Determining the resistance of the LC Tank

[gkini19]

I am designing a cross coupled VCO. The first step is to get the resistance of the LC tank using S parameters in cadence.

My question is that, what are the other techniques where we can get to know the resistance of the LC tank in cadence virtuoso other than S parameter technique

Please let me know

Thanks!

 

[BigBoss]

What else you would ? If you want inject a RF Current Source ( Transient or HB/PS

S/AC ) and measure voltage .. The same thing will be happen.

 

[BradtheRad]

You can get an idea (for a given frequency) by applying the formula for inductive impedance and the formula for capacitive impedance.

You can calculate resonant frequency via another formula. As it turns out this is the frequency which sees the least total impedance in the LC network.

 

[AMS012]

It is important to calculate the Q factor of the tank while designing an LC oscillator. It is one of the first few steps you should do before getting into the cross coupled pair design, as the quality factor largely determines the overall performance of the oscillator namely the phase noise, power consumption etc. The theoretical maxima for the FoM of an oscillator is given by FoM=174+20*log10(Q) dBc/Hz

You can pump an AC current (magnitude=1, phase=0) into the LC tank, and do a simple AC analysis and look at the maxima of the real part of the voltage developed across frequency. The magnitude of the maximum voltage developed is the effective parallel resistance of the LC tank and the frequency at which that happens is the resonance frequency. This is a simple AC analysis and you should be able to get the results quickly.