Wireless, Multi-Sensor System-on-Chip for pH and Amperometry Powered by Body Heat.

This article presents a body-heat-powered, multi-sensor SoC for measurement of chemical and biological sensors. Our approach combines analog front-end sensor interfaces for voltage- (V-to-I) and current-mode (potentiostat) sensors with a relaxation oscillator (RxO) readout scheme targeting << 10 µW power consumption. The design was implemented as a complete sensor readout system-on-chip, including a low-voltage energy harvester compatible with thermoelectric generation and a near-field wireless transmitter. A prototype IC was fabricated in a 0.18 µm CMOS process as a proof-of-concept. As measured, full-range pH measurement consumes 2.2 µW at maximum, where the RxO consumes 0.7 µW and measured linearity of the readout circuit demonstrates R 2 0.999. Glucose measurement is also demonstrated using an on-chip potentiostat circuit as the input of the RxO, with a readout power consumption as low as 1.4 µ W. As a final proof-of-principle, both pH and glucose measurement are demonstrated while powering from body heat using a centimeter-scale thermoelectric generator on the skin surface, and pH measurement is further demonstrated with an on-chip transmitter for wireless data transmission. Long-term, the presented approach may enable a variety of biological, electrochemical, and physical sensor readout schemes with microwatt operation for batteryless and power autonomous sensor systems.

A Reconfigurable Tri-Mode Frequency-Locked Loop Readout Circuit for Biosensor Interfaces.

In this article, a frequency-locked loop (FLL) based multimodal readout integrated circuit (IC) for interfacing with off-chip temperature, electrochemical, and pH sensors is presented. By reconfiguring its switched-capacitor feedback network, the readout circuit is able to measure resistance, current, and voltage without additional active analog front-end circuits. A prototype IC was fabricated in a 0.18 µm CMOS process. Measured results show that when measuring resistance, the input-referred resistance resolution is 10.5 Ω for 100 Hz integration bandwidth. Using an off-chip thermistor, the readout circuit covers a temperature range of 0-75 °C and achieves an equivalent temperature resolution of 16.4 mKrms. In current mode, the readout circuit has an input range of 0.5µA and an input-referred current noise as low as 40.6 pArms for 100 Hz bandwidth. Interfacing with an on-chip potentiostat, glucose chronoamperometry is demonstrated. In voltage mode, a minimum input-referred voltage noise of 31.7 µVrms is achieved, and the IC can measure a pH range from 1.6 to 12 using a commercial pH probe. At a 1.2 V supply, power consumption of the readout circuit is below 10 µW for all three measurement modes. Additionally, the prototype IC includes an integrated wireless transmitter that implements on-off keying modulation, and a wireless multimodal sensing system utilizing the FLL-based readout circuit is demonstrated.