A Battery-Less 0.37 V 126 nW 0.29 mm2 65-nm CMOS Biofuel-Cell-Modulated Biosensing System Featuring an FSK-PIM-Combined 2.4 GHz Transmitter for Continuous Glucose Monitoring Contact Lenses

The battery-less sensor nodes provide a solution to power and environment issues, but they face some challenges while being applied to biosensing systems, such as varying power and communication distance. This work presents a battery-less biosensing system for solar-cell-powered continuous glucose monitoring contact lenses featuring a 2.4 GHz transmitter. The modulation method combines frequency shift keying and pulse interval modulation to send radio frequency signals with two-dimensional information including the solar cell's voltage, which aims to overcome the impact of unstable solar power. The charge-pump-based energy harvester converts the solar-cell voltage above 1.8 V to achieve a transmission distance longer than 40 cm, which allows communications between contact lenses and handsets. The fabricated chip in a 65 nm CMOS process consumes 126 nW at 0.37-V supply, which is manageable by on-lens solar cells in an indoor ambient-light environment.