微功率能量收集系统中片上集成的超低压自启动方法研究

The micro-power energy harvesting system is possible to power the low-power devices instead of battery, such as wearable device, implantable medical devices， and wireless sensor network. The output of micro-power energy harvester is low-power and low-voltage, and it is not possible to regulate by the conventional power management. The ultra-low voltage self-start method is crucial for micro-power energy harvesting system. The proposal is aimed to solve the problem by analyzing the startup voltage under the influence of power loss and startup method, disclosing the chief factor of limiting the minimum startup voltage, and investigating the method to reduce the minimum startup voltage. The conduction loss is reduced by adopting threshold voltage compensation method or increasing the overdrive voltage, and the leakage current is reduced by adopting dynamic body biasing method or increasing the reverse gate-drain voltage. The method by cascading enhanced swing LC oscillator and voltage multiplier is proposed for startup of the energy harvester with dc output. The method by cascading bridge rectifier and charge pump is proposed for startup of the energy harvester with ac output. A method by dynamic detecting the input voltage and load current is proposed to avoid system lockup. The expected solution would be low-voltage, low-power and suitable for on-chip implementation. Furthermore, these theories are crucial to micro-power energy harvesting for low-power application.

微功率能量收集系统在可穿戴设备、植入式医疗电子、无线传感器网络等低功耗电子设备中能够替代电池实现自给供电。微功率能量收集器的输出功率小、电压低，无法采用传统的电源管理电路进行电压调整，需要一种自启动机制。本项目针对微功率能量收集系统面临的超低压自启动问题，研究功率损耗和启动方法对启动电压的影响，揭示限制最低启动电压的关键因素，探索降低最低启动电压的方法。为了减小功率损耗，采用阈值电压补偿或增加过驱动电压的方法减小导通损耗，采用衬底动态偏置或增大器件的栅源反向电压的方法减小漏电流损耗。在启动方法上，直流输入的启动电路采用增大摆幅的LC振荡器与电压倍增器级联的方案，交流输入的启动电路采用桥式整流器与电荷泵级联的方案。为了避免系统锁定，提出了一种对输入电压和负载电流进行动态启动检测的方法。本项目预期的方案具有低压低功耗和易于片上集成的特点，研究成果对于微功率能量收集系统的低功耗应用具有重要意义。

在低功耗电子设备中微功率能量收集系统有望代替电池实现自给供电，但其输出功率小，输出电压低，采用传统的接口电路难以实现自启动。本项目针对能量收集系统的超低压启动问题展开研究工作，深入分析了功率损耗和启动方法对启动电压的影响，揭示了限制启动电压的关键因素，探索了降低启动电压的方法。在直流输入启动电路方面，提出了一种基于增加输出摆幅的LC振荡器与改进电荷泵级联结构的直流超低压启动电路，实现了在50mV输入电压条件下自启动。在交流输入的整流器电路方面，提出两种仅采用单个反馈环路同时实现导通和关断延时的补偿方法，一种方法是通过跨导放大器检测有源二极管导通/关断误差并调整比较器失调电压实现自动延时补偿，另一种方法是通过改变PWM控制信号脉宽来调整有源二极管的导通/关断时间实现自动延时补偿，结果表明这两种方法能够使整流器的能量传输效率提高到90%以上。此外，研究了启动电路中超低功耗时钟电路，提出了通过比较器失调抵消、延时补偿和电荷转移等方法提高频率的稳定性，采用了亚阈值电路设计方法完成电路设计并进行了流片，测试结果表明，提出的方案在功耗以及频率稳定性方面的性能都优于传统结构。在本项的资助下，已取得了以下研究成果：在Electronics Letters, Analog Integrated Circuits and Signal Processing等期刊上发表SCI索引论文5篇，发表EI索引会议论文3篇，申请国家发明专利5项。