[time-nuts] Harmonics suppression in ring oscillators

Hal Murray hmurray at megapathdsl.net
Wed Mar 18 04:28:11 EDT 2015


> 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.


-- 
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