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Offline hrothulf

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DS1054Z distortion issue?
« on: April 27, 2016, 04:15:29 PM »
Can anyone else replicate this effect?
Or is my new DS1054Z defective?

I have been unable to replicate this behavior on an older TDS-210 scope.
Thank you for any assistance in understanding this issue.

I've skimmed most of the big DS1054Z thread and tried to search the forum, but have not found anyone with quite the same issue.
This post was the closest to similar issue I found, but it seemingly had no replies.
http://www.eevblog.com/forum/testgear/new-rigol-ds1054z-oscilloscope/msg868911/#msg868911

The effect occurs on both the positive and the negative sides of the signal.
The issue occurs on all four scope channels. Seemingly identical.

The signal will change shape when changing vertical scale at 500mV and 750mV (in 10x mode).
Changing the signal vertical-offset will change the shape of the signal.

Rings at lower frequency square-wave, but attenuates at higher frequency.
Strangely attenuation doesn't vary much from 1kHz to 1Mhz.
10V square-wave turns into ~6V square-wave.

It seems like maybe signals smaller in amplitude than ~6-volt peak-to-peak (10x-mode) are immune from this issue.

All of the below measurements were taken in 10x-mode with an RP2200 probe.
Can get the same effect with 600mV+ peak-to-peak sine-wave or square-wave in 1x-mode.
Internal 1kHz square-wave gives attenuation effect with 1x-mode probe.
At 50mV vert-scale (1x-mode) internal 1kHz square-wave is min 1.07V, max 1.77V, or ~0.70V peak-to-peak.
At 500mV vert-scale (1x-mode) internal 1kHz square-wave is min -40mV, max 2.98V, ~3.00V peak-to peak.

5V 10Hz sine-wave (+5V to +10V) [seems fine]
6V 10Hz sine-wave (+4.5V to +10.5V) [only top slightly bad?]
6V 10Hz sine-wave (+8V to +14V) [only top slightly bad?]
7V 10Hz sine-wave (+4V to +11V) [top and bottom bad]
7V 10Hz sine-wave (-7V to 0V) [top and bottom bad]
7V 10Hz sine-wave (-12V to -5V) [top and bottom bad]
6V 10Hz sine-wave (-12V to -6V) [top and bottom slightly bad]
5V 10Hz sine-wave (-12V to -7V) [seems fine]

±5V 10Hz sine-wave (-5V to +5V) [bad]
±4V 10Hz sine-wave (-4V to +4V) [bad]
±3.5V 10Hz sine-wave (-3.5V to +3.5V) [bad]
±3V 10Hz sine-wave (-3V to +3V) [seems fine]
+10V 10Hz sine-wave (0V to +10V) [bad]
+10V 10Hz square-wave (0V to +10V) [bad]
±5V 10Hz sawtooth (-5V to +5V) [bad]

±5V 100Hz square-wave (-5V to +5V) [bad]
+10V 100Hz square-wave (0V to +10V) [bad]
+5V 100Hz square-wave (0V to +5V) [seems fine]

See attached pictures...
 

Online ataradov

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Re: DS1054Z distortion issue?
« Reply #1 on: April 27, 2016, 05:00:31 PM »
What is your signal source? I would start looking at impedance mismatch. Your frequencies are kind of low, but who knows.
Alex
 

Online borjam

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Re: DS1054Z distortion issue?
« Reply #2 on: April 27, 2016, 05:02:38 PM »
Found it.

Have a look at this reply and the linked PDF. Vertical zoom is limited by the A/D resolution and dynamic range.


http://www.eevblog.com/forum/testgear/ds1074z-zoom-bug/msg454067/#msg454067
 

Online ataradov

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Re: DS1054Z distortion issue?
« Reply #3 on: April 27, 2016, 05:13:40 PM »
Have a look at this reply and the linked PDF. Vertical zoom is limited by the A/D resolution and dynamic range.
But how I don't see how this can cause sine wave glitches.
Alex
 

Online borjam

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Re: DS1054Z distortion issue?
« Reply #4 on: April 27, 2016, 05:20:41 PM »
Distortion, being non-linear, can sometimes be difficult to figure out. The glitches are curious indeed, but get much more significant when the DC offset is increased.

It can be a compound effect of vertical amplifier distortion *and* A/D converter overdrive. And maybe other more expensive scopes with a better dynamic range in the vertical amplifier will suffer of a less dramatic effect.

Other scopes specify the vertical amplifier dynamic range in +- divisions, but I haven't found that data for the Rigols. (I'm a DS1074Z owner).
 

Online tautech

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Re: DS1054Z distortion issue?
« Reply #5 on: April 27, 2016, 06:05:36 PM »
In ALL cases except the one below the result is because of user error.
Until you know how to use a DSO correctly I suggest you use Autoset to get waveforms to be displayed correctly.



See if you can pick the differences in settings (several) between the above and ALL the others that are wrong.
« Last Edit: April 27, 2016, 06:20:00 PM by tautech »
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Offline jitter

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Re: DS1054Z distortion issue?
« Reply #6 on: April 27, 2016, 06:06:54 PM »
Have a look at this reply and the linked PDF. Vertical zoom is limited by the A/D resolution and dynamic range.
But how I don't see how this can cause sine wave glitches.

I'm reading the document from the other thread.
Overdriving the vertical amplifier causes distortions, as borjam mentions, but the pdf also mentions overdrive recovery. Now to me this should not be a problem on such slow signals, but do we know how well or bad these Rigols perform on this spec? Do they even spec it?

I have a DS1074Z-S on which I can also create nasties in the signal by overdriving it, so as an answer to the OP, I don't think your scope is defective.

And the solution Agilent (yes, not yet Keysight in this document) presents is quite logical: don't overdrive the input. Capture the full wave inside the dynamic range of the scope and make use of DSO functions as averaging and zooming. This Rigol should be able to do that as well...

Oh, and the otherwise dry paper concludes with a bit of humor:
Quote
Conclusion
There is a familiar American joke where a patient says to his doctor, “Doctor, it hurts when I bang my head against the wall.” The doctor then responds, “Well then, don’t bang your head against the wall.”
The same could be said about the problems associated with overdriving a scope’s input amplifier. If you don’t want to make inaccurate measurements, then don’t overdrive the amplifier! Use waveform averaging and digital magnification to make the most accurate measurements on signal perturbations, whether you are using a Tektronix, LeCroy, or Agilent high-speed oscilloscope[/url]
« Last Edit: April 27, 2016, 06:19:37 PM by jitter »
 

Online borjam

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Re: DS1054Z distortion issue?
« Reply #7 on: April 27, 2016, 06:15:48 PM »
Anyway the excellent Agilent note says clearly: "do not overdrive" :)

The conclusion is clear and it indeed applies to cheap oscilloscopes as well!

There is a familiar American
joke where a patient says to his doctor, “Doctor, it hurts when I bang my head against the wall.” The doctor then responds, “Well then, don’t bang your head against the wall.” The same could be said about the problems associated with overdriving a scope’s input amplifier. If you don’t want to make inaccurate measurements, then don’t overdrive the amplifier! Use waveform averaging and digital magnification to make the most accurate measurements on signal perturbations, whether you are using a Tektronix, LeCroy, or Agilent high-speed oscilloscope.



And I admit to falling to this error several weeks ago, when I just unboxed my shiny new DS1074Z, until I realized that I was just being naive. Limited resolution, limited dynamic range. The moral of this story is: never consider your instruments magic boxes, always have their limitations in mind!

« Last Edit: April 27, 2016, 06:21:34 PM by borjam »
 

Offline jitter

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Re: DS1054Z distortion issue?
« Reply #8 on: April 27, 2016, 06:16:43 PM »
Argh, you beat me to it (my edit)  by 11 seconds ;)

I wonder how much affected analogue scopes are by overdriving...
« Last Edit: April 27, 2016, 06:18:55 PM by jitter »
 

Online borjam

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Re: DS1054Z distortion issue?
« Reply #9 on: April 27, 2016, 06:24:16 PM »
Argh, you beat me to it (my edit)  by 11 seconds ;)

I wonder how much affected analogue scopes are by overdriving...
Hahaha, the quote is really briliant.

Analog oscilloscopes can be more forgiving (been ages since I played with one) because you don't have an A/D converter with a brickwall limit.

 

Offline jitter

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Re: DS1054Z distortion issue?
« Reply #10 on: April 27, 2016, 07:03:22 PM »
True, but there will still be a front end amplifier to saturate...
Think I will break out my old analogue scope and experiment a litlle...
 

Online tggzzz

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Re: DS1054Z distortion issue?
« Reply #11 on: April 27, 2016, 07:24:43 PM »
I wonder how much affected analogue scopes are by overdriving...

Depends on the scope, of course!

Read Jim Williams about some of his Tek scopes to find out which are best for examining op-amp settling behaviour and recovery. Those applications require overdriving, since you are observing what happens in the region of, say 10V+-10mV.

Scopes with sampling heads are very good because they "ignore" the signal when the signal isn't being sampled.
There are lies, damned lies, statistics - and ADC/DAC specs.
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Offline alsetalokin4017

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Re: DS1054Z distortion issue?
« Reply #12 on: April 27, 2016, 07:29:56 PM »
In ALL cases except the one below the result is because of user error.
Until you know how to use a DSO correctly I suggest you use Autoset to get waveforms to be displayed correctly.



See if you can pick the differences in settings (several) between the above and ALL the others that are wrong.

Arghhh....    :palm:    This is exactly right. I cringed when I looked at the example scopeshots. User error! Garbage out, due to _setting the scope_ improperly for the signal applied. Channel baseline set way off screen, and vertical scale set way too low (too sensitive) for the amplitude of the signals fed into the channel.
 
Why oh why would someone deliberately do this? There are only a few applications that actually _require_ overdriving to examine small bits of the vertical range of a signal, and I've always been very leery of doing this myself.
 
When scoping a signal of unknown amplitude I think one would normally start with V/div setting at the maximum high end (insensitive) and step down until a reasonable display is obtained, with the entire waveform vertically on-screen without clipping.
The easiest person to fool is yourself. -- Richard Feynman
 

Offline pxl

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Re: DS1054Z distortion issue?
« Reply #13 on: April 27, 2016, 07:31:32 PM »
In ALL cases except the one below the result is because of user error.
Until you know how to use a DSO correctly I suggest you use Autoset to get waveforms to be displayed correctly.

Uhmm, pardon? I am the only one who thinks that these results and distorted waveforms are just unacceptable by any means?
 

Online borjam

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Re: DS1054Z distortion issue?
« Reply #14 on: April 27, 2016, 07:34:33 PM »
In ALL cases except the one below the result is because of user error.
Until you know how to use a DSO correctly I suggest you use Autoset to get waveforms to be displayed correctly.

Uhmm, pardon? I am the only one who thinks that these results and distorted waveforms are just unacceptable by all means?
I think that all of us agree that that distortion makes your measurement useless.

However, I think that most of us agree as well that it's just wrong to ignore the limitations on dynamic range of an instrument. Maybe some instruments can be more lenient than others. But, as the application note explains very well, don't expect that to work wonders with any oscilloscope :) As they say it, it's equivalent to banging your head against a wall.  |O A brickwall it is, as the converter will overdrive.

 

Online tggzzz

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Re: DS1054Z distortion issue?
« Reply #15 on: April 27, 2016, 07:38:30 PM »
In ALL cases except the one below the result is because of user error.
Until you know how to use a DSO correctly I suggest you use Autoset to get waveforms to be displayed correctly.

Uhmm, pardon? I am the only one who thinks that these results and distorted waveforms are just unacceptable by any means?

All equipment on Planet Earth has limitations. Users have to understand the limitations and either live within them or not use the equipment.

If, of course, they can reduce the limitations then they may be able to make money by selling the improvements.

There are lies, damned lies, statistics - and ADC/DAC specs.
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Online borjam

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Re: DS1054Z distortion issue?
« Reply #16 on: April 27, 2016, 07:43:23 PM »
And the effect can be worse with lower frequency signals, as you have more "room" in the scope bandwith to acomodate more higher frequency components due to distortion.
 

Offline Fungus

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Re: DS1054Z distortion issue?
« Reply #17 on: April 27, 2016, 07:56:48 PM »
Uhmm, pardon? I am the only one who thinks that these results and distorted waveforms are just unacceptable by any means?

If I fed an overdriven/clipped signal into an audio amplifier would you declare the output "unacceptable" and not buy that amplifier?

« Last Edit: April 27, 2016, 07:58:44 PM by Fungus »
 

Offline pxl

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Re: DS1054Z distortion issue?
« Reply #18 on: April 27, 2016, 08:12:39 PM »
Uhmm, pardon? I am the only one who thinks that these results and distorted waveforms are just unacceptable by any means?

If I fed an overdriven/clipped signal into an audio amplifier would you declare the output "unacceptable" and not buy that amplifier?

Probably I missed the whole point, I will try to do this on my scope at evening and will back to you.
 

Offline Fungus

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Re: DS1054Z distortion issue?
« Reply #19 on: April 27, 2016, 08:24:31 PM »
Probably I missed the whole point, I will try to do this on my scope at evening and will back to you.

It's an interesting observation and I'm sure people will have fun investigating and explaining it.

Does it make the oscilloscope "unacceptable"? Certainly not.

It will most likely be a product of inductance and/or capacitance that only appears when you overdrive the input amplifier. The only important thing is that there's no distortion on unclipped signals.
 

Offline hrothulf

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Re: DS1054Z distortion issue?
« Reply #20 on: April 28, 2016, 02:22:50 AM »
Thanks for pointing out that this is probably an unreasonable expectation of performance.
I will experiment with the DS1054Z further and make sure it doesn't glitch with most of the signal on-screen.

So the rapid increase in error at the 500mV and 750mV vertical-scale transitions is probably the scope increasing the input amplifier gain and increasing the effective overdrive.
And similarly moving the signal further off the screen at low vertical-scale is increasing the overdrive.

The DS1054Z seems to have rather substantial overdrive recovery time once it starts ringing.
Ringing seems to last around 15-milliseconds or until the (real) signal level goes back down.
So that could explain why it seems worse at lower frequency.
Sweeping the frequency at constant-voltage shows the ring stays the same, but is truncated.
Decreasing voltage at constant-frequency decreases ring amplitude until it suddenly vanishes, but ring time-period remains basically constant.

With a 1V (±0.5V) square-wave (substantially off-screen) toggling from 76mV/div to 75mV/div, the error is ~75mV when the signal is positioned at the top of the screen and ~300mV when the signal is positioned near the bottom (signal more off-screen) so it's just still on screen after it jumps.
This is in 1x-mode, so 750mV transition equivalent in 10x-mode.
But no ringing or other signal shape change, just attenuation.
And then it actually has an increase in signal level at the 51mV/div to 50mV/div scale transition.
Only a few mV of unexpected change with a 500mV square-wave entirely on-screen.
Keeping on-screen seems like it might also help with the unexpected level jumping I was experiencing.

So overdrive on the DS1054Z also seems to cause a voltage-scale error, even without any waveform shape change.

I tried to trigger this sort of glitch on the TDS-210 again, this time trying to maximize overdrive and it seemed to have no perceptible glitches at all. It seems practically immune from this sort of issue.
But maybe it is the unusual one and not the DS1054Z?

After experimenting with the TDS-210 a bunch more I think I have finally induced it to overdrive glitch.
With a -5V to +2V 100KHz square wave I can get it to attenuate and turn slightly sawtooth.
It has a transition at 200mV/div (1x-mode) where the waveform suddenly becomes attenuated and changes shape.
But still no ringing at all.
It shows a change in rounding of the rising edge with no attenuation toggling from 204mV/div to 200mV/div at 10Hz, 100Hz, 1kHz, 10kHz.
Then the same rounding edge runs out of pulse length and starts attenuating at 100kHz and makes the (slighly curved out) sawtooth top.
Maybe it's switching in some sort of filter to prevent ringing and that rounds the edge?
Changing the vertical-offset on the TDS-210 never seems to have any effect on waveform shape.

EDIT:
With different waveform settings, I did get the TDS-210 to ramp the square-wave top slope when adjusting the vertical-offset.
Kinda like the DS1054Z, but more changing slope rather than changing curvature.
So changing the vertical-offset on the TDS-210 _can_ change the waveform shape in overdrive.
With these settings and ramping the frequency I can see that there is a flat angled top separate from the rising-edge curve.
So the TDS-210 definitely does have overdrive issues, it's just a bit more subtle about it with the lack of ringing than the DS1054Z.


With the keywords posted I found another thread:
http://www.eevblog.com/forum/testgear/ds2072-and-sds8102-hw-fail-sw-bug-or-what-the-hell/

Quote from thread:
The first thing I learned from the engineer who taught my how to use an analog scope was:
"If the signal is not fully contained within the graticule, you can't trust that it's being displayed correctly."
The same still holds true for DSOs - and the input errors can possibly affect the measurements. Some scopes handle it better than others - doesn't matter about the price of the scope.

Sort of related:
http://www.eevblog.com/forum/reviews/rigol-ds4014-strange-waveform/
They also mention a TDS-210 not being affected, but they fixed it on the rigol by changing probes.

What is your signal source? I would start looking at impedance mismatch. Your frequencies are kind of low, but who knows.
The internal 1-kHz 3V square wave and a 50-ohm function generator both with and without a 50-ohm terminator connected (didn't seem to make much difference, just cut amplitude about in half).
But then I am using a scope probe and not just coax.

I have a DS1074Z-S on which I can also create nasties in the signal by overdriving it, so as an answer to the OP, I don't think your scope is defective.
It is good to know this is probably expected behavior.

Thanks for the thread link:
http://www.eevblog.com/forum/testgear/ds1074z-zoom-bug/

Overcoming Overdrive Recovery on High-Speed Digital Storage Oscilloscopes
http://cp.literature.agilent.com/litweb/pdf/5989-0068EN.pdf

Component and Measurement Advances Ensure 16-Bit DAC Settling Time
by Jim Williams
http://cds.linear.com/docs/en/application-note/an74f.pdf
Quote
Evaluating Oscilloscope Overdrive Performance
Why do most oscilloscopes have so much trouble recovering from overdrive? The answer to this question requires some study of the three basic oscilloscope types' vertical paths.
« Last Edit: April 28, 2016, 04:13:39 AM by hrothulf »
 

Online tggzzz

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Re: DS1054Z distortion issue?
« Reply #21 on: April 28, 2016, 03:10:06 AM »
It is good to see someone that listens, researches, thinks, learns. It makes helping worthwhile.
There are lies, damned lies, statistics - and ADC/DAC specs.
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Online nctnico

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Re: DS1054Z distortion issue?
« Reply #22 on: April 28, 2016, 03:15:19 AM »
In ALL cases except the one below the result is because of user error.
Until you know how to use a DSO correctly I suggest you use Autoset to get waveforms to be displayed correctly.
Uhmm, pardon? I am the only one who thinks that these results and distorted waveforms are just unacceptable by any means?
Yes  >:D Even high end (>$20k) oscilloscopes will show this behaviour although these usually have more range in their analogue circuitry and faster overdrive recovery.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline pxl

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Re: DS1054Z distortion issue?
« Reply #23 on: April 28, 2016, 04:39:26 AM »
Probably I missed the whole point, I will try to do this on my scope at evening and will back to you.

It's an interesting observation and I'm sure people will have fun investigating and explaining it.

Does it make the oscilloscope "unacceptable"? Certainly not.

It will most likely be a product of inductance and/or capacitance that only appears when you overdrive the input amplifier. The only important thing is that there's no distortion on unclipped signals.

Okay then, I've checked: 10 Vpp (0-10V), 10 Hz sine and square waves, HMO1002, the results:
- down to 500 mV everything is perfect,
- there is no distortion on sine at any level, however the amplitude start to decrease from 200 mV
- the square waves are ok down to 244 mV. Below that distortions start to begin, become strong from 100 mV

I usually use this scope to check the impulses of triacs on 30 Vpp sine waves with zooming in to the hell, and never experienced these kind of problems. Now it seems it is there with square waves, lesson learned, but I am still not impressed.
 

Offline pxl

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Re: DS1054Z distortion issue?
« Reply #24 on: April 28, 2016, 04:50:52 AM »
In ALL cases except the one below the result is because of user error.
Until you know how to use a DSO correctly I suggest you use Autoset to get waveforms to be displayed correctly.
Uhmm, pardon? I am the only one who thinks that these results and distorted waveforms are just unacceptable by any means?
Yes  >:D Even high end (>$20k) oscilloscopes will show this behaviour although these usually have more range in their analogue circuitry and faster overdrive recovery.

I would expect to
- specify this behavior
- to detect this phenomenon in the scope (or just measure the input Vpp) and show a GIGANTIC sign to the user, that they can expect Santa and Rudolf instead of proper waveforms.  :-X
 


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