A 5.5 nW battery-powered wireless ion sensing system

This paper presents a battery-connected wireless ion sensing system comprising a Na+-selective electrode, a 406 pW Potentiometrie front end, a 780 pW reference-free asynchronous SAR ADC, a 2.4 GHz power oscillator-based transmitter that consumes 2.4 nW when transmitting 100 bps, a 485 pW quiescent power 1.8-to-0.6 V switched-capacitor DC-DC converter with 96.8% peak efficiency, and two temperature-stabilized relaxation oscillators that serve as clocks for the DC-DC converter, ADC, and power gating switches, consuming 140 pW each. The system was tested in-vitro, where measurement results exhibit a linear, near-Nertian response to varying Na+ concentration with a slope of 71 mV/Log10[Na+]. With all blocks operating, the entire system consumes only 5.5 nW.