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 transfer phase variation to attain high performance. However, the load impedance dependence of the phase characteristics, which is of significance, has not been analyzed in detail. In this paper, for the analysis of phase characteristics, a new pi-type FET equivalent circuit is proposed in which a negative conductance is introduced in place of the current source. By means of this equivalent circuit, an analysis and a simulation are carried out for the load impedance dependence of the phase charac- teristics. An increase of the drain-gate conductance and a decrease in the drain conductance accounts for the inverted V-shape phase-shift performance. The dependence on the load impedance also is illustrated. Further, the experimental results confirmed the correctness of the analysis since the phase variation is found to be a function of the drain-gate current.