Author Topic: DS1054Z distortion issue?  (Read 16426 times)

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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
 

Offline 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
 

Offline 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).
 

Offline 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 »
 

Offline 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 »
 

Offline 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...
 

Offline 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?
 

Offline 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.

 

Offline 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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Offline 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 »
 

Offline 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
 

Offline Fungus

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Re: DS1054Z distortion issue?
« Reply #25 on: April 28, 2016, 04:51:02 am »
- the square waves are ok down to 244 mV. Below that distortions start to begin, become strong from 100 mV

Screenshots?  :popcorn:

Now it seems it is there with square waves, lesson learned, but I am still not impressed.

I've been reading: http://www.analogzoo.com/2014/12/op-amp-recovery-and-slew-rates/
 

Offline pxl

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Re: DS1054Z distortion issue?
« Reply #26 on: April 28, 2016, 05:08:04 am »
- the square waves are ok down to 244 mV. Below that distortions start to begin, become strong from 100 mV
Screenshots?  :popcorn:

« Last Edit: April 28, 2016, 05:11:32 am by pxl »
 

Offline tautech

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Re: DS1054Z distortion issue?
« Reply #27 on: April 28, 2016, 05:13:46 am »
I really don't get it ^^^  :-//  :scared:  :bullshit:
Just why would anybody want/need to use a DSO in that way?
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Offline pxl

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Re: DS1054Z distortion issue?
« Reply #28 on: April 28, 2016, 05:18:36 am »
I really don't get it ^^^  :-//  :scared:  :bullshit:
Just why would anybody want/need to use a DSO in that way?

E.g: checking a 10 V zero crossing glitch on a 300 Vpp signal (with a 1:10 probe).
« Last Edit: April 28, 2016, 05:20:14 am by pxl »
 

Offline tautech

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Re: DS1054Z distortion issue?
« Reply #29 on: April 28, 2016, 05:54:47 am »
I really don't get it ^^^  :-//  :scared:  :bullshit:
Just why would anybody want/need to use a DSO in that way?

E.g: checking a 10 V zero crossing glitch on a 300 Vpp signal (with a 1:10 probe).
Really  :o Nah, there's gotta be a better method than having the scope free-run and the vertical over-driven like that.

More attenuation, set trigger appropriately, capture the waveform of interest THEN magnify with increased sensitivity.

Make the power of a DSO work for you.  ;)
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Offline pxl

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Re: DS1054Z distortion issue?
« Reply #30 on: April 28, 2016, 06:09:24 am »
I really don't get it ^^^  :-//  :scared:  :bullshit:
Just why would anybody want/need to use a DSO in that way?

E.g: checking a 10 V zero crossing glitch on a 300 Vpp signal (with a 1:10 probe).
Really  :o Nah, there's gotta be a better method than having the scope free-run and the vertical over-driven like that.

More attenuation, set trigger appropriately, capture the waveform of interest THEN magnify with increased sensitivity.

Make the power of a DSO work for you.  ;)

Yes, I can do that with HiRes mode, but what do you magnify with a common 8 bit scope :P
But the problem is, that meanwhile I checking the waveform I have to tune the circuit, so I can't stop-zoom-in-zoom-out-start in an infinite loop. With slow sine waves, however, no problem at all.
 

Offline Fungus

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Re: DS1054Z distortion issue?
« Reply #31 on: April 28, 2016, 06:23:32 am »
More attenuation, set trigger appropriately, capture the waveform of interest THEN magnify with increased sensitivity.

Make the power of a DSO work for you.  ;)

Yes, I can do that with HiRes mode

What about the "virtual screen" mode (as seen in Dave's video at 11min 02s):



Is Dave just a klutz at a trade show or can it actually give more vertical information?
« Last Edit: April 28, 2016, 06:28:04 am by Fungus »
 

Offline pxl

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Re: DS1054Z distortion issue?
« Reply #32 on: April 28, 2016, 07:02:49 am »
It just extends the screen to 6+14 divs, which is mainly targeted for digital channels (and it is also good to reach the hidden +/-1 divs), but the analog channels will clip in about 10 divs. So you won't have 20 div in HiRes mode.
 

Offline tggzzz

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Re: DS1054Z distortion issue?
« Reply #33 on: April 28, 2016, 07:41:36 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

It is unreasonable to expect that manufacturers can specify all ways in which an instrument can mislead the unwary. It is reasonable to expect that users are suitably wary and double-check what they think they are seeing. Yes, that means skill and understanding is required; deal with it.

If you have a way of reliably detecting that form of misuse while not giving many false positives, then patent it and sell it to the manufacturers. Hint: it is a very difficult problem, and I very much doubt that you will find a solution.

Overall it is best to rely that a competent user will exercise skill, wariness, humility, and understanding. The user should not be "wrapped in cotton wool".
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 #34 on: April 28, 2016, 10:47:42 am »
I really don't get it ^^^  :-//  :scared:  :bullshit:
Just why would anybody want/need to use a DSO in that way?

E.g: checking a 10 V zero crossing glitch on a 300 Vpp signal (with a 1:10 probe).
Really  :o Nah, there's gotta be a better method than having the scope free-run and the vertical over-driven like that.

More attenuation, set trigger appropriately, capture the waveform of interest THEN magnify with increased sensitivity.

Make the power of a DSO work for you.  ;)

This. ^

At what point do you start damaging the vertical amplifiers and/or attenuators?

I can just imagine the conversation:
Customer: One channel doesn't work right any more.
CS rep: When did you first notice this?
Customer: When I applied a 30V p-p signal and I had the V/div set at 10 mV/div.
CS rep:   :palm:
The easiest person to fool is yourself. -- Richard Feynman
 

Offline borjam

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Re: DS1054Z distortion issue?
« Reply #35 on: April 28, 2016, 05:29:46 pm »
Anyway, it would be a good idea to have a sticky thread with a pointer to some DSO tutorials. At least the three sisters have produced excellent tutorials available for free ;)
 

Offline tautech

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Re: DS1054Z distortion issue?
« Reply #36 on: April 28, 2016, 06:00:24 pm »
Anyway, it would be a good idea to have a sticky thread with a pointer to some DSO tutorials. At least the three sisters have produced excellent tutorials available for free ;)
There's a few in this sticky in the Beginners board, I thought they were mostly CRO's but Alan (w2aew)does have a few using DSO's if you have a hunt.  ;)

http://www.eevblog.com/forum/beginners/oscilloscope-training-class-(long)/

Heaps of links to good reference material too.
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Offline Fungus

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Re: DS1054Z distortion issue?
« Reply #37 on: April 28, 2016, 06:32:09 pm »
It is unreasonable to expect that manufacturers can specify all ways in which an instrument can mislead the unwary.

Would it help sales if a manufacturer put those screenshots on their web site?    :-/O


 

Offline Keysight DanielBogdanoff

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Re: DS1054Z distortion issue?
« Reply #38 on: April 29, 2016, 02:39:38 am »
Anyway, it would be a good idea to have a sticky thread with a pointer to some DSO tutorials. At least the three sisters have produced excellent tutorials available for free ;)

Shameless plug, I'm actually working on a video series on our YouTube channel that covers scope basics. I have a month or two of videos planned out, but am pretty flexible if there are specific topics that you folks think are extra important.  Just comment on one of those videos with your suggestions; that's where I get my video request list from.

Regarding dynamic range.  Long story short is all scopes have amplifiers, and if the amplifiers saturate there's going to be weird results.  It scares me that some scope vendors don't specify their dynamic range, because then you never know 100% that an off-screen signal isn't violating the DR.
 
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Offline tggzzz

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Re: DS1054Z distortion issue?
« Reply #39 on: April 29, 2016, 03:11:43 am »
Regarding dynamic range.  Long story short is all scopes have amplifiers, and if the amplifiers saturate there's going to be weird results.  It scares me that some scope vendors don't specify their dynamic range, because then you never know 100% that an off-screen signal isn't violating the DR.

It may not be that simple with multiple amplifiers and multiple attenuators.

For comparison, spectrum analysers often quote performance based on power level "at the mixer" - even though that isn't directly related to the input power, plus the position on the display will depend on many of the SA's settings. They presume the user has sufficient knowledge of their system and the SA's internals and settings that the user can mentally calculate that.
There are lies, damned lies, statistics - and ADC/DAC specs.
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Offline borjam

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Re: DS1054Z distortion issue?
« Reply #40 on: April 29, 2016, 03:33:54 am »
Shameless plug, I'm actually working on a video series on our YouTube channel that covers scope basics. I have a month or two of videos planned out, but am pretty flexible if there are specific topics that you folks think are extra important.  Just comment on one of those videos with your suggestions; that's where I get my video request list from.

Regarding dynamic range.  Long story short is all scopes have amplifiers, and if the amplifiers saturate there's going to be weird results.  It scares me that some scope vendors don't specify their dynamic range, because then you never know 100% that an off-screen signal isn't violating the DR.
In those cases, some overload indication would certainly help. Actually, there could be two overload conditions worthy of being reported. Out of the A/D dynamic range and amplifier overload ;)

I'll have to check out those videos, thank you!

And of course I'll pester you with suggestions if I have any!
 

Offline pxl

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Re: DS1054Z distortion issue?
« Reply #41 on: April 29, 2016, 03:43:42 am »
I really don't get it ^^^  :-//  :scared:  :bullshit:
Just why would anybody want/need to use a DSO in that way?

E.g: checking a 10 V zero crossing glitch on a 300 Vpp signal (with a 1:10 probe).
Really  :o Nah, there's gotta be a better method than having the scope free-run and the vertical over-driven like that.

More attenuation, set trigger appropriately, capture the waveform of interest THEN magnify with increased sensitivity.

Make the power of a DSO work for you.  ;)

This. ^

At what point do you start damaging the vertical amplifiers and/or attenuators?

I can just imagine the conversation:
Customer: One channel doesn't work right any more.
CS rep: When did you first notice this?
Customer: When I applied a 30V p-p signal and I had the V/div set at 10 mV/div.
CS rep:   :palm:

It is not specified that the maximum allowable voltage should be used only the largest vertical settings, so it should not damage the scope. :-+
« Last Edit: April 29, 2016, 07:37:14 pm by pxl »
 

Offline Performa01

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Re: DS1054Z distortion issue?
« Reply #42 on: April 29, 2016, 06:36:06 pm »
Regarding dynamic range.  Long story short is all scopes have amplifiers, and if the amplifiers saturate there's going to be weird results.

That's correct. No amplifier will work as specified if the conditions that the specifications are based on aren't met. In this case, the signal exceeds the specified CMR, which causes internal bias points to shift, some transistors to turn off and others to saturate. The output signal might change polarity and in any case it will take a little while until the amplifier recovers after the overload has been removed.


Quote
It scares me that some scope vendors don't specify their dynamic range, because then you never know 100% that an off-screen signal isn't violating the DR.

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. Then we can indeed zoom into a signal vertically, even 100 times, without any adverse effects.
« Last Edit: April 29, 2016, 06:39:07 pm by Performa01 »
 

Offline alsetalokin4017

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Re: DS1054Z distortion issue?
« Reply #43 on: April 29, 2016, 06:53:45 pm »
Quote
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. Then we can indeed zoom into a signal vertically, even 100 times, without any adverse effects.

But... but.... this is a Rigol DS1054z we are talking about here!  You know... the scope that shows RMS voltage measurements on channels that are grounded! That has Measurements that simply stop working at random times when Math is in use, that miscounts "Pluses", that has the horizontal Math error at 500 ns/div..... etc.    :rant:

Should we have confidence that this particular scope model has proper limiters at the front end so that we don't get _really_ adverse effects, like blown inputs, if we zoom in vertically 100 times? Who is willing to put their DS1054z to the test, providing a 300V p-p signal and then zooming in 100x? Sorry... not I.    :scared:
The easiest person to fool is yourself. -- Richard Feynman
 

Offline Performa01

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Re: DS1054Z distortion issue?
« Reply #44 on: April 29, 2016, 07:02:51 pm »
Should we have confidence that this particular scope model has proper limiters at the front end so that we don't get _really_ adverse effects, like blown inputs, if we zoom in vertically 100 times? Who is willing to put their DS1054z to the test, providing a 300V p-p signal and then zooming in 100x? Sorry... not I.    :scared:

Well, there is no input limiter in the DS1000Z as the initial posting clearly demonstrates.
That doesn't mean that it won't withstand the rated max. input voltage. Quite obviously the designers rely on the internal input protection of the first OpAmp, which might well be sufficient to survive, but isn't good design practice for sure.
 

Offline tggzzz

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Re: DS1054Z distortion issue?
« Reply #45 on: April 29, 2016, 07:07:42 pm »
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.

I'm glad you know how to do that, since you can patent and sell your techniques, and they will make you rich.

Unfortunately "adding limiters" isn't that simple, of course.

Limiters are non-linear circuit elements that will affect (i.e. distort) the signals even when they aren't limiting. In a scope distortion is to be avoided, which implies limiters might need to be avoided. Many scope and spectrum analysers are deliberately left "unprotected" for that reason - even though their lack means the instrument would be destroyed by too large signals.

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!
There are lies, damned lies, statistics - and ADC/DAC specs.
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Offline Performa01

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Re: DS1054Z distortion issue?
« Reply #46 on: April 29, 2016, 07:31:51 pm »
I'm glad you know how to do that, since you can patent and sell your techniques, and they will make you rich.

Unfortunately "adding limiters" isn't that simple, of course.

Well, it's not rocket science. Of course it can be done. I have done it and scope vendors seem to have successfully done it as well.
So no chance getting a patent on that.

Quote
Limiters are non-linear circuit elements that will affect (i.e. distort) the signals even when they aren't limiting. In a scope distortion is to be avoided, which implies limiters might need to be avoided. Many scope and spectrum analysers are deliberately left "unprotected" for that reason - even though their lack means the instrument would be destroyed by too large signals.

Yes, for an instrument promising a 3rd order dynamic range of 70dB and operating up to several GHz, a limiter would be a challenge indeed. Not saying it cannot be done, but that's something I haven't tried before and would actually expect some degradation in performance.

But we are talking about general purpose 8-bit scopes in the couple 100MHz range here. With an INL of at least +/- 0.5LSB there's not much to worry about the linearity of the frontend.

Quote
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.

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.

 

Offline Fungus

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Re: DS1054Z distortion issue?
« Reply #47 on: April 29, 2016, 07:33:24 pm »
Should we have confidence that this particular scope model has proper limiters at the front end so that we don't get _really_ adverse effects, like blown inputs, if we zoom in vertically 100 times? Who is willing to put their DS1054z to the test, providing a 300V p-p signal and then zooming in 100x? Sorry... not I.    :scared:

Why don't you tell us, Mr. self-appointed Rigol expert? The schematic is out there.
 

Offline tggzzz

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Re: DS1054Z distortion issue?
« Reply #48 on: April 29, 2016, 08:35:30 pm »
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.

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.

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

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.

Have a look at or similar; if you spot what you are thinking of, please point to it.
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 #49 on: April 29, 2016, 11:42:20 pm »
Should we have confidence that this particular scope model has proper limiters at the front end so that we don't get _really_ adverse effects, like blown inputs, if we zoom in vertically 100 times? Who is willing to put their DS1054z to the test, providing a 300V p-p signal and then zooming in 100x? Sorry... not I.    :scared:

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.

Why don't YOU test _your_ DS1054z for us, using the maximum rated input voltage and then zooming in to more and more vertical sensitivity? I'm sure we all would be interested in seeing your report. Do you have the necessary confidence in the Rigol hardware design?
 
 :popcorn:
« Last Edit: April 29, 2016, 11:45:35 pm by alsetalokin4017 »
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Offline alsetalokin4017

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Re: DS1054Z distortion issue?
« Reply #50 on: April 30, 2016, 12:38:30 am »
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

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Re: DS1054Z distortion issue?
« Reply #51 on: April 30, 2016, 05:13:03 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)
 

Offline Keysight DanielBogdanoff

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Re: DS1054Z distortion issue?
« Reply #52 on: April 30, 2016, 06:15:21 am »
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

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Re: DS1054Z distortion issue?
« Reply #53 on: April 30, 2016, 06:34:54 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)
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.
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Offline hans

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Re: DS1054Z distortion issue?
« Reply #54 on: April 30, 2016, 07:09:36 am »
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 30, 2016, 07:28:17 am by hans »
 

Online nctnico

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Re: DS1054Z distortion issue?
« Reply #55 on: April 30, 2016, 07:15:54 am »
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 30, 2016, 07:26:19 am by nctnico »
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Offline tggzzz

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Re: DS1054Z distortion issue?
« Reply #56 on: April 30, 2016, 07:23:50 am »
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.
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Offline tautech

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Re: DS1054Z distortion issue?
« Reply #57 on: April 30, 2016, 07:31:46 am »
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 30, 2016, 08:15:20 am by tautech »
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Offline hans

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Re: DS1054Z distortion issue?
« Reply #58 on: April 30, 2016, 08:22:58 am »
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 30, 2016, 08:27:58 am by hans »
 

Offline tom66

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Re: DS1054Z distortion issue?
« Reply #59 on: April 30, 2016, 08:45:06 am »
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

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Re: DS1054Z distortion issue?
« Reply #60 on: April 30, 2016, 08:59:49 am »
I think you misunderstood the meaning of my post.
Maybe.
You mean this post?
http://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.
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Offline alsetalokin4017

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Re: DS1054Z distortion issue?
« Reply #61 on: April 30, 2016, 10:59:14 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
 
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Offline tggzzz

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Re: DS1054Z distortion issue?
« Reply #62 on: April 30, 2016, 05:09:20 pm »
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.
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Offline Texacate

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Re: DS1054Z distortion issue?
« Reply #63 on: April 30, 2016, 05:12:22 pm »
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

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Re: DS1054Z distortion issue?
« Reply #64 on: April 30, 2016, 06:26:57 pm »
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

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Re: DS1054Z distortion issue?
« Reply #65 on: April 30, 2016, 06:40:17 pm »
Maybe.
You mean this post?
http://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

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Re: DS1054Z distortion issue?
« Reply #66 on: April 30, 2016, 07:15:33 pm »
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, 07:18:55 pm by pxl »
 

Offline tautech

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Re: DS1054Z distortion issue?
« Reply #67 on: April 30, 2016, 07:48:41 pm »
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.
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Offline tautech

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Re: DS1054Z distortion issue?
« Reply #68 on: April 30, 2016, 07:57:08 pm »
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.  ;)
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Offline pxl

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Re: DS1054Z distortion issue?
« Reply #69 on: April 30, 2016, 09:15:16 pm »
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

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Re: DS1054Z distortion issue?
« Reply #70 on: April 30, 2016, 09:28:08 pm »
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.
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Offline tautech

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Re: DS1054Z distortion issue?
« Reply #71 on: April 30, 2016, 09:41:41 pm »
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......
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Offline hans

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Re: DS1054Z distortion issue?
« Reply #72 on: April 30, 2016, 10:04:43 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, 10:06:21 pm by hans »
 

Offline Fungus

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Re: DS1054Z distortion issue?
« Reply #73 on: April 30, 2016, 10:34:40 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, 10:42:25 pm by Fungus »
 

Offline Fungus

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Re: DS1054Z distortion issue?
« Reply #74 on: April 30, 2016, 10:48:41 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, 10:54:45 pm by Fungus »
 

Offline Fungus

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Re: DS1054Z distortion issue?
« Reply #75 on: April 30, 2016, 10:50:24 pm »
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.

People who agree with that opinion are free to find old oscilloscopes and use them.
 

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Re: DS1054Z distortion issue?
« Reply #76 on: April 30, 2016, 10:54:30 pm »
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.
One solution to your problem is to create a buffer amplifier which can also the input signal. IIRC Analog Devices has amplifiers with signal clipping inputs. Not exactly cheap but still affordable. Otherwise a couple of zener diodes (after a buffer amplifier) may do the job.
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Re: DS1054Z distortion issue?
« Reply #77 on: April 30, 2016, 11:40:38 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?)

I can relate to that. As pointed out, what I'm trying to do is quite niche and can be argued over if this capability should be supported or not (I certainly wish it was). However it likely won't because if you were to support every little niche feature customers require you will end up adding menu buttons, options and knobs at every corner of the menu/screen. It quickly becomes a mess. Hardware specifications get out of hand, product becomes too hard/expensive to engineer or produce, etc.

The place where I used to work every menu button change at 1st or 2nd level was heavily discussed and criticized by service & product engineers, which I think is a good thing. This resulted in some frustration of other colleagues which already promised some features and changes to customers, that did not happen.

I think nctnico also suggests a similar thing, like a fast-signal clamp board that you can safely overdrive but will recover in e.g. <1us or faster so influence on measurements is minimal. That sounds like a nice project idea, maybe something I could work on to solve this once and for all :)
« Last Edit: May 01, 2016, 12:24:54 am by hans »
 

Offline tggzzz

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Re: DS1054Z distortion issue?
« Reply #78 on: May 01, 2016, 12:13:45 am »
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.

Overload recovery affects more than just DSOs; most analogue scopes have similar problems.

Hence it is a poor argument against the DS1054Z.
There are lies, damned lies, statistics - and ADC/DAC specs.
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Offline Fungus

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Re: DS1054Z distortion issue?
« Reply #79 on: May 01, 2016, 12:48:40 am »
Overload recovery affects more than just DSOs; most analogue scopes have similar problems.

It's not just oscilloscopes either, it's every op-amp ever made.

FWIW the DS1054Z says "300V RMS CAT I" on the front.

That suggests it's been designed for up to 300V RMS on every input range. It should also withstand very low energy 1500V transients.



Would anybody disagree with that, based on Dave's schematic?
« Last Edit: May 01, 2016, 12:53:31 am by Fungus »
 

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Re: DS1054Z distortion issue?
« Reply #80 on: May 01, 2016, 01:13:22 am »
Here's the front end from the DS1054Z.

The only part that's switchable is the part labelled "Attenuator" in the schematic. This part can be completely switched out with a relay. When switched out, the input will go directly to point I've labelled "A".

It follows that everything beyond point "A" can therefore withstand 300V:



So ... the only question is whether or not the capacitors in the Attenuator are rated for a 300V input. That doesn't seem expensive to do and I don't see why they wouldn't be.

« Last Edit: May 01, 2016, 01:25:52 am by Fungus »
 

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Re: DS1054Z distortion issue?
« Reply #81 on: May 01, 2016, 02:59:47 am »
I think nctnico also suggests a similar thing, like a fast-signal clamp board that you can safely overdrive but will recover in e.g. <1us or faster so influence on measurements is minimal. That sounds like a nice project idea, maybe something I could work on to solve this once and for all :)

What will be the clamp voltages? And will that prevent problems with internal nodes in the scope entering saturation?
There are lies, damned lies, statistics - and ADC/DAC specs.
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Offline pxl

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Re: DS1054Z distortion issue?
« Reply #82 on: May 01, 2016, 07:55:25 am »
I've made a small investigation, now from the opposite viewpoint: I checked the max voltage for every (well, most of) vertical divisions, where the smallest distortions starts to appear (I stopped and then zoomed in to check the details, HiRes ;)). The signal is 10 Hz, square wave from 0 to the noted voltage:

vertical div.max voltage
1mV60mV
2mV60mV
5mV60mV
10mV60mV
20mV1.38V
50mV1.37V
100mV1.31V
200mV1.18V
500mV>10V

from 500mV and above I cannot spot any distortions, I have 10V square wave max. With keeping this table in mind, it is very easy to find vertical ranges, where it is almost perfect, and the ranges where it is hardly usable for this purpose.
« Last Edit: May 01, 2016, 07:57:49 am by pxl »
 

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Re: DS1054Z distortion issue?
« Reply #83 on: May 01, 2016, 08:04:46 am »
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?)

Seems logical, but in reality it would be very impractical. The first step, when measuring this kind of small parts of largest signals, is to view the whole and then zoom in the interested part. This way, we would need a switchable level, which should be always kept synchronized with the internal vertical settings. :scared:

This limiters should be in the scope, I am afraid.
 

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Re: DS1054Z distortion issue?
« Reply #84 on: May 01, 2016, 08:30:23 am »
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?)

Seems logical, but in reality it would be very impractical. The first step, when measuring this kind of small parts of largest signals, is to view the whole and then zoom in the interested part. This way, we would need a switchable level, which should be always kept synchronized with the internal vertical settings. :scared:

This limiters should be in the scope, I am afraid.
No, use 2 channels (one clipped externally). Alternatively an external trigger channel can also be used.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

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Re: DS1054Z distortion issue?
« Reply #85 on: May 01, 2016, 07:01:55 pm »
I've made a small investigation, now from the opposite viewpoint: I checked the max voltage for every (well, most of) vertical divisions, where the smallest distortions starts to appear (I stopped and then zoomed in to check the details, HiRes ;)). The signal is 10 Hz, square wave from 0 to the noted voltage:

vertical div.max voltage
1mV60mV
2mV60mV
5mV60mV
10mV60mV
20mV1.38V
50mV1.37V
100mV1.31V
200mV1.18V
500mV>10V

from 500mV and above I cannot spot any distortions, I have 10V square wave max. With keeping this table in mind, it is very easy to find vertical ranges, where it is almost perfect, and the ranges where it is hardly usable for this purpose.
@ pxl
Simple checks with the SDS2304
10 Hz square wave (source HiZ SDG1010)
Normal acquisition HiZ

No distortion of the fundamental waveform @ 3V p-p down to 1mV/div (max sensitivity)
No distortion of the fundamental waveform @ 10V p-p down to 200mV/div
Distortion of the fundamental waveform was present @ 4V+ p-p @ 100mV/div and lower

BTW, SDS2304 does not show the clipped off-screen portion of the waveform on the display, there are just the rising edges tracing off the edge of the display.
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Offline rf-loop

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Re: DS1054Z distortion issue?
« Reply #86 on: May 01, 2016, 08:52:54 pm »

BTW, SDS2304 does not show the clipped off-screen portion of the waveform on the display, there are just the rising edges tracing off the edge of the display.

Naturally. ADC is 8bit. It do not clip display top or bottom and so it not also draw false line there like some others.
ADC is 8bit. Display vertical division is 25 ADC levels. Display height is not ADC full scale.
8div (what is Siglent vertical display range isheight) show only 200 from full 256 range.)
Stop scope. Move vertical position up and down, there can see these clips (and straight line where it cut)
But what I hope is that Siglent do small improvement and same as example even in -80 era old HP digital scope. It give warning on the screen about signal clipping. (and also warning about possible aliasing situation)



« Last Edit: May 01, 2016, 09:02:26 pm by rf-loop »
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Offline tautech

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Re: DS1054Z distortion issue?
« Reply #87 on: May 01, 2016, 09:27:35 pm »
But what I hope is that Siglent do small improvement and same as example even in -80 era old HP digital scope. It give warning on the screen about signal clipping. (and also warning about possible aliasing situation)
Where there was confusion early in this thread was with the Rigol displaying this clipped portion on the display, early SDS2000 FW did this too but now this clipped portion is missing in the 2000 series it is quite  (should be) obvious to the user the V/div need be adjusted to display the full waveform. For the 2000 series IMO a warning is not required..... but maybe for the blind.  :palm:
« Last Edit: May 01, 2016, 09:40:34 pm by tautech »
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Offline pxl

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Re: DS1054Z distortion issue?
« Reply #88 on: May 02, 2016, 05:08:24 am »
I've made a small investigation, now from the opposite viewpoint: I checked the max voltage for every (well, most of) vertical divisions, where the smallest distortions starts to appear (I stopped and then zoomed in to check the details, HiRes ;)). The signal is 10 Hz, square wave from 0 to the noted voltage:

vertical div.max voltage
1mV60mV
2mV60mV
5mV60mV
10mV60mV
20mV1.38V
50mV1.37V
100mV1.31V
200mV1.18V
500mV>10V

from 500mV and above I cannot spot any distortions, I have 10V square wave max. With keeping this table in mind, it is very easy to find vertical ranges, where it is almost perfect, and the ranges where it is hardly usable for this purpose.
@ pxl
Simple checks with the SDS2304
10 Hz square wave (source HiZ SDG1010)
Normal acquisition HiZ

No distortion of the fundamental waveform @ 3V p-p down to 1mV/div (max sensitivity)
No distortion of the fundamental waveform @ 10V p-p down to 200mV/div
Distortion of the fundamental waveform was present @ 4V+ p-p @ 100mV/div and lower

Nice, thanks. And after all this long thread, it turned out that there is a scope which seems to be immune to this problem (in the range of our use cases, e.g. with 1:100 probes). Where is the trade-off?
 

Offline tautech

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Re: DS1054Z distortion issue?
« Reply #89 on: May 02, 2016, 06:25:50 am »
And after all this long thread,
Let's make it longer.  ;)

Quote
it turned out that there is a scope which seems to be immune to this problem (in the range of our use cases, e.g. with 1:100 probes).
Problem  :-// 
Isn't it quite clear this style of measurement is outside normal DSO intended functionality and therefore outside what manufacturers might consider incorporating into their designs.

There be a few more as more members contribute. But remember the OP had an old Tek DSO that didn't clip for his measurement needs of what this thread is based on.



Quote
Where is the trade-off?
IMHO, product and FW maturity and front end design.
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Online MarkL

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Re: DS1054Z distortion issue?
« Reply #90 on: May 02, 2016, 07:12:15 am »
...
I think nctnico also suggests a similar thing, like a fast-signal clamp board that you can safely overdrive but will recover in e.g. <1us or faster so influence on measurements is minimal. That sounds like a nice project idea, maybe something I could work on to solve this once and for all :)
Jim Williams has been referenced several times in this thread with his approach to the overdrive problem.

Here's another couple of solutions from him that are fairly simple.  They are in the venerable AN47, starting on page 39:

  http://www.linear.com/docs/4138

(Although a bit dated, it's worth reading the whole AN47.)
 

Online nctnico

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Re: DS1054Z distortion issue?
« Reply #91 on: May 02, 2016, 07:19:54 am »
I've made a small investigation, now from the opposite viewpoint: I checked the max voltage for every (well, most of) vertical divisions, where the smallest distortions starts to appear (I stopped and then zoomed in to check the details, HiRes ;)). The signal is 10 Hz, square wave from 0 to the noted voltage:

vertical div.max voltage
1mV60mV
2mV60mV
5mV60mV
10mV60mV
20mV1.38V
50mV1.37V
100mV1.31V
200mV1.18V
500mV>10V

from 500mV and above I cannot spot any distortions, I have 10V square wave max. With keeping this table in mind, it is very easy to find vertical ranges, where it is almost perfect, and the ranges where it is hardly usable for this purpose.
Did you set the offset so you can see the flat piece of the square wave or did you look at the edges? In case of the latter you are not likely to find any distortions because when the opamp is driving the edge it has already recoverd from the overdrive. You need to look at the flat parts of the square waves!
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 #92 on: May 02, 2016, 07:30:08 am »
I've made a small investigation, now from the opposite viewpoint: I checked the max voltage for every (well, most of) vertical divisions, where the smallest distortions starts to appear (I stopped and then zoomed in to check the details, HiRes ;)). The signal is 10 Hz, square wave from 0 to the noted voltage:

vertical div.max voltage
1mV60mV
2mV60mV
5mV60mV
10mV60mV
20mV1.38V
50mV1.37V
100mV1.31V
200mV1.18V
500mV>10V

from 500mV and above I cannot spot any distortions, I have 10V square wave max. With keeping this table in mind, it is very easy to find vertical ranges, where it is almost perfect, and the ranges where it is hardly usable for this purpose.
Did you set the offset so you can see the flat piece of the square wave or did you look at the edges? In case of the latter you are not likely to find any distortions because when the opamp is driving the edge it has already recoverd from the overdrive. You need to look at the flat parts of the square waves!

Yep, this is. From this point up there is no distortions. So 500 mV and 10 Vpp is ok. (1:1 BNC)

 

Offline pxl

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Re: DS1054Z distortion issue?
« Reply #93 on: May 02, 2016, 07:46:10 am »
Quote
Where is the trade-off?
IMHO, product and FW maturity and front end design.

I mean that I can spot 3 amp steps in my table: 1mV-10mV, 20mV-200mV and from 500mV. From your data I suspect, there is only two steps in siglent: one is from 1mV to 100 mV and one step from 200mV. Why the difference? What are the benefits having 3 steps if there is any?
 

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Re: DS1054Z distortion issue?
« Reply #94 on: May 02, 2016, 07:51:46 am »
I just did a similar test on my GDS2204E. With 10Vpp input it can display the signal correctly up to 50mV/div. IMHO an easy test is to input a 100kHz square wave to channel 1 & 2 (terminate properly!), set the vertical position of both channels to 0 and set the trigger level to 0. Set channel 2 as the trigger source and adjust the volt/div so channel 2 displays the signal. Adjust the timebase so that channel 2 shows a slope instead of a sharp edge. Now increase the sensitivity of channel 1 until the trace of channel 1 shows a significant (>0.2 div) horizontal offset from channel 2. Once that happens you are in overdrive territory. Another good indicator of when an oscilloscope will overdrive is the horizontal offset range. On the GDS2204E the 50mV/div has a +/-5V offset range so it seems it has been designed to not overdrive at 50mV/div when driven with a 10Vpp input.
« Last Edit: May 02, 2016, 07:53:17 am by nctnico »
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Re: DS1054Z distortion issue?
« Reply #95 on: May 02, 2016, 08:13:22 am »
Quote
Where is the trade-off?
IMHO, product and FW maturity and front end design.

I mean that I can spot 3 amp steps in my table: 1mV-10mV, 20mV-200mV and from 500mV. From your data I suspect, there is only two steps in siglent: one is from 1mV to 100 mV and one step from 200mV. Why the difference? What are the benefits having 3 steps if there is any?
Much TE will differ in this respect as overdriven input measurements are not part of normal DSO use.
So any perceived benefits you imagine are just design idiosyncrasies.

There are so many other features to consider when buying a DSO, so don't sell yourself short by focussing entirely on this issue.

I might add, my tests/checks were done using a square waveform with 0V offset ie. all amplitude was above the DSO ch 0V baseline.

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Re: DS1054Z distortion issue?
« Reply #96 on: May 02, 2016, 08:17:06 am »
Quote
Where is the trade-off?
IMHO, product and FW maturity and front end design.

I mean that I can spot 3 amp steps in my table: 1mV-10mV, 20mV-200mV and from 500mV. From your data I suspect, there is only two steps in siglent: one is from 1mV to 100 mV and one step from 200mV. Why the difference? What are the benefits having 3 steps if there is any?
Much TE will differ in this respect as overdriven input measurements are not part of normal DSO use.
I beg to differ. IMHO when the input signal is within the offset adjust range there should not be any distortions because the oscilloscope has been designed to be able to handle such signals.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Online nctnico

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Re: DS1054Z distortion issue?
« Reply #97 on: May 02, 2016, 08:45:14 am »
I think nctnico also suggests a similar thing, like a fast-signal clamp board that you can safely overdrive but will recover in e.g. <1us or faster so influence on measurements is minimal. That sounds like a nice project idea, maybe something I could work on to solve this once and for all :)
What will be the clamp voltages? And will that prevent problems with internal nodes in the scope entering saturation?
a) whatever you want them to be
b) make sure that the clamped signal doesn't exceed the scope's specifications (the answer to a).
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline tautech

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Re: DS1054Z distortion issue?
« Reply #98 on: May 02, 2016, 05:30:26 pm »
Another good indicator of when an oscilloscope will overdrive is the horizontal offset range. On the GDS2204E the 50mV/div has a +/-5V offset range so it seems it has been designed to not overdrive at 50mV/div when driven with a 10Vpp input.
A check of the SDS2000 manual shows a table with these vertical offset ranges:

Volt Scale Range of Vertical Position

2 mV/div - 100 mV/div   ±1V
102 mV/div - 1 V/div      ±10 V
1.02 V/div - 10 V/div      ±100 V
« Last Edit: May 02, 2016, 06:31:04 pm by tautech »
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Re: DS1054Z distortion issue?
« Reply #99 on: May 02, 2016, 06:44:44 pm »
GW Instek GDS2000E offset ranges:
1mV/div ~ 20mV/div : ±0.5V
50mV/div ~ 200mV/div : ±5V
500mV/div ~ 2V/div : ±25V
5V/div ~ 10V/div : ±250V
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline hgjdwx

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Re: DS1054Z distortion issue?
« Reply #100 on: January 19, 2017, 01:22:21 pm »



« Last Edit: January 19, 2017, 01:54:35 pm by hgjdwx »
 

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Re: DS1054Z distortion issue?
« Reply #101 on: January 19, 2017, 09:01:53 pm »
Rigol DS 1000Z series:


Offset Range (Probe ratio is 1X):

1 mV/div to 499 mV/div: ±2 V
500 mV/div to 10 V/div: ±100 V

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