[time-nuts] Advantages & Disadvantages of the TPLL Method

WarrenS warrensjmail-one at yahoo.com
Tue Jun 15 17:43:25 EDT 2010


Didier

Please consider just because I can not explain it in words that you can 
understand does make it not work.
The dynamic high gain EFC feedback is so much greater then the static 
injection lock signal, by typ >100db, the injection lock just does not have 
enough effect to change anything enough to be significant. My test prove 
that (to my satisfaction).
 If you have a paper or theory that  says otherwise, it should include a 
reason (besides Luck) that says why my test show otherwise.

Maybe best proof of that is the results from TPLL testing.
If you assume it is not all just luck,

Check out how close the simple TPLL matches the TSC5120A over the full tau 
range,
OR for an even better example, see how good the simple TPLL does with the 
swinging OSC test.
The advantage of the swinging Osc test is that it can easily be seen what 
the waveform should look like, so no need to guess if it is right or not.
Hey, it works, better than ANYTHING else so far on that test, what else is 
there to prove?  (besides that I know how to integrate and add)

ws
**********
[time-nuts] Advantages & Disadvantages of the TPLL Method
Didier Juges didier at cox.net
Tue Jun 15 19:54:43 UTC 2010
I promised myself I would not get into this any more, but here we go 
again...

---- WarrenS <warrensjmail-one at yahoo.com> wrote:
>
> Charles posted:
> but the locked frequency will be different from both oscillators'
> free-running frequency and
> the EFC will not correctly indicate the test oscillator deviation
> because it isn't the only control input in the system.
>
> Good point and No argument  (except for the deviation part)
> Because the EFC is the only control input THAT IS VARYING.
>

Any parasitic control input is a problem in that system, like any other 
system.
I thought the point of all this was to measure the noise of an oscillator?
If it is noisy (and they all are, to some level, otherwise you would not 
need to measure it), then its frequency (or phase) is varying.

If the test oscillator is coupled (via injection locking) to the reference 
oscillator, the test oscillator will force the ref oscillator to follow its 
noise without the need to move the EFC. The EFC voltage will be stable 
(because the oscillators move together), while you have two synchronously 
noisy oscillators. If you measure the EFC, you will be left to believe your 
oscillator is better than it is.

Please note that the effect is not simply a scaling factor, because 
injection locking is a non-linear effect, or rather it is a mostly linear 
effect over a typically very limited dynamic range. Small variations will be 
totally coupled, where larger ones could possibly unlock the oscillators, 
producing steps in the EFC voltage. Said another way, you cannot eliminate 
the effects of injection locking by post-processing the data.

Injection locking is a parasitic control input and it is a problem with ANY 
method that purports to measure noise. Ignore it at your own risk, but don't 
say it does not matter, unless you want to prove something we already know.

Didier 
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