Three Different Methods for Determining the Microwave Noise Parameters of HEMT's at Decreasing Temperatures

Abstract

The noise characteristics of any transistor are usually represented by means of four parameters which are frequency-, bias- and temperature-dependent, similarly to the scattering parameters. The noise parameters are determined by a standard indirect procedure based on multiple noise figure measurements and appropriate data processing techniques requiring a complex instrumentation set-up and skilled operators. As an alterative way, we have shown that the noise parameters of packaged HEAMT's can be computed with very good accuracy from the analysis of a noisy circuit model derived from the scattering parameters plus a single noise figure measurement. A third way exists for the determination of transistor's noise parameters which consists of a direct measurement based on the search for the minimum noise figure condition. In this paper, we present the compaison among these three procedures to characterize the noise performance of HEAMI's over the 6-18 GHz frequency range at different temperatures. It is shown that the last two methods indeed allow the correct extraction of the noise parameters of HEMT's avoiding the time-consumption and the complexity of the standard procedure.