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Does a capacitor charges smooth, or in stairs?

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StillTrying:

--- Quote from: rhb on June 23, 2020, 01:43:15 pm ---should be able to measure the DSO timebase jitter.
--- End quote ---

On my trigger diagram I was thinking maybe the trigger's low Y position was an even a bigger problem than the X position.
If the trigger position was going to do some clever sub 1ns position timing it wouldn't have any slope to work with if every ADC sample at that trigger low Y position was 00, - other than wait until the input V and ADC values start counting up from 00 - at some random time. :)
IF it does work like that I can imagine(why not!) up to 1ns of jitter creating some nice stairs somewhere.

On your latest capture, a 1 Vpp ? arriving at the scope on 10mV/div. shouldn't overload or out of range anything, - even the trigger!
- in theory.
DS1202Z-E  1 mV/div to 499 mV/div: Offset Range ±2V

While I'm there:
Trigger Level Range  Internal ±5 div from center of the screen

But even with the trigger's X and Y within the screen area you've beaten your record near infinite rise times with some slightly negative ones.
Whatever it's doing I don't think a scope showing any negative rise times on relatively simple waveforms is much use, I hope you've still got its box!

Labrat101:

--- Quote ---The failure of a DSO to produce analog scope trace quality is a design failure.  It is not inherent in the scope being digit

--- End quote ---
Try using  a good analog scope and then all those filters are not needed.
You see what is really there and not a computation Of the signal .
Adding the wrong filter in  the wrong place does not solve a problem. 
Tipex would also work . Unless you have a high end DSO the signal is being processed by  simulation. So if you play enough with filters etc you can get what looks good.
But is it correct . ?

rhb:
Is a Tektronix 1 GHz 7104 "good enough"?  There is implicitly a BW filter on every analog scope.  The step response tells you what that filter shape is.

Is a 1.5 GHz LeCroy DSO "high end"?  The LeCroy has all the jitter analysis tools enabled, but I've not tried them out yet.  Not really much point until I have a GPSDO clock input set up to feed it.

I spent 30+ years in the oil industry writing and fixing seismic DSP codes.   That is far more exotic DSP than anything the EE community does.  Always has been.  In the 60's when ADCs barely existed we could live with 4 ms sample rates and had the money to pay for them and the computers to process the data.  A common seismic imaging operation today  takes 10,000 to 20,000 core clusters 7 to 10 days to complete.  The input is 10-15 TB.  Each output sample takes several gigaflops to compute.  What's more, this is not a one shot.  It's iterative.  You run the job, look at the results, update the velocity model and repeat.

Texas Instruments was a wholly owned subsidiary of Geophysical Services Inc created specifically to build seismic recording equipment.

The trigger point is shown on the last plot I posted. The signal is about 900 mVpp.  It's adjustable, but I have to run a program on the PC to do that and I don't have a Windows machine I can boot easily at the moment.

I'm afraid I don't grok "negative rise times".  Where is that from? I think the persistence for that plot was 1 second.

As best I can tell what's happening is the scope is triggering and the steps are slightly less than 200 ps.  So the vertical segment is samples at various points on a slope which then gets displayed at the same time.  As I remarked before, the 11801 will tell the truth about what the front end looks like.  If the steps are ringing in the front end they will show up as reflection events on the 11801 & SD-24.

Have Fun!
Reg

StillTrying:

--- Quote from: rhb on June 23, 2020, 07:50:04 pm ---I'm afraid I don't grok "negative rise times".  Where is that from? I think the persistence for that plot was 1 second.
--- End quote ---

Well it's not going back in time by a massive amount.

The first part of the trace in the bottom left very near the trigger point looks about right and sharp, but the thin spike rising from there has no fall time, - at least not in the forward time direction.
Perhaps 1sec of persistence wasn't enough to catch any of the fall time, but there's nowhere else where a full division or even part of the trace is missing.

At 2ns/div I'd expect the next rising edge in the middle to look like it's always sloping slightly forward in time even if the slope is only around 5 degrees, at least to me it looks like it's curving back in time but only by about 2 or maybe 3 pixels, I make it 1 pixel width = 25ps.

Perhaps it is doing quite a bit of 25ps to 100ps dithering to capture every bit of the waveform, but they're forgetting to correct the dot sample positions by 1 to 4 pixel widths.

Could it be some interaction between the charging steps and sample rate both being 1ns wide.

Perhaps it's all fine and only some of us are seeing the verticals as unrealistic!

rhb:
I think that is just jitter.

What caught my eye is the change from linear interpolation of pixels on the DS1102E to what looks like clock dithering on the DS120Z-E.

Leo's pulser has a few ps of jitter.  Not specified, but he's tried to minimize it. He's also working to a pretty brutal price point.  But I have other reference sources with less than 1 ps of jitter.  So just give me time.

More in the "Scope Wars" thread.

Have fun!
Reg

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