Class-AB power amplifier design guidelines

The design of high-power high-efficiency narrowband amplifiers implies a carefull choice of bias point, loading and power level. The choice of class A, AB, B, or C is based on a compromise between gain , output power, efficiency and total and/or specific distortion content[1]. Qualitative and quantitative considerations must therefore be made by the designer in order to obtain the best performances from a power stage [2-7]. A detailed study of a power amplifier can be performed either experimentally (load-pull measurements [9]). General guidelines and quick design procedure are however highly desirable for the sake of precious design time saving and of clarity of interpretation of the results; alternatively, they can be used to get an accurate staring poin for further optimisation. This is particularly important in the field of monolithic microwave integrated circuits where the optimisation procedure in the phase of the software "breadbording" represents a real crucial step. The contribution of this paper is to give design guidelines consisting of a simple and reliable anlysis method together with design tables; the results have been veritied by comparison with a more accurate but lengthy non-linear analysis programme.