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

Richard (Rick) Karlquist richard at karlquist.com
Fri Jun 19 05:32:13 UTC 2015

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.  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.


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