Design and Simulation of a 3-Transistor Active Pixel Sensor Using MATLAB Simulink

Abstract

This paper proposes a Simulink model to simulate the pixel circuit with variable light intensities to investigate the impact of the light intensity on the CMOS image sensor pixels. This article also explores the CMOS image sensor pixel categories and presents the design and the simulation of the 3- Transistor (3T) Active Pixel Sensor (APS) in the MATLAB/Simulink tool. The analysis investigates the conversion of the light into an electrical signal for a single-pixel sensing circuit which consists of a photodiode and three NMOS transistors. The paper also proposes three modes for pixel operation; reset, integration, and readout modes. The simulations of the electrical signals for each of the studied modes of operation show how the output electrical signals are correlated to the input light intensities. The charging/discharging speed for the photodiodes is also investigated. The output voltage for different light intensities, including the dark case, is simulated, and it is shown its inverse proportionality with the light intensity. As a result, the Cpd discharges faster if the amount of light is increased. The more the light intensity, the lower value for the output voltage.

Keywords: APS, CMOS image sensor, Light intensities photodiode, Simulation