Langevin Approach to understand the Noise in Microwave Transistors

A noise analysis procedure for microwave devices based on Langevin approach is presented. The device is represented by its equivalent circuit with the internal noise sources included as stochastic processes. Fromthe circuit network analysis a stochastic integral equation for the output voltage is derived and fromits power spectrumthe noise figure as a function of the operating frequency is obtained. The theoretical results have been compared with experimental data obtained by the characterization of an HEMT transistor series (NE20283A, by NEC) from6 to 18 GHz at a low noise bias point. The reported procedure exhibits good accuracy, within the typical uncertainty range of any experimental determination. The approach allows to extract all the information required for a complete knowledge of the noise performance of the device without any restriction on the statistics of the noise sources.