Author Topic: EEVblog #1213 - The Oscilloscope Interpolation Trap  (Read 2633 times)

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Offline vk6zgo

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Re: EEVblog #1213 - The Oscilloscope Interpolation Trap
« Reply #25 on: May 22, 2019, 08:59:31 am »
In the interpolated signal there is a dead give away that the ringing is due to some kind of digital filtering / interpolation: there was ringing before the transition. Ringing from a probe or poor signal quality has ringing only after the transition.

In the case of testing a limited bandwidth system, like analog TV, the signal I mentioned in my previous posting (a "T"or "2T" "sine squared pulse)* will often show both "pre shoot" & "post shoot", the amplitude of which are primarily related to the bandwidth & Group Delay of the system.

Unfortunately, the artefact at 2:40 in Dave's video looks like a typical result of such testing
Another "trap for old players!"

*In the early days of TV, a rectangular pulse with sharp rise & fall times was used, but massive ringing due to the limited system bandwidth caused difficulties in measurement, so the " sine squared pulse"was devised.
 

Offline wilfred

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Re: EEVblog #1213 - The Oscilloscope Interpolation Trap
« Reply #26 on: May 22, 2019, 09:38:22 am »
Hm, is is just me or does that red sinc drawing look a bit "pubertal"? I mean I would totally expect things like that in a school toilet but I guess some people (who don't even bother to look into the video) could be offended by this on Youtube.

Look at the bright side. Fewer people will fall for the interpolation trap as a result of the increased popularity of the video. I have recently become aware that catchy thumbnails is one way of fertilising the seeds of knowledge.

 

Offline EEVblog

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Re: EEVblog #1213 - The Oscilloscope Interpolation Trap
« Reply #27 on: May 22, 2019, 01:29:11 pm »
As Dave said, it's "the 10 year old" in him that saw that.  I didn't see it myself until after watching the video and hearing that comment from Dave.
Personally, if people want to see that, then I think they are looking for it and complaining would be their childish tantrum way of making themselves feel good.  Edit:  I was not referring to you, 0xdeadbeef!
I'd have been a little happier if it hadn't been pointed out - but, hey, Dave's channel ... Dave's call.  I can live with it.

Obviously the 40+ yo in me saw it too.
I put out a public call on twitter the other week for the first person to get a manufacturer to silkscreen a dick'n'balls onto their chip wins The Internet.
The world has gone to politically correct hell, the "easily offended" need to be ridiculed, not pandered to. Dick'n'Balls on everything.
 

Offline schmitt trigger

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Re: EEVblog #1213 - The Oscilloscope Interpolation Trap
« Reply #28 on: May 22, 2019, 05:17:50 pm »
I've seen Mickey Mouse and other goofy stuff etched on chips, a politically incorrect Viva Cuba Libre, would be a quantum step improvement.
« Last Edit: May 22, 2019, 05:19:26 pm by schmitt trigger »
 

Offline Bud

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Re: EEVblog #1213 - The Oscilloscope Interpolation Trap
« Reply #29 on: May 22, 2019, 06:56:04 pm »
Dick'n'Balls on everything.

...and IN everything, like firmware  ;)
Facebook-free life and Rigol-free shack.
 

Online rhodges

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Re: EEVblog #1213 - The Oscilloscope Interpolation Trap
« Reply #30 on: May 22, 2019, 08:22:12 pm »
Look at the Broadcom logo...
Currently developing STM8. Past includes 6809, Z80, 8086, PIC, MIPS, PNX1302, and some 8748 and 6805.
 

Offline vk6zgo

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Re: EEVblog #1213 - The Oscilloscope Interpolation Trap
« Reply #31 on: May 23, 2019, 02:32:22 am »
Dick'n'Balls on everything.

...and IN everything, like firmware  ;)

Well they dick around with,the firmware & balls it up! ;D
 

Offline David Hess

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Re: EEVblog #1213 - The Oscilloscope Interpolation Trap
« Reply #32 on: May 23, 2019, 03:23:28 am »
Equivalent time sampling scopes don't have the same trouble with aliasing provided the signal you are observing is repetitive.

That is true but DSOs that support equivalent time sampling usually do not at slower sweep speeds (1) where the real time sample rate will completely fill the acquisition record in one acquisition and many DSOs back then did not support equivalent time sampling at all.  For a while it was a premium feature.

So detecting possible aliasing by comparing the processed trigger and sample rate would still be useful even on a DSO which supports equivalent time sampling.  It would be useful even with the huge record lengths available today.

Quote
Unfortunately Tek has dropped this feature on its newer scopes in favour of interpolation with all the issues of aliasing. It's a pity because they did it extremely well on the scopes that offered it.

Most manufacturers dropped it and the reason is simple enough; the performance of integrated ADCs and memory reached a point where real time sampling rates were sufficient to support digital triggering at a cost lower than the dedicated hardware needed to measure the trigger to sampling clock delay for equivalent time sampling.

Support for equivalent time sampling is still found in higher end DSOs were the cost of supporting a real time sample rate high enough for increased bandwidth is prohibitive.

(1) DPO style DSOs do not care a whit about this.  They effectively always operate in equivalent time mode.
 


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