This paper presents the design and measurement of an RF energy harvesting and power management unit that operates across a wide range of available input power, from-24 to +15dBm. The system comprises an adaptive impedance matching network, a single-stage cross-coupled differential-drive rectifier, a start-up charge pump, an adaptive buck-boost converter, a maximum power point tracking (MPPT) circuit and a control loop to regulate the load voltage. The MPPT circuit controls the switching frequency of the buck-boost converter and configures the impedance matching network, optimizing the interfaces between the rectifier and antenna and between the rectifier and the storage capacitor, guaranteeing that the power is being harvested at maximum efficiency. To boost the rectifier output, to accumulate energy in the storage capacitor and to provide energy to the load, a single-inductor buck-boost converter that has two inputs and three outputs is used. Circuit techniques that reduce the power consumption of the control circuits and that allow for adapting the interfaces between the antenna, the rectifier and the load are presented. The peak harvesting efficiency of the system is 40.2%, when presented with an RF source of-9.1dBm available power and 403.5MHz frequency.

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In this paper we present the design and simulation results of an RF energy harvesting circuit that operates across a wide range of available input power, from -27 dBm to 6 dBm. The system comprises an adaptive impedance matching network, a single-stage cross-connected differential rectifier, a start-up charge pump, an adaptive buck-boost converter and a Maximum Power Point Tracking (MPPT) circuit. The MPPT circuit controls the switching frequency of the buck-boost converter and configures the impedance matching network, optimizing the interfaces between the rectifier and antenna and between the rectifier and the storage capacitor, thereby guaranteeing that maximum power is being harvested. The system is designed in a standard 0.18 pm CMOS technology. The peak efficiency is 49.1% at an available input power of -18 dBm and signal frequency of 403.5 MHz.

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The continuous improvement in reducing the power consumption of electronic devices, including biomedical ones, makes the use of energy harvesting systems instead of batteries attractive. Conventionally, energy harvesting systems are optimized to operate in a single worst-case scenario. However, it is often the case that the available input power varies in different situations, which creates a need for energy converters that operates efficiently over a broader input power range. In this paper, a versatile buck-boost converter suitable for wireless energy harvesting and transfer is proposed. The converter maximizes the system's efficiency by maintaining its input resistance fixed during harvesting. Harvested energy is stored in a storage capacitor. The converter can be dynamically adjusted for different available input power and voltage levels. This is accomplished by employing pulse frequency modulation and reconfigurable power switches. A novel adaptively biased zero-current-detection comparator is employed to increase the converter's efficiency, its input having an offset that depends on the output voltage. The converter was simulated for input power levels from 1μW to 1 mW and input voltage level from 0.38 to 1.3 V. Its peak efficiency is 76.3% at an input power of 1μW and 86.3% at 1 mW.@en

Some systems like RF energy harvesters have power transfer efficiency as one of the most important specifications. Therefore, the efficiency of the matching network, which affects the entire system’s efficiency, plays an important role. When the impedance transformation factor between the antenna and its load is high, the matching network efficiency is decreased. In this paper we present the efficiency analysis and optimization of multistage matching networks at a single frequency using lumped components. Considering complex source and load impedances at each stage of the network, we show that it is possible to obtain
better results than prior art.@en