800 MHz power amplifier using envelope following technique

This work describes a 2-W peak-envelope linear power amplifier based upon the envelope following (EF) technique. Both drain voltages of a two stage monolithic GaAs IC power amplifier are modulated with respect to the input RF signal using a high efficiency class-S modulator. The class-S modulator is implemented as a silicon IC consisting of a high-speed comparator and driver circuitry to supply currents in excess of 1 A. The RF amplifier IC utilizes two GaAs HEMT devices designed for class A/B operation. An envelope-feedback loop provides equalization of time delay differences between the envelope and RF signal paths as well as amplitude linearization. The resulting transmitter has adequate bandwidth to amplify an IS-136 π/4 DQPSK signal with required spectral linearity achieving 49% total efficiency at 1-W average output power using a 3.5 volt supply. At 10 dB power back-off, the system efficiency remains above 30%. Targeting low cost portable wireless handsets, the complete amplifier is realized using two integrated circuits with minimal off chip components