CMOS image sensor for the analysis of fast-moving luminous objects

We present an image sensor dedicated to the analysis of fast moving luminous objects. The circuit is fabricated in standard 0.6 μm CMOS technology with an image sensing array of 64 x 64 pixels. Its working principle is as follows: An electronic unit integrated at the pixel level measures the elapsed time since the beginning of the acquisition till the passage of the luminous object in front of the pixel under consideration. This value that corresponds to a number of clock cycles is stored in a 4-bit memory at the pixel level and translated into a gray level, the brighter ones corresponding to the shortest time. The result is a 16-gray level image that represents the trajectory and direction of motion of the object. Knowing the frequency of the clock, the distance between the pixels and the difference in gray levels of the pixels, the speed of the moving object can be determined. Alternatively, the 16-gray level image can be considered as a superposition of 16 one gray level images that represent the 16 positions of the moving object at 16 different time instances in the course of its displacement. The frequency of the clock can be as high as 20 MHz for the analysis of very high speed phenomena. The working principle and the architecture of the image sensor will be described in details in this paper. Moreover, the results of the tests carried out on the circuit, namely the analysis of the movement of the spot on an oscilloscope screen, will also be reported and the potential applications of the image sensor discussed.