Image reading device for reversing polarity of stored charge in capacitor

#The present invention relates to image reading devices for reading images such as a document and photograph, and particularly to image reading devices using a photosensitive thin-film transistor (TFT) for a photo-detecting element.

#Conventionally, there has been developed a two-dimensional image sensor (image reading device) of an active-matrix type in which a photo-detecting element (photo diode, photo transistor) and a switching element (thin-film transistor) are disposed on a two-dimensional plane, as disclosed in Japanese Utility Model Application No. 8055/1990 (Jitsukaihei 2-8055; published on Jan. 18, 1990).

#Such a two-dimensional image sensor has an active-matrix array (active-matrix substrate), as shown in FIG. 9, including source lines s1, s2, . . . , sm, and gate lines g1, g2, . . . , gn intersecting with each other, and pixels that are arrayed in an X-Y matrix at the intersections of these lines. Each pixel has a photo-detecting TFT (photo-detecting thin-film transistor), a switching TFT (switching thin-film transistor), and a capacitor.

#For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.

#FIG. 1 is a timing chart representing Cs reverse driving in one pixel when reading a document image in an image reading device according to one embodiment of the present invention.

#FIG. 2 is a circuit diagram schematically showing a structure of the image reading device of the present invention.

#Referring to FIG. 1 through FIG. 7, the following describes an image reading device and an image reading method according to one embodiment of the present invention.

#As illustrated in FIG. 2, an image reading device 20 of the present embodiment includes TFT elements 21 that serve as a photo-detecting TFT and a switching TFT.

#The image reading device 20 includes: gate lines g1 through gn (simply “g” hereinafter) and source lines s1 through sn (simply “s” hereinafter) intersecting with each other; capacitor lines Cs provided parallel to the gate lines g; a TFT element (thin-film transistor) 21 and a pixel capacitor (capacitor) 22 provided at each intersection of the gate lines g and the source lines s; a driving circuit 23 connected to the gate lines 23; and a reading circuit 24 connected to the source lines s.