Products > Test Equipment
10 MHz on Sampling Scope w/40 MHz Trigger, Not As Expected
points2:
hi 2N3055
--- Quote from: 2N3055 on January 25, 2024, 06:21:49 am ---Fast scopes are expansive..
--- End quote ---
well... thanks to confirm something that everyone knows simply by watching at price tags whatever the seller website...
--- Quote from: 2N3055 on January 25, 2024, 06:21:49 am ---Eye diagram is a diagram. It is useful for certain type of signals and usage.
--- End quote ---
well... what else ?...
--- Quote from: 2N3055 on January 25, 2024, 06:21:49 am ---Many scopes have segmented mode. If you have SDS2000X+ then you already have one that has it.
Problem is that retrigger time on scopes is much slower that <25ns period you have here..
So it won't be able to catch every consecutive period as trigger sequentially. But by simply using history mode you can "walk" and see what they are..
--- End quote ---
so what ?
you're just saying what I said above => a DSO is crap when you have to deal with fast signal.
Honestly, I never used the segment mode of my scope... because no-trust 8) ; but as you confirm it is not trusty... I'll stay away from it :-DD
ok,
I stop complaining about your post, let's be efficient & measurement-driven :
what's your experience using a SA vs a DSO, in such an example like TheWaterbug above ? Your post is about DSO, not about the perf of SA vs a the perf of a DSO in such a case => why ? I find this no-answer "weird"...
@ TheWaterbug : only 1 basic remark vs your setup :
let's be honest, what kind of guy has adivised you to run such precise measurements on such "quite" fast signal, with SO MANY stuff between the DUT (DUT = where you "probe") and the scope !?
I do this remark based upon a farily basic lesson & calculations any pupil learn at +/- 15-17years-old in chemistry (sorry, I've only that example in mind :-DD ) : what's the OVERALL uncertainty of my experiment !? Each step has its own incertainty, thus as I need x step to run my expriment => uncertaintly builds up. But if the overall uncertaintly remains negligeable vs the results => that's ok.
Here, honestly, no EE can stand your hypothesis that the overall uncertainty of your setup is negligeable vs the final result ! And espcially given the huge uncertainty given by the scope vs the overall uncertainty of all these boxes between the scope & the DUT !
my 2 cents.
If I'm wrong, anyone is welcome to teach me I'm wrong of course ! (my story : I got a degree in process&chem engineering some time ago. I've leanrt only ONE thing : "you know nothing, but you can learn" :-DD ; as any science guy, after years, I still know nothing... and keep learning :-DD ; by the way, thanks to Dave to enable us to share knowledge, just to be aware about how "I still know nothing" |O WTF ! :-DD )
2N3055:
--- Quote from: points2 on January 26, 2024, 03:57:36 am ---hi 2N3055
--- Quote from: 2N3055 on January 25, 2024, 06:21:49 am ---Fast scopes are expansive..
--- End quote ---
well... thanks to confirm something that everyone knows simply by watching at price tags whatever the seller website...
--- Quote from: 2N3055 on January 25, 2024, 06:21:49 am ---Eye diagram is a diagram. It is useful for certain type of signals and usage.
--- End quote ---
well... what else ?...
--- Quote from: 2N3055 on January 25, 2024, 06:21:49 am ---Many scopes have segmented mode. If you have SDS2000X+ then you already have one that has it.
Problem is that retrigger time on scopes is much slower that <25ns period you have here..
So it won't be able to catch every consecutive period as trigger sequentially. But by simply using history mode you can "walk" and see what they are..
--- End quote ---
so what ?
you're just saying what I said above => a DSO is crap when you have to deal with fast signal.
Honestly, I never used the segment mode of my scope... because no-trust 8) ; but as you confirm it is not trusty... I'll stay away from it :-DD
ok,
I stop complaining about your post, let's be efficient & measurement-driven :
what's your experience using a SA vs a DSO, in such an example like TheWaterbug above ? Your post is about DSO, not about the perf of SA vs a the perf of a DSO in such a case => why ? I find this no-answer "weird"...
@ TheWaterbug : only 1 basic remark vs your setup :
let's be honest, what kind of guy has adivised you to run such precise measurements on such "quite" fast signal, with SO MANY stuff between the DUT (DUT = where you "probe") and the scope !?
I do this remark based upon a farily basic lesson & calculations any pupil learn at +/- 15-17years-old in chemistry (sorry, I've only that example in mind :-DD ) : what's the OVERALL uncertainty of my experiment !? Each step has its own incertainty, thus as I need x step to run my expriment => uncertaintly builds up. But if the overall uncertaintly remains negligeable vs the results => that's ok.
Here, honestly, no EE can stand your hypothesis that the overall uncertainty of your setup is negligeable vs the final result ! And espcially given the huge uncertainty given by the scope vs the overall uncertainty of all these boxes between the scope & the DUT !
my 2 cents.
If I'm wrong, anyone is welcome to teach me I'm wrong of course ! (my story : I got a degree in process&chem engineering some time ago. I've leanrt only ONE thing : "you know nothing, but you can learn" :-DD ; as any science guy, after years, I still know nothing... and keep learning :-DD ; by the way, thanks to Dave to enable us to share knowledge, just to be aware about how "I still know nothing" |O WTF ! :-DD )
--- End quote ---
Scopes are simply a tool.. User provides the thinking.
Every tool will have limitations. Very small screwdriver is needed to work on watches, but it will break if you try to use it on something big.
Understanding how tool exactly works and what are the limitations is the key to using it to maximum effect.
It is user's responsibility to know how to use it to good result...
As a science guy you know that, i suspect...
Best,
Siniša
TheWaterbug:
--- Quote from: TheWaterbug on January 25, 2024, 12:20:26 am ---
--- Quote from: 2N3055 on January 25, 2024, 12:05:57 am ---It is simple.
You are always seeing only one edge from 10MHz synchronized with first edge from 40MHz signal.
Other 3 trigger events from 40Mhz signal will not show any edges from 10 MHz one, but will show low or high (hence the solid line on top and bottom).
40Mhz signal is actually 4 periodic events repeated at 10Mhz period in perfect synch with original 10Mhz.
It is not jittery 40Mhz but asymmetrical pattern repeated at 10 Mhz.
This can be simply demonstrated on a scope with segmented memory, where all 4 consecutive trigger events are captured separately and can be observed sequentially.
--- End quote ---
Ah, now this is finally making sense! It's exactly the inverse of the ABCD diagram, above, when triggering on the 10 MHz:
Each time I trigger on a 40 MHz edge it'll be associated with one of an A, B, C, or D edge from the 10 MHz, but they'll always be in those positions relative to my trigger edge, so the A edge never jitters, and the B edge never jitters, but the interval from A to B is different from the interval from B to C, etc.
Thank you!! This has been driving me crazy for a week.
--- End quote ---
. . . and now I think I also understand why this trace from the sampling scope differs from this trace from the DPO.
The sampling scope sees the trigger and starts sampling, but doesn't sample (only) the edge that caused the trigger, whereas it looks like the DPO does do that.
Correct?
2N3055:
--- Quote from: TheWaterbug on January 26, 2024, 05:47:29 pm ---
--- Quote from: TheWaterbug on January 25, 2024, 12:20:26 am ---
--- Quote from: 2N3055 on January 25, 2024, 12:05:57 am ---It is simple.
You are always seeing only one edge from 10MHz synchronized with first edge from 40MHz signal.
Other 3 trigger events from 40Mhz signal will not show any edges from 10 MHz one, but will show low or high (hence the solid line on top and bottom).
40Mhz signal is actually 4 periodic events repeated at 10Mhz period in perfect synch with original 10Mhz.
It is not jittery 40Mhz but asymmetrical pattern repeated at 10 Mhz.
This can be simply demonstrated on a scope with segmented memory, where all 4 consecutive trigger events are captured separately and can be observed sequentially.
--- End quote ---
Ah, now this is finally making sense! It's exactly the inverse of the ABCD diagram, above, when triggering on the 10 MHz:
Each time I trigger on a 40 MHz edge it'll be associated with one of an A, B, C, or D edge from the 10 MHz, but they'll always be in those positions relative to my trigger edge, so the A edge never jitters, and the B edge never jitters, but the interval from A to B is different from the interval from B to C, etc.
Thank you!! This has been driving me crazy for a week.
--- End quote ---
. . . and now I think I also understand why this trace from the sampling scope differs from this trace from the DPO.
The sampling scope sees the trigger and starts sampling, but doesn't sample (only) the edge that caused the trigger, whereas it looks like the DPO does do that.
Correct?
--- End quote ---
Yes.
It will sometimes take only a single sample (dot) and take all 1000 others from 1000 consecutive separate triggers...
Realtime sampling scope takes whole screen in one go from the trigger.
Repetitive sampling scopes (ETS and RIS) "assemble" the screen worth of data from many, many separate trigger events.
Best,
Siniša
David Hess:
--- Quote from: TheWaterbug on January 26, 2024, 05:47:29 pm ---The sampling scope sees the trigger and starts sampling, but doesn't sample (only) the edge that caused the trigger, whereas it looks like the DPO does do that.
--- End quote ---
Modern sampling oscilloscopes work that way, but nothing prevents sampling before the trigger like some old Tektronix models do. Sampling before the trigger allows displaying the trigger edge and earlier without a delay line which would limit bandwidth.
In order to do this, the sampling oscilloscope phase locks to the trigger source allowing for a negative trigger delay to be applied to the sampling strobe.
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