A Low-Voltage Complementary Metal Oxide Semiconductor Image Sensor Using Pulse-Width-Modulation Scheme for Biomedical Applications

In this paper, we present a detailed characterization and evaluation of the performance of a source-modulated pulse-width-modulation (PWM) scheme image sensor designed for biomedical applications. The image sensor is based on the PWM readout scheme that we proposed in a previous study. The PWM sensor is equipped with a novel three-transistor PWM pixel to realize low-voltage and high-resolution on-chip bioimaging. We explain the sensor operation and capability of the low-voltage PWM scheme by comparing it with a conventional active pixel sensor (APS). We successfully demonstrate the function of the image sensor with a 1.35 V single power supply voltage. We discuss the characteristics in terms of the effect of the IR drop, tradeoffs, and our evaluation of the capability of the PWM sensor of pixel size for biomedical applications.