AN IMPROVED SPICE MODEL FOR HIGH-FREQUENCY NOISE OF BJTS AND HBTS

An improved compact model for the high-frequency noise of bipolar junc tion transistors (BJT's) and heterojunction bipolar transistors (HBT's ) is presented and implemented in SPICES. It properly takes into accou nt the frequency function of thermal noise in the input circuit, which is related to the real part of the input admittance, This quantity is the result of an interplay between the base resistance, the internal emitter-base capacitance, the small-signal input conductance of the in trinsic transistor, and the emitter series resistance, This requires t he replacement of the noisy base resistance in SPICE by a frequency-de pendent expression consisting of the appropriate SPICE parameters. A s imilar substitution is needed in the output circuit. For a Si/SiGe HBT these improvements lead to excellent agreement between the noise figu re and device simulation results.