[time-nuts] Framework for simulation of oscillators

[Magnus Danielson]

Attila,

On 03/17/2016 10:56 AM, Attila Kinali wrote:
> Moin,
>
> Measurement we recently did showed some quite unexpected behaviour
> and I am trying to figure out where this comes from. For this
> I would like to simulate our system, which consists of multiple
> crystal oscillators that are coupled in a non-linear way (kind of
> a vector-PLL with a step transfer function) with a "loop bandwidth"
> of a few 10kHz.
>
> My goal is to simulate the noise properties of the crystal oscillators
> both short term (in the 10us range) and long term (several 1000 seconds)
> in a way that models reality closely (ie short term instability is uncorrelated
> while long term instability is correlated through temp/humidity/...)
>
> As I am pretty sure not the first one to attempt something like this,
> I would like to ask whether someone has already some software framework
> around for this kind of simulation?
>
> 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.

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.

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.

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

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.

I wonder how complex model you need to build before you have catched the 
characteristics you are after.

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.

Cheers,
Magnus