(_{L})
The (complex) impedance presented to the output port of a device. Load impedance determines output power, linearity, and efficieny. It influences device gain and stability.
For maximum gain (minimum output reflection coefficient), _{L} = s_{22}'^{*}
[The load impedance is equal to the conjugate of the output reflection coefficient, modified by any loading from the generator impedance.]
For power, _{L} is set to present the correct load line to deliver the desired output power.
[_{L} for power is a function of desired output power, bias point, and device parasitics. It can be approximated by the desired load impedance R_{L} in parallel with the output capacitance at half operating voltage (C_{CB} @ V_{CE}/2), that combination in series with the output inductance (bond wires plus package parasitics). For class C (nonlinear operation), R_{L} ~ (V_{CE}V_{Csat})^{2}/2P_{out}. For class A (linear operation), R_{L} ~ (V_{CE}V_{Csat})^{2}/7P_{out}.
See also:
Gain, Generator Impedance, Impedance, Impedance Matching, reflection coefficient, sparameters
