ECL will get you a 500MHz clock. When I did it for real, we actually used Gigabit Logic's GaAs and an 800MHz clock, then interpolated between clock edges with analog ramps to get down to 10psec resolution
- the jitter on our clock was about 60psec so the 10psec was entirely theoretical.
The version I designed a few years later using ECLinPS and a 500MHz clock was to have used a 500MHz Vectron crystal oscillator with around
Bill mentioned the digital + analog method which is what I'd do. If you feel uncomfortable around blazingly fast analog stuff either get help or:
Run several fast counters in parallel but shift their clocks. For example, if your ECL counter runs 500MHz but you want a 500psec granularity you run four in parallel. #1 gets the straight clock. #2 gets the clock delayed by 500psec, #3 delayed by 1nsec and #4 delayed by
1.5nsec.
They all receive the same start and stop signal. Of course, you'll have to look into the setup and hold stuff so you don't accidentally choke a counter. Now your PC needs to read the results of all four and then determine the exact timings by looking at which one started first, how many clock cycles it did, which one stopped last and how many cycles that one did. The readout process can be slow because now the counters are stopped.
That one interpolates a 40 Mhz clock! I just sold 8 of them to a guy who's going to shine a laser beam through turbine blades, time the interruptions, and figure out blade vibration modes.
before you start up to construct something on your own which is by FAR not trivial go out and buy one of the following devices:
Racal Dana 1991 or Racal Dana 1992 or Racal Dana 1996 counters.
These have a nominal 1 ns resolution for single shot time interval measurements. If you use their IEEE488 you get out some digits more and you can see that the rms jitter of the counter itself is in the order of 300 ps. These devices are no more build today but can be bought surplus at very cheap prices. Most of them are equipped with a high quality OCXO timebase.
If you are out for a bit more resolution and want to spend some dollars more, go out and get yourself a HP/Agilent 53131 counter which has a nominal
500 ps resolution. If you want even more resolution and spend more $s buy the HP/Agilent 53132 with nominal 150 ps resolution. Both models are from the current program.
If you need to get better, choices start to get rare: A surplus HP5370A/B (no more build today) will give you a 20 ps resolution for single shots at a reasonable price. A Stanford Research SR620 will give you the same resolution but be prepared for a smaller shock when looking at the price tag.
If you can avoid DON'T build something on your own. There are hundreds of ways to perform sub-ns timing measurement but you can spend months to years in order to learn the tricks that are necessary to make simple sounding theory work in reality.
Best regards Ulrich Bangert
schrieb im Newsbeitrag news: snipped-for-privacy@m73g2000cwd.googlegroups.com...
If you can use averaging, you can count an accurate clock several thousand times and average the counts. This is how at least one of the HP counters worked. The rms error decreases with the square of the number of counts. This places a practical limit on the minimum error you can achieve before you run out of time, or the signal drifts.
If you can use averaging, you can also use the Binary Sampling technique descibed below. This bypasses the square root averaging barrier. The example shown is a 1MHz square wave, and using this technique gave 1 picosecond rms jitter in one second.
This is good advice, but while we spent three years getting our prototype working, the interpolation system only needed a month or so of work.
Our biggest single problem was caused by the printed circuit department, who "knew" that the ordering of the inner layers of a printed circuit board didn't matter, so had a six layer board made with the ground planes on layers 3 and 4, rather than 2 and 5 as I'd carefully specified in my release note to the printed circuit department.
It took us months to work out why the board wouldn't work - every time I looked in on the engineer who was working on the board (nominally my boss at that point) I'd point out to him that he had the board layers stacked up wrong in his pile of documentation, but it took about six weeks before he drilled down through the board to check. Once the penny dropped, he sort of got the board working by replacing all the critical tracks with lengths of sub-minature coax (50VMTX, still stocked by Farnell) but we had to get another batch of boards made before we had anything that looked like a prototype.
The two outer layers of the board weren't FR4 epoxy glass, but Teflon cloth bonded with isocynate resin, and the board were biggish - triple extended Eurocards, largely to accomodate mixed DIN41612 connectors with coax inserts - and they cost us about $1500 each. Populating them cost as much again.
They'd be a lot cheaper today and - as John Larkin has pointed out - appreciably faster.
There is a cuter variation on this called the vernier chronotron. See
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which points to an article of that name in Review of Scientific Instruments -- March 1959 -- Volume 30, Issue 3, pp. 159-166 by Harlan W. Lefevre and James T. Russell of the Hanford Laboratories Operation, General Electric Company, Richland, Washington.
I got to hear about it in 1970, when one of my colleagues at Plessey Pacific got talking about his Ph.D. project which involved building a similar instrument with bistables built with pairs of tunnel diodes.
I'd known him - vaguely - when we were both Ph.D, students at Melbourne, both using the university mainframe for our - very different
- projects. He was simulating his tunnel diode bistables and thought that he had proved that he'd made them designable. They were certainly very fast.
I like that term "millimicrosecond region". That must have driven the physicists among the readers crazy. Can't read the full paper, I wish they would make these public domain after such a long time.
Ah, Plessey. Good old company. Before things folded I stocked up on their famous mixer SL6440. It has a dynamic range from here to the Klondike yet doesn't need a lot of L.O. power. It's a pity no other company bought the rights and kept producing it.
Even rather mundane test equipment could possibly be capable after some mods. When I repaired the HP4191 here in the lab I found that it had two very nice 300psec timed samplers in there, plus triggered ramp generators with remarkable precision. Milled module enclosures, rigid coax and all the good stuff.
Very pretty design! Did he have a pro do that enclosure? The only thing I wouldn't like is the buttons. Those tend to wear out quickly.
Why claim 1ps when the system jitter is so large? You are paying for useless digits. Averaging to improve the SNR would take forever, and the system would probably drift before the rms error got close to 1ps. So the resolution spec is meaningless. IMHO, the resolution spec should be >= rms jitter. Regards,
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