Linearised class-B transistor amplifiers

The linearity and efficiency of microwave amplifiers were improved by operating the active devices in a linearised class-B mode. Good linearity, i.e., low intermodulation distortion, derives from a cancellation effect of the intermodulation products. At the same time, high efficiency is obtained because of operation in class B. Special active bias circuits were designed to extend the maximum modulation bandwidth of the amplifiers. Under low intermodulation conditions, the output power and efficiency were improved five to six times over those of amplifiers operating in class A. Moreover, the maximum modulation rate was extended to 100 MHz. These high-efficiency, high-power amplifiers are well suited for telecommunication satellite transponders.