Ulrich Bangert wrote: > Hi Folks, > > >> You mentioned that locking to a crystal at the receiving end >> as an option. Does this mean that signal transmission is >> primarily plagued by short term noise? >> > > While it is not exactly locking a crystal to a input frequency HP has > used crystal filters in the 'reference input stages' of many devices > like the one shown on the JPG. The 10 Ohms trimmer has no noticeable > influence on the circuit. Today the circuit is more easily built with > integrated amplifiers as the MAX477. > > Best Regards > Ulrich Bangert, DF6JB > > >> -----Ursprüngliche Nachricht----- >> Von: [EMAIL PROTECTED] >> [mailto:[EMAIL PROTECTED] Im Auftrag von Stephan Sandenbergh >> Gesendet: Mittwoch, 25. Oktober 2006 13:07 >> An: 'Discussion of precise time and frequency measurement' >> Betreff: Re: [time-nuts] Comparison of Logic Standards for >> Clock Distribution >> >> >> Hi Bruce, >> >> Thank you for the elaborate answer covering different logic >> types. Funny enough, I have just read the excellent book you >> recommended cover to cover - probably the origin of many of >> my questions. >> >> As I said in reaction to Said's response - I am not surprised >> that analog (sine wave) transmission is superior. But, it >> takes a lot more effort to do it well. >> >> You mentioned that locking to a crystal at the receiving end >> as an option. Does this mean that signal transmission is >> primarily plagued by short term noise? >> >> I have never really touched the topic of optical fibre, but I >> realise that it is superior to conventional methods. The >> superiority of optic fibre is probably not as pronounced at >> short distances, is it? >> >> I realise that a better reference clock will only improve a >> system's performance up to the point where the jitter and >> phase noise of the other components in the system begins to >> dominate. However, I would like to have a good grip on the >> basics. Are there any good books you can recommend on the >> topic of clock distribution? >> >> Kind regards, >> >> Stephan Sandenbergh >> >> >>> Differential signalling using current mode drivers (open collector >>> long tailed pair or equivalent) can be more effective than ECL and >>> LVDS in that the output common mode range may be >>> >> significantly larger. >> >>> This allows larger differences in ground potential between the >>> transmitter and receiver and hence greater immunity to >>> >> this. ECL can >> >>> have problems when the ground potential differences between the >>> receiver and transmitter are large enough. Whre a current >>> >> mode driver >> >>> will work well even with several volts of difference in ground >>> potentials. Transformer coupling is also effective when dc coupling >>> isnt necessary, however the transsformer characteristics >>> >> will degrade >> >>> the signal rise and fall times. >>> >>> It is difficult to preserve the subnanosecond rise and fall >>> >> times of >> >>> digital signals when transmitted over a significant length >>> >> of circuit >> >>> board trace (particularly when using an FR4 or equivalent board >>> substrate). >>> >>> >>> Distributing a standard frequency using a well screened dedicated >>> shielded balanced transmission line presents fewer >>> >> difficulties (for >> >>> distances of a few hundred meters or so) than attempting to >>> >> distribute >> >>> a relatively small amplitude logic level signal. RF transformers at >>> each end can be used to provide good common mode rejection >>> >> and it is >> >>> relatively easy to transmit higher power signals than is >>> >> feasible with >> >>> logic signals. If noise is perceived as a problem then one >>> >> can always >> >>> phase lock a crystal oscillator at the receiving end to the >>> transmitted signal. >>> >>> Eventually cable losses associated with long cables limits the >>> bandwidth and hence the signal risetime. Optical fibre is >>> >> used when a >> >>> reference frequency has to be transmitted over several >>> >> kilometers as >> >>> in Radio telescope interferometer arrays. The fibre is relatively >>> immune to differences in ground potential, and other noise sources. >>> Fibre can also have a significantly lower propagation delay >>> >> temperature >> >>> coefficient. >>> Fibre bandwidth degrades less rapidly with length than >>> >> cable bandwidth. >> >>> Analog transmission techniques also have the advantage of degrading >>> the signal short term stability less than digital transmission >>> techniques. The jitter of a digital device adds more phase >>> >> noise than >> >>> a well designed analog amplifier. >>> >>> A good reference on the problems of high speed digital design is: >>> >>> HIGH-SPEED DIGITAL DESIGN >>> A Handbook of Black Magic >>> Howard W Johnson >>> Martin Graham >>> PTR Prentice Hall >>> ISBN 0-13-395724-1 >>> Bruce >>> >>> _______________________________________________ >>> time-nuts mailing list >>> time-nuts@febo.com >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> >> _______________________________________________ >> time-nuts mailing list >> time-nuts@febo.com >> https://www.febo.com/cgi-> bin/mailman/listinfo/time-nuts >> >> >> ------------------------------------------------------------------------ >> >> _______________________________________________ >> time-nuts mailing list >> time-nuts@febo.com >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts But the input voltage noise of the MAX477 is 5nV/rtHz, the corresponding value for a discrete transistor circuit may be as low as 1nV/rtHz.
Bruce _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts