[time-nuts] Close in phase noise of microwave VCOs

Magnus Danielson magnus at rubidium.dyndns.org
Thu Jun 18 16:20:35 EDT 2015


On 06/18/2015 08:36 AM, Attila Kinali wrote:
> Moin Rick,
> On Wed, 17 Jun 2015 13:08:04 -0700
> "Richard (Rick) Karlquist" <richard at karlquist.com> wrote:
>> Having said that, if an ordinary engineer had asked me this question,
>> I would think that he needed some coaching on how to clean up the
>> VCO with a synthesizer of sufficiently wide loop bandwidth.  However,
>> you are very knowledgeable, so I will assume you are going to do
>> that and just want to predict the phase noise after clean up.  The
>> trick (as most time nuts know) is to use a small enough capacitor
>> in the loop filter so that you get clean up at a 40 dB/decade rate
>> so you can actually make some headway against the 30 dB/decade
>> 1/f slope.
> Do you have any recomendation, where an ordinary engineer could
> read up on this topic?

The trick is to convert the 2nd degree loop to a 3rd degree loop, which 
then allows for a 12 dB/oct slope, to counteract the 9 dB/oct slope.
As the reference experience a low-pass action, the steered oscillator 
experience a high-pass action, and it's the slope of the later which is 
important here to combat the noise of the steered oscillator and then 
replace it with the noise of the reference.

I can show you on a piece of paper when we meet.


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