A 2.5-nW Radio Platform With an Internal Wake-Up Receiver for Smart Contact Lens Using a Single Loop Antenna

The human eye has been considered to be a promising platform for real-time diagnosis of various biomarkers in tears. The smart contact lens (SCL), as a device which directly accesses surface of human eye, is a miniaturized autonomous system integrating all the required functions on the surface of a thin film. This article presents the first implementation of a set of radio including a wake-up receiver required for SCL. The system performs RF transmission upon wake-up call using a single loop antenna. The receiver path has a baseline-tracking offset control loop to successfully detect wakeup signal in the standby state under noisy environment. The operating frequencies for uplink and downlink are 346 and 433 MHz, respectively. A magnetic-coupled wireless charging of an OFF-chip battery is also provided through the same loop antenna. The designed IC is fabricated using 0.18- $\mu \text{m}$ CMOS process, consuming a power of 2.5 nW in wakeup-ready standby state. The IC is also verified with a loop antenna and a thin-film battery integrated on a substrate of SCL.