Continuous Mode Power Amplifier Design Using Harmonic Clipping Contours: Theory and Practice

A novel graphical power amplifier (PA) design tool, the “clipping contour,” is introduced and described. Using the now well-publicized continuous Class-B/J voltage waveform formulation as a starting point, a process is derived that allows contours to be constructed on a Smith chart that define the “zero-grazing” fundamental and harmonic impedance conditions. Theoretical equations are defined and solved whereby the contours can be drawn in real time in a computer-added design environment. A key and novel result from this theory is the definition of a 2-D harmonic design space that opens up rapidly as small concessions from optimum power and efficiency matching conditions are made. A design example is described and fabricated, which demonstrates the utility of using the second harmonic clipping contour during the PA design process. A 10-W GaN demonstrator gives measured continuous wave power > 8.5 W, efficiency > 60%, and better than -30-dB adjacent channel power ratio over a bandwidth of 1-2.9 GHz.