[time-nuts] Framework for simulation of oscillators
Magnus Danielson
magnus at rubidium.se
Mon Mar 21 07:20:04 UTC 2016
Hi Ulrich,
Interesting article. Did you see Craig Nelsons article on building a
mixer out of 2N2222A transistors?
Cheers,
Magnus
On 03/21/2016 12:45 AM, KA2WEU at aol.com wrote:
> http://joerg-berkner.de/Fachartikel/pdf/2000_AKB_Berkner_1f_noise.pdf
> In a message dated 3/20/2016 5:33:21 P.M. Eastern Daylight Time,
> magnus at rubidium.se writes:
>
> Ulrich and Attila,
>
> As you read the appendixes of ITU-T Rec. G.823, G.824 and G.825 they
> will not give very detailed information, but hints. The flicker noise
> model comes from Jim Barnes and Chuck Greenhalls PTTI 19 article "Large
> Sample Simulation of Flicker Noise". Be aware of Chuck's follow-up
> correction. Further, they model the amount of noise and add into the
> loop in place of the oscillator, which then has a normal PI-loop.
> Such a
> simulation can be done fairly efficiently considering that the
> oscillator and loop is very simple linear models of phase, not too
> different to what I proposed. For the stuff that Attila needs to
> simulate, some additional thought needs to go into how to simulate the
> effect he is seeing, but a fairly simple approach should be interesting
> to try out initially.
>
> The Barnes&Greenhall flicker generator builds on a filter-bank where
> the
> poles and nulls is placed such that they approximate the flicker noise
> slope of 1/tau. This is a generalized variant of Jim Barnes PhD work
> where he had fixed relations and where Chuck Greenhall have contributed
> significantly by providing means to setup the state of the filter such
> that the filter will act as a filter in equilibrium from start, rather
> than taking much time to converge, something which may introduce a bias
> into the measurement results. I have re-implemented their BASIC-code
> into C and run Chuck's original code along-side to verify (just to find
> where I did my mistake in converting it).
>
> If this simulation approach is sufficient for either of your
> efforts, or
> not, depends on what you try to capture. For instance, the oscillators
> performance have been idealized in assuming fully linear EFC, fully
> linear integrator of the crystal, assuming noise profile etc. This may
> or may not be sufficient. Inherent lowpass filtering may be
> important or
> not.
>
> I've done PLL simulations many times, in fixed integer, in floating
> point and in VHDL. It's always a challenge to model it right to the
> needs.
>
> Let me also have reader of this thread reminded of TvB's simulator
> for a
> GPSDO, which is interesting as it adds real GPS PPS data and real open
> loop oscillator data with a simple PLL oscillator core you can then
> tweak. Great fun in all it's simplicity and nice way to do reality
> check. I've done similar things with about the same code amount that
> have proved very useful.
>
> However, recall that whenever you make a model, you do it with
> assumptions for your particular problem, so some stuff will be left out
> and some will be particular to your problem. One guys model may be crap
> to another ones problem. There is a few tricks to be learned and a few
> things to recall to include.
>
> Cheers,
> Magnus
>
> On 03/20/2016 09:19 PM, KA2WEU at aol.com wrote:
> > 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
> > _______________________________________________
> > time-nuts mailing list -- time-nuts at febo.com
> > To unsubscribe, go to
> > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> > and follow the instructions there.
> >
>
More information about the Time-nuts_lists.febo.com
mailing list