An RF power amplifier with a variable drain load impedance for efficiency and/or output power control

摘要

The impedance presented to the output port of the amplifying device 22 may be altered by adjusting the value of one or both of the capacitors C1 and C2 respectively in parallel with the primary and secondary inductors L1 and L2 of the output transformer 24. The amplifier efficiency may thus be maintained at a high level despite changes in the supply voltage Vdd or the load impedance RL. The capacitors may be controlled in real time in response to changes in Vdd or the load impedance, in order to achieve the maximum efficiency or a predetermined lesser efficiency. Alternatively, the power delivered to the load may be varied without a requirement to alter the supply voltage Vdd. Differential arrangements are contemplated. Drain impedance control and/or output power control is obtained without altering the geometry of the transformer.