Adaptive methods to preserve power amplifier linearity under antenna mismatch conditions

Abstract

Under antenna mismatch conditions at high output power, voltage clipping (due to collector voltage saturation) is the main cause of power amplifier linearity degradation. To preserve linearity under mismatch three adaptive methods are presented that make use of the detected minimum collector peak voltage. This detected signal controls either the amplifier output power, load-line, or supply voltage. These concepts are generalized analytically, and calculated results compare well to simulations. Measurements demonstrate am error vector magnitude reduction of 5% and an adjacent channel power ratio improvement of 10 dB at a voltage standing wave ratio of 4 for an EDGE amplifier with adaptively controlled output power. These adaptive methods offer a cost and size effective alternative to the use of an isolator.