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, mag...@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, ka2...@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, > mag...@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@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.