Optimization theory applied to dynamic biasing for power amplifier performance enhancement

Driving the gate and drain biases as a function of the input power significantly enhances the efficiency of class-A and -AB amplifiers. These functions are described as low-order polynomials in order to limit the bias bandwidth, especially at the drain. This work formulates the optimization of the bias polynomial coefficients as a constrained optimization problem, describing in detail the formulation of the constraints, the structure of the cost function, as well as a relevant linearity measure. Using the random search algorithm within the field of stochastic search optimization, a set of solutions was obtained yielding power added efficiency nearly as high as 50%, while the linearity was comparable to that of a class-A amplifier.