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
