ANALYSIS OF PHASE CHARACTERISTICS OF A GAAS-FET POWER-AMPLIFIER FOR DIGITAL CELLULAR PORTABLE TELEPHONES

The GaAs FET power amplifier in a Class AB operation used for digital cellular portable telephones must be studied for reduction of the tran sfer phase variation to attain high performance. However, the load imp edance dependence of the phase characteristics, which is of significan ce, has not been analyzed in detail. In this paper, for the analysis o f phase characteristics, a new pi-type FET equivalent circuit is propo sed in which a negative conductance is introduced in place of the curr ent source. By means of this equivalent circuit, an analysis and a sim ulation are carried out for the load impedance dependence of the phase charac- teristics. An increase of the drain-gate conductance and a de crease in the drain conductance accounts for the inverted V-shape phas e-shift performance. The dependence on the load impedance also is illu strated. Further, the experimental results confirmed the correctness o f the analysis since the phase variation is found to be a function of the drain-gate current.