在物聯網的願景中，所有物品皆可透過安裝無線感測器連線上網。其中，最有效率的方式便是利用現有基礎建設連線上網傳遞資訊，例如藍芽、Wi-Fi與LTE等通訊協定。然而，由於環境中遍佈大量通訊產品，這些感測器為了維持良好的通訊品質，除需具備高靈敏度與低通訊延遲，也要能夠抵抗雜訊干擾。此外，在電池供電的感測器中，無線收發機消耗大部分能量，限制電池使用壽命，亦是物聯網成立的一大挑戰。因此一個具備超低功耗的喚醒接收機（Wake-up receiver，WuRx）被提出，用以不間斷地監控環境之無線喚醒訊號，僅在收到正確喚醒訊號時喚醒主要收發機進行資料交換，打破傳統無線通訊系統的省電方法中，降低功耗所導致通訊延遲惡化的瓶頸，有效節省電池之電力消耗、延長設備使用時間並維持通訊品質。但這意味著喚醒接收機需具備遠低於主要收發機的超低功耗，此外，良好的靈敏度與對於不同類型訊號的高度適用性亦是所需追求的目標。如此方能易於與多種類型的無線感測網路實現高度整合，降低建置成本。
對於喚醒接收機的實現，相對於傳統的線性接收機，基於包絡檢測器（Envelope detector，ED）的非線性架構因具有較佳之能源效率而較廣為使用。一個直接包絡檢測喚醒接收機在文獻中僅消耗極低功耗便可實現開關鍵控訊號（On-off keying，OOK）的解調變方案。然而，包絡檢測器也僅能解調振幅調變訊號，且靈敏度與訊號選擇性極差，大大地限制此類接收機的應用。在文獻中，最常被提出與無線通訊基礎設施整合的架構則是混頻器優先的包絡檢測喚醒接收機，因其具備良好之效能且能以簡易的方式實現對二進制頻率偏移鍵控調變（Binary frequency-shift keying，BFSK）訊號的解調變方案。然而若進一步壓低功耗預算至目標的100微瓦，則需以靈敏度來交換，並可能需要外接高品質的射頻濾波器來確保選擇性。此外，對於二進制相位偏移鍵控調變（Binary phase-shift keying，BPSK）訊號的解調仍需仰賴高複雜度的傳統解調器。超再生振盪器（Super-regenerative oscillator）由於具有高能源效率的極高增益，也可置於包絡檢測器前端有效提升性能。然而，其特殊的離散式操作卻也會使得對頻率與相位的解調變更為複雜進而限制了整體功耗。最後，注入鎖定振盪器（Injection-locked oscillator）可將注入訊號不論是振幅、頻率或是相位的變化通通轉變為自身輸出振幅的變化。加上包絡檢測器，便可以統一且有效率的方式實現多種類型的訊號解調變方案。然而其功耗需求與轉換效率取決於振盪器本身諧振器的品質因數。限於低能源成本情況下，文獻中展示一個放大器透過適當正回授的設計可等效提升輸出阻抗，藉以實現品質因數增強。因此，若透過品質因數增強的概念，實現一個能額外提升對注入訊號之增益的注入鎖定振盪器，將可實現一個具備高能源效率與高度適用於各種調變訊號的喚醒接收機。
本文展示一個基於注入鎖定技術與包絡檢測架構提供高靈敏度與高能源效率的喚醒接收機，並且適用多種調變訊號方案，包含開關鍵控調變、二進制頻率偏移鍵控調變與差分二進制相位偏移鍵控調變（Differential binary phase-shift keying，DBPSK），可搭載於多種調變類型的無線感測器。此外，透過極趨近於起振條件的小電流偏壓，實現品質因數增強之注入鎖定振盪器，同時提升接收機對訊號的靈敏度、與對干擾的抵抗能力。文中包含兩個晶片設計，操作於433 MHz之工業、科學和醫學頻段（ISM band）並具備多重模式，實現於180奈米互補式金屬氧化物半導體製程。第一個晶片（Chip #1）在OOK/BFSK/DBPSK解調變模式下，達到–80/–78/–77 dBm之靈敏度，僅消耗54 μW；其中，資料傳輸率為200 kbps，且位元錯誤率低於千分之一。在200 kHz的頻率偏移下，對三種調變訊號具有至少18 dB的通道選擇性。而在±3 MHz 的頻率偏移下，對於單一頻率或是具調變的干擾訊號分別有至少 33/24/33 dB 的抵抗能力。此外，由於注入鎖定振盪器整合了實現於印刷電路板上的高品質因數環形電感，可將接收機轉變為低功耗模式，直接將電感作為環形天線使用，如此一來避免了射頻放大器的使用，在11 μW的功耗下，實現了優於–71 dBm的靈敏度，符合近距離感測網路之基本需求。第二個設計承襲了前作的核心架構，再整合了平衡不平衡轉換低雜訊放大器與數位基頻解碼電路，減少外部原件的需求，實現一個具備更高效能與高整合度的喚醒接收機（Chip #2）。在高靈敏度的需求下，振盪器改採市售之線圈電感可降低面積需求，並以金屬氧化物半導體電容切換陣列實現更佳的通道選擇能力。在OOK/BFSK/DBPSK解調變模式下，其靈敏度提升至–90/–88/–87 dBm，並獲得最高達151 dB的效能指標（FoM）。偵測64位元長度OOK/BFSK/DBPSK調變方案的喚醒封包時，在低於千分之一的喚醒封包錯誤率與低於每小時一次的誤喚醒條件下，分別達到–97/–96/–94 dBm的靈敏度，僅消耗187 μW，並僅有320 μs的低通訊延遲。
本論文所提出之喚醒接收機，透過簡單的架構實現高適用度，具備超低功耗、高靈敏度與低延遲，此外也具有良好之抗干擾能力，可易於與許多種通訊系統進行整合，廣泛適用於不同場域之物聯網應用。

In the vision of the Internet-of-Things (IoTs), all objects are enabled to connect to the internet by deploying wireless sensors. The most effective way to connect to the internet is using the established infrastructures, such as Bluetooth, Wi-Fi, and LTE. However, the radio of the sensor node requires a high sensitivity and high interference immunity with a short latency to ensure the quality of service in such a dense environment. In addition, the lifetime of the sensor node is dominated by the radio. The wake-up receiver (WuRx) is then proposed to monitor the channel and awake the main radio only if the wake-up request is detected. As the result, the average power consumption of the sensor node can be significantly reduced with a low latency, which means the WuRx should feature an ultralow-power consumption. Moreover, decent performance with high compatibility to provide multiple demodulation schemes is also pursued enabling highly integration with various WSN systems.
To implement a WuRx, the envelope detector (ED) based topology is preferred for the high energy efficiency. A direct envelope detection WuRx is demonstrated to provide an ultralow-power consumption for on-off keying (OOK) demodulation in the literature. However, the ED has poor sensitivity and selectivity, and it is limited to demodulate OOK signals. The mixer-first envelope detection WuRx is the most popular topology to integrating with the infrastructure in the literature since it features a decent performance and enables a simple binary frequency-shift keying (BFSK) demodulation scheme. However, for the ultralow-power target of near 100 μW, the sensitivity would be traded, and the high quality factor RF filter would be required. In addition, a complicated demodulator is still needed for the binary phase-shift keying (BPSK) signal. The super-regenerative oscillator can provide extremely high gain with high efficiency to the ED. However, the discrete operation complicates the demodulation schemes for BFSK and BPSK signals and hence limits the power consumption. The injection-locked oscillator (ILO) enables the conversion of all amplitude, frequency, and phase variations to amplitude response, and therefore provides a simple and unified means for multiple demodulations with the ED. Nevertheless, the power consumption and the conversion efficiency are limited with LC-ILO. To effectively improve the sensitivity with high energy efficiency, the Q-enhanced low noise amplifier (LNA) can be further deployed toward various architecture. This work presents the ILO, which provides an extremely high gain to the injected signal through the Q-enhancement technique, as the best candidate for an ultralow-power and high compatibility WuRx.
Two 433 MHz multi-mode prototypes are implemented in 0.18-μm CMOS process. These WuRxs are based on ILOs and EDs to provide the capabilities of reliable demodulation for OOK, BFSK, and differential binary phase-shift keying (DBPSK) demodulation schemes. For a data rate of 200 kbps and a bit error rate (BER) < 10-3, the first prototype (Chip #1) consumes 54 μW and achieves sensitivities of –80/–78/–77 dBm under the OOK/BFSK/DBPSK demodulation schemes, respectively. With the Q-enhanced ILO, a selectivity of at least 18 dB at 200 kHz adjacent channel has been measured; while the blocker rejection ability of 33/24/33 dB with ±3 MHz frequency offset is achieved. Furthermore, incorporating an external loop antenna with a reception of an injection-locked oscillator, the WuRx features a low-power mode of just 11 μW with a sensitivity of at least –71 dBm. The second prototype (Chip #2) follows the same architecture, and further improves the performance and integrativeness by adopting the balance-to-unbalance LNA and digital baseband decoder. For the target of high sensitivity, the commercial surface-mount coil inductor has been adopted to the ILO, which can also save the area. The channel selection ability of the ILO is also improved by an 8-bit Metal-Oxide-Semiconductor switched capacitor bank. Under three demodulation schemes, the sensitivity of –90/–88/–87 dBm has been measured and the best FoM of 151 dB has been achieved. For a packet error rate (PER) < 10-3 and the false alarm rate < 1 time per hour, the WuRx consumes 187 μW and achieves sensitivities of –97/–96/–94 dBm for the 64-bit OOK/BFSK/DBPSK modulated wake-up packets, where the total transmission latency is only 320 μs.
The proposed wake-up receiver based on injection locking and envelope detection architecture has been demonstrated to provide high compatibility to demodulate all OOK/BFSK/DBPSK signals, which can be provided by the massive established infrastructure wireless sensor networks. The measured high performance and ultralow power consumption enable a great potential to integrate with various IoT applications.

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