Power amplifier linearization using a diode

The emphasis on higher data rates and spectral efficiency has driven the industry towards linear modulation techniques such as QPSK, 64 QAM, or multi-carrier configurations. The result is a signal with a fluctuating envelope which generates intermodulation distortion (IMD) from the power amplifiers. Since most of the IM power appears as interference in adjacent channels, it is important to use a highly linear power amplifier. This paper describes the novel approach of using a diode as an active linearizer in view of minimizing non linear distortion introduced by the power amplifiers in wireless communication circuits. In case of pHEMTs, this technique reduces the effect of nonlinear terms generated by the voltage variable input capacitance of the active device. A two stage power amplifier using 0.5 mum gate length GaAs pHEMT process shows that the power amplifier is linear up to 5 dBm of input power after linearization, where as it becomes nonlinear at -4 dBm of input power before linearization