This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination. IEEE JOURNAL OF SOLID-STATE CIRCUITS 1 A Wake-Up Receiver With a Multi-Stage Self-Mixer and With Enhanced Sensitivity When Using an Interferer as Local Oscillator Vivek Mangal , Student Member, IEEE, and Peter R. Kinget , Fellow, IEEE Abstract— An ultra-low power wake-up receiver with an energy-detection passive-RF architecture uses a multi-stage self- mixer that has a better conversion gain than the conventional envelope detector. The self-mixer, co-designed with the RF match- ing network, optimizes the sensitivity and minimizes the power consumption of the receiver. A wake-up receiver prototype in 0.13-μm CMOS operates at 550 MHz, consumes 220 nW from 0.5 V, and achieves a sensitivity of -56.4 dBm at a 400-kb/s chip rate using an 11-bit wake-up code. When a large inter- ferer is present, the receiver operates in an interferer-enhanced mode, leveraging the interferer as a local oscillator to improve the sensitivity; in the presence of a -43.5-dBm interferer, a -63.6-dBm sensitivity is achieved while consuming 1.1 μW. Index Terms— Envelope-detectors, low-power wide-area net- work (LPWAN), self-mixer, low-power wireless, wake-up radios, wake-up receivers (WuRXs). I. I NTRODUCTION T HE deployment of the Internet of Everything will lead to tens of billions of sensor nodes connected to the Internet. Deployments in hazardous or inaccessible environments or applications with a very high number of nodes make battery replacement infeasible and drive the need for transceivers that can be self-powered on harvested energy. A survey performed in [1] used credit card-sized solar cells, deployed them in indoor settings, and measured a typical available light energy of 1.1–2.9 J/cm 2 /day; assuming a 1% conversion efficiency and a 10-cm 2 solar cell, the available electrical energy for the self-powered sensor node is 1.1 J/day or an average available power of 13 μW. Such low-power sensor nodes typically rely on wake-up receivers to initiate wireless RF communications. Wake-up receivers are constantly ON and typically dominate the energy needs of the node. In prior research [2]–[4], the power con- sumption of direct down-conversion wake-up receivers was reduced, but they still consume >50 μW. An energy-detection (ED) receiver with active-RF amplification using shifted lim- iters has been proposed in [5] but consumes >100 μW. Manuscript received July 30, 2018; revised October 28, 2018; accepted November 20, 2018. This work was supported in part by Analog Devices, Inc. This paper was approved by Associate Editor Kenichi Okada. (Corresponding author: Vivek Mangal.) The authors are with the Electrical Engineering Department, Columbia University, New York, NY 10027 USA (e-mail: vm2442@columbia.edu; kinget@ee.columbia.edu). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JSSC.2018.2884919 Fig. 1. Typical sub-μW ED receiver architecture (after [8]). Hence, RF amplification or local oscillator (LO) generation is beyond the power budget of self-powered wake-up receivers. Ultrasound has been studied for wake-up applications [6], [7] but does not penetrate through walls and is best suited for applications with short ranges. ED receivers with a passive RF front end are promising for wake-up applications. Most ED receivers consuming <1 μW are implemented using an RF matching network followed by an energy detector and an adaptive thresholding comparator (AT-RX) (Fig. 1) [8], [9]. ED receivers with active rectifiers have been proposed in [10] and [11], but their sensitivity suffers from the added flicker noise of the rectifier. We will review existing ED receivers and their sensitivity, latency, and data rate relative to the requirements for wake-up receivers in Section II. The sensitivity analysis for receivers using an active rectifier has been described in [12]. Co-optimizing the RF matching network with a passive energy detector requires an independent sensitivity analysis which we carry out in Section III. The passive CMOS rectifiers proposed in [11] and [12] for energy harvesting require zero-V TH devices to support a cold startup. By adding biasing, these rectifiers can operate as RF self-mixers [15], without needing zero-V TH devices, while providing an extra degree of freedom to reduce the input capacitance, optimize the receiver sensitivity, and use multi-stage gain to reduce the power consumption. Section IV discusses the proposed self-mixer architecture with its con- version gain and noise analysis and Section V describes the implementation of a 0.13-μm CMOS receiver prototype [Fig. 2(b)] using the optimized multi-stage self-mixer. Since surface acoustic wave (SAW) filters or high- Q match- ing networks provide limited channel selectivity in this appli- cation, we propose an alternate interferer-enhanced receiver operating mode where the interferer, when present, is used as 0018-9200 © 2019 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.