基於快速鎖定鎖相迴路及FPGA的無線能量傳輸波束成型系統

Abstract

本論文研究了基於FPGA及四個鎖相迴路，並應用於無線功率傳輸的四通道波束成型系統的電路和系統設計，且主要著重於系統的發射端，此系統能為分佈在特定區域內的裝置進行無線充電。此系統主要是利用FPGA產生四個具有特定相位的數位訊號，並分別用作四個鎖相迴路的參考訊號，以控制波束成型的方向，這取代了一般波束成型系統中的移相器，從而減少系統中射頻訊號的路徑損耗。此外，整合快速鎖定的鎖相迴路可以增強系統的響應能力，進而實現快速的方向切換。 本論文可分為兩部份，第一部分為快速鎖定之鎖相迴路，第二部分則為基於FPGA與此鎖相迴路之的無線能量傳輸波束成型系統。本論文設計之鎖相迴路採用可調式充電泵，使得此鎖相迴路能在鎖定時間與相位雜訊性能之間做出取捨，此鎖相迴路使用TSRI的U18 (Full-Custom)製程完成電路設計及佈局，在模擬階段，此鎖相迴路在輸入20MHz方波時，能在約1.2μs左右將輸出訊號鎖定在2.4GHz，而量測時則大約需要4.5μs完成鎖定。而本論文設計之無線能量傳輸波束成型系統經過量測，能在系統上方往左右各偏移45度的範圍內調整發送波束的方向，且在距離50cm處能接收到之最大功率為-23.18dBm。

This paper examines the circuit and system design for a reconfigurable four-channel beamforming system for wireless power transfer based on an FPGA and four PLLs, with a particular emphasis on the transmitting end of the system. The system is capable of wireless charging devices that are distributed throughout a given area. In contrast to conventional beamforming systems, FPGA generates four digital signals with specific phase timings, which are used as reference clocks for the four PLLs to adjust the beamforming direction. This can replace the phase shifters in a traditional beamforming transmitter and reduce the RF path loss. Furthermore, integrating a fast-locked PLL enhances the system's responsiveness, enabling rapid direction switching. This paper consists of two main parts: the design of a fast-locked phase-locked loop (PLL) and a beamforming system for wireless power transfer based on fast-locked PLLs and FPGA. The proposed PLL utilizes an adjustable charge pump to deal with the trade-off between locking time and phase noise performance. The circuit was developed using TSRI's U18 (Full-Custom) process. In simulation, the PLL achieved a locking time of approximately 1.2 μs to a 2.4 GHz output when driven by a 20 MHz input square wave, while measurement results showed a locking time of about 4.5 μs. Additionally, the wireless power transfer beamforming system developed in this paper was measured to adjust the transmission beam direction within a ±45-degree range above the system and the maximum power that can be received at a distance of 50cm is -23.18dBm.