# tank quality factor & passive mixer input impedance measurment

1. ## tank quality factor & passive mixer input impedance measurment

Does any body know how to measure the lc tank quality factor with software(rf spectre .i.e cadence) and by calculations too?
is it possible to get 900 ohm impedance of an lc tank ?(this lc tank was used for an lna load.)( l=5.49nH , c=651fF).the lna has a dc blocking cap of 2pF value after the tank.
what is the relation between the impedance, l and c of a tank( i mean the formula of them)?
how can i measure the input impedance of a passive mixer by tran analysis in rf spectre?
TANK YOU.

•

2. ## Re: tank quality factor & passive mixer input impedance measurment

Q = 2 X pi X L/R or centre frequency/delta bandwidth (3dBpoints).
Frank

•

3. ## Re: tank quality factor & passive mixer input impedance measurment

how can i measure the input impedance of a passive mixer by tran analysis in rf spectre?
For Finding the Input impedance of Passive Mixer, you should use PSS+PAC simulation.

how to measure the lc tank quality factor with software(rf spectre .i.e cadence) and by calculations too?
Q=Rp*sqrt(C/L) for a parallel combination of RLC.

For your Case Rp=900 ohms and then the Required Q=9.8. This means that the Q of your Inductor should be 9.8 which may difficult on chip. Therefore, if you really need 900 ohms, you should scale up the inductor and scale down the capacitor by the same factor. Here is an example derived from you data. Assume that you are limited by Q=6. Rp=L*w*Q , from your data w=2.66GHz=1/(2*pi*sqrt(l*c)). L will be equal to 9nH and C is equal to 400fF. Also using 2pF floating cap for ac coupling purposes increases the parasitic caps. Maybe, you can decrease it.

For finding the Q of inductor in cadence, just use one inverter in parallel with AC current source and do AC simulation and then Q= Imaginary part of voltage on the inductor/Real part of voltage on the inductor.

•