[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)

[Bob kb8tq]

Hi

Regardless of what you call the “ 1 Hz normalized noise “ of a digital
phase detector, it does predict what the noise floor does on it as the
reference frequency is changed over some reasonable range. This has
been demonstrated a lot of times and on a lot of different parts. 

Based on a number of RF designs using them ( and using gates for RF 
purposes ) the basic gate is what is at fault here. They are noisy and that 
noise changes with frequency. Frequency goes up / noise goes up. There
are very good reasons for this. 

Getting a gate with a noise figure below 6 db is highly unlikely …. That 
is what you would have to do in order to make a gate based circuit measure
a lower noise floor than the DBM based approach. Folks have spent a lot
of time searching for the magic “zero noise gate”. 

The sine wave component present at the DBM output at 2X the input 
frequency ( in the case of the phase noise test setup) are *way* higher
than the highest noise you are after. You put in 10 MHz or 100 MHz and
you go up to *maybe* 100 KHz on the noise. With a sound card, even 
getting to 100 KHz is going to be a challenge. 20 KHz may be the max. 

Knocking down the 2 x Fin component with a low pass filter is pretty easy.
Indeed the sound card or audio spectrum analyzer likely has some filtering 
already. The design and implementation of an adequate LPF is far from the 
biggest challenge that the person building the circuit will face. 

Indeed 1/F noise and noise corners do matter. All of the above has been
simply talking about noise floor. Gates have significant 1/F issues along
with their other “features”. This carries over to the detectors based on
them. As the gate speed goes up ( and the floor typically comes down),
the 1/F corner normally moves up ….

Bob

> On Jul 11, 2022, at 8:05 AM, Mike Monett via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> To Bob kb8tq
> 
>  Figure Of  Merit  sounds like a useless number. I  have  a different
>  approach that yields immediate and useful results. Before  I explain
>  my method, let me introduce myself.
> 
>  In  1970,   I   invented,   and   Memorex   patented,   the original
>  zero-deadband phase-frequency detector. You can see it in page  3 of
>  my '234 patent at https://patents.google.com/patent/US3810234A/
> 
>  This invention  soon   led   to   another   invention  of tremendous
>  significance to today's world.
> 
>  In 2014, researchers published a study in the journal Supercomputing
>  Frontiers and  Innovations  estimating the storage  capacity  of the
>  Internet at 1e24 bytes, or 1 million exabytes.
> 
>  When I  started  working for Memorex, an IBM  2314  disk  pack could
>  store 29.2  million  bytes.  At that  rate,  today's  internet would
>  require 1e24/29e6=3.44e16,  or 34,400,000,000,000,000 IBM  2314 disk
>  drives. This  is an impossible number. Other estimates  give equally
>  outrageous numbers.
> 
>  The problem  in those days was improvements in  disk  drive capacity
>  were basically  trial and error. This is a slow  and  very expensive
>  business.
> 
>  My new  invention allowed peering into the hard disk  and separating
>  out all   the   variables   that   affect   performance.   With this
>  information, researchers could see the effect of changes and quickly
>  optimize the performance. This allowed the tremendous improvement in
>  tape and  disk drive capacity that now allows the internet  to store
>  all the needed data.
> 
>  You can  see  how  this   invention   works  in  the  Katz  paper at
>  https://tinyurl.com/2bmuz3n2
> 
>  Now for my new method. 
> 
>  The schematic   for   a   phase-frequency   detector   is   shown in
>  DBAND2S.PNG. In  operation, a pulse arrives at the DATA pin  and pin
>  U1Q goes high. Then a pulse arrives at the VCO pin and pin  U2Q goes
>  high.
> 
>  This allows  the  NAND  gate  to bring  the  CLR  signal  low, which
>  immediately resets both d-flops.
> 
>  The result  is shown in ZERODB.PNG. It is a very  narrow  pulse with
>  both d-flops superimposed.
> 
>  This is the basis for my new approach. Simply tie both inputs of the
>  PFD together  and  measure  the noise spectrum  of  the  output. (Of
>  course, you have to ensure that both outputs match at zero error.)
> 
>  Once you have the PFD noise, you can enable the loop and measure the
>  total noise  spectrum. Then simply subtract the PFD spectrum  to get
>  the OCXO  noise.  If  you   have   two  identical  VCXO's,  each one
>  contributes half the noise.
> 
>  I don't know if this method would work with a double-balanced mixer.
>  The problem is a DBM requires quadrature signals, so the noise  is a
>  function of the OCXO noise as well as the mixer diodes. But the OCXO
>  noise is what you are trying to measure.
> 
>  This method  works with the PFD since only a single pulse  is needed
>  to activate both d-flops, so you are measuring only the PFD noise.
> 
>  Et Voila.
> 
>  Now that you can measure the OCXO noise, you might want to  try your
>  hand at designing an oscillator with minimum noise.  You immediately
>  run into  a problem. The high Q of the crystal means  the oscillator
>  takes a very long time to start up.
> 
>  I solved this problem in my OSC.ZIP file at
>  https://tinyurl.com/2p9yrxmy
> 
>  Steve Wilson is me. Just start at the README.TXT file and you are on
>  your way.
> 
>  Now that you are a fully qualified Time-Nut, you might be interested
>  in some of the following papers:
> 
> Rohde, 1994 How to improve phase noise by multiple varicaps in parallel
> http://www.arrl.org/files/file/Technology/ard/rohde94.pdf
> 
> Leeson Equation
> http://rfic.eecs.berkeley.edu/~niknejad/ee242/pdf/eecs242_lect22_phasenoise.pdf
> 
> Oscillator Phase Noise: A Tutorial
> Thomas H. Lee, Member, IEEE, and Ali Hajimiri, Member, IEEE
> http://smirc.stanford.edu/papers/JSSC00MAR-tom.pdf
> 
> Hajamiri
> Virtual Damping and Einstein Relation in Oscillators
> https://authors.library.caltech.edu/523/1/HAMieeejssc03.pdf
> <DBAND2S.PNG><ZERODB.PNG>_______________________________________________
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