A high sensitivity and high full well capacity CMOS image sensor using active pixel readout feedback operation with positions of pixel select switch, operation timings and initial bias conditions has been reported. 1/3-inch 5.6-μm pixel pitch 800(H) x 600(V) color CMOS image sensors with the switch X set on or under the pixel SF have been fabricated by a 0.18-μm 2-Poly 3-Metal CMOS technology. The comparison of the active pixel readout feedback operation between two CMOS image sensors, which only have the deference of the switch X's position, has performed. As to the result, the switch X set on the pixel SF is favor for the active pixel readout feedback operation to improve the readout gain and the S/N ratio. This CMOS image sensor achieves high readout gain, high conversion gain, low input-referred noise and high full well capacity by the active pixel readout feedback operation.
It is indispensable for high quality image sensors to have performances of high sensitivity, low noise, high full well capacity and good linear response. The CMOS image sensor with the lateral overflow integration capacitor (LOFIC) has been accomplishing these performances because of its wide dynamic range capability in one exposure. Recently, we have improved the SNR of the LOFIC CMOS image sensor and achieved the number of input-referred noise electrons of 2 e- or below without any column amplifier circuits by increasing the photo-electric conversion gain at the floating diffusion (FD) in pixel as keeping low dark current, good uniformity and high well capacity. It is clear that the relation among the conversion gain, the SNR and the full well capacity decides the optimum design for the FD capacitance and the LOFIC to realize a high quality image sensor. In this paper, the optimum design method of the LOFIC CMOS image sensor for high sensitivity, low noise and high full well capacity is discussed through theoretical analysis and experiments by using the fabricated LOFIC CMOS image sensor.