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| Building my own scope |
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| tautech:
OP, balnazzar, you have mail. |
| David Hess:
--- Quote from: Mechatrommer on October 23, 2022, 03:15:05 pm --- --- Quote from: David Hess on October 23, 2022, 01:59:28 pm ---All modern sampling oscilloscopes use sequential sampling which further limits their general applicability. Past instruments which were more general purpose include the Tektronix 7T11, 7S14, and 3T2 which provided either random sampling, or in the case of the 7S14, a delay line, allowing them to sample the leading part of a signal like a conventional oscilloscope. --- End quote --- but random sampling still needs repetitive (any shape) signal to show meaningful display. glitches, close loop control system, noises and many other areas (non-repetitive) cannot be shown correctly. --- End quote --- Sure, and the same applies to equivalent time sampling when used by a digital storage oscilloscope. Sampling oscilloscopes can capture the same thing, but it takes longer because of their lower sample rates. I once measured the rise time of a coaxial relay type of pulse generator operating at 120 Hz. With a general purpose digital storage oscilloscope using 500 MS/s equivalent time sampling, this takes only a fraction of a second. With a random sampling oscilloscope, it took half an hour. The advantage of the sampling oscilloscope was 10+ GHz bandwidth and predictable transient response versus 100s of MHz. Glitches and the transient response of closed loop control systems can be repetitive. In many applications, including eye diagrams, a histogram is desired anyway, but histogram will not distinguish between noise and non-repetition. |
| rob77:
--- Quote from: David Hess on October 24, 2022, 03:01:46 pm ---Glitches and the transient response of closed loop control systems can be repetitive. In many applications, including eye diagrams, a histogram is desired anyway. --- End quote --- "can be" doesn't mean that all glitches are repetitive, in wast majority of cases glitches are non repetitive. each tech has it's own use case... but if you're hunting a bug on a 40MHz SPI bus then all your sampling scopes and the 1GHz bandwith scope with 40MS/s are useless.... |
| tggzzz:
--- Quote from: rob77 on October 24, 2022, 03:16:51 pm --- --- Quote from: David Hess on October 24, 2022, 03:01:46 pm ---Glitches and the transient response of closed loop control systems can be repetitive. In many applications, including eye diagrams, a histogram is desired anyway. --- End quote --- "can be" doesn't mean that all glitches are repetitive, in wast majority of cases glitches are non repetitive. each tech has it's own use case... but if you're hunting a bug on a 40MHz SPI bus then all your sampling scopes and the 1GHz bandwith scope with 40MS/s are useless.... --- End quote --- 40MHz? Do you mean 40Mb/s? A 100MHz scope (say) with 1GS/s (or 10GS/s for that matter!) would be hard put to spot signal integrity issues or create a useful eye diagram. As you say, each tool has its own use cases. That means it is unwise to make global statements without reference to use cases or preconditions for the statement's validity. |
| rob77:
--- Quote from: tggzzz on October 24, 2022, 05:10:26 pm --- --- Quote from: rob77 on October 24, 2022, 03:16:51 pm --- --- Quote from: David Hess on October 24, 2022, 03:01:46 pm ---Glitches and the transient response of closed loop control systems can be repetitive. In many applications, including eye diagrams, a histogram is desired anyway. --- End quote --- "can be" doesn't mean that all glitches are repetitive, in wast majority of cases glitches are non repetitive. each tech has it's own use case... but if you're hunting a bug on a 40MHz SPI bus then all your sampling scopes and the 1GHz bandwith scope with 40MS/s are useless.... --- End quote --- 40MHz? Do you mean 40Mb/s? A 100MHz scope (say) with 1GS/s (or 10GS/s for that matter!) would be hard put to spot signal integrity issues or create a useful eye diagram. As you say, each tool has its own use cases. That means it is unwise to make global statements without reference to use cases or preconditions for the statement's validity. --- End quote --- i meant 40MHz because it's 40MHz... it's pretty common to specify the SPI speed by it's clock frequency. --- Quote ---A 100MHz scope (say) with 1GS/s (or 10GS/s for that matter!) would be hard put to spot signal integrity issues or create a useful eye diagram. --- End quote --- your sampling scope would not even catch the runt pulse, and your 1GHz bandwidth 40MS/s scope you love so much would not even notice half of the data... so what to use ? Mr. Tggzzz with a sharp pencil and a paper roll will do the trick i guess... while everyone else is happily using the 1GS/s scopes which are in fact not usable because the almighty omnipresent and omnipotent Mr. Tggzzz said so :-DD --- Quote ---it is unwise to make global statements without reference to use cases or preconditions for the statement's validity --- End quote --- that's exactly what You were doing in this thread :-DD peace for everyone ! i'm signing off ;D |
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