Dynamic range extension of a CMOS active pixel sensor by in-pixel charge mixing

Various approaches have been utilized to extend the dynamic range of the CMOS image sensor, which are based on a linear-logarithmic CIS, overflow integration capacitor and multiple sampling or individual pixel resetting. These approaches, however, suffer from noise, nonlinearity, lower sensitivity, reduced operating speed and lower resolution. In order to overcome these problems, we have previously proposed a dynamic range extension method by combining output signals from two photodiodes with different sensitivities, such as a high-sensitivity photodiode and a low-sensitivity photodiode. The proposed active pixel sensor has been fabricated by using 2-poly 4-metal standard CMOS process and its characteristics have been measured. It is found that charges in the high- and low-sensitivity photodiodes could be mixed each other and the lost image information of the high-sensitivity photodiode could be regenerated using the charges in the low-sensitivity photodiode, as shown by simulation results. Dynamic range extension of the proposed active pixel sensor has been experimentally verified.