[time-nuts] Framework for simulation of oscillators
Attila Kinali
attila at kinali.ch
Sun Mar 20 21:20:44 UTC 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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