Author Topic: DS2072 HW FAIL SW BUG or What the hell? SOLVED  (Read 13841 times)

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Offline Carrington

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DS2072 HW FAIL SW BUG or What the hell? SOLVED
« on: November 23, 2013, 03:29:54 pm »
Please look carefully these images (If anyone wants try to replicate it. The sigal is a pulse of 3.3V, wide 50ns and rise time 2ns):








First, all the measurements were performed under the same conditions and with the same probe (Agilent 10073D).
Now let us assume that the signal integrity is maintained in both oscilloscopes, and that ~8bits can't give us more.
The wave "form" is constantly changing in the SDS8102V, depending of the scale V/div, but at least it maintains the peak's amplitude within of a range, between the different scales (at least as far as ~ 8 bits reach).

But please:
 - One volt peak that comes and goes in the DS2072 depending of the scale V/div. For 200mV/div the peak's amplitude is 1V and for 50mV/div and 100mV/div the peak's amplitude is ~ 300mV! :wtf:

Note 1: In both oscilloscopes the acquisition mode is peak (for all the acquisition modes occurs exactly the same).
Note 2: I've tried with all these probes:
               - RP3300  BW: 350MHz.
               - P6200    BW: 250MHz.
               - T5100    BW: 100MHz.
             And the same thing is still happening.

What the hell is going on?  :-//
« Last Edit: November 25, 2013, 09:07:22 pm by Carrington »
My English can be pretty bad, so suggestions are welcome. ;)
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Offline sync

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Re: DS2072 HW FAIL SW BUG or What the hell?
« Reply #1 on: November 23, 2013, 06:07:05 pm »

You are overdriving the input. Maybe the spike is a input amplifier saturation artifact.
 

Offline Carrington

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Re: DS2072 HW FAIL SW BUG or What the hell?
« Reply #2 on: November 23, 2013, 06:17:41 pm »
You are overdriving the input. Maybe the spike is a input amplifier saturation artifact.
I doubt it.
My English can be pretty bad, so suggestions are welcome. ;)
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Offline RRobot

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Re: DS2072 HW FAIL SW BUG or What the hell?
« Reply #3 on: November 23, 2013, 06:20:35 pm »
You've calibrated the Agilent probe and are re-triggering after each change in vertical?
 

Offline Carrington

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Re: DS2072 HW FAIL SW BUG or What the hell?
« Reply #4 on: November 23, 2013, 06:23:08 pm »
You've calibrated the Agilent probe and are re-triggering after each change in vertical?
Yes! And no matter the acquisition mode, Auto, Normal or Single. Or what probe. Is completely replicable.

Even with BW limit set to 100MHz.
« Last Edit: November 23, 2013, 06:40:20 pm by Carrington »
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Offline Galaxyrise

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Re: DS2072 HW FAIL SW BUG or What the hell?
« Reply #5 on: November 23, 2013, 06:52:41 pm »
I suggest looking at it in dots display to make sure that spike is actually being measured and isn't the result of interpolation.   I suspect peak + vectors could exaggerate overshoot.  Why are you using peak acquisition mode?
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Offline Carrington

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Re: DS2072 HW FAIL SW BUG or What the hell?
« Reply #6 on: November 23, 2013, 06:57:11 pm »
I suggest looking at it in dots display to make sure that spike is actually being measured and isn't the result of interpolation.   I suspect peak + vectors could exaggerate overshoot.  Why are you using peak acquisition mode?
Note 1: In both oscilloscopes the acquisition mode is peak (for all the acquisition modes occurs exactly the same).
And in dots display occurs exactly the same.



« Last Edit: November 23, 2013, 07:04:52 pm by Carrington »
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Offline Galaxyrise

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Re: DS2072 HW FAIL SW BUG or What the hell?
« Reply #7 on: November 23, 2013, 07:10:33 pm »
Have you applied one of the bandwidth keys to the Rigol, or is it still 70MHz?
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Offline Carrington

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Re: DS2072 HW FAIL SW BUG or What the hell?
« Reply #8 on: November 23, 2013, 07:13:53 pm »
Even with BW limit set to 100MHz.
And between 70 and 100MHz exists little or any difference.

Have you applied one of the bandwidth keys to the Rigol, or is it still 70MHz?
Clearly yes.
« Last Edit: November 23, 2013, 07:24:24 pm by Carrington »
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Offline marmad

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Re: DS2072 HW FAIL SW BUG or What the hell?
« Reply #9 on: November 23, 2013, 07:31:00 pm »
You are overdriving the input. Maybe the spike is a input amplifier saturation artifact.
I doubt it.
As sync suggests, it also looks like overdrive to me. On both analog and digital scopes, you can't really be certain of measurements taken if the trace is not fully contained on the display screen. And it doesn't matter if it works on one scope - it might not work on the next.

I was unable to replicate your problem if I measure a pulse fully contained in the display @ 200mV, 100mV and 50mV. It works completely fine.

As written by Jim Williams in his AN74:

Quote
Analog and digital ‘scopes are susceptible to overdrive. The classical sampling ‘scope is the only architecture that is inherently immune to overdrive.
« Last Edit: November 23, 2013, 08:27:13 pm by marmad »
 

Offline Carrington

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Re: DS2072 HW FAIL SW BUG or What the hell?
« Reply #10 on: November 23, 2013, 07:37:36 pm »
As sync suggests, it also looks like overdrive to me. On both analog and digital scopes, you can't really be certain of measurements taken if the trace is not fully contained on the display screen - and your's doesn't look like it is. And it doesn't matter if it works on one scope - it might not work on the next.

I was unable to replicate your problem if I measure a pulse fully contained in the display @ 200mV, 100mV and 50mV. It works completely fine.

As written by Jim Williams in his AN74:
Thanks, I will read it.

Quote
Analog and digital ‘scopes are susceptible to overdrive. The classical sampling ‘scope is the only architecture that is inherently immune to overdrive.
What do you want mean, that the internal DC offset in conjunction with the input stage distort the signal.

Why this does not happen with a cheap SDS8102V?

But can you replicate the problem with a completely different signal source?
I don't have the equipment to do.
« Last Edit: November 23, 2013, 07:42:24 pm by Carrington »
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Offline marmad

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Re: DS2072 HW FAIL SW BUG or What the hell?
« Reply #11 on: November 23, 2013, 07:42:22 pm »
And what do you want mean, that the internal DC offset in conjunction with the input stage distort the signal.

Yes.

Quote
Why this does not happen with a cheap SDS8102V?

As mentioned, it can vary from scope to scope - some analog scopes I've used do it easily - while other's don't.

I don't have the equipment to do.

I'm not sure I understand you - I just mean can you cause the Rigol to give different measurements at those scale settings using any other signal source.
« Last Edit: November 23, 2013, 07:44:36 pm by marmad »
 

Offline Carrington

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Re: DS2072 HW FAIL SW BUG or What the hell?
« Reply #12 on: November 23, 2013, 07:43:27 pm »
But can you replicate the problem with a completely different signal source?
I need a equipment to add an external offset to the pulse, without disturbing the signal. Or a goog AWG.



The previous pulse was generated with a Asix OMEGA LA.
« Last Edit: November 23, 2013, 08:01:56 pm by Carrington »
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Offline Carrington

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Re: DS2072 HW FAIL SW BUG or What the hell?
« Reply #13 on: November 23, 2013, 08:05:54 pm »
I'm not sure I understand you - I just mean can you cause the Rigol to give different measurements at those scale settings using any other signal source.
Sorry, but I don't understand exactly what do you want mean.

Perhaps achieve that the results obtained on that scale settings does not correspond with a well known signal. With that signal completely within of this scale settings or not?
« Last Edit: November 23, 2013, 08:14:44 pm by Carrington »
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Offline marmad

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Re: DS2072 HW FAIL SW BUG or What the hell?
« Reply #14 on: November 23, 2013, 08:15:22 pm »
Sorry, but I don't understand exactly what do you want mean.

Perhaps achieve that the results obtained on that scale does not correspond with a well known signal. With that signal completely within of this range or not?

I don't get any cursor measurement variations when I measure a signal @ 200mV and 50mV that is contained within the graticule. Even expensive digital scopes, if displaying signals beyond the graticule limits, can overload and saturate - so unless you can show the problem with a contained signal, I can't consider it a fail or bug of the Rigol.
 

Offline Carrington

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Re: DS2072 HW FAIL SW BUG or What the hell?
« Reply #15 on: November 23, 2013, 08:22:07 pm »
Sorry, but I don't understand exactly what do you want mean.

Perhaps achieve that the results obtained on that scale does not correspond with a well known signal. With that signal completely within of this range or not?

I don't get any cursor measurement variations when I measure a signal @ 200mV and 50mV that is contained within the graticule. Even expensive digital scopes, if displaying signals beyond the graticule limits, can overload and saturate - so unless you can show the problem with a contained signal, I can't consider it a fail or bug of the Rigol.
Ok, now I understand.



Sorry, my English is so bad that I have to edit my post constantly to correct my grammatical errors (when I detect this).  :-[

« Last Edit: November 23, 2013, 08:24:27 pm by Carrington »
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Offline marmad

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Re: DS2072 HW FAIL SW BUG or What the hell?
« Reply #16 on: November 23, 2013, 08:25:56 pm »
Sorry, my English is so bad that I have to edit my post constantly to correct my grammatical errors (when I detected this).

No problem  ;)

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.
 

Offline Carrington

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Re: DS2072 HW FAIL SW BUG or What the hell?
« Reply #17 on: November 23, 2013, 08:30:17 pm »
Sorry, my English is so bad that I have to edit my post constantly to correct my grammatical errors (when I detected this).

No problem  ;)

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.
Well, you have been the engineer who has taught me that.

LOL... Thank you very much.
« Last Edit: November 23, 2013, 08:34:36 pm by Carrington »
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Offline Carrington

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Re: DS2072 HW FAIL SW BUG or What the hell?
« Reply #18 on: November 23, 2013, 08:40:12 pm »
Is there any solution to inspect a signal and get a good level of detail (distorting the signal as little as possible), as a zoom?
« Last Edit: November 23, 2013, 08:43:09 pm by Carrington »
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Offline marmad

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Re: DS2072 HW FAIL SW BUG or What the hell?
« Reply #19 on: November 23, 2013, 08:56:35 pm »
Is there any solution to inspect a signal and get a good level of detail (distorting the signal as little as possible), as a zoom?

Vertical detail is always difficult because of the limitations of the low resolution ADC (as opposed to horizontal detail - which is only limited by the sample rate). Sometimes it helps to filter the signal with AC coupling or limiting filters to isolate a particular portion you're trying to get more vertical resolution on - sometimes it's best to export the sampled data to external software for more detailed examination.
 

Offline Carrington

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Re: DS2072 HW FAIL SW BUG or What the hell?
« Reply #20 on: November 23, 2013, 09:04:12 pm »
Sometimes it's best to export the sampled data to external software for more detailed examination.
Sure, because probably in the sampled data there are more information than that shown on the oscilloscope screen.
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Online MarkL

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Re: DS2072 HW FAIL SW BUG or What the hell?
« Reply #21 on: November 23, 2013, 10:40:53 pm »
Is there any solution to inspect a signal and get a good level of detail (distorting the signal as little as possible), as a zoom?
One approach is to build a circuit to limit the vertical amplification to a narrow voltage range.  Take a look at (yet another) famous Jim Williams app note, "AN47 - High Speed Amplifier Techniques":

  http://www.linear.com/docs/4138

On pages 39-41, he describes two possible circuits for a "Differential Comparator Amplifier with Adjustable Offset" using the LT1193 and LT1194 op amps which can recover quickly from overloaded inputs.

You would set up the circuit to give you amplification in the voltage range of interest, and then anything outside the range would be clamped by the op amp.  The scope should be set up so that the clamped range is on-screen (or at least at levels guaranteed to be unsaturated and free of distortions).
 

Offline Carrington

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Re: DS2072 HW FAIL SW BUG or What the hell?
« Reply #22 on: November 23, 2013, 10:47:01 pm »
@ MarkL.

Thank you so much Markl, this forum is great.

Great people make a great forum.




@ sync

My apologies for questioning his answer, now I see that you was right.
« Last Edit: November 23, 2013, 10:54:13 pm by Carrington »
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Offline Carrington

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Re: DS2072 HW FAIL SW BUG or What the hell?
« Reply #23 on: November 23, 2013, 11:44:45 pm »
What's Up is Down and What's Down is Up.

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Offline Carrington

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Re: DS2072 HW FAIL SW BUG or What the hell?
« Reply #24 on: November 24, 2013, 01:36:13 am »
Artifacts?
If anyone wants try to replicate it. The sigal is a pulse of 3.3V, wide 50ns and rise time 2ns.

« Last Edit: November 24, 2013, 01:38:19 am by Carrington »
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