16.8 nW Ultra-Low-Power Energy Harvester IC for Tiny Ingestible Sensors Sustained by Bio-Galvanic Energy Source

Herein, we present a 16.8 nW ultra-low-power (ULP) energy harvester integrated circuit (IC) for ingestible biomedical sensors. The energy harvester can be powered from the electro-galvanic operation inside a human body, which provides a sustainable and long-term energy source. The challenge of dealing with relatively high input impedance (similar to k omega) of the bio-galvanic energy source is addressed by introducing two design techniques. The first technique is an adaptive V-MPP-controlled algorithm (AVCA) for a maximum power point tracking (MPPT) controller, and the second technique is a ULP delay-line-based zero current switching (ZCS) controller. Different from the conventional fractional open-circuit voltage (FOCV) method for MPPT, the proposed AVCA allows continuous source tracking without detachment of the harvester from the source. The ZCS operation is achieved using a delay-line controller without using either a comparator or an opamp. The proposed AVCA is realized using a 12.1 nW MPPT controller. Successful ZCS operation is achieved using a 2.1 nW delay controller. Overall power consumption of the IC is 16.8 nW. The converter has been fabricated in a 0.18 mu m CMOS process with 2 mu m thick top-metal option. The measured result shows that the converter achieves a peak efficiency of 72.1% to generate 507 nW output power. The ULP operation allows a significant reduction in electrode size down to the submillimeter scale (similar to 0.4 mm(2)), demonstrating the good potential of the proposed energy harvester IC.

Automated summary

This article introduces an ultra-low-power energy harvester integrated circuit for ingestible biomedical sensors, addressing the challenge of high input impedance of bio-galvanic energy source. By using techniques such as adaptive MPPT controller and zero current switching controller, the IC achieves successful operation with a total power consumption of 16.8 nW and peak efficiency of 72.1%. The proposed IC demonstrates a good potential with significant reduction in electrode size.