UC San Diego

Internet of Things (IoT) have significantly heightened the level of our awareness about the world and extended the dimension of our interaction with it. While creating unprecedented growth opportunities for semiconductor industry in areas such as biomedical and wearable devices and health and environmental monitoring, IoT has revolutionized the design of integrated circuits and systems for such applications wireless and small for unobtrusive and massive deployment, ultra-low-power for long-term operation, and full integration of all functionalities.

By virtue of low-frequency signals in most of such applications, integrated circuits and systems for IoT nodes are usually heavily duty-cycles and as a result the overall power is usually dominated by the standby circuitry timers and bias blocks. A reference-free timer structure is proposed by using capacitive-discharging topology to avoid the necessity of the conventional power-hungry reference generators. Thereby, it is imperative to minimize the power consumption of the bias circuits. A voltage and current reference generator is implemented leveraging gate-leakage transistors to achieve temperature-stabilized voltage and current references with pW power consumption and being able to generate pA low current reference, which is then employed to implement a timer achieving improved temperature- and supply-stability.

Temperature is an important parameter to measure in a variety of IoT applications. A new temperature sensing technique that relies on complementary temperature dependencies of different types of MOSFETs biased in the subthreshold region, together with constant-with-temperature tunneling currents and a capacitive charging-time-to-digital feedback architecture that digitizes temperature is proposed that consumes 113 pW in a fully monolithically-integrated manner. Another important parameter ion concentration, for example ion homeostasis in sweat, blood, or saliva can potentially provide valuable additional insight into a user’s overall health status. An ion sensing platform that integrates ion-selective electrodes with ultra-low-power sensor instrumentation, a wireless transmitter, and power management circuits is proposed to implement complete sensing-to-transmission functionality, achieving a linear near-Nernstian response with a slope of 71 mV/log10[Na+] through in-vitro testing across a NaCl solution concentration range of 0.1-100 mM.