On Friday, May 22, 2015 10:48:16 AM Gerhard Hoffmann wrote: > Am 21.05.2015 um 23:32 schrieb Magnus Danielson: > > On 05/21/2015 12:15 AM, Richard (Rick) Karlquist wrote: > >> The counter front ends seem to be modeled after scope front ends > >> and scope triggering circuits, where you can adjust the triggering > >> level. Any jitter in the triggering would normally only affect > >> the interpolator. The interpolators in general were no great shakes, > >> so the triggering wasn't the limiting factor. > > > > Depends on the signal. > > > >>> Now, remind me why ECL is lousy, I can't recall there being very high > >>> gain in them, but fairly high bandwidth and they stay in the linear > >>> operation region. > >>> > >>> > >>> Magnus > >>> _______________________________________________ > >> > >> ECL is bad because the voltage swing is low; because as you say, > >> a lot of the circuitry is in the active region all the time, and > >> because the current source in the emitters generates a lot of > >> noise. > > > > Yes, it is bound to have 1/f noise with it's 50 Ohm current load. > > I was thinking about the continuous current, as I do know of the > > gating effect. Today there is other interface standards having lower > > swings than ECL. > > > >> In the early 1990's, I thought I had proved that the high ECL > >> noise was mostly common mode and that you could reduce it > >> 20 dB by using a transformer to couple the output. Alternately, > >> a good differential amplifier with high CMRR would do the trick. > >> I had actual measurements to back up this theory. > >> > >> Subsequently, other people tried to reproduce this and could not. > >> By that time, I had moved on and didn't have the bandwidth to > >> continue to own the problem. > >> > >> It would make a nice project for some time-nut to prove or disprove > >> my hypothesis regarding ECL. > >> > >> ECL line receivers as squarers are not as bad as comparators, but > >> are much noisier than 74AC. > > > > Interesting. > > > > Don't have a lot of ECL lying around, but some toys that might measure > > things. > > Could we agree on a test procedure? > > A friend of mine did some tests for synthesizers in mil. avionics and he > told me > that Motorola's MOSAIC3 process was the worst thing that has hit the > planet wrt > phase noise. That was used for a lot of fast ECL. (Some years have > passed since > he made the test.) > > Comparators have their advantages, too. At least, someone has been thinking > about dispersion, constant flowthrough time against frequency and > overdrive; > there are even specs that include overdrive. Just that comparators can > switch > cleanly at mV levels does not mean that they are to be used that way. > > More gain may mean more noise voltage, but it also means less time spent > in the transition region. Once the decision has been made the noise is > squelched > anyway. And I prefer setting the bandwidth with thin film Rs and np0 > capacitors, > not with oversized junctions. > > The fairest shootout between the logic families that we have is the LTC6957. > > < http://cds.linear.com/docs/en/datasheet/6957f.pdf > > > Probably just bondout options of the same chip. The PECL version wins > hands-down, LVDS is worst and CMOS is in-between. > > Especially at low offsets PECL is best, that clearly contradicts the > above-assumed 1/f problem and the lower swing standard of today > comes out worst. > > regards, Gerhard > > > > _______________________________________________ > 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. The LT6957 dtasheet PN curves differ from what I measured with a 10-MHz input in that when shielded from air currents the flicker noise corner is much lower than 100Hz offr a 100MHz input. I have only tested the LTC6957-4 evaluation board.
Bruce set shown fo _______________________________________________ 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.
