[time-nuts] Simulation of oscillator noise

Wolfgang Wallner wolfgang-wallner at gmx.at
Sat Nov 30 09:32:42 UTC 2013


Hello,

thanks a lot for all your feedback (also in the other threads)!
It will take some time to read reed through all your recommendations :)

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.

The interest comes from IEEE 1588, which is an interesting standard, but
the equipment is quite expensive (a single switch with transparent clock
support for >1000$).
This means it is hard to estimated what could be achieved with 1588, as
it is rather impossible to just buy some devices and try it out.
Questions which would be interesting are things like:

*) what synchronization interval is need to achieve a specific
precision, and where are the limits
*) how does a long daisy chain behave (with/without syntonization in
each hop)
*) what happens when a link breaks and comes up some time later (how far
will the parts drift away)

At my institute (TU Vienna, Computer Engineering) there has been a
bachelor thesis which dealt with simulation of IEEE 1588 in OMNeT++ (a
discrete event simulator).
But the assumptions where rather simple (both of the clock model and the
implemented version of IEEE 1588).

For my master thesis I would like to enhance both aspects.
I would like to do a full implementation of IEEE 1588 and to use a more
realistic clock model.

Implementing IEEE 1588 is rather straight forward. The standard is easy
to read, and it is not rocket science to implement this it in C++.

But as already stated in my first message, I underestimated how hard it
would be to get a realistic clock model.

>> 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
> 
> 



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