A Fully LTPS-TFT-Based Bidirectional Biomedical Interface Circuit for Large-Area Healthcare Applications

This article proposed a fully low-temperature polysilicon thin-film transistor (LTPS-TFT)-based bidirectional biomedical pixel interface integrated with a high linearity stimulator and a high-performance biopotential sensing front-end circuit to amplify and digitize biological signals for high robustness data transmission. All circuits are designed and manufactured under a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {3-}\mu \text {m}$ </tex-math></inline-formula> LTPS process. We demonstrated the experiment in saline using the stimulator circuit to simulate stimulation inside the organism, achieving stimulation with different average currents under different duty cycles. The proposed front-end circuit has a gain of 40 dB. The referred input voltage noise of the entire signal chain is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$86.2~\mu \text {V}/\sqrt {\text {Hz}}$ </tex-math></inline-formula>, and the effective number of bits (ENOB) is 9.13 bits at an input of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.5~\text {mV}_{\text {PP}}$ </tex-math></inline-formula>. Simultaneously conducting statistical testing on 20 chips has achieved a 1.05 dB SNDR standard deviation. Finally, we use a function signal generator to simulate the input signals of electrocorticography (ECoG), electrocardiogram (ECG), and electrooculogram (EOG), then use front-end circuits to read and reconstruct them to demonstrate that the proposed pixel interface can correctly read common biomedical signals for healthcare applications.