Design of Integrated, Efficient Power Amplifiers for Next-Generation Wireless Communications

Abstract

An integrated power amplifier and DC-DC converter are presented to create a variable supply voltage power amplifier to improve battery life in cellular handsets. This system has the ability to reduce the average battery current drawn by a handset power amplifier by operating at lower supply voltages when not transmitting at maximum power. This type of system has not been adopted because of the need for additional circuitry when used with traditional power amplifier modules. To be attractive to system designers, advanced power amplifiers need to exhibit the integration that has been seen in modern radio receivers. In this work, SiGe BiCMOS technology is harnessed to achieve the integration of both circuits on one die, presenting a solution to the desire for high efficiency in a single chip solution. The design of power amplifiers in SiGe technology is explored, with a focus on the design of a WCDMA handset power amplifier for third generation mobile systems. The design challenges of such a circuit are presented, along with a design methodology involving a mix of time and frequency domain simulation techniques. Layout concerns are addressed in regards to the SiGe BiCMOS process, and their impact on power amplifier performance is highlighted. Measured results are presented which meet the linearity requirements of WCDMA. A high switching frequency DC-DC converter is also examined, with a focus on integration of such a circuit with a power amplifier. The impact of frequency selection and converter efficiency is analyzed, and several techniques to improve the efficiency are presented. Simulation and measurement results are presented which show excellent agreement over the broad range of converter operating conditions. An analysis method for determining the average reduction of battery current in a variable supply voltage system is presented, with results given for the DC-DC converter/power amplifier integrated system. The integration issues and system performance in regards to physical layout are discussed. The final system measurements show the successful performance of the power amplifier under variable supply voltage operation with the DC-DC converter. The results of this work demonstrate the feasibility of such an integrated, efficient power amplifier and provide a path for integration of advanced power amplifier systems with other transceiver components.