Hi folks - Just one note about ECL. It was intentionally designed for slow rise-time. That was a feature that improved signal integrity in the 70's when board designers had no clue. I am mostly referring to MECL 10K. MECL III had faster rise-times.
John K1AE, ECL designer at DEC in the early 70's. Co-designer of the KL10/DecSystem 2060. Dec's first signal integrity person and the first person to bring Berkeley Spice to DEC in 1974. -----Original Message----- From: time-nuts [mailto:[email protected]] On Behalf Of Magnus Danielson Sent: Monday, April 13, 2015 3:15 PM To: Richard (Rick) Karlquist; Discussion of precise time and frequency measurement Cc: [email protected] Subject: Re: [time-nuts] Ultra High Stability Time Base Options for 53132A Rick, On 04/13/2015 01:48 AM, Richard (Rick) Karlquist wrote: > > > On 4/12/2015 2:22 PM, Magnus Danielson wrote: >> Hi, >> >> The buffer transistors has not AC-bypass of the emitter resistance, so >> that the DC current becomes large and thus contributes flicker noise. >> >> The comparator at the bottom isn't doing a beutifull work of squaring >> things up without contributing noise, considering the sine output of the >> 10811. >> >> Was that it, Rick? >> >> Cheers, >> Magnus >> > > The resolution of page 13 is poor, and it seems to be a bitmap instead > of a vector file. The fuzzy thing in the lower right corner looks > like it might be a comparator. I think this was the smoking gun. I checked the component listing, which provided very good hints. > There was a saying by H.L. Menken to the effect that for every > complex problem, there is a simple, obvious, invalid solution. Oh yes. Some people say that you should not overcomplex things. My experience is that oversimplifying them can cause a long stretch of complex problems and complex workarounds making the total solution more expensive in development, customer relations and more complex than starting with a more advanced solution, that actually attempts to address the design issues. Ah well. > Squaring up a 10811 with a comparator is a perfect example of this > principle. Non-time-nuts always seem to gravitate to this design. Oh, they defend their choice with that they use a schmitt-trigger. *facepalm* > Of course you're right, any comparator will add jitter to a 10811. > The faster they are, the more jitter they add. Indeed. Hello Noise-bandwidth. > I noticed that the standard 10 MHz oscillator is built with > an ECL line receiver. Another example of Menken's saying. > This is a TERRIBLE oscillator design, but one that would appeal > to the non-initiated. I built one of these oscillators in 1976 > at the suggestion of my boss. After seeing how bad it was, I > quietly designed it out and never used it again. Go and check the HP5370A/B reference amplifier board. It has an ECL circuit to detect the presence of 10 MHz. It does this by producing a 5 MHz 25% PWM signal... with ECL... with very good rise-time. ECL have never been known for its speed and rise-time (irony might have been used). So, it turns out that the board spewes out a wide spectrum of 5 MHz spikes. All this to drive a LED that goes green if there is a 10 MHz to aid the fault analysis once you lift the lid. A bad design. Disabled the detector by grounding a base on a transistor, and got a much more quiet box. The Motorola ECL handbook warns about the rise-time issue, it's a standard signal integrity and EMC issue. Cheers, Magnus _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. --- This email has been checked for viruses by Avast antivirus software. http://www.avast.com _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
