Overview

From APPLIED MICROWAVE & WIRELESS, VOL. 6, NO. 4, FALL 1994

Advanced portable communication products require high-efficiency power amplifiers operating at low voltage. The size and weight of the portable units can be reduced markedly by decreasing the number of battery cells. RF power amplifiers are the highest energy consumption components of portable communication equipment and are therefore responsible for the limit on talk time or battery life, a limit that is directly related to the transmitter RF conversion efficiency.

Conversion efficiency must be evaluated within all of the functions associated with the RF power signal, such as the receiver transmitter duplexer, harmonic filtering, power control, and antenna gain. As the RF and DC dissipation are reduced within the transmitter, the battery consumption and need for heat radiators are decreased. In addition, there are opportunities for system improvement, such as adaptive power control and increased spectral and data efficiency.

Power amplifiers based on Silicon MOSFETs, GaAs MESFETs and HBTs have been reported by several authors [1, 2, 3, 4]. The introduction of GaAs MESFET, HFET and HBT into portable communications equipment increases significantly the DC to RF conversion efficiency compared to bipolar RF power amplifiers, the preceding technology. However, this improvement is not without drawbacks, for example, the need for a negative bias voltage source, more complex turn on procedures, added...