Optimal Adaptation Methods and Class of Operation: Keys to Improving Feedforward Amplifier Power Efficiency

This paper studies the influences of two new adaptation methods and the class of main amplifier operation on the achievable power efficiency of the feedforward amplifier under typical design constraints. These two influences are weak for a two-tone driving signal, but they interact powerfully for a real-life high-stress signal, leading to optimal designs involving Class AB or even Class B main amplifiers, depending on the required output linearity. Assuming a code-division multiple-access signal, typical MESFETs, and an output linearity commonly used in mobile systems design, the new adaptation methods allowed relative efficiency improvements of 21% and 36% using main amplifiers biased near Class B and at Class B, respectively.