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, [email protected] 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,
[email protected] 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, [email protected] 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,
> [email protected] 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
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