Quote:Why does the OP's phase noise degrade
Any extra circuitry you add is gonna inject its own noise. Hence, phase noise of the signal coming from VCO is bound to increase.
Quote:I would have thought since its outside the VCO loop, the noise is just going to raise the thermal noise floor rather than get integrated.
The noise neednt be just thermal. The circuit's flicker noise will also gt injected into the system, which is not getting affected by preceding PLL's XF. Hence, unmodulated noise(both flicker n thermal) get added to the signal, thus degrading phase noise.
If by integration, you mean converting freq. signal to phase, then that you would have to do at FD-SE converter's output too.
Quote:BTW, how do your solutions help.
Quote:Do not use Tail Current Source. Keep sizes large.
No TCS means no flicker upconversion. Hence lower phase noise. Large sizes keep flicker from i/p pairs in control.
--M