How to simulate the quality factor of CMOS LC VCO tank?

[frankcui]

When I finished the design of varactor, inductor and cross-coupled nmos pair, how to simulate the composite quality factor of the tank?

 

[khouly]

simply plot the group delay of the tank circuit u want , hen use the realtion
Q=Π*freq*dealy
or plot the transfer function of the tank and the Q=center frequency/bandwidth of the tank

 

[frankcui]

Thanks khouly! According to your suggestion, the resulted Q is just the value under the condition that VCO cross-coupled differential pair(NMOS pair) bias only with DC value. My mean is how to simulate the Q value when the VCO oscillate. I think the Q value under the two cases is different.

 

[khouly]

as far as i know u donot need to calculate the Q when the oscillator is running