High-efficiency power amplifier for wireless sensor networks

We designed a high-efficiency class-E switched-mode power amplifier for a wireless networked micro-sensor system. In this system, where each sensor operates using a micro-battery, has local processing capability, and contains on the same chip integrated sensing elements and an RF transmitter, most of the power is dissipated by the transmitter. The proposed amplifier achieves 92.4% maximum drain efficiency and can vary the transmitted power between -4.2 to -0.2 dBm with almost constant efficiency. This last feature is obtained by controlling the modulation duty cycle and by switching the capacitors´ values in the parallel circuit. The possibility of choosing the transmitted power depending on the distance from a base station or other sensors and on the charge level of the battery, combined with power aware network protocols, improves network lifetime, reliability, and adaptability. The amplifier is designed in 0.18 μm CMOS process and operates with a nominal 1.2 V supply.