[time-nuts] Fwd: Harmonics suppression in ring oscillators

Alex Pummer alex at pcscons.com
Tue Mar 17 10:52:07 EDT 2015

Hi Attila, just think how all ring/delay line oscillators working: a 
status change is traveling trough a delay, and after its arrival at the 
next active component it will release a new status change, which will 
travel and arrive at the next active component, and after once it will  
get back to the "begin of the loop". Basically time which required to 
travel between the active devices will determine the frequiency, and 
--as it now obvious -- the status change can not release new status 
change at the following active component before arriving to that next 
active component , therefore self the oscillator can not run at higher 
frequency that as it determinated by the delays. Of course depending on  
the wave form at the output of the system you could see many other 
spectral components
Alexander, Pummer

-------- Original Message --------
Subject: 	[time-nuts] Harmonics suppression in ring oscillators
Date: 	Tue, 17 Mar 2015 11:28:59 +0100
From: 	Attila Kinali <attila at kinali.ch>
Reply-To: 	Discussion of precise time and frequency measurement 
<time-nuts at febo.com>
Organization: 	Geist
To: 	Discussion of precise time and frequency measurement 
<time-nuts at febo.com>


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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