[time-nuts] Framework for simulation of oscillators

Attila Kinali attila at kinali.ch
Sun Mar 27 19:48:43 EDT 2016


N'abend Magnus,

On Tue, 22 Mar 2016 01:11:41 +0100
Magnus Danielson <magnus at rubidium.dyndns.org> wrote:

> > Yes, of course. Noise is generally not i.i.d. and thus one cannot use
> > the same generator for more than one model in the same simulation.
> >
> > Oh.. and just to make things more complicated: Gaussian noise is not
> > necessarily white (only if it's Gaussian distributed and i.i.d.).
> > And noise with white spectrum is not necessarily Gaussian or i.i.d.
> > (only if phase and amplitude noise are both white).
> 
> Indeed.
> 
> BTW. You are increasingly PhD damaged in your use of abbreviations 
> without explaining them on first use, as you should.

Oops.. sorry about that.
i.i.d = independent, identically distributed.
I.e. the samples have all the same probability density function,
which does not change over time and does not depend on any previous samples.
 
> >> Consider that you have an integrator for the oscillator, and a null due
> >> to the Q. Look at the Leeson model (Feb 1966), see also Enrico's book on
> >> phase noise.
> >
> > I don't see how the Q, beside acting as an integrator, will affect my system
> > (keep in mind, the "loop" is non-linear). But I havent gone through the
> > math here...
> 
> Without going through Leeson in details, only the part of the spectrum 
> being inside of the f/Q bandwidth will behave as integration for the 
> noise inside the loop. Signals from the outside will integrate, after 
> being low-pass filtered by the f/Q bandwidth. The oscillator is just 
> like a loop.

I think I get what are are hinting at, but I do not fully understand it.
I guess we should discuss this next week in York.

 
> >> Something according to those lines might be where your systems behavior
> >> can be explained.
> >
> > Well, we do not really have a deadband (save the TDC resolution and
> > my guess is that the inherent noise in the system does a good job
> > in decreasing this "deadband" as well). The long cycle time results
> > rather in a small loop bandwidth. As we only measure one pulse per
> > cycle, everything that happens between pulses averages out. Ie if we
> > have any deadband like jitter behavior, we don't see it.
> 
> Well, maybe not really, but what you have is kinda similar as the 
> outermost will have a higher gain being pushed back and the more central 
> will have weaker pull-in. The time between pulses is indeed a measure to 
> loop time-constant/bandwidth.
> 
> I just say the dead-band give similar pulses.

We currently have a long term measurement running. And there are
intermittent rises in "noise" of the node pair we are measuring. 
My assumption is that the order of the center frequencies of the
oscillators changed, thus swapping two of the nodes in their pulse
time order. When two nodes get close to eachother the algorithm
switches between using nodes A & B and using nodes A & C. This can
indeed be seen as a deadband behaviour.

I'll look further into that behavior as soon as we have some simulation
system running and I see more than one node pair.


BTW: I discovered that Timelab stops processing after 10'000'000 datapoints,
which is kind inconvenient when doing a long term measurment...

			Attila Kinali


-- 
Reading can seriously damage your ignorance.
		-- unknown


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