Geometry optimization of SiGe HBTs for noise performance of the monolithic Low noise amplifier

The influence of various geometry sizes of SiGe HBTs on noise performance of the monolithic Low noise amplifiers(LNAs) is investigated in this paper. Four types of LNAs using SiGe HBTs with different emitter widths, emitter lengths and emitter strip numbers are fabricated in a 0.35-¿m Si BiCMOS process technology. The die areas are only 0.2 mm² due to the absence of inductors. The noise figure(NF), associated gain(G_A) and the optimum source resistance(R_s,opt) of the LNAs are compared. Simplified analytical expressions of NF and R_s,opt are presented to give additional insight. Geometry scaling data show that the LNA using SiGe HBT with A_E=4×40×4¿m² has the minimum NF of 2.7dB, the maximum gain of 26.7dB and the optimum R_s,opt of nearly 50¿ compared to other devices geometries. These experiment results provide a guide of device geometry optimizing to develop monolithic LNA for lower noise application.