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Frequency Divider for older Oscilloscopes??

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2N3055:

--- Quote from: bdunham7 on July 18, 2021, 08:28:34 pm ---
--- Quote from: 2N3055 on July 18, 2021, 07:44:18 pm ---With RIS (random interleaved sampling) we also trigger, but it is upside down: we sample at random intervals, not sequentially from the trigger. But we do keep triggering, and measure time from trigger and sample so we know where to position the point in time domain. It is funny to look at how it assembles the waveform by plotting random  dots left and right until it starts to resemble the waveform...

That is how analog sampler scopes worked, with different details in implementation of S/H circuit, and actual timing and trigger circuits. Some samplers didn't even have real trigger circuit, but you had to provide trigger yourself, already conditioned...

--- End quote ---

I understand ETS and sampling scopes, I even have several still.  I don't see how what Jorge is describing could possibly do any of those things.

--- End quote ---

Funny thing is that sometimes non native English speakers understand better other non native English speakers because to us it is a logical process, not natural simple recognition. We go by logic of the said words and not by what it should be in good English.  Trust me, he's is talking about sequential sampling principle (ETS style).  And if you do 10000 points per second, you don't even need A/D and storage. You simply show it on slow CRT scope screen where phosphor persistence will act as a storage for some miliseconds, enough to build full screen.

Jorge Ginsberg:
I made this drawing using paint.  It's not a good drawing, but just by looking at it you will understand exactly how I was able to get a 100 Mhz signal to transform into a 10 Khz signal.  If the samples are thousands per cycle, the reconstituted waveform is a perfect copy of the sampled signal.  See the attached png file.

bdunham7:

--- Quote from: 2N3055 on July 18, 2021, 09:55:33 pm ---Funny thing is that sometimes non native English speakers understand better other non native English speakers because to us it is a logical process, not natural simple recognition. We go by logic of the said words and not by what it should be in good English.  Trust me, he's is talking about sequential sampling principle (ETS style).  And if you do 10000 points per second, you don't even need A/D and storage. You simply show it on slow CRT scope screen where phosphor persistence will act as a storage for some miliseconds, enough to build full screen.

--- End quote ---

Sometimes by approaching things from different angles, two people can describe the same phenomenon in different ways.  If you look at his picture and read my description, I think they match exactly.  How would you describe that other than as an alias?  It's only going to work if the sampling frequency is offset from the signal frequency slightly, and by a known amount if you want to have a predictable display.

I'm not sure what you mean when you say that you can just put it on the screen at 10,000 samples per second.  ETS also has a way of knowing the timing of each sample so that it knows where (horizontally) to display it.  Can you show me an example where this would work otherwise?  Without storing the samples, to put them up at the right position would require the sweep rate to be synced to the input frequency.  Unless I'm missing something, which is always possible, I think the method described here is some sort of alias-based downmixing and can't work for arbitrary frequencies unless the sampling rate is somehow automatically tuned with a fixed offset.

Now if the circuit is complex enough that it can trigger on the 100MHz signal and then produce a ramp to trigger the sample point at calibrated and increasing time offsets, then it might be able to accomplish the task without depending on any particular characteristic of the input other than repeatability.  Then you'd have a phosphor-based storage sampling scope like you describe.  I don't see that what he describes could accomplish all that--it would require a bit more complexity than he describes.

bdunham7:

--- Quote from: Jorge Ginsberg on July 18, 2021, 10:05:29 pm ---I made this drawing using paint.  It's not a good drawing, but just by looking at it you will understand exactly how I was able to get a 100 Mhz signal to transform into a 10 Khz signal.  If the samples are thousands per cycle, the reconstituted waveform is a perfect copy of the sampled signal.  See the attached png file.

--- End quote ---

OK, but it seems clear that your sampling rate is just slightly slower than the input signal, not equal to it, right?  How does the circuit determine and set the sampling rate?

Ian.M:
I agree with Bdunham.  To down-convert a 100.000MHz signal to 10KHz, you need to sample at 99.990MHz, not at 100.000MHz.   If you want to automate this so that the output frequency is always 1/10000 of the input frequency, at the very least you'll need a good VCO for the sampling clock that covers the input range you are interested in, and to PLL lock it to 9999/10000 of the input frequency (which is a whole other can of worms if the input is not a nice quasi-sinusoid).

The requirements for the sample and hold are also rather stringent - it may well be easier to implement as a pair of carefully matched track and holds that alternate acquiring the signal, and a fast analog switch to select the one currently holding.

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