What does this Q mean?

Discussion in 'General Electronics Chat' started by spbhu, Jun 10, 2005.

  1. spbhu

    Thread Starter New Member

    Apr 27, 2005
    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
  2. n9xv

    Senior Member

    Jan 18, 2005
    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.