[time-nuts] Simulation of oscillator noise

[Magnus Danielson]

On 11/28/2013 08:18 PM, Attila Kinali wrote:
> On Thu, 28 Nov 2013 10:35:33 +0100
> Wolfgang Wallner <wolfgang-wallner at gmx.at> wrote:
>
>> I'm interested in the simulation of oscillator noise (especially in discrete event simulators).
>> I came across this topic as part of the literature research for my master's thesis, and have to admit that I really underestimated how complex this topic is.
> Hehe. Join the club. But treat carefully, this can become quite addictive ;-)
>
> Can you explain what you are exactly doing? You talk about noise, but
> only mention allan deviation. ADEV is the right tool to measure stability,
> but not so much phase noise.
On the contrary, ADEV (and MDEV even more so) is designed to separate
noise-types such that they can be estimated separately. It is only of
lately that you can use both phase-noise plots and timer-based ADEV/MDEV
plots to achieve the same thing, not that the phase-noise
characteristics have been hard to estimate from, but rather that it has
been hard to achieve qualitative measures for precision sources such
that all noise-forms can be used for estimation. This have been easier
in the TIC-driven measurement.
>
>> In the past weeks, I have spent a lot of time reading about different kinds 
>> of variances, and I think I have a basic understanding now.
>>
>> I would like to ask you two questions:
>>
>> 1) Do you have any advice for me on what papers to read concerning 
>> oscillator noise simulation?
> What part of the oscillator? Noise of the feedback electronics?
> Noise of the output stage? Noise from environmental factors?
> Noise intrinsic to the quartz crystal resonator?
>
> How accurate do you want the model to be?
>
> How do you simulate the complete oscillator? 
> (this is a big topic of its own, and definitly not easy)
>
> Did you read Enrico Runbiolas Book "Phase Noise and Frequency Stability
> in Oscillators"? If not, you should start with that. It gives a nice
> overview of all the basics you need to understand this topic.
Strongly recommended reading. His view is phase-noise driven.

I think one should study "both sides of the coin" since they have
different benefits and different usages.
> Gangepain did a lot of research on noise sources and stability of
> quartz oscillators. You might want to look up papers from him.
> (there was somewhere a collection of them)
>
>
> A couple of weeks ago, i did a literature search on various stuff
> around low noise/high stability oscillators. But i didn't have the
> time to sort those papers yet, much less read them. But i can search
> for things in there, if you tell me what you are looking for.
>
>
>> I have read different kinds of papers up to now, but non of them was really 
>> what I was looking for:
> What are you looking for?
>
>  
>> *) One of the papers I have read is "Accurate Clock Models for Simulating 
>> Wireless Sensor Networks" by Ferrari, Meier and Thiele.
>> But I don't think their simple model is of any use, as they completely 
>> ignore the typical allan variance of oscillators.
> Well, Thieles group does mostly wireless sensor networks (catually most
> of the TIK institute does wireless sensor networks in one form or another). 
> Their use for an "accurate" clock is to minimize the on time of the RF
> circuit in order to minimize power consumption. IIRC their goal was to
> get down from synchronisation window of 1s to 0.1 on a time scale of
> a couple of minutes to a couple of hours. And the whole calculation
> had to be simple enough to be done on an 8bit ATMega while not
> taking considerable computation time.
> These requirements lead to a rather simple model of clock deviation.
>
>> *) On the other hand, the paper "Achieving a Realistic Notion of Time in 
>> Discrete Event Simulation" by Gaderer, Nagy, Loschmidt and Sauter describes 
>> a very realistic model, but they keep the implementation details to 
>> themselves.
>> *) What could be of use for my purpose could be "Simulation of Oscillator 
>> Noise" by Barnes, but as it is from 1988 it is quite dated.
> I dont know these two papers, but they dont look too bad.
>
> As for the age. Most of the theoretical work on quartz oscillators
> was done in the 70s and 80s. Also most of the books on quartz
> oscillators are from that time. There are very few books from the 90s
> and later.
If you want more modern papers on simulation of noise, then there is a
few from JPL that applies, but the site where unfortunatly dropped in
one of the server-roundups.
>> 2) Do you know any public data samples of the allan variance of a real oscillators?
> febo.com (John Ackermann) and leapsecond.com (Tom van Baak) have both some
> data on various crystall oscillators. 
>
>> When I look in the data sheets of oscillator that I find on the internet,
>> they only have precision estimates like 1ppm or 1ppb, but no detailed allan
>> variance graphs.
> Yes. Because in the class of cheap AT cut oscillators, you dont worry about
> allan variance. The instability due to temperature dependence of your
> system is much higher than the temperature-free (in)stability. The ADEV
> becomes "relevant" only after you do at least a temperature compensation
> or temperature control.
The specification for temperature variations is a poor excuse too. Some
vendors have learned that the hard way.
>> PS: When I use the word oscillator I mean the cheap quartz oscillators as 
>> found in typical consumer electronic stuff.
>> PPS: I'm not sure if this mailing-list is the right place to ask my 
>> questions, as simulation is not listed in your mailing-list topics.
>> Sorry if this mail is off-topic.
> Don't worry, you are at the right place :-)
I agree. :)

Cheers,
Magnus