# What does this Q mean?

#### spbhu

Joined Apr 27, 2005
2
For an inductive degeneration LNA, the input circuit takes the form of a series-resonant network: Gm=gm1*Qin=gm1/( ω0*Cgs*(Rs+ ωT*Ls)), where Qin is the effective Q of the amplifier input circuit. Can anybody why does this Q mean? How to get value of Q? Thanks

#### n9xv

Joined Jan 18, 2005
329
The "Q" of a coil or inductive circuit is the measure of the inductive effects of that coil or circuit. Sometimes refered to as the (Q)uality rating of the coil or circuit. A coil or circuit that is highly inductive with little resistance can be said to have a high Q rating. A coil or circuit with alot of resistance to dampen the inductive effects is said to have a low Q rating. Q can be found by the ratio of inductive reactance to DC resistance;

Q = XL / Resistance,

Where XL = 6.28 * F * L

F = frequency, L = inductance

If the inductive reactance of a coil was 1000-Ohms and the internal DC resistance of the coil winding itself was 100-Ohms then the Q of that coil would be 10.