Scanning Modulation Transfer Function Model of TDI CMOS Image Sensor

An analytical model of Modulation Transfer Function (MTF) for Time-Delay-Integration CMOS Image Sensor (TDI-CIS) in the scanning direction is proposed. Impacts of pixel valid sensitive ratio, scanning efficiency, velocity mismatch ratio and TDI stage on MTF are studied based on the analysis of TDI-CMOS temporal oversampling rolling-shutter readout timing principle. By establishing a TDI-CIS imaging-simulation system according to geometric perspective and light transmission relationship from continuous known objects to a discrete image on the pixel plane, simulations of TDI-CIS imaging process under different circumstances are carried out. Then knife-edge method is used to calculate MTF of the TDI image. The simulation results show that MTF is inversely proportional to valid sensitive ratio and scanning efficiency. MTF keeps steady when velocity mismatch ratio is 0, and it decreases with the increase of TDI stage when velocity mismatch ratios are non-zero values. At the same time, the tendency that the MTF decreases with the increase of velocity mismatch ratio is getting more obvious when TDI stage increases. MTF at a specific frequency can even drop to almost 0 when the velocity mismatch ratio increases to 30 % and the number of TDI stages is 16.