[time-nuts] Harmonics suppression in ring oscillators

Tim Shoppa tshoppa at gmail.com
Wed Mar 18 10:08:35 EDT 2015


The "modern digital" model of gates having inputs and outputs is in fact a
simplified case. It's unlikely that a digital logic student today would
ever have been exposed to gate elements that can work bidirectionally (I'm
not talking about tri-state, I'm talking about logic elements that have no
preferred input vs output). In general, even symmetrical ring oscillator
circuits using elements that do not have a preferred direction, will settle
down into rotating one way or the other depending on infinitesimal details
of initial conditions. See in particular the neon-light ring oscillator
here: http://donklipstein.com/sillyne2.html

This is an example of "symmetry breaking", a term I learned in quantum
electrodynamics class!, and the reason particles have mass! I don't
actually understand the Higgs Boson but I do understand that neon light
ring oscillator because I built it long before I took QED :-).

Tim N3QE


On Wed, Mar 18, 2015 at 4:28 AM, Hal Murray <hmurray at megapathdsl.net> wrote:

>
> > While for (optical/electrical) delay line oscillators, the way to go is
> to
> > add a frequency selective element, this is not done for ring oscillators.
>
> > So, how do people keep ring oscillators from oscillating at higher modes?
>
> I think the answer is that you don't have to do anything.  It takes care of
> it by itself.
>
> Suppose you have a long string of buffers and 1 inverter in a ring.
> Suppose
> you start out with 3 transitions.  That's the normal 1 transition with an
> extra pulse.  The key idea is that the edges don't propagate at exactly the
> same speed.  So one edge will catch up with another and they will self
> destruct.
>
> It would be fun to set that up and watch it on a scope.  You could do that
> with 3 NAND gates.  Feed a reset signal into the other side of all 3 gates.
> (watch the wire lengths)  Maybe in a FPGA.
>
>
> --
> These are my opinions.  I hate spam.
>
>
>
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