A Fully Integrated, Regulatorless CMOS Power Amplifier for Long-Range Wireless Sensor Communication

Abstract

This paper presents a CMOS power amplifier (PA) system designed with the explicit goal of customizing a high-output power transmitter for sensor applications, where the supply voltage from an energy storage element is often time varying. The PA is intended for use in a long-range sensor transceiver and can operate directly off a super-capacitor source. A constant output-power, regulatorless, series power-combined PA with a fully integrated tunable matching network is implemented in an attempt to eliminate all energy losses associated with a high-current voltage regulator. The PA monitors the output voltage at the off-chip antenna and digitally modulates the PA load impedance to maintain a constant target output power as the super-capacitor discharges. The PA system, integrated in a 90-nm CMOS process, has a peak output power of 24 dBm with an efficiency of 12% at 1.8 GHz, making it suitable for sensor data communication over distances of several hundred meters. As the PA supply varies from 2.5 to 1.5 V, the power control loop maintains a constant output power with an accuracy of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\pm$</tex> </formula> 0.8 dB.