[time-nuts] Framework for simulation of oscillators

Attila Kinali attila at kinali.ch
Sun Mar 20 17:20:44 EDT 2016


God kväll Magnus,

On Sun, 20 Mar 2016 20:43:00 +0100
Magnus Danielson <magnus at rubidium.dyndns.org> wrote:

> > If not, does someone have pointers how to write realistic oscillator models
> > for this kind of short and long term simulation?
> 
> It is a large field that you tries to cover. What you need to do is 
> actually find the model that models the behavior of your physical setup.

Yes, there is quite a bit I need to cover. I started out to put some stuff
together yesterday, but I guess it will take me two or three weeks until
i have something half way usable.
 
> You need to have white and flicker noises, there is a few ways to get 
> the flicker coloring. I did some hacking of the setup, and ran tests 
> against Chuck Greenhalls original BASIC code.

I'm currently using the code from Brooker and Inggs[1,2], but the code
is quite convoluted and it will take me some time to extract it and
get it working properly. (but then, it's the only piece of code
that I found that does seem to be viable at all)

> You probably want a systematic effect model of phase, frequency and 
> drift. Also a cubic frequency vs. temperature. All the properties needs 
> to be different for each instance. Similarly, the flicker filter needs 
> to be independent for each oscillator.

What do you mean with "the flicker filter needs to be independent"?
Each oscillator will get its own noise source, if you mean that.

> Similar enough things have been tried when simulating the jitter and 
> wander in the G.823-825 specs.

Thanks, i will have a look at those.


> An aspect you need to include is the filtering properties of the EFC 
> input, it acts like a low-pass filter, and the Q of the resonator is 
> another catch-point.

The low pass filter is easy to implement, and yes, this will be one
of the first things i need to implement. One of our guesses is, that
this low pass filtering helps us getting the high performance we saw.
I am not sure yet, how to model the Q, or whether that actually needs
to be modelled with anything else but the proper noise/stability
characteristics and the low pass on the EFC.
 
> I wonder how complex model you need to build before you have catched the 
> characteristics you are after.

The current plan is to implement an oscillator model that mimics the
correct stability i'm seeing, then add EFC (first w/o low pass filtering).
This should already work "properly" and give a first indication on how
the system behaves. Then step by step add the non-idealities, like the
low pass filter on the EFC, the high DNL of the TDC, the noise on the
pulse output and the TDC input, ... until I get close to what we measure.


> The EFC measures you have done so far indicate that your steering 
> essentially operates as if you do where doing something similar to 
> charge-pump operation.

Hmm.. can you elaborate a bit on why you think so?

	

			Attila Kinali


[1] "Efficient Generation of f^a Noise Sequences for Pulsed Radar Simulation",
by Brooker, Inggs, 2010
http://dx.doi.org/10.1109/TAES.2010.5461653

[2] http://rrsg.ee.uct.ac.za/fers/

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