If you haven't already, you should also check out the HP Journal edition that was dedicated to this counter: http://www.hparchive.com/Journals/Low-Resolution/HPJ-1978-08....

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mlyle 2 days ago | parent [-]

This is really great.

Bummed I didn't see it before. I made a really precise timebase and a fairly precise interval counter a decade ago using pretty different techniques (ECL and staggered delay lines and a lot of calibration). It would have been nice to know more about these techniques.

	▲	tverbeure 2 days ago \| parent [-]
		I've been wondering if it's possible to recreate this with today's technology. The HP implementation uses a custom ASIC with very fast transistors, so it's not obvious. https://febo.com/pipermail/time-nuts_lists.febo.com/2025-Jul... If you want to make your own interval counter today, the to-go-to method is to use a TDC7200 chip. If that's not good enough, you can also look at the schematics of an SRS SR620 time interval counter. It has a similar 25ps precision and uses an ADC to interpolate between samples of a 90 MHz clock. These kind of ADCs weren't available in 1978.