High-linearity two-watt power amplifier for multiband wireless applications

Amplifiers in the final stages of wireless transmitters boost the power level of the up-converted signals, but the ultimate power level is not same for all transmitters. One specific amplifier can be used as a driver in a cellular base station or as last stage in applications like a pico-cell. However, the amplifier has to meet the stringent linearity requirement imposed by these different standards. In this paper, we present a highly linear single stage two watt power amplifier in GaAs HBT process. The amplifier can be externally matched at the input and output, thus provides flexibility to optimize it across a specific frequency band of interest between 400 MHz and 2700 MHz. The design includes a novel approach of utilizing the nonlinear base-collector and base-emitter diode capacitances of a transistor biased in the saturation region to improve the linearity of the amplifier. The transistor provides a nonlinear feedback path between the output and input of the amplifier and thus minimizes the third order intermodulation distortion (IM3) component.