I. Introduction
Nowadays, Low Power Wide Area Networks (LPWAN) and Wireless Body Area Networks (WBAN) Receivers (Rx) are widely used in applications such as environmental sensors and Internet-of-Things (IoT). The main design challenge associated with these devices is to extend the lifetime of these networks under limited energy sources. A Radio Frequency (RF) transceiver consumes high power consumption when it is active. Therefore, it would be efficient if we make the transceiver off and wake it up only when it is needed. A Wake-up Receiver (WuRx) continuously listens for the wake-up signal and activates the main Rx when the wake-up signal is detected. As the distance between sensors increases the sensitivity of the WuRx needs to be increased, which results in consuming more power by the WuRx. In contrast, power consumption is the major criterion in the design of a WuRx. A WuRx can be implemented in two ways, with/without the mixer [1]. A mixer-based WuRx utilizes a Local Oscillator (LO), generated by a Phase-Locked Loop (PLL) to convert down the received RF signal by the Low-Noise Amplifier (LNA) to a specified Intermediate Frequency (IF). The PLL is the most power-hungry building block of a WuRx. Hence, a low power PLL can highly lower the power consumption of the whole WuRx.
Block diagram of the proposed PLL.