Solid state image sensor device and its driving method

Abstract: A solid state image sensor comprising a matrix of photosensitive elements adapted to accumulate signal charges corresponding to at least two different aspect ratios, a plurality of vertical shift registers disposed adjacent to columns of the photosensitive elements for a vertical transfer of the signal charges and a plurality of horizontal shift registers corresponding to the respective aspect ratios and disposed in parallel with each other for a horizontal transfer of the signal charges from the vertical shift registers. As a horizontal shift register exclusive to each aspect ratio is provided in the above manner, it is no longer necessary to superimpose the signal outputs of a plurality of buffer amplifiers so that a picture signal corresponding to the desired aspect ratio can be easily read out.

Description: The present invention relates to a solid state image sensor compatible with a plurality of aspect ratios (dissimilar vertical-to-horizontal dimensional ratios of the television picture frame) and to a method of driving the image sensor. A television system with an aspect ratio of 16:9, i.e. a picture frame with a relatively greater horizontal dimension than the existing frame with an aspect ratio of 4:3, is now being implemented commercially and some solid image sensors compatible with both systems have been developed. An exemplary solid state image sensor compatible with the two systems is illustrated in Fig. 1. This solid state image sensor comprises an imaging region 1 consisting of a matrix of photosensitive elements (not shown) and a plurality of vertical shift registers (not shown) disposed adjacent to columns of said photosensitive elements and corresponding to an aspect ratio of 16:9, three horizontal shift registers 5, 6, 7 and three buffer amplifiers 8, 9 and 10 connected to said horizontal shift registers 5, 6 and 7, respectively. The imaging region 1 is divided into three segments, viz. a first segment 2 corresponding to an aspect ratio of 4:3, a second segment 3 and a third segment 4 which are not required for said aspect ratio of 4:3 but are required for said aspect ratio of 16:9, and the three horizontal shift registers 5, 6 and 7 are disposed in correspondence with said segments 2, 3 and 4, respectively. Indicated by A1, A2, A3 and A4 are terminals for supplying driving pulses to transfer gate electrodes of the vertical shift registers. The arrowmarks indicate the direction of flow of signal charges. The method of driving the above solid state image sensor is now described. For both aspect ratios of 4:3 and 16:9, signal charges are read out from the imaging region 1 to the vertical shift registers in the first place. Then, vertical transfer signals are applied to the vertical shift registers from terminals Al - A4 to transfer the signal charges accumulated in the groups of photosensitive elements in said first segment 2, second segment 3 and third segment 4 to said first horizontal shift register 5, second horizontal shift register 6 and third horizontal shift register 7, respectively. Then, horizontal transfer pulses are applied to the respective horizontal shift registers to transfer the signal charges therein to the corresponding buffer amplifiers 8, 9 and 10 to thereby output picture signals. In the described arrangement, a picture signal corresponding to the aspect ratio of 4:3 is available from the buffer amplifier 8 and a picture signal for the aspect ratio of 16:9 is obtained by superimposing the signal outputs of the buffer amplifiers 8, 9 and 10 in an external circuit. However, this prior art solid state image sensor is complicated in construction because each of the horizontal transfer and buffer amplifier stages has been divided into three segments. Moreover, in order to obtain a picture signal corresponding to an aspect ratio of 16:9, signal outputs of the three buffer amplifiers must be superimposed and this requirement adds complexity to the signal processing and driving circuitry. The document EP - A - 0 547 697 discloses another prior art: an image sensor device comprising a matrix of photosensitive elements adapted to accumulate signal charges corresponding to two different aspect ratios. All the charges are vertically transferred to a unique horizontal register, in which in the case of the smaller aspect ratio the useless data before and after the active line are discarded by draining them from the horizontal register during the time interval which lies between two consecutive active line times. The object of the present invention is to provide a solid state image sensor device compatible with at least two different aspect ratios, from which a picture signal corresponding to each of the aspect ratios can be easily read out, and a method of driving the image sensor device. The solid state image sensor device of the invention comprises, in one embodiment thereof, a matrix of photosensitive elements adapted to accumulate signal charges corresponding to at least two different aspect ratios, a plurality of vertical shift registers disposed adjacent to columns of said photosensitive elements and adapted to transfer said signal charges in a vertical direction and a plurality of horizontal shift registers corresponding to each of said aspect ratios and disposed in parallel with each other. By providing horizontal shift registers each exclusive to each of different aspect ratios in this manner, it is no longer necessary to superimpose the signal outputs of a plurality of buffer amplifiers, with the result that a picture signal for the desired aspect ratio can be easily obtained. The method of the invention for driving a solid state image sensor device, in one embodiment thereof, comprises a step of reading signal charges from a matrix of photosensitive elements adapted to accumulate signal charges corresponding to at least two different aspect ratios and transferring said signal charges to vertical shift registers, a step of selecting one horizontal shift register from among the horizontal shift registers corresponding to said respective aspect ratios and transferring the signal charges from said vertical shift registers to the selected horizontal shift register and a step of transferring signal charges from said horizontal shift register to a buffer amplifier. In this driving method, it is no longer necessary to superimpose the signal outputs of a plurality of buffer amplifiers for reading out a picture signal corresponding to the desired aspect ratio, with the result that the picture signal corresponding to the desired aspect ratio can be easily obtained. Fig. 1 shows the construction, in plan view, of the conventional solid state image sensor; Fig. 2 shows the construction, in plan view, of a solid state image sensor according to Embodiment 1; Fig. 3 is a partial view, on exaggerated scale, of the above construction; Referring to Fig. 2, which is a schematic diagram showing the solid state image sensor according to Embodiment 1 which is compatible with the two television systems having aspect ratios of 16:9 and 4:3, this solid image sensor comprises an imaging region 21, a couple of horizontal shift registers 25, 26 for a horizontal transfer of signal charges vertically read out from said imaging region 21, and a couple of buffer amplifiers 27, 28 connected to said respective horizontal shift registers 25, 26. The imaging region 21, as shown in Fig. 3, comprises a matrix of photosensitive elements 29 for accumulating signal charges and vertical shift registers 30 disposed adjacent to columns of said photosensitive elements 29. The photosensitive elements 29 constitute a matrix consisting of 948 column and 486 rows. The vertical shift registers 30 are disposed in 948 columns, each of which comprises transfer gate electrodes in 972 stages. The signal charges accumulated in the entire imaging region 21 are utilized for reading the picture signal corresponding to the aspect ratio of 16:9 and the signal charges accumulated in a first segment 22 situated centrally in the imaging region 21 are utilized for reading the picture signal corresponding to the aspect ratio of 4:3. The first segment 22 corresponds to 710 columns of said photosensitive elements 29 and vertical shift registers 30. The second segment 23 and third segment 24 at both ends are the region which is not required for the aspect ratio of 4:3. Indicated by B1, B2, B3 and B4 are terminals for supplying vertical transfer pulses to the transfer gate electrodes of said vertical shift registers 30. The horizontal shift register 25, adapted to transfer signal charges from the entire imaging region 21, is used for the aspect ratio of 16:9. The horizontal shift register 26 for transferring the signal charges from the first segment 22 is used for the aspect ratio of 4:3. Buffer amplifiers 27, 28 convert signal charges from the horizontal shift registers 25 and 26, respectively, to picture signals. The arrowmarks indicate the direction of flow of signal charges. In order to read a picture signal corresponding to the aspect ratio of 16:9, the signal charges accumulated in photosensitive elements 29 are read out to the vertical shift registers 30 and, then, vertical transfer pulses are applied to terminals B1 - B4 to transfer the signal charges in a vertical direction. These signal charges are then transferred sequentially, row by row, to the horizontal shift register 25, and in response to a horizontal transfer pulse, are further transferred to the buffer amplifier 27 which, accordingly, outputs the picture signal corresponding to the aspect ratio of 16:9. In this arrangement, the horizontal shift registers 25 and 26 must be electrically independent of each other. A picture signal corresponding to the aspect ratio of 4:3 can be obtained as follows. Thus, among the signal charges read out from the imaging region 21, only the charges from the first segment 22 are transferred to the horizontal shift register 26. These signal charges are then transferred by a horizontal transfer pulse to the buffer amplifier 28 which, accordingly, outputs the picture signal corresponding to the aspect ratio of 16:9. In this mode, signal charges from the second segment 23 and third segment 24 remain in the horizontal shift register 25 but these unnecessary charges can be swept while the transfer of signal charges by the horizontal shift register 26 is in progress. By providing exclusive horizontal shift registers 25 and 26 for different aspect ratios in the described manner, a picture signal corresponding to the desired aspect ratio can be easily obtained without resort to a complicated external circuit for superimposition of the signal outputs of plural buffer amplifiers. The above description is directed to a solid state image sensor device comprising an imaging region and horizontal shift registers as main components but the concept of providing a horizontal shift register for each aspect ratio is applicable to a solid state image sensor of the progressive scan type including a storage region interposed between an imaging region and a horizontal shift register stage for temporary storage of signal charges from the imaging region. Moreover, although the above description pertains to the image sensor including a horizontal shift register 25 for the aspect ratio of 16:9 and a horizontal shift register 26 for the aspect ratio of 4:3, there can be provided a solid state image sensor compatible with other aspect ratios by modifying the horizontal shift register 26. In addition, although an image sensor having two horizontal shift registers has been described above, three or more horizontal shift registers can be installed within limits allowable from the consideration of transfer efficiency. In addition to the specific Embodiments described hereinabove, one skilled in the art may contrive a variety of modifications of the invention without departing from the scope of the invention. For example, although the solid state image sensors described in the foregoing description are compatible with the two aspect ratios of 16:9 and 4:3, solid state image sensors compatible with three or more different aspect ratios are also subsumed in the claimed category of solid state image sensor compatible with a plurality of aspect ratios. Furthermore, the buffer amplifier need not necessarily be disposed within the solid state image sensor but may be disposed externally of the image sensor.

Claims: A solid state image sensor comprising a matrix of photosensitive elements (29) adapted to accumulate signal charges corresponding to at least two different aspect ratios, a plurality of vertical shift registers (30) disposed adjacent to columns of said photosensitive elements (29) for a vertical transfer of said signal charges, and characterized in that it further comprises: a plurality of horizontal shift registers (25, 26) corresponding to said respective aspect ratios and disposed in parallel with each other for a horizontal transfer of signal charges from said vertical shift registers (30). The solid state image sensor of claim 1 wherein said aspect ratios are 16:9 and 4:3. A method of driving a solid state image sensor which comprises a step of reading signal charges from a matrix of photosensitive elements (29) adapted to accumulate signal charges corresponding to at least two different aspect ratios and transferring said signal charges to vertical shift registers (30), characterized by: a step of selecting one of a plurality of horizontal shift registers (25,26) corresponding to said aspect ratios and disposed in parallel with each other and transferring said signal charges from said vertical shift registers (30) to the selected one of the horizontal shift registers (25,26) and a step of transferring signal charges from said one selected horizontal shift register to a buffer amplifier (27,28). The method of driving a solid state image sensor as claimed in claim 3 wherein said aspect ratios are 16:9 and 4:3.

Inventors: ITAKURA KEIJIROU, KOKUSENYA NOBURO, NAGAYOSHI RYOUICHI, NOBUSADA TOSHIHIDE, OZAKI MASAYOSHI, SAITOH YUKIO, TANAKA HIRONORI, TOYODA YASUYUKI, ITAKURA, KEIJIROU, KOKUSENYA, NOBURO, NAGAYOSHI, RYOUICHI, NOBUSADA, TOSHIHIDE, OZAKI, MASAYOSHI, SAITOH, YUKIO, TANAKA, HIRONORI, TOYODA, YASUYUKI
Applicants: MATSUSHITA ELECTRONICS CORP, MATSUSHITA ELECTRONICS CORPORATION
Application year: 1993
Main classification: H04N5
IPC codes: H04N3