SUMMARYThis paper presents the design method, properties and driving techniques of a linear 0.5 W 1 GHz LDMOS power amplifier used in a supply modulated envelope tracking transmitter with real-time predistortion. Causes of nonlinearities are identified, and various supply voltage drives are experimented. Measured results show that the power efficiency can be improved while maintaining high linearity.

Power amplifier (PA) efficiency is a criticalfactor in any portable device. Two ofthe most popular architectures to improve the efficiency, envelope tracking (ET) and envelope elimination and restoration (EER), are discussed in this paper. A test systemfor characterization ofsuch a system is presented. A Class E based EER system is tested and characterized and software corrections are implemented to linearize the transmitter Test results show an ACPR improvement of 15 dB by only tuning the phase signalk amplitude and adding AM/PM correction. EVM improves from 2.8% to 0. 71% at the same time.

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This paper describes the design of an integrated tuned power amplifier specified to operate at Inmarsat satellite uplink frequencies from 1626.5 to 1660.5 MHz. The basic topology of the amplifier lies on the parallel tuned inverse class E amplifier that is modified by placing the DC-blocking capacitor into a new position and by adjusting the size of the capacitor to improve stability below the desired band. Further, the new positioning reduces losses between drain and load. The high currents flowing in the circuit made it necessary to use wide inductor width and high-Q finger capacitors in the on-chip resonator. The amplifier was implemented as a Gallium Arsenide (GaAs) integrated circuit (IC) that delivered 2 W of output power while the drain efficiency was ca. 56%. Measurements included source and load pulls to further improve the performance of the amplifier and to investigate the stability at small input drive levels.

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This paper describes advantages and characteristics of a class E power amplifier when used in a polar transmitter system. Basic principles of class E operation and information about different nonlinearities are given. Also, modifying the transistor model for switch-mode use is discussed briefly. A 1 GHz, 0.5 W class E power amplifier was implemented for a polar transmitter. Performance measurements of a total transmitter system with and without predistortion are presented.

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