributor
  • ***
  • Posts: 1873
  • Country: us
Re: DS1054Z distortion issue?
« Reply #61 on: April 30, 2016, 12:59:14 am »
Why don't you tell us, Mr. self-appointed Rigol expert? The schematic is out there.
I've never claimed to be a Rigol expert.  I'm a USER of this model scope-- at least I try to use its features and functions, in spite of its many problems. My post points out that we may not be justified in having supreme confidence in the hardware design, bearing in mind the many software problems that plague this model scope.

The problem being discussed applies to many more oscilloscopes than Rigol but you came in here with your usual Rigol-bashing post.

(and not just oscilloscopes, it's a general problem with op-amps)

1. Read the title of this thread.  Certainly, if you overdrive "many more" oscilloscopes they will exhibit similar behaviour. But this thread started out being about the problem as shown in the Rigol DS1054z scope, not "many more" scopes or op-amps. Several people agree that using a scope -- "many more" scopes in fact -- in this way will produce similar garbage results.

My point, which you seem deliberately to miss, is that this usage might even put the RIGOL DS1054z scope's inputs at risk of permanent damage, which is not likely to be covered under warranty, as it is a misuse or user error.  Do YOU have the confidence to test YOUR DS1054z with a maximum voltage input, then zooming in to extremely sensitive vertical resolution? If you do, fine, demonstrate it. I base my _lack_ of confidence and my caution on my experience with the scope. Go ahead and prove that my lack of confidence is not justified, by performing your own tests and demonstrations and reporting them, on your RIGOL DS1054z. By the way, just so you know, I have blown an input FET and pin diode on my Tek 2213a (and repaired it).

2. Rigol bashing? You're funny.   :box:    Should I remain silent about bugs that I find in normal use of the scope? Normal, for me, involves using many of the scope's features properly and expecting to get valid results, and I realize that this isn't normal for you, based on your previous posts. You seem to be in the group that thinks a 400 dollar scope only needs to light up and display a trace or two from a function generator to be worth what you paid for it. If so, fine, that's your opinion. Me, I think a scope that can display 5 bugs simultaneously, including three _invalid_ readings, may not be totally confidence-inspiring, no matter how cheaply the manufacturer chooses to sell it for.  Is this "Rigol-bashing" according to your definition?  I laugh at you, while I continue to use my DS1054z every day in my daily benchwork. 


The screenshot I posted above shows these bugs, all of which are present in scopes running the SP2 firmware:
1. Non-zero RMS voltage indicated on a channel that has no inputs and is grounded.
2. "Pluses" spelling error.
3. Pulses miscounted.
4. Math horizontal timing error at 500 ns/div, Average acquisition mode.
5. Measurements are frozen, not updating, requires power-cycling to restore any measurement functions.

Rigol-bashing? Not at all. Buy the scope and use it. But be aware, and wary, of its failings. If you want to overdrive the inputs, that's your business; I still think it's "scope abuse" and will avoid it on _my_ DS1054z, because I depend on it in my workshop and don't want to take the chance of _yet another_  return. 

The easiest person to fool is yourself. -- Richard Feynman
 
The following users thanked this post: Marcos

Offline tggzzz

  • Super Contributor
  • ***
  • Posts: 9649
  • Country: gb
    • Having fun doing more, with less
Re: DS1054Z distortion issue?
« Reply #62 on: April 30, 2016, 07:09:20 am »
My point, which you seem deliberately to miss, is that this usage might even put the RIGOL DS1054z scope's inputs at risk of permanent damage, which is not likely to be covered under warranty, as it is a misuse or user error.  Do YOU have the confidence to test YOUR DS1054z with a maximum voltage input, then zooming in to extremely sensitive vertical resolution? If you do, fine, demonstrate it. I base my _lack_ of confidence and my caution on my experience with the scope. Go ahead and prove that my lack of confidence is not justified, by performing your own tests and demonstrations and reporting them, on your RIGOL DS1054z.

What mechanism do you propose for that assertion?

The input amplifiers are standard, with the standard overvoltage protection. They will fail if the stated maximum input voltage is exceeded, but that's reasonable and to be expected. Later stages are unlikely to be damaged by an internal voltage saturating, unless you have a specific reason to believe otherwise.

I'm certainly not going to defend Rigol, but why pluck imagined hypothetical faults out of thin air when there are significant real faults?

If you have a reason to believe such damage could occur, then I'll listen. Otherwise you contaminate your other (probably valid) points.
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
 

Offline Texacate

  • Contributor
  • Posts: 19
  • Country: us
Re: DS1054Z distortion issue?
« Reply #63 on: April 30, 2016, 07:12:22 am »
I would like to thank the original poster for bringing up an issue which, on the surface, looked like bad distortion in the 1054Z.  Despite some of the subsequent posts getting a bit snippy, I have actually learned thing or two about using my DS0.  Especially concerning overdriving the inputs.  Good stuff to keep in mind.  Thanks for raising the issue up.
 

Offline Performa01

  • Frequent Contributor
  • **
  • Posts: 799
  • Country: at
Re: DS1054Z distortion issue?
« Reply #64 on: April 30, 2016, 08:26:57 am »
Look again. Start with the discrete components in the input stage signal path. Then move onto looking inside the ICs such as the LMH6552 (or similar), and others.

Why should I do this? If there are active discrete components not just dedicated to some auxiliary task, well, then there is a discrete amplifier, but it’s still just an amplifier.

The LMH6552 is just a differential amplifier – albeit a very good one. Neither does the datasheet include any circuit details for its proprietary differential current mode input stage architecture, nor do I get the point why to analyze the internals of an IC, all the more so as it’s not even used in the Rigol DS1000Z.

In a scope like the DS1000Z, we have a total of two amplifiers: the input buffer and the PGA.
Anything else not in the signal path, like all the amplifiers dedicated to the DC offset generation, is purely auxiliary and irrelevant when we’re looking for distortion.


Quote
Hint: all oscilloscopes have multiple amplifiers, some in series and some in parallel.

Hint: While you can connect any two-terminal-pair networks in series or parallel in principle, I have never seen any practical application of this with amplifiers in a scope.

So we’re rather talking about cascading amplifiers, when we connect the output of the first one to the input of the next one.

And we use split-path amplifiers if we have to process several frequency bands differently, such as in a scope frontend where we want to have wide bandwidth and high DC accuracy at the same time – a principle introduced by Tektronix in the early 70s of the last century.

So we still have a total of two amplifiers: A split path input buffer and a PGA.


Quote
Quote
Apart from that, I'm pretty sure even the Rigol DS1000Z will have some clamping diodes at the input - just clamping to the supply rails instead to a specific voltage level that prevents the amplifier from leaving its specified common mode range.

They do have diodes, just like other low-end scopes. But they are nothing whatsoever to do with common mode ranges.

Diodes have nothing to do with low end. Rigol resembles pretty closely what has been published by Tektronix around 1971, who of course have used protection diodes as well - and these scopes were certainly high end back then.

Other than that, not sure why you felt like repeating what is already quoted, i.e. that there are most likely diodes, but only for the sake of input protection. And of course, for a single ended JFET buffer, there is no common mode range. But for any differential amplifier there is.

Anyway as I had a closer look in the meantime, it might be that the DS1000Z only protects the discrete HF path, but leaves the LF path (with the OpAmp) alone. But on the HF path they might have even done the right thing, as the diodes are actually used as limiters here. Only question is, if it always works as intended, given the high manufacturing tolerances of the JFET behind.

This could explain why the distortion effect is worse at lower frequencies, as the OP seems to indicate.

Maybe someone could test this at frequencies >10MHz?


Quote
Have a look at ... or similar; if you spot what you are thinking of, please point to it.

I had a look at the schematics – and I might post some analysis later.
 

Offline hans

  • Super Contributor
  • ***
  • Posts: 1038
  • Country: nl
Re: DS1054Z distortion issue?
« Reply #65 on: April 30, 2016, 08:40:17 am »
Maybe.
You mean this post?
https://www.eevblog.com/forum/testgear/new-rigol-ds1054z-oscilloscope/msg868911/#msg868911
Yes that is the one.
Most of those screenshots were added to illustrate the limitation.
Quote
Me too.

But there are other ways to make these measurements.
100:1 probes
Current probes.
[..]
Filters can be useful.
Yes there are alternatives and supplements to measurements units. Unfortunately, as a hobbyist on a budget, I do not have access to those. Hence the purchase of a "budget" 4-ch scope like the Rigol DS1000Z. Filters can help in cleaning up signal of DUT, but averaging works best when the scope can retrigger often (in this case the waveform only repeats at 1-2x a second).

Quote
I disagree.

Not all instruments will easily deliver the measurements you need, when they don't/won't it's time for other solutions and they might include investment in other scope accessories.

Most measurement is easy, how you solve the trickier ones is partly experience, available tools and full use of the functionality within your scope.

Yes I can see what you're trying to say. The scope is a powerful instrument because of the 'many knobs' and supplements available. :) It's just unfortunate the Rigol/DSO's hits a brick wall when you're exposing it to brief vertical overdrive to make a measurement. I read upon Jim Williams application note (AN79 Appendix A I believe?) for this purpose to determine settling time; and his weapon of choice was an old-style sampling oscilloscope. It has the clamping diodes right at the input, which will only clamp when close to the instrument's absolute maximum instead of the maximum for vertical sensitivity selected.

Arguably this scope is not the best weapon of choice for my measurement, because of the high-dynamic range of DUT. At the time I was working on a power meter board (which has that 16-bit fast ADC), that I expanded in the subsequent days to do these horizontal measurements for me automatically. See attached screenshots for a similar DUT. The blue area can be activated by DUT (an extra digital on/off input) to mark area's and measure time-length and energy of those area's automatically. This gives satisfactory results for my purpose; but then again it's unfair to compare both 'instruments', they were designed for different purposes.
 

Offline pxl

  • Regular Contributor
  • *
  • Posts: 126
  • Country: hu
Re: DS1054Z distortion issue?
« Reply #66 on: April 30, 2016, 09:15:33 am »
But there are other ways to make these measurements.
100:1 probes

Well, it is just worst with 1:100 probes. Here are the limits, when this phenomenon starts to occur (again, HMO1002), 0-10 V, square wave:

BNC: 242 mV -> 8.1x zoom
1:10: 121 mV (adjusted value to the probe) -> 16.2x zoom
1:100: 1.21 V (also adjusted)-> 1.6x zoom

In this regard and range, the 1:100 probe is the worst by far, actually, you can't zoom 1 step without distortions. With the 1:10 probe, however, I have pretty awesome range without any distortions, and after that the distortions are much smaller than with straight connection.

Which essentially means, this vertical zooming method is perfectly works in a useful range with 1:10 probes. I don't have 300 V square wave to test, sorry, there are no problems with mains, though  :popcorn:
« Last Edit: April 30, 2016, 09:18:55 am by pxl »
 

Offline tautech

  • Super Contributor
  • ***
  • Posts: 15688
  • Country: nz
  • Taupaki Technologies Ltd. NZ Siglent Distributor
    • Taupaki Technologies Ltd.
Re: DS1054Z distortion issue?
« Reply #67 on: April 30, 2016, 09:48:41 am »
But there are other ways to make these measurements.
100:1 probes
Current probes.
Yes there are alternatives and supplements to measurements units. Unfortunately, as a hobbyist on a budget, I do not have access to those. Hence the purchase of a "budget" 4-ch scope like the Rigol DS1000Z.
Budget has little to do with it, purchase of a DSO is just the start.....liken it to having a tractor without attachments/implements, you have the engine and wheels but not all the tools to actually do a job.  :scared:

Accessories of the likes of Differential, Current, Active and HV (100x +) probes are essential to gain full use of a scope. Period.

Most measurement is easy, how you solve the trickier ones is partly experience, available tools and full use of the functionality within your scope.

Yes I can see what you're trying to say. The scope is a powerful instrument because of the 'many knobs' and supplements available.

Arguably this scope is not the best weapon of choice for my measurement......
You sound defeated, you shouldn't be, think of it as a challenge and the opportunity to learn new tricks.  ;)
I can't see any reason why you can't get the measurements you require with any reasonably modern DSO like the 1054, really I can't.

From the images I've seen there are several levels and durations of current pulses, each of which can be targeted with trigger levels and/or pulse duration trigger settings to obtain Single shot captures than then can be analysed.
This is how I've broken down my measurement requirements in the past with DSO's far less capable than a 1054.
Avid Rabid Hobbyist
 

Offline tautech

  • Super Contributor
  • ***
  • Posts: 15688
  • Country: nz
  • Taupaki Technologies Ltd. NZ Siglent Distributor
    • Taupaki Technologies Ltd.
Re: DS1054Z distortion issue?
« Reply #68 on: April 30, 2016, 09:57:08 am »
But there are other ways to make these measurements.
100:1 probes

Well, it is just worst with 1:100 probes. Here are the limits, when this phenomenon starts to occur (again, HMO1002), 0-10 V, square wave:

BNC: 242 mV -> 8.1x zoom
1:10: 121 mV (adjusted value to the probe) -> 16.2x zoom
1:100: 1.21 V (also adjusted)-> 1.6x zoom

In this regard and range, the 1:100 probe is the worst by far, actually, you can't zoom 1 step without distortions. With the 1:10 probe, however, I have pretty awesome range without any distortions, and after that the distortions are much smaller than with straight connection.

Which essentially means, this vertical zooming method is perfectly works in a useful range with 1:10 probes. I don't have 300 V square wave to test, sorry, there are no problems with mains, though  :popcorn:
WRT Hans' problem, I'm guessing he's measuring across a shunt as the screenshots are of voltages and to reduce the p-p input is why I offered the suggestion of 100x probes. That they might not be helpful in his or another case is accepted, they are just one of the tools required to extend a DSO's usefulness.  ;)
Avid Rabid Hobbyist
 

Offline pxl

  • Regular Contributor
  • *
  • Posts: 126
  • Country: hu
Re: DS1054Z distortion issue?
« Reply #69 on: April 30, 2016, 11:15:16 am »
Here are the limits, when this phenomenon starts to occur (again, HMO1002), 0-10 V, square wave:

BNC: 242 mV -> 8.1x zoom
1:10: 121 mV (adjusted value to the probe) -> 16.2x zoom
1:100: 1.21 V (also adjusted)-> 1.6x zoom

@tautech, I wonder, how the SDS2000X behaves with the above premises. I am still looking for a 4ch scope :)
 

Offline tggzzz

  • Super Contributor
  • ***
  • Posts: 9649
  • Country: gb
    • Having fun doing more, with less
Re: DS1054Z distortion issue?
« Reply #70 on: April 30, 2016, 11:28:08 am »
Look again. Start with the discrete components in the input stage signal path. Then move onto looking inside the ICs such as the LMH6552 (or similar), and others.
Why should I do this? If there are active discrete components not just dedicated to some auxiliary task, well, then there is a discrete amplifier, but it’s still just an amplifier.

Sigh. Deliberately and repeatedly deleting the relevant parts of the context, i.e. your incorrect assertions, doesn't inspire confidence in yout arguments. Here is a repeat of the context, so you can see why it would benefit your argument...
Well, some scope vendors don't need to, as with proper design all these nasty things will not happen in the first place. It's just a matter of having a proper limiter at the input of the amplifier, preventing it to get overloaded.
Note your key incorrect assertion: "just a matter...". That was then followed by...
Plus, of course, there are many amplifiers in a scope, any of which could be overloaded. "Protection" would require many non-linear elements in the signal path, which is even more problematic!
No, there aren't. Neither many amplifiers, nor particular non-linear elements.
There are many amplifiers, and theyu all contain non-linear components. And any of them can be overloaded when an internal node saturates. Another example of that is, of course, slew rate limiting.

Quote
The LMH6552 is just a differential amplifier – albeit a very good one. Neither does the datasheet include any circuit details for its proprietary differential current mode input stage architecture, nor do I get the point why to analyze the internals of an IC, all the more so as it’s not even used in the Rigol DS1000Z.

In a scope like the DS1000Z, we have a total of two amplifiers: the input buffer and the PGA.
Anything else not in the signal path, like all the amplifiers dedicated to the DC offset generation, is purely auxiliary and irrelevant when we’re looking for distortion.

And either or both of those can introduce distortion - just as in almost all scopes. Limiting the input voltage, which was your assertion, simply cannot avoid that.

Quote
Quote
Hint: all oscilloscopes have multiple amplifiers, some in series and some in parallel.
Hint: While you can connect any two-terminal-pair networks in series or parallel in principle, I have never seen any practical application of this with amplifiers in a scope.

Sigh. You contradict yourself lower down in the your same posting! So, yes, you have seen exactly that.

Quote
So we’re rather talking about cascading amplifiers, when we connect the output of the first one to the input of the next one.

And we use split-path amplifiers if we have to process several frequency bands differently, such as in a scope frontend where we want to have wide bandwidth and high DC accuracy at the same time – a principle introduced by Tektronix in the early 70s of the last century.

So we still have a total of two amplifiers: A split path input buffer and a PGA.


Quote
Quote
Apart from that, I'm pretty sure even the Rigol DS1000Z will have some clamping diodes at the input - just clamping to the supply rails instead to a specific voltage level that prevents the amplifier from leaving its specified common mode range.

They do have diodes, just like other low-end scopes. But they are nothing whatsoever to do with common mode ranges.

Diodes have nothing to do with low end. Rigol resembles pretty closely what has been published by Tektronix around 1971, who of course have used protection diodes as well - and these scopes were certainly high end back then.

Other than that, not sure why you felt like repeating what is already quoted, i.e. that there are most likely diodes, but only for the sake of input protection. And of course, for a single ended JFET buffer, there is no common mode range. But for any differential amplifier there is.

Anyway as I had a closer look in the meantime, it might be that the DS1000Z only protects the discrete HF path, but leaves the LF path (with the OpAmp) alone. But on the HF path they might have even done the right thing, as the diodes are actually used as limiters here. Only question is, if it always works as intended, given the high manufacturing tolerances of the JFET behind.

This could explain why the distortion effect is worse at lower frequencies, as the OP seems to indicate.

Maybe someone could test this at frequencies >10MHz?


Quote
Have a look at ... or similar; if you spot what you are thinking of, please point to it.
I had a look at the schematics – and I might post some analysis later.
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
 

Offline tautech

  • Super Contributor
  • ***
  • Posts: 15688
  • Country: nz
  • Taupaki Technologies Ltd. NZ Siglent Distributor
    • Taupaki Technologies Ltd.
Re: DS1054Z distortion issue?
« Reply #71 on: April 30, 2016, 11:41:41 am »
Here are the limits, when this phenomenon starts to occur (again, HMO1002), 0-10 V, square wave:

BNC: 242 mV -> 8.1x zoom
1:10: 121 mV (adjusted value to the probe) -> 16.2x zoom
1:100: 1.21 V (also adjusted)-> 1.6x zoom

@tautech, I wonder, how the SDS2000X behaves with the above premises. I am still looking for a 4ch scope :)
I haven't got mine yet, I have only the 2304 that I've had for a couple of years.
SDS2304X ordered and paid for, just waiting to be included in my next stock order.  :)

Getting late now here, if I get a chance tomorrow......
Avid Rabid Hobbyist
 

Offline hans

  • Super Contributor
  • ***
  • Posts: 1038
  • Country: nl
Re: DS1054Z distortion issue?
« Reply #72 on: April 30, 2016, 12:04:43 pm »
You sound defeated, you shouldn't be, think of it as a challenge and the opportunity to learn new tricks.  ;)
I can't see any reason why you can't get the measurements you require with any reasonably modern DSO like the 1054, really I can't.

From the images I've seen there are several levels and durations of current pulses, each of which can be targeted with trigger levels and/or pulse duration trigger settings to obtain Single shot captures than then can be analysed.
This is how I've broken down my measurement requirements in the past with DSO's far less capable than a 1054.

I not meant to sound defeated; I think I was yesterday a bit more tetchy than I am now. :=\

I understand scope accessories are great to have. But I'm not rushing out to spend threefold or more Rigol-money on 1 current probe that is used less than any other equipment in my home lab. And that is all budget related. Not everyone has hundreds of dollars of dispensable income or relates to lend equipment suited for 1 job.

These are not high voltages, so I don't see the use of a 1:100 probe.
I'd rather have a 1:0.1 differential probe or better.. but those are not cheap, not even on Ebay.

The DSO measurements shown earlier are the output from an instrumentation amplifier. It amplifies a voltage drop of 10 ohm 0.1% shunt (high-side) by 1, 10, 100 or 1000x. At 10x (100mV/mA) it has a -3dB bandwidth of 4MHz, and at 100x (1V/mA) 550kHz. In effect this is quite a nice DC current probe for a DSO.

However, I want to emphasize the limit of dynamic range once more. I can use all high-res and averaging I want; but the Rigol only has memory to store 8-bits per sample and high-res or averaging will not fix that. It will only get rid of the noise.  With a peak current of 25mA and zooming into details smaller than 'hundreds of uA', those details are smaller than 1-2 LSB and are a straight line on the screen.
To examine those details I need to capture at a higher vertical sensitivity. That is fine for measurements pre-peak, but post-peak the scope inputs were overdriven (especially with 1x probes) so any (absolute) measurements become inaccurate. Trigger is not a problem, if needed I can set up a digital trigger signal from the microcontroller at any stage of the test sequence. It is just a limitation of 8-bit vertical resolution & not being able to make measurements with overdriven inputs.

It is probably also a niche thing what I am trying to do (scopes have 3% vertical accuracy any way) and so probably an application for higher-resolution ADC instruments like higher-end bench scopes, USB scopes etc. In that case I don't have to overdrive inputs to be able to capture the minuscule details. I don't have a 10-bit or better scope either, so instead I built a solution my self. Building test equipment is both fun and also an learning experience for a whole range of skill sets.
« Last Edit: April 30, 2016, 12:06:21 pm by hans »
 

Offline Fungus

  • Super Contributor
  • ***
  • Posts: 9875
  • Country: 00
Re: DS1054Z distortion issue?
« Reply #73 on: April 30, 2016, 12:34:40 pm »
The problem being discussed applies to many more oscilloscopes than Rigol but you came in here with your usual Rigol-bashing post.

(and not just oscilloscopes, it's a general problem with op-amps)
As alsetalokin4017 owns one, has found bugs in it, struggles with trust of it, has documented such,  he has more right than most to offer comment. That you take it as personal is a surprise  :-// are you Rigol's knight in shining armour?

If he wants to start his own thread about spelling mistakes in the menu, etc., he's free to do so (there may be one already).

But that isn't what's being discussed here. This discussion was about a problem that potentially affects all DSOs.

There's a couple of people who try to hijack every oscilloscope related thread and turn it into a DS1054Z-hating thread. I don't see any need for it.


« Last Edit: April 30, 2016, 12:42:25 pm by Fungus »
 

Offline Fungus

  • Super Contributor
  • ***
  • Posts: 9875
  • Country: 00
Re: DS1054Z distortion issue?
« Reply #74 on: April 30, 2016, 12:48:41 pm »
Having to fiddle 6 knobs to make 1 measurement, and then doing it all over again 2 minute later after a change is not productive. That is my view on it anyway - I'm fine turning all the knobs a hundred times on an oscilloscope to find, lock and explain the details I am looking for (I disgust auto set), but not when I'm measuring 1 quantity repeatably in a very limited changing environment while still needing to make adjustments back and forth for the scope to work. This level of interface is maybe acceptable for some, but not for me.

The reality of manufacturing/marketing is that you're an edge case. This problem could be solved in entry level DSOs but at the risk of going out of business because the resulting instruments would be unsalable to most people (they'd cost a lot more).

If you need this function a lot and all the fiddling is costing you money then you either need a more specialized oscilloscope or some sort of front-end adapter to clamp the signals before they even reach the oscilloscope (a fun project?)
« Last Edit: April 30, 2016, 12:54:45 pm by Fungus »
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf