# Determining the resistance of the LC Tank

#### gkini19

Joined Jun 15, 2021
17
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

Thanks!

#### Janis59

Joined Aug 21, 2017
1,348
May measure R of tank by Q-meter. Measure Q of coil and Q of capacitor (or ESR) separately. Then recalculate them together. Formulas find at Wikipedia, only be careful, You need the serial representation of both resistors, not parallel. Thus, R(ser)=2*pi()*f*L/Q. For capacitor, ESR=(1/2/pi()/C)*tan(delta)=1/Q(cap). Then, ESR and R(ser) stays both serially, You may them add brutally. And if need, by first formula calc back to summary system Q-factor. PS: sometimes ESR may be got simpler with ESR-meter instead of Q-meter. P.P.S: Beware measure it to the work frequency, if not, then recalculate by formula sqrt(f1/f2). Last but no least technique is to measure resonance graph with an oscilloscope and calc out from deltaB. Of course, good antennoscope as an example Nano-VNA (some models even 50 kHz to 3.7 GHz) will be far more accurate to do this.

Last edited: