32.1 A Behind-The-Ear Patch-Type Mental Healthcare Integrated Interface with 275-Fold Input Impedance Boosting and Adaptive Multimodal Compensation Capabilities
Hyunjoong Kim, Myeongwoo Kim, Kwangmuk Lee, Sanghyeon Cho, Chan Park, Solwoong Song, Dae Sik Keum, Dong Pyo Jang, Jae Joon Kim
Abstract
Conventional brain activity monitoring devices including head bands and scalp caps are still not appropriate for daily-life monitoring applications because of their wearing discomfort and electrode-related artifacts. A proposed behind-the-ear (BTE) device, where motion artifacts are significantly reduced, would be a promising candidate for continuous mental healthcare platforms. This proposed BTE-based measurement allows multimodal bio-signals such as electroencephalogram (EEG), electrocardiogram (ECG), photoplethysmogram (PPG), and galvanic skin response (GSR), whereas most conventional brain devices only monitor EEG. However, these bio-signals become much weaker at the BTE location, and their signal quality is more important, being seriously degraded by artifact-related corruptions during daily activities. For this purpose, an offset-compensated auxiliary path (OCAP) and a dual-resolution external positive feedback loop (DR-EPFL) are proposed to boost the input impedance and to improve its AC characteristics further. For small-featured device sizes, the number of electrodes is reduced by utilizing a proposed GSR-embedded ECG readout structure where electrodes are shared and monitored together. For system-level feasibility, a direct-conversion PPG readout with a proposed parasitic capacitance compensation, a transcutaneous vagus-nerve stimulator <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\text{tVNS})$</tex> with an electrode-monitored adaptive charge pump, and a high-resolution bio-impedance channel are integrated together. A BTE-based mental healthcare patch-type device prototype is also manufactured and its multimodal functionality is experimentally verified.