Author Topic: Project Yaigol: Fixing Rigol scope design problems.  (Read 83103 times)

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Offline scummos

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #275 on: September 02, 2016, 04:20:19 pm »
The screenshot in Bud's PDF has a span of 50 kHz. This one has 4 MHz ... with 4 MHz spread, you are .25% off, I can imagine you can see that. But yeah, you're right -- it could cause this kind of problem
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Offline marmad

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #276 on: September 02, 2016, 04:33:50 pm »
The screenshot in Bud's PDF has a span of 50 kHz. This one has 4 MHz ... with 4 MHz spread, you are .25% off, I can imagine you can see that. But yeah, you're right -- it could cause this kind of problem

As well as being a different model of DSO.
 

Offline wraper

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #277 on: September 02, 2016, 05:07:52 pm »
As well as being a different model of DSO.
It's irrelevant, same clock stability issue will cause the same jitter problem on different models.
 

Offline marmad

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #278 on: September 02, 2016, 05:09:25 pm »
As well as being a different model of DSO.
It's irrelevant, same clock stability issue will cause the same jitter problem on different models.

It's relevant since many of us with DS2000s have measured no clock instability issue whatsoever (read thread). IIRC, it was much more common (and much worse) in the DS1000Z, the model in the video you posted.
« Last Edit: September 02, 2016, 05:11:43 pm by marmad »
 

Offline wraper

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #279 on: September 02, 2016, 05:18:45 pm »
As well as being a different model of DSO.
It's irrelevant, same clock stability issue will cause the same jitter problem on different models.

It's relevant since many of us with DS2000s have measured no clock instability issue whatsoever (read thread). IIRC, it was much more common (and much worse) in the DS1000Z, the model in the video you posted.
The same of you also likely don't have oscillating Vregs. As I posted before, my scope uses different flavor of 1117 and there is no oscillation.
 

Online RoGeorge

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #280 on: October 20, 2016, 05:03:11 pm »
This post is just to easily follow the subject.

Offline Fungus

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #281 on: October 20, 2016, 05:19:49 pm »
This post is just to easily follow the subject.

What on earth for? It's just a bunch of sourpusses who can't actually demonstrate any effect on screen.

 

Online Bud

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #282 on: October 20, 2016, 10:40:21 pm »
This thread is about proper engineering, not about Walmart shopping.

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Offline madires

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #283 on: October 21, 2016, 11:34:43 am »
This post is just to easily follow the subject.

What on earth for? It's just a bunch of sourpusses who can't actually demonstrate any effect on screen.

He posted that text in 8 threads. :-//
 

Offline rch

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #284 on: October 21, 2016, 11:48:46 am »
This post is just to easily follow the subject.

What on earth for? It's just a bunch of sourpusses who can't actually demonstrate any effect on screen.

He posted that text in 8 threads. :-//

Perhaps he hasn't noticed the 'notify' button?
 

Offline Zbig

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #285 on: October 21, 2016, 12:05:51 pm »
This post is just to easily follow the subject.

What on earth for? It's just a bunch of sourpusses who can't actually demonstrate any effect on screen.

He posted that text in 8 threads. :-//

Perhaps he hasn't noticed the 'notify' button?

He's actually been advised to do just that by a seasoned EEVBlog member: https://www.eevblog.com/forum/chat/show-unread-messages-but-filter-only-the-topics-where-i-wrote-something/msg1052861/#msg1052861 :palm:
 

Offline bitseeker

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #286 on: October 21, 2016, 07:32:43 pm »
The notify button will email you new replies, but won't add the thread to the new replies page. Unfortunately, you have to reply to a thread to have the forum track it on the new replies page.
I TEA.
 

Offline rch

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #287 on: October 21, 2016, 10:15:44 pm »
The notify button will email you new replies, but won't add the thread to the new replies page. Unfortunately, you have to reply to a thread to have the forum track it on the new replies page.

The answer is to try very hard to say something relevant to the thread.  People may not think it very profound, but at least they may not spot what one is up to!
 

Offline bitseeker

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #288 on: October 21, 2016, 11:30:30 pm »
The answer is to try very hard to say something relevant to the thread.  People may not think it very profound, but at least they may not spot what one is up to!

Certainly.

To that end, since the conclusion of this investigation, has anyone else opened up a newer hardware version of a 2000-series scope for comparison?
I TEA.
 

Online RoGeorge

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #289 on: September 10, 2017, 08:22:54 pm »
There were some questions about the Rigol DS1000Z PLL in another thread, and most of the arguments were coming from this topic, so I read the PDFs posted at the beginning, then the whole thread, and decided to ask here, even if it's been a while since the last post.

By the way, very good findings and well documented, thank you very much for posting them, Bud.

For testing my DS1054Z jitter at 5us distance from the trigger point, I used the latest firmware (which is supposed to fix the PLL issue in software by using better values for programming the PLL), and indeed at 5 us distance the Jitter is not visible any more on the screen.

Still, if I increase the distance from the trigger point long enough, there still is some jitter, and the jitter is apparently increasing linearly with the distance in time from the trigger point.

I measured the jitter by setting the display to memorize the trace on the screen for the last 10 seconds, and try to guess the best spread in time of the edges by averaging 5 different captures. Both instruments were on for a couple of hours at constant temperature before measuring. Here are some values measured with a square signal from a Rigol DS4102 DDS (that is supposed to have +/- 2ppm frequency accuracy, and a max jitter of 500ps according to its specs) using a 50 ohms cable and an external terminator at the oscilloscope's BNC.

As can be seen in the attached captures, the jitter is increasing almost linearly with the time distance from the sync point. Why is that? Isn't the PLL jitter supposed to be random and independent of the test signal, so the jitter of the displayed test edges wouldn't accumulate with the distance from the trigger point?

The PLL is trying to sync with the internal oscillator, which is running continuously and independently from the test signal, so if the PLL jitter is randomly distributed, then I expect to see on the screen the same jitter for any edge of the test signal, no matter how far from the trigger point is the displayed test edge.

Why does the displayed jitter of the edges from the test signal increases (almost linearly) with the distance (in time) from the trigger moment?

Offline TimNJ

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #290 on: September 13, 2017, 02:35:16 pm »
There were some questions about the Rigol DS1000Z PLL in another thread, and most of the arguments were coming from this topic, so I read the PDFs posted at the beginning, then the whole thread, and decided to ask here, even if it's been a while since the last post.

By the way, very good findings and well documented, thank you very much for posting them, Bud.

For testing my DS1054Z jitter at 5us distance from the trigger point, I used the latest firmware (which is supposed to fix the PLL issue in software by using better values for programming the PLL), and indeed at 5 us distance the Jitter is not visible any more on the screen.

Still, if I increase the distance from the trigger point long enough, there still is some jitter, and the jitter is apparently increasing linearly with the distance in time from the trigger point.

I measured the jitter by setting the display to memorize the trace on the screen for the last 10 seconds, and try to guess the best spread in time of the edges by averaging 5 different captures. Both instruments were on for a couple of hours at constant temperature before measuring. Here are some values measured with a square signal from a Rigol DS4102 DDS (that is supposed to have +/- 2ppm frequency accuracy, and a max jitter of 500ps according to its specs) using a 50 ohms cable and an external terminator at the oscilloscope's BNC.

As can be seen in the attached captures, the jitter is increasing almost linearly with the time distance from the sync point. Why is that? Isn't the PLL jitter supposed to be random and independent of the test signal, so the jitter of the displayed test edges wouldn't accumulate with the distance from the trigger point?

The PLL is trying to sync with the internal oscillator, which is running continuously and independently from the test signal, so if the PLL jitter is randomly distributed, then I expect to see on the screen the same jitter for any edge of the test signal, no matter how far from the trigger point is the displayed test edge.

Why does the displayed jitter of the edges from the test signal increases (almost linearly) with the distance (in time) from the trigger moment?

I haven't been following this thread nor am I an expert on PLLs, but perhaps you are witnessing some level of frequency modulation and not "jitter"?

In a control loop with frequency control, like in a switchmode power supply, this behavior is common. Let's say the modulating signal is sinusoidal. That would mean that the PLL clock signal would constantly be sweeping up and down from fmin to fmax. In a digital scope, when you are triggered on the rising edge of a clock signal, to the left and right of the trigger point, you see the "past" and "future" of the signal. Now, keeping the trigger point locked down, superimpose fmin onto fmax. You will see as you move farther away from the trigger point, the difference in time (phase difference) between the clock edges will get greater and greater. This phase difference is continuously compounded as you move away from the trigger point. I attached a little picture to help illustrate.

I'm not entirely sure if that's what you're seeing but that's what it sounds like to me.
 

Online RoGeorge

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #291 on: September 17, 2017, 09:17:43 am »
Yes, it could be some kind of frequency modulation.

Still, on the oscilloscope's screen, the edges are jumping around a middle position. The jumping seems pretty random to me, it doesn't look like a continuous drift or a modulation, but I didn't made any statistics, so I might be wrong. Next time I will try to record the screen, and post it here. My experience with stable oscillators is zero, it might be just normal to see an edge randomly jumping inside a 100ns range window when looking at 1 second later after the trigger point, I don't know.

I also suspect that the oscilloscope might not use a circular buffer for storing the ADC's samples (which would be crazy, but who knows), and for delays longer than 24ms (max scope's memory is 24 million samples, at a sample rate of 1Gs/s that would be 24ms) the scope is just waiting for the required delay without sampling, then start sampling and memorizing. If this is true, and the waiting delay is calculated using the reference oscillator (25MHz) and not the PLL (1GHz), that might make the seen "jitter" to accumulate for longer delays.

For my own curiosity, for the next step I want to save all 24 Msamples in the PC (for many times) and do some Fourier analysis. The hope here is to clarify if what is seen on the screen is because of a jitter, a drift, a frequency modulation or maybe something else.

For the next measurements, I will try to use the sync output from the generator, as Teneyes PM'ed me, in the hope that the edges from the sync output will be faster then the edges of the signal output, and this will reduce the oscilloscope's trigger jitter. Trigger jitter should not accumulate with the viewing delay, but the more stable, the better.

Also, I searched about jitter accumulation in PLLs, and found a few PDFs online, but didn't have the time to parse them, so I'm not sure yet if the jitter accumulation described in those PDFs is applicable here.

TL;DR
Just to be clear: The 5us PLL jitter bug from a couple of years ago was fixed long time ago. That bug is not present any more in my DS1054Z.

What I am testing here is just because I want to have a better understanding about PLLs in general.

Online RoGeorge

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #292 on: September 26, 2017, 01:10:42 am »
Since I'm not sure this is related to this thread, I am posting the new measurements in a new topic:
https://www.eevblog.com/forum/testgear/rigol-dg4102-and-ds1054z-skew-and-accumulating-jitter/msg1309844/


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