Modified derivative superposition method for linearizing FET low-noise amplifiers

Intermodulation distortion in field-effect transistors (FETs) at RP frequencies is analyzed using the Volterra-series analysis. The degrading effect of the circuit reactances on the maximum IIP3 in the conventional derivative-superposition (DS) method is explained. The noise performance of this method is also analysed and the effect of the subthreshold biasing of one of the FETs on the noise figure (NF) is shown. A modified DS method is proposed to increase the maximum IIP3 at RF It was used in a 0.25-mum Si CMOS low-noise amplifier (LNA) designed for cellular code-division multiple-access receivers. The LNA achieved +22-dBm IIP3 with 15.5-dB gain, 1.65-dB NF, and 9.3 mA@2.6-V power consumption.