[time-nuts] OCXO PLL gains?

[Richard (Rick) Karlquist]

On 2/1/2019 3:22 PM, Magnus Danielson wrote:
> 
> The Gardner book is the one book I recommend. Few books has core 
> knowledge so well compressed. If one only gets one book, this would be 
> the one I would recommend.
> 
> Cheers,
> Magnus
> 

I'm glad someone mentioned this classic.  45 years ago, this
was my first training in PLLs.  In the first 10 or 20 pages,
I learned just about all I needed to know about designing PLL's.
Design for a natural frequency around 1% of the sampling rate,
set damping factor to at least 1, and I was off and
running.

As far as PN "bumps" are concerned:  they are generally unavoidable,
but you want keep them from being very peaky.  You either need to
reduce loop bandwidth or reduce extraneous poles in the tuning
voltage path.

You can easily build a SPICE model where voltage represents phase
and simulate the loop, both open and closed.  The open loop
response should have one and only one dominant pole.  That is
what gives you a stable loop without a lot of peaking.

Gardner has an interesting chapter on 3rd order PLL's utilizing
double integrators.  Unless you are tracking out doppler shift
on a moving signal source, you should never need double integrators.

We used a double integrator on the oven control loop on the HP1938A
OCXO.  It was tricky to get it working correctly, due to
a phenomenon known as "wind up".  We also used a double integrator
on the 5071A cesium standard, but cesium loops are NOT PLL's.

Rick