[time-nuts] Framework for simulation of oscillators

KA2WEU at aol.com KA2WEU at aol.com
Sun Mar 20 20:19:54 UTC 2016


 
I am interested in this topic too, thanks, Ulrich 

 
 
In a message dated 3/20/2016 4:10:12 P.M. Eastern Daylight Time,  
magnus at rubidium.dyndns.org writes:

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
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