Author Topic: Rigol MSO5000 HiRes mode  (Read 10727 times)

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Offline Anding

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Re: Rigol MSO5000 HiRes mode
« Reply #25 on: October 30, 2022, 01:15:31 am »
Scope self-noise, nothing connected
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« Last Edit: October 30, 2022, 01:29:38 am by Anding »
 
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Offline Anding

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Re: Rigol MSO5000 HiRes mode
« Reply #26 on: October 30, 2022, 01:18:04 am »
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Offline Anding

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Re: Rigol MSO5000 HiRes mode
« Reply #27 on: October 30, 2022, 01:23:08 am »
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Offline Anding

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Re: Rigol MSO5000 HiRes mode
« Reply #28 on: October 30, 2022, 01:25:49 am »
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Offline gf

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Re: Rigol MSO5000 HiRes mode
« Reply #29 on: October 30, 2022, 09:33:47 am »
First and very simply, you can check it´s own noise with and without hi-res mode, visually.

Self-noise w/o any input signal is basically THE important thing to check.
It should be checked at different V/div settigs, comparing normal and hires mode at each V/div.

The quantities of interest which should be measured are

- Standard deviation (gives the RMS voltage of the noise as a single number, with DC excluded)

- FFT spectrum of the self noise over the full 0...fs/2 frequency span, on a vertical dBV scale, where fs is the sample rate
  Ensure that the FFT sample rate is the same as the capture sample rate (i.e. that neither up- nor down-sampling is involved)
  The resolution does not need to be very high, 16k points (for instance) are certainly sufficient.

[ If enabling hires does not lead to the expected amount of noise reduction (and there is a suspicion that it does not), then the key may be spectral power distribution of the noise, so it is advisable to check it. ]

Initially I'd only consider a timebase with the maximum sample rate.
In subsequent steps, slower timebases can be checked too.
« Last Edit: October 30, 2022, 09:38:31 am by gf »
 
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Offline FungusTopic starter

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Re: Rigol MSO5000 HiRes mode
« Reply #30 on: October 30, 2022, 09:52:45 am »
Self-noise w/o any input signal is basically THE important thing to check.
It should be checked at different V/div settigs, comparing normal and hires mode at each V/div.

Not every possible V/div setting, but not only at 1mV/div either.

Maybe 1mV (already done), 100mV and 1V.

Also try changing the horizontal timebase, see if Hires works better/worse at different settings. Try and  find anything interesting.


If enabling hires does not lead to the expected amount of noise reduction (and there is a suspicion that it does not)

The mathematics behind Hires mode are very simple, it's hard to imagine why it wouldn't work.

Then again, there must be a reason why it wasn't in there on initial release.
« Last Edit: October 30, 2022, 09:54:45 am by Fungus »
 

Offline Anding

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Re: Rigol MSO5000 HiRes mode
« Reply #31 on: October 30, 2022, 10:31:27 am »
single-shot mode, force trigger

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Offline Anding

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Re: Rigol MSO5000 HiRes mode
« Reply #32 on: October 30, 2022, 10:34:15 am »
10mV / division

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Offline Anding

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Re: Rigol MSO5000 HiRes mode
« Reply #33 on: October 30, 2022, 10:36:57 am »
100mv / division

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Offline Anding

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Re: Rigol MSO5000 HiRes mode
« Reply #34 on: October 30, 2022, 10:39:32 am »
1V / division

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Offline gf

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Re: Rigol MSO5000 HiRes mode
« Reply #35 on: October 30, 2022, 10:40:06 am »
Not every possible V/div setting, but not only at 1mV/div either.

Do you know what combination of attenuation and (re-)amplification is used at each V/div setting?
On many scopes the attenuator has only a few coarse steps, and all V/div steps in between need different amount of amplification, which implies different amount of noise. It really depends on the exact frontend architecture. You can only know for sure once you have tested them.

Quote
The mathematics behind Hires mode are very simple, it's hard to imagine why it wouldn't work.

For white noise it is clear what to expect, but if the noise power happens to be already concentrated at low frequencies, then a lowpass filter won't help too much. You can only find out if you check the spectrum.
« Last Edit: October 30, 2022, 10:45:56 am by gf »
 

Offline gf

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Re: Rigol MSO5000 HiRes mode
« Reply #36 on: October 30, 2022, 10:44:13 am »
single-shot mode, force trigger

Can you enable standard deviation measurement, and add FFT?
 

Offline Anding

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Re: Rigol MSO5000 HiRes mode
« Reply #37 on: October 30, 2022, 10:50:29 am »
Various timebses, SD measure enabled

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Offline Anding

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Re: Rigol MSO5000 HiRes mode
« Reply #38 on: October 30, 2022, 10:56:50 am »
FFT

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Offline gf

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Re: Rigol MSO5000 HiRes mode
« Reply #39 on: October 30, 2022, 10:59:37 am »
FFT

Unfortunately, the span is too small. At 8GSa/s, the full 0...4GHz range is of interest.
 

Offline Anding

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Re: Rigol MSO5000 HiRes mode
« Reply #40 on: October 30, 2022, 11:04:23 am »
Sure - can you give instructions of what to adjust?
 

Offline Anding

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Re: Rigol MSO5000 HiRes mode
« Reply #41 on: October 30, 2022, 11:11:59 am »
FFT 2GSa/S

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Offline Anding

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Re: Rigol MSO5000 HiRes mode
« Reply #42 on: October 30, 2022, 11:14:51 am »
Repeated measurements

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Offline balnazzar

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Re: Rigol MSO5000 HiRes mode
« Reply #43 on: October 30, 2022, 11:19:52 am »
I'm not understanding why hires seems to do nothing at mitigating the scope's self noise...
 

Offline FungusTopic starter

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Re: Rigol MSO5000 HiRes mode
« Reply #44 on: October 30, 2022, 11:20:12 am »
Do you know what combination of attenuation and (re-)amplification is used at each V/div setting?

No, but it doesn't really matter for noise.

There's usually two paths, you should hear a relay click over at 200mV or 500mV/div. You need to test both of those.

In these Rigols the noise seems to be in the ADC though, so it probably makes no difference what the rest of the circuit is doing.

Quote
The mathematics behind Hires mode are very simple, it's hard to imagine why it wouldn't work.
For white noise it is clear what to expect, but if the noise power happens to be already concentrated at low frequencies, then a lowpass filter won't help too much. You can only find out if you check the spectrum.

Low frequency noise would give a thick trace when you're zoomed out (due to the decimation) but it should disappear as you go towards maximum horizontal zoom.
 

Offline FungusTopic starter

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Re: Rigol MSO5000 HiRes mode
« Reply #45 on: October 30, 2022, 11:21:05 am »
Repeated measurements





These two are very interesting. There should be a sharp dropoff in noise at the high end with Hires enabled.

All I'm seeing is a slight sag in the middle.
« Last Edit: October 30, 2022, 11:31:56 am by Fungus »
 

Offline Anding

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Re: Rigol MSO5000 HiRes mode
« Reply #46 on: October 30, 2022, 11:22:11 am »
1GSa/S

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Offline FungusTopic starter

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Re: Rigol MSO5000 HiRes mode
« Reply #47 on: October 30, 2022, 11:46:39 am »
I'm not understanding why hires seems to do nothing at mitigating the scope's self noise...

Yep. The math is simple.

This is what hires mode should do:


If the MSO5000 doesn't do that at least resembles that then something is wrong.
« Last Edit: October 30, 2022, 11:52:07 am by Fungus »
 
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Offline Mechatrommer

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Re: Rigol MSO5000 HiRes mode
« Reply #48 on: October 30, 2022, 12:05:20 pm »
I'm not understanding why hires seems to do nothing at mitigating the scope's self noise...
its a bell and whistle after the signal path, like averaging... so take it as what it is... https://www.electronicdesign.com/technologies/test-measurement/article/21801317/why-you-should-care-about-oscilloscope-acquisition-modes if point to point averaging takes, say 8 points averaging to do 1 hi-res point (hires is someone hiring someone), at 8GSa/s, i read it as equivalent 1GSa/s of sampling rate, if the noise bandwidth is way below this rate, say few KHz, then hope to destroy this noise in averaging (hi-res mode) is almost nill, ymmv.
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Offline nctnico

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Re: Rigol MSO5000 HiRes mode
« Reply #49 on: October 30, 2022, 12:12:01 pm »
I'm not understanding why hires seems to do nothing at mitigating the scope's self noise...
its a bell and whistle after the signal path, like averaging... so take it as what it is... https://www.electronicdesign.com/technologies/test-measurement/article/21801317/why-you-should-care-about-oscilloscope-acquisition-modes if point to point averaging takes, say 8 points averaging to do 1 hi-res point (hires is someone hiring someone), at 8GSa/s, i read it as equivalent 1GSa/s of sampling rate, if the noise bandwidth is way below this rate, say few KHz, then hope to destroy this noise in averaging (hi-res mode) is almost nill, ymmv.
That is a good observation. Well spotted! Basically 4Gs/s or even 8Gs/s is complete, total and utter overkill for a 70MHz oscilloscope. Heck, it would be better to implement a decimation  algorithm that turns 16 samples into 1 sample. That would give 2 extra bits of ADC resolution. There is enough noise to make that work like a charm.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 
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