Dual mode RF CMOS power amplifier with transformer for polar transmitters

Abstract

Polar transmitters are expected to be very popular owing to their many advantages over conventional Cartesian transmitters, especially in GSM and EDGE systems. Accordingly, their power amplifiers based on GaAs HBTs are being studied intensively. However, few works have focused on CMOS power amplifiers for polar transmitters. Although CMOS power amplifiers are expected to be cheaper than GaAs HBT power amplifiers and easier to integrate with other circuits, they are not considered as a useful RF power amplifier with a watt-level output power. Recently, the possibility of a CMOS power amplifier has been successfully demonstrated using a distributed active transformer (DAT). The DAT has been considered as lending possible improvements to the performance of a CMOS power amplifier. In this thesis, several CMOS power amplifiers for polar transmitter applications are designed. At first, the power transistor and transmission line transformer for the CMOS power amplifiers are studied. The power transistor for the amplifier is the key component for the high efficiency and output power. The design of the power transistor is therefore one of the most important steps for the design of the power amplifier. A power transistor with interdigitated body-contact is proposed. The junction breakdown voltage of the proposed power transistor is improved by approximately 0.5 V. The transmission line transformer is also the key component of the designed CMOS power amplifier. The transmission line transformer is investigated. There are two important specifications of power amplifiers for polar transmitters. The first is the output dynamic range. It is crucial to obtain enough dynamic range with a given supply voltage range. The second specification is related to efficiency at a low output power. In general, a power efficiency close to the maximum output power is fairly high. A power amplifier only achieves its peak efficiency at a maximum output power. The efficiency usually degra...