Hello
I am designing an Integer N PLL. For the phase noise of the entire PLL, which method is more efficient.
1. By using PSS and PNoise simulation in spectre
or
2. By using MATLAB code in which phase noise of individual block is used.
the formula used in MATLAB code is
PN_out = 10*log10(10.^(PN_out_ref/10)+10.^(PN_out_div/10)+10.^(PN_out_pcl/10)+10.^(PN_out_vco/10));
MatLAB information is completely wrong, there is no such equation at all for PLL Noise Calculation.
PLL is a Closed Loop structure and Every Noise Source Contributes into overall Noise Characteristic of a PLL in Different Way due to their Different Transfer Functions from Output to Input.
Review Banerjee's PLL Book.
A complete phase noise simulation of a PLL in Cadence can take quite sometime. I did something which is quite similar to what you did, namely, take the spectrum of noise from each of the components in your circuit (by components I mean PD, VCO, LPF...) and then multiply by the transfer function between that component and the output and then integrate it in MATLAB.