應用於無電池式太陽能物聯網標籤(IoT Tag)之具最大功率點追蹤電荷幫浦

Abstract

本篇論文中提出一種適用於無電池式太陽能物聯網標籤IoT (Internet of things) tag之升壓電路，目的在於最大化獵取前端太陽能電池所吸收之環境光能，並提供給後端可見光通訊電路能夠正常操作的電壓。本電路包含交互式耦合電荷幫浦、最大功率點追蹤電路、以及時序控制電路。預期在80-100微瓦的狀態下，將0.55V-0.65V的輸入電壓升至1V~1.1V輸出。此電路之交互式耦合電荷幫浦的負載電晶體使用了基底選擇電路，能夠使得整體電路的能量轉換效率提升，也讓後級設計的電容值能夠下降，節省面積，降低成本；此外，為了維持此電路的高轉換效率，時序控制電路所耗的能量需要非常小，許多時序控制電路將電晶體操作於次臨界傳導區，能夠大幅降低整體控制電路所消耗的功率，並將更多的太陽能源轉換至後端電路。開關式頻率電路亦被採用於此最大功率點追蹤電路來調變頻率，以達到追蹤太陽能內阻之功能。此系統於台積電0.18UM製成下線兩次並於N製程廠0.35UM製程下線一次，第二次晶片之測量結果顯示在30微瓦的輸入功率下，電壓轉換效率為97%而功率轉換效率為11.7%。低落之功率轉換效率原因已被找出且被重新設計，經由調大幫浦電容將轉換效率提升。此步驟已於Hspice電路模擬軟體進行驗證，並於N製程廠進行第三次電路設計，其模擬結果顯示轉換效率可提升至81.2%。

A dc-dc regulator is proposed to attach to the battery-less solar tag applied in the Internet of Things (IoTs) market. Two main purposes in this design is to maximize the transfer efficiency and to provide a high enough supply voltage to the back-end circuit. The overall circuit consists of the cross-coupled charge pump, optimal power point tracking and timing control circuit. It is expected to boost the input voltage around 0.55-0.65V to the output 1-1.1V at 80-100μW condition. Gated PFM circuit is adopted in the optimal power point tracking system to modulate the input frequency of the charge pump to match the inner resistance of the solar cell. This system has been taped-out by TSMC 0.18UM 1P6M process twice and N-fab 0.35UM process once. The experimental results of 2nd chip show that the voltage conversion efficiency (VCE) is 97% and the power conversion efficiency (PCE) is 11.7% at 30μW input power condition. The reason of the low efficiency has been found and improved by enhancing the pumping capacitance. This has been proven by the hspice. The efficiency of the 3rd tape-out in N-fab has been improved to 81.2% according to the simulation results.