Analysis of Gated CMOS Image Sensor for Spatial Filtering

Pulsed gated vision systems are essential tools in obtaining images in obscure environmental conditions. Contrary to the existing gated systems, which use intensifiers and other external equipment, we present a design of gated sensor, which is implemented in a CMOS process. The proposed sensor is capable to filter out the objects according to their distance to the camera. This ability enables to remove the undesired reflections and to see more clearly the target. Such gated vision principle is implemented using a unique multishuttering regime. Various properties of this regime such as charge-transfer mechanisms, frequency of switching, pulsewidth, slew rate, etc., are described and thoroughly analyzed. Upon the performed analysis, we optimize the shape of the shutter pulses and substantially reduce the charge-transfer time. A 128 × 256 CMOS gated image sensor was fabricated in 0.18-μm process and successfully tested. The included experimental results fully corroborate with the theory, showing the sensor functionality and proving the feasibility of the proposed design.