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

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.