Microwave and RF Design of Wireless Systems
Microwave and RF Design of Wireless Systems
Design of Integrated Circuits for Optical Communications
Design of Integrated Circuits for Optical Communications
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This paper proposes a step-up transformer impedance transformation technique to improve the power efficiency of radio-frequency power harvesters of passive transponders. The step-up transformer with a large turn ratio is inserted between the antenna and the voltage multiplier to boost the amplitude of the RF signals at the input of the voltage multiplier while providing a matching impedance to the antenna for maximum power transfer and zero reflection. By making the spiral of the primary winding wider and that of the secondary narrower, the ohmic loss of the primary winding and the spiral-substrate loss of the secondary winding of the transformer are minimized simultaneously. The silicon consumption of the step-up transformer impedance transformation network is also minimized by employing the stack configuration of transformers with the secondary winding implemented using an upper metal layer and the primary winding implemented using a lower metal layer. Two RF power harvesters, one with the proposed step-up transformer impedance transformation network and a modified Nakamoto rectifier and the other with a resonating LC impedance transformation network and the same rectifier, are designed in TSMC-0.18@mm 1.8V CMOS technology. Both operate at 2.4GHz. They are analyzed using ADS from HP and Spectre from Cadence Design Systems. Simulation results demonstrate that the power efficiency of the power harvester with the proposed step-up transformer impedance transformation is significantly higher than that with the LC resonating impedance transformation.