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.

A 3.5 mV Input Single-Inductor Self-Starting Boost Converter with Loss-Aware MPPT for Efficient Autonomous Body-Heat Energy Harvesting.

A single-inductor self-starting boost converter is presented suitable for thermoelectric energy harvesting from human body heat. In order to extract maximum energy from a thermoelectric generator (TEG) at small temperature gradients, a loss-aware maximum power point tracking (MPPT) scheme was developed that enables the harvester to achieve high end-to-end efficiency at low input voltages. The boost converter is implemented in a 0.18 µm CMOS technology and is more than 75% efficient for a matched input voltage range of 15 mV-100 mV, with a peak efficiency of 82%. Enhanced power extraction enables the converter to sustain operation at an input voltage as low as 3.5 mV. In addition, the boost converter self-starts with a minimum TEG voltage of 50 mV leveraging a dual-path architecture without using additional off-chip components.

A Batteryless Motion-Adaptive Heartbeat Detection System-on-Chip Powered by Human Body Heat.

This paper presents a batteryless heartbeat detection system-on-chip (SoC) powered by human body heat. An adaptive threshold generation architecture using pulse-width locked loop (PWLL) is developed to detect heartbeats from electrocardiogram (ECG) in the presence of motion artifacts. The sensing system is autonomously powered by harvesting thermal energy from human body heat using a thermoelectric generator (TEG) coupled to a low-voltage, self-starting boost converter and integrated power management system. The SoC was implemented in a 0.18 µm CMOS process and is fully functional with a minimum input power of 20 µW, provided by a portable TEG at 20 mV with a ~0.5 °C temperature gradient. The complete system demonstrates motion-adaptive, power-autonomous heartbeat detection for sustainable healthcare using wearable devices.

Integrated Cold-Start of a Boost Converter at 57mV using Cross-Coupled Complementary Charge Pumps and Ultra-Low-Voltage Ring Oscillator.

This paper demonstrates an on-chip electrical cold-start technique to achieve low-voltage and fast start up of a boost converter for autonomous thermal energy harvesting from human body heat. An improved charge transfer through high gate-boosted switches by means of cross-coupled complementary charge pumps enables voltage multiplication of the low input voltage during cold start. The start-up voltage multiplier operates with an on-chip clock generated by an ultra-low-voltage ring oscillator. The proposed cold-start scheme implemented in a general purpose 0.18µm CMOS process assists an inductive boost converter to start operation with a minimum input voltage of 57mV in 135 ms while consuming only 90 nJ of energy from the harvesting source, without using additional sources of energy or additional off-chip components.