pll injection noise
if we design injection locked oscillator(ILO) and ,injection locked PLL (ILPLL)
three type injection source we use
they are first harmonic , subharmonic , and superharmonic
if we use first harmonic technic , the frequency of injection source is equal or close
to free running frequency of oscillator , then phase noise of injection locked oscillator or phase noise of ILPLL outside loop bandwidth is dominated by injection source
my question is since we have low phase noise injeciotn source and its frequency is close to free running oscillator , why we use first harmonic injection locked oscillator , we can use this low phase noise source as clock generator
what is the contribution of first harmonic ILO ?
I am not familiar with the term "injection locked pll". Injection locking is inherently a frequency-locking technique, and the absolute phase can vary freely (and often does over temperature).
There are some papers by Kurkowa I think that explain the process. They are your bible.
Basically, like any control loop, you have a reference (your good source) the process to be controlled (your VCO), and you are trying to control the vco with the source. The amount of improvement of the VCO's phase noise is going to be directly proportional to the "loop gain" of your system. Unfortunately, the "loop gain" is loosly definced as the amount of coupling between your VCO's resonator and the outside injection source. If the coupling is tight, then you will have move effective "dB's" of loop gain, and the phase noise will be improved by that many effective "dB's". So the tighter the coupling (or equivalently the wider the frequency pulling bandwidth), and/or the more RF power of the injecting source, the greater the phase noise improvement.