Efficient, linear amplification of varying-envelope signals using FETs with parabolic transfer characteristics.

A new, linear, high-efficiency mode of operation is described for FET power amplifiers of varying-envelope signals (e.g., single-sideband, quadrature-amplitude-modulation and multicarrier signals). It makes use of FETs having parabolic transfer characteristic (PTC). It is shown theoretically and experimentally that the efficiency of PTC mode is about 2 dB higher than that of standard class-A mode. For example, two-tone, 4-GHz measurements on a Western Electric FET model 131-L showed that, for an output power of about 1.5 watts, and for a relative third-order intermodulation level of -35 dB, the power-added efficiency of the PTC mode was 20% while that of class-A mode was 13%. Comparisons are also made with other high-efficiency modes of operation proposed elsewhere.