Issues on the Design of a Variable Power LINC Amplifier System in SiGe Operating at 2.4 GHz

An increasing number of wireless communication systems require linear transmitters that can achieve high efficiency. Good linearity is necessary for bandwidth efficient modulation while poor efficiency directly affects operational costs and causes thermal losses in the base station. This paper examines the implementation of the outphasing technique, also known as Linear Amplification with Nonlinear Components (LINC) using a 0.25 mum SiGe BICMOS process. Adaptation of the amplifier in order to achieve different power levels, via the use of Class-F amplifying sections working in parallel is also examined. The effects of the input and output mismatch introduced when changing the power level are discussed and possible solutions presented. Furthermore, specific problems which arise when using a bipolar technology are addressed. This work also discusses the adaptation of a tunable phase shifter for a 1 V supply and wide-linear range. The 2.4 GHz amplifier system presented in this work achieved a 3-level power control with a maximum PAE in the range of 58-73%.