[time-nuts] Harmonics suppression in ring oscillators

Attila Kinali attila at kinali.ch
Sun Mar 22 10:36:30 EDT 2015


On Tue, 17 Mar 2015 11:28:59 +0100
Attila Kinali <attila at kinali.ch> wrote:

> So, how do people keep ring oscillators from oscillating at higher modes?
> 
> So far, my google skills have failed me to turn up any answer.

Ok, sofar i've dug up two papers (and a comment on one) that explicitly
deal with harmonics generation in ring oscillators. One is by Sasaki [1]
and quite old the other is current enough that it seems applicable today.

Sasaki[1] argues, that process variations between transistors
will prevent harmonics in small rings (see also comments in [2]),
but cannot be prevented reliably in large rings.

Bushan and Ketchen[3] on the other hand say nothing about harmonics in long
or short rings, but say that the proper startup sequence will inject
only a single edge into the ring.

			Attila Kinali

[1] "Higher Harmonic Generation in CMOS/SOS Ring Oscillators",
by Nobuo Sasaki, 1982
http://dx.doi.org/10.1109/T-ED.1982.20696

[2] "Comments on 'Higher harmonic generation in CMOS/SOS ring oscillators'",
by T.W. Huston, 1983
http://dx.doi.org/10.1109/T-ED.1983.21244

[3] "Generation, Elimination and Utilization of Harmonics in Ring Oscillators",
by Manjul Bushan, Mark B. Ketchen, 2010
http://dx.doi.org/10.1109/ICMTS.2010.5466847

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