Is this maybe using some form of correlated double sampling?

> It looks like the signal doesn’t scan out of the CCD memory in the order it was received, hence the signal discontinuity in the middle.

Or maybe the samples are also interleaved in the low-order bits in some way. This could be because the organization of the CCD isn't symmetric for the input and output paths, perhaps to reduce area or power, since only one path has to be fast. This would make sense because if you implement the CCD using n parallel CCD bucket brigades you only have to put a fast S&H and multiplexer in front of it, then you can drive the CCD brigades at a fraction of the actual sample rate, and the capacitive load of each of those clock phases is much lower as well.

In order to be able to design equipment, the instrumentation generally needs to outperform the equipment, sometimes by a significant margin. If I'm looking at the eye of a digital signal, I need to capture much faster than the signal.

It'd be fun to have a book of tricks from this era. At some point, it will fade into obscurity. Right now, it's a whole different bag of tricks for the state-of-the-art. They feel less... more textbook and less clever.

On the other hand, what's nice is that in 2025, decent equipment is cheap. There's a breakpoint where below around 100MHz, you can't do basic work, and above you can. That's roughly where FM pickup and a lot of oscillations sit. That used to cost a lot, but as technology progressed, we're at a point where a decent home lab can be had for well under a grand.

I mean, I think this would be a very nice project for someone with hardware skills and some time on their hands, and it would be useful too.

The HP logic analyzers back then had a really neat touchscreen interface based on criss-crossing infrared beams in front of the CRT face. The only thing that I've ever used that felt even better than a capacitive touchscreen, though obviously lower resolution.

I remember pulling a 486 out of its socket in the 1990s and putting it back with the wrong orientation. There was a poc and a bit of smoke. Something on the mainboard had burnt and it wasn't working anymore.

I used smell to locate the fault, a big trace on the PCB, which I soldered back and magic, it all worked again...

I have an entry level standalone oscilloscope that i got but never used. I once looked for tutorials and unpacked it, ready to test, but:

It's covered in that kind of plastic that goes all gooey if left unattended for a long time.

Any hints on how I can clean it up so i can touch it again?

Thinking about it, I might still have the device somewhere in the attic.

I recently got a TDS684A and also made the same discovery, and wrote half a blog post about it which remains unfinished/unpublished. I don't have much of an EE background (at least, not on this level) so my article was certainly worse. It's also my only decent scope, so I don't have a good way to take measurements of the scope itself.

Relatedly, I dumped the firmware of mine (referencing Tom's notes on a similar model) and started writing an emulator for it: https://github.com/DavidBuchanan314/TDS684A

It boots as far as the vxworks system prompt, and can start booting the Smalltalk "userspace" but crashes at some point during hardware initialization (since my emulation is very incomplete!) - some screenshots/logs: https://bsky.app/profile/retr0.id/post/3ljzzkwiy622d

Edit: heh, I just realised I'm cited in the article, regarding the ADG286D

Because that's more than enough for scanning a screen-width's-worth of samples from the analog CCD snapshot.

In a digital camara, the CCD columns basically capture the image instantaneously. It has an infinite sample rate!

Then the data is shifted out the CCD some rate that basically doesn't matter, as long as it isn't so slow that it takes seconds.