An autotransformer impedance transformation technique for efficient power harvesting of passive transponders and wireless microsensors

A novel autotransformer impedance transformation technique to improve the power efficiency of RF-to-DC power harvesting of passive transponders and wireless microsensors is proposed. The method utilizes a step-up autotransformer with a large turn ratio inserted between the antenna and the voltage multiplier to boost the signal prior to rectification while providing a matching impedance to the antenna. To have a large voltage gain while minimizing the silicon consumption of the step-up autotransformer, the number of turns of the spiral of the primary winding is kept low and the width of the spiral of the secondary winding is made smaller than that of the primary winding. This also effectively minimizes the effect of spiral-substrate parasitic capacitances of the transformers, eliminating the drawback of the widely used impedance transformation with resonating LC networks. Implemented in IBM-130 nm 1.2 V CMOS technology, simulation results have demonstrated that the proposed step-up autotransformer impedance transformation technique significantly improve the power efficiency.