RFICDUDE
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There is relevance; however, it is not in the same sense as conjugate power matching. For a PA, efficiency, linearity, and stability are the main considerations. To maximize efficiency, we want to produce the largest possible amount of power delivered to the load given the power supply constraints available. Note this is not power transfer since we want to maximize the power delivered AND minimize the power dissipated by the source. If the transistor is an ideal current source then this condition occurs when the current source delivers a peak value which causes the peak load voltage to be Vdd for a common source amp with an ideal choke connected to the drain and AC coupling cap from the drain to the load.
Of course in a real device there is capacitance and little bit of resistance. In this case we look for a load impedance which permits the required amount of peak current swing and voltage swing at the drain of the power device. The somewhat empirical technique for characterizing or finding the optimal load is called "load pull."
There is a somewhat infamous paper by Steve Cripps on the concept. Cripps, S.C., "A Theory for the Prediction of GaAs FET Load-Pull Power Contours," Microwave Symposium Digest, MTT-S International , vol.83, no.1, pp. 221-223, May 1983
He has published a few books on PA design too.
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