[time-nuts] Simulation of oscillator noise

[Attila Kinali]

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.

> 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.

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.


> 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.

 
> 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 :-)


			Attila Kinali


-- 
1.) Write everything down.
2.) Reduce to the essential.
3.) Stop and question.
		-- The Habits of Highly Boring People, Chris Sauve