This paper aims to review the recent architectures of power management units for ultrasound-based energy harvesting, while focusing on battery-less implantable medical devices. In such systems, energy sustainability is based on piezoelectric devices and a power management circuit, which represents a key building block since it maximizes the power extracted from the piezoelectric devices and delivers it to the other building blocks of the implanted device. Since the power budget is strongly constrained by the dimension of the piezoelectric energy harvester, complexity of topologies have been increased bit by bit in order to achieve improved power efficiency also in difficult operative conditions. With this in mind, the introduced work consists of a comprehensive presentation of the main blocks of a generic power management unit for ultrasound-based energy harvesting and its operative principles, a review of the prior art and a comparative study of the performance achieved by the considered solutions. Finally, design guidelines are provided, allowing the designer to choose the best topology according to the given design specifications and technology adopted.

This paper proposes a comparative study of regulation schemes for charge-pump-based voltage generators using behavioral models in Verilog- Analog Mixed Signal (AMS) code. An accurate and simple model of the charge pump is first introduced. It allows reducing the simulation time of complex electronic systems made up by both analog and digital circuits while maintaining a good agreement with transistor-level simulations. Finally, a comprehensive comparative study of the different regulation schemes for charge pumps is reported which allows the designer to choose the most suitable topology for a given application and Charge Pump (CP) operative zone.

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