Products > Test Equipment

Building my own scope

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py-bb:

--- Quote from: tggzzz on October 22, 2022, 07:06:36 pm ---
--- Quote from: py-bb on October 22, 2022, 06:43:44 pm ---
--- Quote from: tggzzz on October 22, 2022, 06:36:54 pm ---
--- Quote from: py-bb on October 22, 2022, 04:51:02 pm ---
--- Quote from: pcprogrammer on October 22, 2022, 04:48:01 pm ---
--- Quote from: py-bb on October 22, 2022, 04:41:26 pm ---I work very hard to know where I'm fit to comment and I do not like your tone.

--- End quote ---

Well that is your prerogative. As it is mine to make observations, and what I wrote is what my opinion is, based on what I have seen today.

--- End quote ---

Well in my opinion you're a git, you should never mock someone for asking a question about how to operate equipment safely.

That's a very bad habit to have indeed.

--- End quote ---

If pcprogrammer had done that, I would agree with you.

--- End quote ---

Thanks for sharing your unique view of the world..... I guess.

Hopefully now you've got that out of the way we can get back on topic.

--- End quote ---

There are solid grounds for stating it is not a unique view of the world.

I agree that your becoming the subject of a subthread is indeed distracting.

--- End quote ---

Hey I've been trying to drop hints I'm not interested for a while.

For some reason you seem to think you're worth listening to.

The post I am replying to, why did you feel the need for that?

All you're doing is making yourself look bad, the regulars might know you but I'm new! To me you look like this weird contrary loon arrogant enough to to think crap like that is worth posting.

Take 10 minutes, think before you press enter. Otherwise I don't see what good can come of interacting with you.

David Hess:

--- Quote from: balnazzar on October 22, 2022, 12:36:14 am ---Thanks. You seem to be remarkably knowledgeable. Do you work in the field of oscilloscope manufacturing?
--- End quote ---

I never have, but I have studied oscilloscope design for years, and am considering doing a similar project based on the Tektronix 2232.


--- Quote from: py-bb on October 22, 2022, 03:03:02 am ---With digital ones the problem is that you need to have 1 amplifier (at least for each channel) and one thing sampling it (the ADC). This is because if you had 2 and switched between them (say taking it in turns) they'd be slightly different in gain and sampling. We often don't expect channels to be exactly the same so you can get away with it but still.
--- End quote ---

The Tektronix 2230 and its predecessor, the 468, use a single digitizer for two channels with analog channel switching without any problems.  The 2230 even weirdly supports chop or alternate mode when operating as a digital storage oscilloscope.  Of course it would be silly to design a DSO this way today, and the 2232 which replaced the 2230 uses one digitizer per channel.

Most DSOs even now use analog channel switching to support more than one channel per digitizer, or more than one digitizer per channel, but it is done internally as part of the ADC.  This has been done for a long time to support higher sampling rates when fewer channels are in use.  It is not difficult to do, but is an unneeded complication.


--- Quote from: pcprogrammer on October 22, 2022, 05:57:32 am ---
--- Quote from: David Hess on October 21, 2022, 11:14:55 pm ---A low sampling rate sampling oscilloscope could be made for bandwidths above 1 GHz but that entails several other design disciplines and is less generally useful.
--- End quote ---

Correct. Take equivalent time sampling, but for that to work you need a reliable fine scaled delay, or more useful for spectrum analysis a heterodyne mixer to bring your signal down in frequency. But these require a lot of additional electronics to make it work.
--- End quote ---

I was thinking in terms of a sampler and the timing circuits.  Neither are a trivial exercise at GHz bandwidths and picosecond resolution.

I have been looking into the requirements to design a modern "sampling DSO" based on the random sampling capability of the Tektronix 7T11.  This would combine 4+ GHz sampling bandwidth with conventional operation from the user's perspective without a delay line.


--- Quote ---
--- Quote from: David Hess on October 21, 2022, 11:14:55 pm ---Last year I figured there should be standard interface ADCs and processors to allow for a high sample rate design without an FPGA or custom logic, and there are, but they are incredibly expensive.
--- End quote ---

You mean the FMC based systems?
--- End quote ---

I do not remember if that was it, but there is a standard for high speed ADC interfacing and I did a search for ARM microcontrollers which support it.  The cost of the ADC and microcontroller were much higher than the cost of a more conventional ADC and microcontroller and an FPGA to interface them.


--- Quote from: pcprogrammer on October 22, 2022, 08:21:47 am ---Well most likely money. High speed ADC's are expensive and using two that are capable of half the speed might cost way less than the single high speed one.
--- End quote ---

There are plenty of reasonably priced sampling ADCs now that are fast enough to make a useful DSO.


--- Quote from: tggzzz on October 22, 2022, 10:10:40 am ---Delay isn't too much of a problem: see the very simple circuits in the Tektronix 1502 TDR.
--- End quote ---

A TDR has the advantage of operating synchronously and generating its own trigger.  A sequential sampling oscilloscope has two triggers, one for the external signal and one for the sampling strobe.  A random sampling oscilloscope in addition has to measure positive and negative delay, and includes a rate generator.


--- Quote ---Triggering from the signal is more challenging. The Tek 1502 avoids that by having an, ahem, external trigger that is generated internally :)
--- End quote ---

In most cases the triggering does not need to have as high a bandwidth as the input signal.  What does matter however is trigger noise which requires careful design to minimize.  The required performance was easier when tunnel diodes were available, but there are some modern comparators which are good enough.  What is missing now however are fast PNP transistors.

Mechatrommer:
now i found the guy (apart from the Ted Yapo OSHW thread). 12GHz $300 Kickstarter was no go... official website out of stock. the BOM should be lesser than $300 in case somebody want to follow the trail, or implement the concept into slower MHz much cheaper, much fewer like maybe 200 Sa/s? i think we can push arduino to 2KSa/s so GHz frontend with arduino sampler should not be improbable ;D jk..

https://www.kickstarter.com/projects/1855991221/10-ghz-usb-oscilloscope
http://www.fastsampling.com/
https://www.eevblog.com/forum/crowd-funded-projects/10-ghz-usb-oscilloscope/

if you want to get fancy $35K sequential ETS PicoTech:
https://www.picotech.com/oscilloscope/9300/picoscope-9300-sampling-oscilloscopes



and here recap from not a marketing manager, the Tek.. to whoever missed the bus... befriending Al Zimmerman alone will not make you right..
https://w140.com/tekwiki/wiki/Sampling_oscilloscope
here quoted to get into context:

--- Quote ---Equivalent time sampling requires repetitive signals

--- End quote ---
thats the Tek's saying, not me.

not the best guy i can find explaining to prejudice, but best demonstration i can see in my top google list for those who are lazy to read texts...


talk about Compressive (Random Time) Sensing but link is broken..
Shannon also mentioned theory of lossless reconstruction through subsampling...
https://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theorem#Sampling_of_non-baseband_signals
https://en.wikipedia.org/wiki/Compressed_sensing

for those who want to dig into the math and hence to the possibility of application... i can barely understand, but my ignorance doesnt make me right when bragging fallacies :-DD fwiw..

David Hess:

--- Quote from: Mechatrommer on October 23, 2022, 01:17:18 pm ---now i found the guy (apart from the Ted Yapo OSHW thread). 12GHz $300 Kickstarter was no go... official website out of stock. the BOM should be lesser than $300 in case somebody want to follow the trail, or implement the concept into slower MHz much cheaper, much fewer like maybe 200 Sa/s? i think we can push arduino to 2KSa/s so GHz frontend with arduino sampler should not be improbable ;D jk..
--- End quote ---

An Arduino easily has the processing power, but significant external hardware is required for the sampler, triggers, and time-to-digital conversion.


--- Quote ---https://www.kickstarter.com/projects/1855991221/10-ghz-usb-oscilloscope
http://www.fastsampling.com/
https://www.eevblog.com/forum/crowd-funded-projects/10-ghz-usb-oscilloscope/

if you want to get fancy $35K sequential ETS PicoTech:
https://www.picotech.com/oscilloscope/9300/picoscope-9300-sampling-oscilloscopes
--- End quote ---

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.


--- Quote ---and here recap from not a marketing manager, the Tek.. to whoever missed the bus... befriending Al Zimmerman alone will not make you right..
https://w140.com/tekwiki/wiki/Sampling_oscilloscope
here quoted to get into context:
--- Quote ---Equivalent time sampling requires repetitive signals

--- End quote ---
thats the Tek's saying, not me.
--- End quote ---

Sampling oscilloscopes require a repetitive signal, but it is possible to sample a repetitive but irregular signal.

Mechatrommer:

--- 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.

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