Design And Research On Simulation Model For CMOS Image Sensor

Urgent needs of the CMOS image sensor simulation and test model for the satellite platform in China, contributed to the design and research of this article on it. With the rapid increase in IC technology, CMOS image sensor has been able to solve the shortcomings existed in the past. Thus, it became the current research focus in the field of imaging device, also became the future development direction of the image device for satellite.In order to establish a simulation model of the CMOS image sensor for the satellite platform, this paper mainly studies the structure of the APS sensor without circuit, and simulation of physical processes in properties of photodetector.First, the article describes the significance of the establishment of image sensor simulation model for satellite, introduces the working principle of the CMOS image sensor, and analyzes the photoelectric conversion principle and working process of the photodiode. Then it analyzes the source of CMOS image sensor noise, including thermal noise, shot noise, 1/f noise and FPN. And this paper also describes all major noise measurement methods and possible solutions.Then, this design starts from the physical structure of the photodiode. We utilize the minority carrier equilibrium continuity equations to establish a one-dimensional mathematical and physical model of photodiode. Based on this mathematical model, three photodiode structures of n+/p-sub type, n-well/p-sub type and p+/n-well/p-sub type are simulated by using MATLAB. The simulation results are analyzed and compared with practical data. The results show the correctness of the established model. We confirm the model can basically reflect the actual physical situation. The model is also used to extract the related data for analyzing. This illustrates the model can be used for the photodiode design and analysis.Finally, we perform a theoretical analysis of the MTF for three common structural active area shapes and derive explicit formulas for two-dimensional transfer function, and generalize for any connected active area shape. Proved that for any possible connected active area shape, MTF with such a structure can be calculated. By using the calculated formula, the two dimensional MTF simulation results of three actual pixel arrays show that the active area shape contributes significantly to the behavior of the overall MTF. Also, PSF results which are calculated by MTF model, basically validate the model response to the real situation of the actual device.This paper establish a one-dimensional photodiode carrier motion model, which is perpendicular to the surface of illumination, and MTF model which is parallel to the surface. So that the carriers in photodiode can be simulated substantially in the direction of movement throughout all three-dimensional. Finally we get a practical simulation model.