[time-nuts] Harmonics suppression in ring oscillators

Attila Kinali attila at kinali.ch
Tue Mar 17 06:28:59 EDT 2015


I stumbled over something that does not seem to be properly documented
anywhere. A ring oscillator (like any delay line oscillator) has an
infinte number of poles (on the complex plane), which are on a straight
line (disregarding the effect that the transistor acts like a first
order low pass filter, as f_t is usually a lot higher than the oscillation
frequency). This means that a ring oscillator will always excite more than
just one mode and oscillate on multiple frequencies. 

While for (optical/electrical) delay line oscillators, the way to go
is to add a frequency selective element, this is not done for ring

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.

			Attila Kinali

It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
                 -- Miss Matheson, The Diamond Age, Neil Stephenson

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