Precise and simple DC-electrothermal characterization of MMIC power amplifiers

A new indirect electrical method for the thermal characterization of microwave monolithic integrated circuit (MMIC) power amplifiers is presented. Unlike other methods previously proposed, the suggested procedure is easy to apply on power amplifiers with complex structures, formed by the combination of several amplifying stages on the same die. The new technique is specially indicated for MMICs formed by FET devices and mounted with epoxy attachment. The procedure uses the thermal coupling response between multiple amplifying stages to characterize the thermal behavior of the complete MMIC structure. It is a non-invasive method and requires the amplifier to operate under normal working conditions. Experimental results are given to demonstrate the precision and usefulness of this new procedure. The technique was applied to a commercial X-band MMIC power amplifier under different bias, temperature and mounting conditions.