Millimeter-Scale Node-to-Node Radio Using a Carrier Frequency-Interlocking IF Receiver for a Fully Integrated 4 $\times$ 4 $\times$ 4 mm3 Wireless Sensor Node

Ultralow-power (ULP) mm-scale Internet-of-Things (IoT) platforms enable newly emerging applications such as pervasive agricultural monitoring and biosensing. Although there is an increasing interest in node-to-node communication as defined in Bluetooth v5.0, prior research in mm-scale wireless systems is mostly limited to asymmetric node-to-gateway communications. We present a 2.4-GHz node-to-node communication system for an ultra-small wireless sensor node fully integrated within a 4 × 4 × 4 mm
³
form factor. The system integrates multiple stacked layers including an RF transceiver, a ULP processor, a photovoltaic (PV) cell, a 32-kHz crystal, and a 3-D magnetic dipole antenna. The transceiver front-end circuit is co-designed with a printed 3-D magnetic dipole antenna to form a power oscillator for the transmitter (TX) as well as a Q-enhanced amplifier (QEA) for the receiver (RX). A new carrier frequency-interlocking IF architecture successfully mitigates the TX-RX carrier frequency synchronization challenge that is critical to the mm-scale radio systems. The complete system achieves -94-dBm sensitivity with 97-μW power consumption and -12.6-dBm equivalent isotropically radiated power (EIRP). Standalone operation of a sensor node is demonstrated through bi-directional wireless communication to another sensor node over 1-m distance in real, uncontrolled wireless channels.