Linear image sensor with shutter gates for draining excess charge

Abstract

In a linear sensor, a charge transfer part is disposed between a one-dimensional array of photodetectors and an overflow drain and includes a CCD having four or more transfer gates for each photodetector for transferring signal charges from the photodetector array in a direction of the photodetector array, transfer gates controlling charge transfer from the photodetectors to the CCD, and shutter gates for controlling charge transfer from the charge transfer part to the overflow drain. Each transfer gate is disposed between each photodetector and a prescribed one of the four or more transfer gates, and each shutter gate is disposed between the prescribed transfer gate and the overflow drain. The four or more CCD transfer gates are controlled by four or more phase driving clocks. Therefore, during charge transfer, at least three adjacent CCD transfer gates are all closed so that signal charges are drained from the photodetector into the overflow drain through the transfer gate in the middle of the three transfer gates without mixing the drained signal charges with the signal charges transferred. The charge drain operation is carried out during the charge transfer operation in the charge transfer part whereby the timing of opening the shutter gate can be set at an arbitrary time in the charge read cycle.