隨著無線應用像是IoT跟無線感應器變的日益重要，如何無線充電以增加使用壽命跟減少維修費用已成為重要的課題。射頻能量截取提供了一個環境限制最少的能量來源，但其可用的能量相對是最小的，因此如何在每個介面都做到匹配並減少政個系統的損耗來達到最高的效率就是這次設計的重點。主要的能量傳輸路徑是一個高Q匹配電路、高效率整流器與切換式電桿升壓器。經由系統自行隨著不同輸入能量而調整整流器的附載，讓系統可以在很大的輸入能量範圍內都有不錯的效率。模擬中超過30%的整體系統效率可以在20db的輸入能量中達成。

As wireless applications like sensor networks and Internet of Things (IoT) become popular, how to charge the devices easily without physical connection has become an important topic. Radio frequency (RF) energy harvesting provides the least-restricted solution among all other sources. However, its low power density imposes great challenges on the energy extraction process. An autonomous system with reconfigurable structure to extend the operating range is proposed. The main power path is constructed by matching network, main rectifier and DC-DC boost converter. Matching network achieve both impedance matching and voltage amplification at targeted 10 $\mu$w of available power; differential-driven rectifier can operate under low input voltage amplitude and the effective loading is set by the reference voltage – which can track optimal loading condition of main stage rectifier under wide input power range without consuming extra power – generated by reference rectifier along with the following DCDC converter. The asychronize control of DC-DC boost converter is done by an open-loop, low power adaptive control which is sense the instantaneous voltage of $V_{DC}$ and $V_{OUT}$ and control the switching timing such that boost converter can operate under discontinuous mode (DCM) with close-to-optimal efficiency. Due to the nonlinearity of rectifier, impedance mismatch becomes more severe at large input power case, but it can be relaxed by adopting adaptive rectifier to increasing rectifier input impedance under large input power scenario. The pulse width the asychronize control implies the current input power and allows the system to adjust rectifier size internally. Since the boost converter is not regulated, a voltage limiter shunts down the charging progress once $V_{OUT}$ is too high. At fully discharged state, startup stage rectifier is utilized to charge $V_{OUT}$; once $V_{OUT}$ is high enough for control circuit to operate, the high efficient power path is activated and start to supply output loading with much higher efficiency. More than 30\% of total power conversion efficiency is achieved in post-layout simulation for input power ranges from 0dbm to -20dbm, and the simulated sensitivity is -23dBm, generating an output voltage of 1.8V with 5.4-M ohms loading.

1 Introduction 1
1.1 Background Introduction and Motivation . . . . . . . . . . . . . 1
1.2 System Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2 Matching Network 11
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.2 Maximum Power Transfer Theorem . . . . . . . . . . . . . . . . 12
2.3 Scattering Parameter and Smith Chart . . . . . . . . . . . . . . . 16
2.4 Input Impedance of Rectifier . . . . . . . . . . . . . . . . . . . . 21
2.5 Design Consideration of Matching Network . . . . . . . . . . . 33
2.5.1 Single Ladder Matching Network . . . . . . . . . . . . . 33
2.6 Implementation of Matching Network . . . . . . . . . . . . . . . 36
3 AC-DC Converter 42
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
3.2 Power Conversion Efficiency (PCE) Calculation . . . . . . . . . 45
3.3 Basic Operation of Rectifier . . . . . . . . . . . . . . . . . . . . . 46
3.4 Rectifier Design Consideration . . . . . . . . . . . . . . . . . . . 54
iii
3.4.1 Rectifier Size and PN Ratio . . . . . . . . . . . . . . . . . 54
3.4.2 Low Threshold Voltage Device and Hybrid Structure . . 58
3.4.3 Parasitic Capacitance Analyse . . . . . . . . . . . . . . . 61
3.4.4 On-resistance Analyse . . . . . . . . . . . . . . . . . . . . 69
3.4.5 Frequency Dependency . . . . . . . . . . . . . . . . . . . 72
3.5 Adaptive Rectifier . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
3.5.1 Adaptive Rectifier Design Flow . . . . . . . . . . . . . . . 84
3.6 2 Stage Rectifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
4 DCDC Converter 92
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
4.2 Basic Operation of Boost Converter . . . . . . . . . . . . . . . . 93
4.2.1 Boost Converter Design Consideration . . . . . . . . . . 101
4.3 Resistor Emulation of Boost Converter . . . . . . . . . . . . . . . 106
4.4 Asynchronize Control of Boost Converter . . . . . . . . . . . . . 114
4.4.1 Comparator Design Consideration . . . . . . . . . . . . . 123
4.5 System Simulation Results . . . . . . . . . . . . . . . . . . . . . . 125
4.6 Power Meter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134
5 Startup Mechanism and Biasing Circuit 136
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
5.2 2nd Stage Rectifier . . . . . . . . . . . . . . . . . . . . . . . . . . 137
5.2.1 Power-on Reset and Corner Variations . . . . . . . . . . 138
5.3 Supply Insensitive Circuit and Voltage Limiter . . . . . . . . . . 141
6 Measurement Results 143
iv
6.1 PCB Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
6.2 Layout and Die Photo . . . . . . . . . . . . . . . . . . . . . . . . 145
6.3 Measurement Results . . . . . . . . . . . . . . . . . . . . . . . . . 146

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