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

[WarrenS]

Bruce posted

>But Adler's equation indicates that an oscillator is much more
>susceptible to injection effects when the injected signal frequency is
>very close to the oscillator frequency.
No argument,
BUT
The thing that you  (and maybe Adler?) are missing is that effect goes away 
when the two frequencies ARE exactly the same.
I'm not talking close, I'm talking the exact same freq with phase held in 
quadrature within single digit femtoseconds.
BIG difference, Once that is understood, then that sort of answers your 
other comments.

>For each and every oscillator pair someone may try?????
Can't say for sure, I've only tried the ones I've tried, but even the ones 
that are highly susceptible were OK.


>At best you've only shown this to be true for the particular oscillator 
>pair being compared.
Yep, maybe I'm just real lucking again and it only applies to all the ones 
I've tested.


>That's descending into the murky realms of pseudoscience.
OR as I see it, it is using just a little common sense.
When is the last time you heard of a problem with an oscillator injection 
locking to it's self?


>Not only must the effect of injection locking be insignificant for the
> reference, it has to be insignificant for the test oscillator as well.
NO argument, If you are testing a DUT what this does effect, then one should 
buffer it or take other precaution.
If you want to make sure the tester is not effecting the osc there is 
another choice besides the Buffer.
DON'T connected it. The tester will work at better than -60 dB signal levels 
and if one just gets a couple of small wires close that is enough signal 
coupling that one can made 1 sec and slower tau readings.
OR you do both the buffer and antennas you can test the OSC from across the 
room.
Which side of the list do you think that should go on, advantages or 
disadvantages?


>If injection locking is an issue the efc gain with the loop
> open will differ from the efc gain with the loop closed.
>It will change the loop parameters in particular the efc gain.
>Its just a matter of how much it affects the efc gain.
NO argument, The PLL loop is never opened. THAT will screw up everything and 
cause the injection, delta gain,  etc.

Sounds like it is time for someone to find or write another one of the fancy 
math papers that covers this case.

ws

*************************
[time-nuts] Advantages & Disadvantages of the TPLL Method
Bruce Griffiths bruce.griffiths at xtra.co.nz
Tue Jun 15 05:39:31 UTC 2010

WarrenS wrote:
> Bruce posted
>> "If and only if injection locking isn't significant."
>
> No problem then, because it is not significant.
For each and every oscillator pair someone may try?????
> Can place this one under the 'ADVANTAGE' side.
>
That's descending into the murky realms of pseudoscience.
At best you've only shown this to be true for the particular oscillator
pair being compared.
Not only must the effect of injection locking be insignificant for the
reference, it has to be insignificant for the test oscillator as well.
If injection locking is an issue the efc gain with the loop open will
differ from the efc gain with the loop closed.

> I have tested this thoroughly in many ways.
> I do understand the concerns and doubts, especially with an unbuffered
> HP 10811 as the reference.
> The 10811s are pretty sensitive to injection locking and "phase pulling".
> Unlike most other methods, one of the many unique properties that the
> TPLL method has is that injection locking is normally not a problem
> with it.
It will change the loop parameters in particular the efc gain.
Its just a matter of how much it affects the efc gain.
> I find it is generally unnecessary to buffer either the Ref Osc or the
> DUT.
> This is one of the many features that helps make the simple TPLL so
> simple.
> (also it does not hurt or change anything to add a proper buffer)
> The lack of injection locking is one of the advantages that
> contributes to its exceptional and unbelievable performance.
>
But Adler's equation indicates that an oscillator is much more to
susceptible to injection effects when the injected signal frequency is
very close to the oscillator frequency.

> I did not leave the buffers out of the simple TPLL BB that was tested
> because of my lack of knowledge, but because of my "extra" knowledge
> on the subject that showed that they were unnecessary.
> More than once, I have tried to explain the reason why injection
> locking is not a problem with my version of the TPLL method, but until
> one proves it for their self, more words from me will not help.
> I do understand the skepticism and doubt, and I know why it is so hard
> to believe this for those that have not worked with is this type of
> method before.
> I guess someone should write one of those fancy math papers, if it has
> not already been done, that explains it in more convincing terms than
> I've been able to.
> It is hard for me to believe that paper has not already been written,
> But then it is hard for me to believe that the TPLL is not used more
> often. There are plenty of places that one of the TPLL methods well
> give the best overall solution.
>
> ws
>
> ***************************
>
Bruce
> [time-nuts] Advantages & Disadvantages of the TPLL Method
> Bruce Griffiths bruce.griffiths at xtra.co.nz
>
> WarrenS wrote:
>> Long explanations, cause I try to explain, the best I can, when I say
>> something is "WRONG or misleading"
>>
>> Magnus Posted:
>>> EFC linearity will remain an issue for analog oscillators.
>>> The oscillator gain will differ depending on offset voltage and
>>> temperature.
>>
>> TRUE it is an issue, but somewhat misleading because it need NOT be a
>> problem or limitation (mostly)
>> EFC Linearity can be an issue because the TPLL is limited by the
>> "performance" of the reference oscillator in lots of ways.
>> BUT
>> Oscillator EFC gain or linearity are not likely to be of much concern
>> or a limitation for high end performance.
>>
>> The gain nonlinearity I've measured can vary two to one over the full
>> range of a good Oscillator but it is more like 10% over the normally
>> used range, if one stays well away from the end points.
>> NOT so good but livable if you are not making something real accurate.
>> BUT
>> For all my accurate stuff, when using a HP 10811, I limit the
>> full-scale change to 1e-9 or 1e-8 at most.
>> This uses such a small part of the total EFC range, that the
>> nonlinearity effects are generally below the noise level and of little
>> concern at all.
>>
>> The fact that Oscillator gain does differ with the EFC voltage (offset
>> voltage), means if you want to get max accuracy out of the TPLL, it
>> will need to be calibrated at the EFC offset voltage it is being used
>> at.  One simple solution, if the OSC also has a independent manual
>> Freq adjustment like the single oven 10811, is to use it always set
>> the EFC voltage to be near zero volts.
>> BTW calibration need not be much of a problem, because it can be a
>> static calibration.
> If and only if injection locking isn't significant.
> This needs to be established for each setup.
> The simplest way to take the effects of injection locking into account
> is to measure the effective EFC "gain" with the loop closed.
>
>
>> What I use for a finial calibration & check is the 2G turn over, which
>> I measure very accurately by other means before hand and then use that
>> as a known freq offset to check operation and calibration. Of course
>> there are any number of other ways.
>>
>> As far as temperature having ANY effect on EFC gain, that is a total
>> NON issue.
>> If temperature had any effect on EFC Gain then Temperature would also
>> effect Osc Frequency at a fixed EFC voltage,
>> which would then effect the OSC freq drift and stability,
>> that would then effect anything that the Osc was used for, NOT just
>> the TPLL.
>> The TPLL actually has a slight advantage over other methods,
>> because the PLL will adjust the freq to be correct, even if the EFC
>> effect should change.
>>
>>
>>
>>>> I think it is reasonable to assume that a TPLL weighs in at about
>>>> 200 USD with all support mixers, amplifiers, ADCs etc.  if you don't
>>>> have the parts
>>> It is still a fairly cheap solution.
>>
>> Yes I think that is ONE reasonable number to use and a fair conclusion.
>> BUT there are others.
>> The EBAY cost of the TPLL can be easy under $10, not including the
>> reference Osc and the ADC.
>>
>> Do note, NONE of items above are plural, Only one is needed per system
>> unlike some other methods.
>> Because the cost of the Ref Osc is so variable and depends so much on
>> what one is doing, I have noticed that its cost is generally not
>> included in the base price. I think even on the $20K+  TSC 5120A that
>> the reference Osc is an extra cost option.
>>
>> The ADC is another BIG variable, depending on your needs and skill
>> level and junk box, almost no limit in cost at the high end,
>> and can be as low as $0.00 dollars if you are a student doing a
>> science project.
>> It can also be as low as $1.00 if one is good at programming PICS or
>> other micros with built in ADC's.
>>
>> The only other major part in the TPLL with any cost over $1 is the
>> Phase detector.
>> The one I use most is a micro-circuits $15 single price device, but
>> I've used all sorts of dual balanced mixers,
>> and if one is real cheap and good at design, I have found that a PD
>> based on a 50 cent XOR gate works fine.
>>
>> ws
>>
>> *****************************