Class-BJ power amplifier modes: The IMD behavior of reactive terminations

For the first time a two-tone intermodulation distortion behavior for the class-BJ power amplifier mode is studied. The right phase combination of fundamental and second harmonic terminations lead to new output solutions where the power-efficiency is maintained optimum. However, no IMD behavior has so far been investigated for such terminations on a power transistor through load-pull investigation. In this paper, the class-BJ IMD analysis is investigated theoretically and experimentally through measurement activity on a 1.2 mm AlGaN/GaN power transistor under a two-tone excitation. The measurement results show that the standard class-B and reactive class-BJ solutions deliver same power-efficiency as well as same IM3 performance when driving the device into compression. However, when driving the device at 6 dB input power back-off, despite power and efficiency are similar with varying the terminations, the standard class-B state reveals better IM3 values of -40.5 dBc compared with the class-BJ solution of -31.8 dBc.