how to model noise contribution of LPF in PLL

[hearter]

hello everyone, I am trying to model LPF noise contribution to PLL output. do I need to simulate the LPF alone to get noise profile(like CP and VCO), then put the noise in PLL closed loop sim(verilog or matlab)?

my question is what is the phase noise contribution of LPF? is it low pass(I believe so) ? what is the transfer function?

the LPF is resistor in series with a CAP.

thanks appreciate

Heater

 

[saro_k_82]

The resistor is the only noise component in the LPF and it's noise in the loop is bandpass. It appears between two poles at the origin one in the forward path to the output and the other in the feedback path.

 

[hearter]

saro,
thanks for reply. well you are right if you look at this way(resistor itself), but PLL loop is a low pass to the noise generated from LPF. now the cap forms a high pass to the noise of the resistor, so as a result, resistor noise shows up at VCO ouput at bandpass.
let me know if you disagree.