A Wireless Battery-Free Cerebral-Oxygen-Monitoring Micro-System Featuring 0.21-mmHg Sensing Resolution

Cerebral oxygen reflects the oxidative metabolism in neurons, which can be monitored by detecting the partial pressure of oxygen (PO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>) in brain, to evaluate various brain diseases such as traumatic brain injury (TBI) as well as study the brain activities in response to transient oxygenation changes. To continuously detect the cerebral oxygen of freely moving subjects, cerebral oxygen monitoring (COM) devices are required to be wireless, high resolution, and long lifetime. In conventional wireless PO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> sensors, the optical devices present a short lifetime due to the power-hungry LED driver, whereas the existing electrochemical sensors suffer from both a bulky battery and a low resolution. In this work, we propose two techniques to address the issues in conventional PO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> sensors: 1) a sensing-current-reuse technique is proposed to cut down the power of current-detection circuit, which eliminates the power-hungry trans-impedance amplifier (TIA) and current-mirror amplifier in conventional potentiostats and 2) a bipolar residual zoom-in (BRZ) technique is proposed to improve the current-sensing resolution with low power dissipation. The proposed wireless COM chip is fabricated in a 55-nm CMOS process, which is integrated with a self-designed electrochemical PO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> sensor. The measured results show that an in vitro sensing resolution of 0.21 mmHg in oxygen value is achieved by the proposed BRZ technique. In addition, the 25-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $</tex-math> </inline-formula>W low power enables 2-m range battery-free telemetry based on wireless power transfer (WPT) and backscatter communication.