Class-J2 Power Amplifiers

This paper presents the theoretical introduction and experimental validation of the “Class-J2Mode Power Amplifier,” which provides higher efficiency and output power compared with conventional class-J mode counterpart. This mode of operation is realized by injection of the second-harmonic current to drain node of a class-J power amplifier (PA) to reduce the 45° phase shift between drain current and voltage signals. Similar to class-J PAs, the second-harmonic impedance of class-J2PAs is purely reactive to simplify the design of the output matching network. The auxiliary second-harmonic injection circuit comprises a transistor biased in class-B mode followed by a class-C biased amplifier to achieve high second-harmonic current conversion efficiency. Theoretical formulations suggest that a 5% improvement in drain efficiency (ηD) as well as a 1.5-dB increase in output power can be achieved for the class-J2mode in comparison with the typical class-J operation. To check the accuracy of theoretical predictions, a proof-of-concept 1-GHz class-J2PA with 12.2-dBm output power and 43% PAE is implemented in a 0.18-μm CMOS technology. For better comparison, a 1-GHz class-J PA with the same transistor size and bias condition as the class-J2PA is also fabricated. The output power and PAE of the reference class-J PA are 11.4 dBm and 40.6%, respectively, which are in agreement with theoretical predictions.