[time-nuts] Digital tight PLL method

Bruce Griffiths bruce.griffiths at xtra.co.nz
Wed May 26 11:11:14 UTC 2010


Close in spurs generated by the synthesiser may also be problematic.
One feature being that the spur levels will depend (in a complex way) on 
the synthesiser output frequency.

One of the first problems to solve is making the close in spurs 
sufficiently low.
Another problem is to ensure that the synthesiser output is phase 
continuous (not a problem with DDS but close in spurs may be).


Ulrich Bangert wrote:
> Warren,
> you are not the only person to have ideas like this!
> I managed to get me a Stanford Research DS345 generator which gives 1E-6 Hz
> frequency resolution for any frequency below 30 MHz (Can be locked to any 10
> MHz reference). At 10 MHz this resembles a relative resolution of 1E-13. I
> used this generator in a digital pll where the phase error was measured by a
> DBM and a a HP3457. The digital PLL was a simple script written with my
> EZGPIB utility which controlled the DS345 and read the HP3457 via IEEE488.
> The main difference to your analogue solution is that it delivers a
> frequency measurement value immediately (= the current setting of the DS345)
> without any knowledge needed about the mixer's phase gain properties. And it
> is not limited to a certain frequency. Of course, the generator may be
> exchanged by an DIY DDS and the multimeter may be exchanged against a DIY
> A/D converter. Injection locking is not a topic with the DDS circuit.
> Nevertheless my measurement were not exactly encouraging. May be that I
> missed to apply the important math that Bruce has been suggesting in the
> discussion with you. All the stuff is on my workbench and is ready to use.
> May be I give it another try.
> Best regards
> Ulrich Bangert
>> -----Ursprungliche Nachricht-----
>> Von: time-nuts-bounces at febo.com
>> [mailto:time-nuts-bounces at febo.com] Im Auftrag von WarrenS
>> Gesendet: Montag, 24. Mai 2010 18:49
>> An: John Miles; Tom Van Baak; Discussion of precise time and
>> frequency measurement
>> Betreff: [time-nuts] Digital tight PLL method
>> Concerning the simple, $10, Low cost, Tight PLL method of doing ADEV.
>> "If you accept that the measurement is going to be limited by
>> the Reference
>> Osc,
>> Then for Low COST and SIMPLE, with the ability to measure
>> ADEVs at very low
>> levels,
>> Can't beat a simple analog version of  NIST's "Tight
>> Phase-Lock Loop Method
>> of measuring Freq stability".
>> http://tf.nist.gov/phase/Properties/one.htm#oneone    Fig 1.7"
>> Here is some more information on the subject that may help
>> inspire some of
>> the great minds out there.
>> In spite of all the unjustified criticism, the latest test
>> will show, at
>> least to the more open minded nuts,
>> There is NOTHING inherently wrong with the tight PLL method
>> as I have done
>> it. It gives about as good of answers as anything out there.
>> As I've implemented it, there are some disadvantages, because
>> there is just
>> so much one can do with a single Op amp design.
>> If one does the calculation they will also see the OP amp is
>> not a limiting
>> factor in the performance of this method.
>> AS I have said before, the disadvantage of my simple BB
>> version that was
>> tested, is that it is limited by the Ref Osc and the way it's freq is
>> modified.
>> The accuracy is limited by the fact the first simple BB
>> version I built is
>> an all analog system.
>> That is solely because the frequency control I used on the
>> simple version is
>> the analog EFC input of the reference Osc.
>> I've also pointed out, that is not a limitation of the
>> method, there are
>> solutions for that.
>> Now I'm amazed that no one has had a New inspiration.
>> Maybe a more direct approach will help some to see the next
>> logical step. Using the same basic tight PLL method, make
>> some of the unit digital. Do not modify the freq of the
>> reference osc with analog,  GET it yet? That way the device
>> would be half digital without any of the analog
>> shortcoming or the need to physically change the reference
>> freq. Do I really need to explain more?
>> Have fun
>> ws
>> ***************
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