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
    2
    0
    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
    329
    1
    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.
     
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