The bias smith tube: Simultaneous optimization of bias voltage and load impedance in power amplifier design

Multiple factors must be considered in power-amplifier design for wireless communications and radar, including bias voltage, input power, and load impedance. The Bias Smith Tube is presented as a three-dimensional extension of the Smith Chart with bias voltage as the vertical axis. It allows simultaneous visualization of nonlinear output characteristic behaviors over transistor bias voltage and load reflection coefficient. Simulated and measured three-dimensional surfaces of constant power-added efficiency (PAE), adjacent channel power ratio (ACPR), and delivered power are shown in the Bias Smith Tube, and a design approach is illustrated that finds the combination of load impedance and bias voltage providing maximum PAE under ACPR and/or delivered power constraints.