[time-nuts] Harmonics suppression in ring oscillators

Hal Murray hmurray at megapathdsl.net
Fri Mar 20 03:01:54 EDT 2015

> Hmm...  maybe the assumption that all edges walk around at the same speed is
> wrong?

It's really really hard to make things like edges travel at exactly the same 
speed.  If it isn't exact, then one will eventually catch up with another and 
self destruct.

The signal integrity wizards discuss eye patterns for multi gigabit serial 
links.  They now divide jitter into two parts: random and data-dependent.  If 
you have a long string of 0s as compared to a single 0 between 1s, the data 
line will have a chance to get closer to a solid low.  Starting from closer 
to 0 takes slightly longer to make a transition.  You can see it in the eye 

Does anybody have a scope on a ring oscillator?  Is the signal symmetric?  If 
not, that says that the H-L transition travels at a different speed than the 
L-H transition.

Actually, just looking at the prop times on a gate mignt be good enough.  The 
ring is just a handy signal generator.

It would be fun to make a ring with no inverters, inject a pulse, and watch 
to see how long it lasts.  I'll bet there is matastability type math that 
depends on the width of the pulse.  If you get the width exactly right it 
will last a long time.  Too long and it settles to all 1s.  Too short and it 
settles to all 0s.

These are my opinions.  I hate spam.

More information about the time-nuts mailing list