A TFT-Based Flexible PPG Acquisition Circuit in a 3-μm LTPS Process for Packaging-Free Smart Ring Applications

Photoplethysmography (PPG) is a commonly used non-invasive biological signal detection technique that can analyze the heart rate and blood oxygen saturation, which plays an important role in daily health monitoring. In Fig. 1 (top), integrating biological acquisition into smart rings is an emerging trend in the consumer electronics [1]. However, integrating all building blocks into a space-limited device encounters challenges. It also bring discomfort to the users. A feasible integrate solution is soldering Si chips onto a flexible substrate which requires costly packaging [2]. The semi flexible system constrains its bendability, still requiring an extensive dynamic range (DR) to mitigate motion artifacts [3].