Products > Test Equipment
DIY Logic Analyzer Probe and Pods for Siglent (and LeCroy) scopes
2N3055:
--- Quote from: oz2cpu on March 13, 2021, 10:47:24 am ---here a lot of timebase settings, (this apply to all types of LA hardware, DIY and official hardware, it is a scope thing, confirmed)
the Digital got 2ns resolution (500MSa/s) so of course we expect the level change to be detected in 2ns steps...
however the clock to the digital sampler is NOT in phase or locked to the 2G samples the analog part uses !!!
so the jitter is random, and actually sometimes looking a bit funny depending on your curve frequency. (sample interference)
The same thing apply the other way : if you trigger on digital, they are now steady and locked to each other in fixed 2nS steps.
and now the analog curve gets "wide" from the random jitter. again it is 2nS wide, and it is only visible at speeds under 100nS/div.
the only way to fix this : is to lock the clocks together inside the scope design.
--- End quote ---
While you're at it, call Keysight and tell them to fix their scopes too.... :-DD
oz2cpu:
looks like the same 2nS digital resolution,
but see !! is the fixed :-) that is nice to see no random free running sub ps jitter
so this unit uses the same clock source,
how does it look, if you trigg on digital ? how is your analog looking ?
rf-loop:
--- Quote from: oz2cpu on March 13, 2021, 10:47:24 am ---here a lot of timebase settings, (this apply to all types of LA hardware, DIY and official hardware, it is a scope thing, confirmed)
the Digital got 2ns resolution (500MSa/s) so of course we expect the level change to be detected in 2ns steps...
however the clock to the digital sampler is NOT in phase or locked to the 2G samples the analog part uses !!!
so the jitter is random, and actually sometimes looking a bit funny depending on your curve frequency. (sample interference)
The same thing apply the other way : if you trigger on digital, they are now steady and locked to each other in fixed 2nS steps.
and now the analog curve gets "wide" from the random jitter. again it is 2nS wide, and it is only visible at speeds under 100nS/div.
the only way to fix this : is to lock the clocks together inside the scope design.
--- End quote ---
Look like there is now some kind of misunderstanding about how oscilloscope works, how trigger works and how analog channel (yes only these) signal position is fine adjusted for minimal visible trigger jitter, as long as trigger is in analog channel. Btw, analog channels trigger engine is totally in digital side after ADC, fully and infinitely. But digital channels are just raw sampled after comparators, and just its 1/0 state is sampled.
And absolutely sure analog ADC and this digital channels sample use same clock. I do not believe, I know it. Period.
For stop this bullshit spreading, please take pen and paper and analyze this and after 5 minutes you understand whu there exist random jitter. If you can not analyze it, then you need only believe when peoples who know, tell it. 3055 sure know it. Also I know.
Only problem is now your thinking and logical reasoning does not work properly. Where is this blind spot, you need solve it - or believe what others who know, say.
Analog and digital side clock is same and samples synchronized.
Random jitter occurs and this is a natural and inevitable consequence of the operation of the system and is not even affected by the name of the manufacturer.
Btw, even with scope you can do some very simple demonstrations. Turn scope acquisition mode to slow. Turn display mode to Dots. After then use some different signals and also use single shots.
Do you find ANY single case when analog side and digital side do not stay hand in hand. No, there is not exceptions.
Also you need understand that analog side use fine positioning system based to fine interpolation between samples. But, digital side do not have this mechanism at all... because it can not do. Why, because there is not data for do it. Also this is true, independent of manufacturers. There is no manufacturer who can adjust something when there is no data for it. Only what can do for less jitter (based to this mechanism) is rise digital side sampling speed. It is very different when some may have 5GSa/s and one have 0.5Gsa/s. some manufactures have in some models same samplerate for digital and analog. Still there is is this jitter, and it is random. Inside one sample period edge can be where ever. If it is used for trig, then analog channel jitters relative to digital channel edge. Because true edge is randomly somewhere between these digital channel samples. But analog channel draw it, if there is more samples in this edge if you stop scope you can look where is true edge and then look how much digital side edge is in wrong place... think carefully now why this digital edge is in wrong place... even when trigger was in digital channel. This is perhaps part of your blind point. With pen and paper you can easy see it. Think carefully what happen in analog side and digital side and how digital side trig.
Digital side do not trig to rising edge at all!! Digital side trig to state! State may have changed in every position between previous and next sample. When sample state is changed, digital side generate trig. True state change can be just here or it can be just after previous sample. But same time analog side display where and how signal change (and if equal propagation delay with digital channel, same time). Now every turn it can be randomly where ever between these digital side samples. Random! Because external world is not locked to oscilloscope clock signal. (Random until you phaselock used test signal to oscilloscope sampling clock.)
If I have native english this is more easy to explain. But I have this FinChinglish.
oz2cpu:
>stop this bullshit spreading
here where i come from, we try to talk nice, even if we dont agree
I would not call it BS, I just say : there is a free running clock on the digital 500MHz and another 2GHz on the analog,
since they are not locked in this unit, you get time jitter, when combining digital and analog and trig on one, and look at the other.
2nS is far from a real problem, all know that for sure.
but you need to go all the way down to 100ns/div for this not to bother your visual look and feel of your curves,
again : compleetly normal and there is a fundamental reason for this.
rf-loop:
--- Quote from: oz2cpu on March 14, 2021, 11:23:09 am --->stop this bullshit spreading
there is a free running clock on the digital 500MHz and another 2GHz on the analog,
since they are not locked in this unit, you get time jitter, when combining digital and analog and trig on one, and look at the other.
--- End quote ---
And still you continue this.
Where from you get this idea these clocks run wild. ETA: I think this incorrect reasoning happen or can see here « Reply #45 on: Yesterday at 07:47:24 pm ».
Please think carefully why it is random. I have many times advice some small tools for correct this misunderstood.. paper and pen... run scope in dots mode... and run scope in slow acquisition mode so that every frame have only one acquisition. Watch these dots and watch these digital signal edges. Switch trig source between analog and digi ch. Use enough fast time scale (old term time base) I hope some day blind spot get light.
I can not understand what is base reason for this claim. ETA: (except if it is what can see in reply #45 what I just read more carefully)
Perhaps you can tell how much jitter is between these clock signals. Perhaps you can also tell where this jitter is added to this clock (this amount what we are now talking here). Source for both clocks is same. Amount of this jitter is and must be totally in different ballpark if think this 2ns sample interval time window and then external signal what can randomly be where ever inside this time window. This is main part of this jitter.
If you do not believe open it and measure these clocks.
Even when these clocks have some small jitter between each others (because in real world zero jitter is absolutely impossible than DC what do not exist in this universe) this is not reason for this random jitter we are talking now here.
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