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

Magnus Danielson magnus at rubidium.se
Fri Jun 19 04:44:54 EDT 2015


Rick,

On 06/19/2015 07:32 AM, Richard (Rick) Karlquist wrote:
> On 6/18/2015 1:20 PM, Magnus Danielson wrote:
>
>> 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.
>
> No this is not correct.  A very conventional Type 2 loop, where the
> loop filter consists of an integrator with series RC for the feedback,
> and a resistor for the input, will suppress noise at 12 dB/octave with
> the corner at w=1/RC.

Which was what I meant. You have your third pole in that filter, but you 
put away from the dominant pair.

> A 3rd order loop is rarely helpful because
> the noise is typically limited by phase detector noise floor.
> Of all the many hundreds of PLL's I have designed, I don't remember
> ever using 3rd order.

I think I just didn't use the terms you expected. Cool it.

Cheers,
Magnus



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