Source: http://www.google.com/patents/US5870142?dq=6,202,008
Timestamp: 2015-06-02 03:40:40
Document Index: 570639411

Matched Legal Cases: ['art 4', 'art 4', 'art 4', 'art 4', 'art 4', 'art 24', 'art 24', 'art 45', 'art 45', 'art 47', 'art 45', 'art 47', 'arts 45', 'art 45', 'art 47', 'art 45', 'art 47', 'art 45', 'art 134', 'art 135', 'art 134']

Patent US5870142 - Image sensor, image reading device, and image reading method - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsAn image sensor includes a plurality of photosensitive pixel lines adjacent to each other in the sub-scanning direction, each of the photosensitive pixel lines having a number of photosensitive pixels arranged in the main scanning direction, and horizontal transfer registers disposed outside of the photosensitive...http://www.google.com/patents/US5870142?utm_source=gb-gplus-sharePatent US5870142 - Image sensor, image reading device, and image reading methodAdvanced Patent SearchPublication numberUS5870142 APublication typeGrantApplication numberUS 08/634,671Publication dateFeb 9, 1999Filing dateApr 18, 1996Priority dateApr 21, 1995Fee statusLapsedPublication number08634671, 634671, US 5870142 A, US 5870142A, US-A-5870142, US5870142 A, US5870142AInventorsSatoshi Noda, Yoshiya Imoto, Hirokazu IchikawaOriginal AssigneeFuji Xerox Co., Ltd.Export CitationBiBTeX, EndNote, RefManPatent Citations (9), Referenced by (15), Classifications (20), Legal Events (6) External Links: USPTO, USPTO Assignment, EspacenetImage sensor, image reading device, and image reading method
US 5870142 AAbstract
1. An image sensor comprising:a photosensitive pixel part including a plurality of photosensitive pixel lines adjacent to each other in a sub-scanning direction, each of said photosensitive pixel lines having a number of photosensitive pixels arranged in a main scanning direction; a horizontal transfer register disposed outside of said photosensitive pixel part and connected to external output lines, for transferring signal charges of said photosensitive pixel lines in the main scanning direction; storage means interposed between said photosensitive pixel lines and said horizontal transfer register, for saving therein signal charges on a pixel-by-pixel basis, wherein said storage means includes a semiconductor having an impurity density or a thickness that is so set that a potential of said semiconductor is on a negative side of potentials of said adjoining photosensitive pixel line and said horizontal transfer register when given potentials are applied to said shift gates; and shift gates for controlling transfer of signal charges between said photosensitive pixel lines, said storage means, and said horizontal transfer register, wherein at a time point when exposure of an inside photosensitive pixel line not adjoining said storage means has been finished, signal charges of an outside photosensitive pixel line adjoining said storage means and under exposure are saved into said storage means, and then signal charges of said inside photosensitive pixel line are transferred through said outside photosensitive pixel line to said storage means and said horizontal transfer register by controlling potentials of said photosensitive pixel lines, said storage means, said horizontal transfer register, and said shift gates as well as switching timing of the potentials. 2. The image sensor as set forth in claim 1, wherein said storage means and said shift gates are so constructed as to be able to transfer a signal charge in the main scanning direction.
7. An image reading device comprising:an image sensor comprising:a photosensitive pixel part including a plurality of photosensitive pixel lines adjacent to each other in a sub-scanning direction, each of said photosensitive pixel lines having a number of photosensitive pixels arranged in a main scanning direction; a horizontal transfer register disposed outside of said photosensitive pixel part and connected to external output lines, for transferring signal charges of said photosensitive pixel lines in the main scanning direction; storage means interposed between said photosensitive pixel lines and said horizontal transfer register, for saving therein signal charges on a pixel-by-pixel basis; and shift gates for controlling transfer of signal charges between said photosensitive pixel lines, said storage means, and said horizontal transfer register; and control means for controlling potentials of said photosensitive pixel lines, said storage means, said horizontal transfer register, and said shift gates as well as switching timing of the potentials so that signal charges of an outside photosensitive pixel line adjoining said storage means and under exposure are saved into said storage means, and then signal charges of said inside photosensitive pixel line are transferred through said outside photosensitive pixel line to said storage means and said horizontal transfer register at a time point when exposure of an inside photosensitive pixel line not adjoining said storage means has been finished, whereby said image reading device reads an image based on the signal charges received from said horizontal transfer register, and wherein said storage means is so constructed as to be able to transfer signal charges in both vertical and horizontal transfer directions, and wherein said control means selectively operates said shift gates so that after the signal charges of said inside photosensitive pixel line are transferred to said storage means and said horizontal transfer register, the signal charges of said outside photosensitive pixel line are returned to photosensitive pixels where the signal charges existed before being saved. 8. The image reading device as set forth in claim 7, wherein said control means determines exposure start timing and exposure end timing of said respective photosensitive pixel lines in accordance with a reduction/enlargement magnification of image reading.
9. An image reading device comprising:an image sensor comprising:a photosensitive pixel part including a plurality of photosensitive pixel lines adjacent to each other in a sub-scanning direction, each of said photosensitive pixel lines having a number of photosensitive pixels arranged in a main scanning direction; a horizontal transfer register disposed outside of said photosensitive pixel part and connected to external output lines, for transferring signal charges of said photosensitive pixel lines in the main scanning direction; storage means interposed between said photosensitive pixel lines and said horizontal transfer register, for saving therein signal charges on a pixel-by-pixel basis; and shift gates for controlling transfer of signal charges between said photosensitive pixel lines, said storage means, and said horizontal transfer register; and control means for controlling potentials of said photosensitive pixel lines, said storage means, said horizontal transfer register, and said shift gates as well as switching timing of the potentials so that signal charges of an outside photosensitive pixel line adjoining said storage means and under exposure are saved into said storage means, and then signal charges of said inside photosensitive pixel line are transferred through said outside photosensitive pixel line to said storage means and said horizontal transfer register at a time point when exposure of an inside photosensitive pixel line not adjoining said storage means has been finished, whereby said image reading device reads an image based on the signal charges received from said horizontal transfer register, and wherein said control means selectively operates said shift gates so that after the signal charges of said inside photosensitive pixel line are transferred to said storage means and said horizontal transfer register, the signal charges of said outside photosensitive pixel line being saved in said storage means are added to signal charges accumulated in corresponding photosensitive pixels of said outside photosensitive pixel line after saving of the signal charges. 10. An image reading device comprising:an image sensor comprising:a photosensitive pixel part including a plurality of photosensitive pixel lines adjacent to each other in a sub-scanning direction, each of said photosensitive pixel lines having a number of photosensitive pixels arranged in a main scanning direction; a horizontal transfer register disposed outside of said photosensitive pixel part and connected to external output lines, for transferring signal charges of said photosensitive pixel lines in the main scanning direction; storage means interposed between said photosensitive pixel lines and said horizontal transfer register, for saving therein signal charges on a pixel-by-pixel basis; and shift gates for controlling transfer of signal charges between said photosensitive pixel lines, said storage means, and said horizontal transfer register; and control means for controlling potentials of said photosensitive pixel lines, said storage means, said horizontal transfer register, and said shift gates as well as switching timing of the potentials so that signal charges of an outside photosensitive pixel line adjoining said storage means and under exposure are saved into said storage means, and then signal charges of said inside photosensitive pixel line are transferred through said outside photosensitive pixel line to said storage means and said horizontal transfer register at a time point when exposure of an inside photosensitive pixel line not adjoining said storage means has been finished, whereby said image reading device reads an image based on the signal charges received from said horizontal transfer register, and wherein said horizontal transfer register includes plural lines of divisional horizontal transfer registers for outputting signal charges in accordance with a pitch of said photosensitive pixels of said photosensitive pixel lines, and wherein said control means selectively operates said shift gates so that after the signal charges of the photosensitive pixels of the outside photosensitive pixel line are saved into said storage means, the signal charges of said inside photosensitive pixel line are transferred to different locations of said storage means from locations where the signal charges of said outside photosensitive pixel line are saved or to said divisional horizontal transfer registers. 11. An image reading device comprising:an image sensor comprising:a photosensitive pixel part including a plurality of photosensitive pixel lines adjacent to each other in a sub-scanning direction, each of said photosensitive pixel lines having a number of photosensitive pixels arranged in a main scanning direction; a horizontal transfer register disposed outside of said photosensitive pixel part and connected to external output lines, for transferring signal charges of said photosensitive pixel lines in the main scanning direction; storage means interposed between said photosensitive pixel lines and said horizontal transfer register, for saving therein signal charges on a pixel-by-pixel basis; and shift gates for controlling transfer of signal charges between said photosensitive pixel lines, said storage means, and said horizontal transfer register; and control means for controlling potentials of said photosensitive pixel lines, said storage means, said horizontal transfer register, and said shift gates as well as switching timing of the potentials so that signal charges of an outside photosensitive pixel line adjoining said storage means and under exposure are saved into said storage means, and then signal charges of said inside photosensitive pixel line are transferred through said outside photosensitive pixel line to said storage means and said horizontal transfer register at a time point when exposure of an inside photosensitive pixel line not adjoining said storage means has been finished, whereby said image reading device reads an image based on the signal charges received from said horizontal transfer register, and wherein said storage means includes plural lines of storage means arranged in a vertical transfer direction, and forms two systems of vertical transfer passages, and wherein said control means selectively operates said shift gates so that after the signal charges of said outside photosensitive pixel line are saved into said storage means of one of said two systems of vertical transfer passages, the signal charges of said inside photosensitive pixel line are transferred to said storage means of the other system. Description
In the image reading device using the 3-line color sensor, as shown in FIG. 29, to read an image of a document placed on a document placement glass 201, a reflection image of the document is reduction-projected progressively onto a 3-line color CCD sensor 205 through a lens 204 with scanning by a full-rate mirror 202 and half-rate mirrors 203. In this image reading device, for example, the pixel pitch of the sensor is 14 μm, the document read resolution of the sensor is 16 dots/mm, and the projection magnification of the lens is 0.224 (=0.014�16). In the conventional 3-line color CCD sensor, the read pixel lines R, G and B are arranged in parallel to one another and, therefore, as shown in FIG. 30, different positions on the document surface are read. If the gap between the sensor pixel lines is 168 μm, positions on the document surface which are spaced apart by 0.75 mm (=0.168/0.224) are read.
Del=Gap�Res�Mag
TABLE 1______________________________________Read magnification      100%    97.9%   95.8%  93.8% 91.7%______________________________________Number of delay      24      23.5    23     22.5  22lines of R withrespect to BNumber of delay      12      11.75   11.5   11.25 11lines of G withrespect to B______________________________________
As for a specific structure of each block, first, a shift gate 7r used to read out the signal charges of G is interposed between the right photosensitive pixel 2r of G and the right photosensitive pixel 3r of R, while a shift gate 7l is interposed between the left photosensitive pixel 2l of G and the left photosensitive pixel 3l of R. Also, a shift gate 8r used to read out the signal charges of R is interposed between the right photosensitive pixel 3r of R and the right saving electrode 4r of a saving and storage part 4, while a shift gate 8l is interposed between the left photosensitive pixel 3l of R and the left saving electrode 4l of the saving and storage part 4. Further, a shift gate 11 is interposed between the right saving electrode 4r and the left saving electrode 4l. Here, the right side of the signal charges read out from the photosensitive pixels is read out by the right saving electrode 4r, while the left side thereof is read out by the left saving electrode 4l. And the signal charges of the photosensitive pixel line 2 of G situated in the center of the 3 lines are read out through the photosensitive pixel line 3 of R. Further, between the right horizontal transfer electrode 5r of G and the saving electrode 4r, there is interposed a shift gate 10r and, between the left horizontal transfer electrode 5l of G and the left saving electrode 4l, there is interposed a shift gate 10l. Similarly, between the right horizontal transfer electrode 5r of G and the right horizontal transfer electrode 6r of R, there is interposed a shift gate 12r and, between the left horizontal transfer electrode 5l of G and the left horizontal transfer electrode 6l of R, there is interposed a shift gate 12l.
In FIG. 3, time t0 shows a timing at which the exposure of a photosensitive pixel line of G by an amount corresponding to one line is completed. At this timing, the photosensitive pixel line of R is being exposed. First, when the exposure of the photosensitive pixel line of G has been completed, then at time t1, a shift gate 8r is changed from 0 V to 4 V, while the signal charge of the right pixel of R is moved along a potential gradient in a high potential direction and is input into the saving electrode 4r. Next, at time t2, the saving electrode 4r is changed from 5 V to 1 V and the shift gate 11 is changed from 0 V to 3 V, while the right signal charge of R is moved to the saving electrode 4l. This makes it possible to secure a passage for transferring the right signal charge of G to the horizontal transfer electrode of G. Therefore, by controlling the respective electrodes 7r and 8r at time t3 and t4, the right signal charges of G can be sequentially moved downwardly in a vertical direction and can be thereby carried to the horizontal transfer electrode.
Then, there is carried out an operation in which the signal charge of R taken out during the exposure thereof is returned to a photosensitive pixel in which the signal charge was initially present. That is, in this operation, at time t5, the saving electrode 4l is changed from 5 V to 2 V and the shift gate 11 is changed from 0 V to 3 V, while the right signal charge of R saved to the saving electrode 4l is transferred to the saving electrode 4r. Next, at time t6, the saving electrode 4r is change from 5 V to 2 V and the shift gate 8r is changed from 0 V to 2 V, while the right signal charge of R is returned to the photosensitive pixel of R. At the same timing, the shift gate 8l is changed from 0 V to 4 V, the saving electrode 4l is changed from 1 V to 5 V, the left signal of R is transferred to the saving electrode 4l for its saving operation, and, at the same time, the shift gate 11 is returned to 0 V.
Similarly, at time t7, the left signal charge of R is saved to the saving electrode 4r and, at time t8 and t9, the right signal charge of G is transferred to the horizontal transfer electrode 5l. At time t10 and t11, the left signal charge of R is returned to its original photosensitive pixel.
In FIG. 5, time t13 expresses the exposure end timing of R. When the R exposure has ended, then firstly at time t14, the horizontal transfer electrode 5l of G is changed from 5 V to 2 V, the shift gate 10l is changed from 0 V to 3 V, and the signal charge of G under suspension of horizontal transfer is taken out into the saving electrode 4l. Next, at time t15, the horizontal transfer electrode 5l and shift gate 10l are respectively returned to their original states, that is, from 2 V to 5 V and from 3 V to 0 V, the saving electrode 4l is changed from 5 V to 2 V, the shift gate 11 is changed from 0 V to 3 V, and the signal charges of G are saved into the saving electrode 4r. By use of the thus-formed passage which extends from the photosensitive pixel 3l of R to the horizontal transfer electrode 6l, at time t16, t17 and t18, the signal charges of the left photosensitive pixel 3l of R are transferred sequentially to the horizontal transfer electrode 6l of R.
At time t18, the saving electrode 4r is changed from 5 V to 1 V, the shift gate 11 is changed from 0 V to 3 V, the signal charges of G saved to the saving electrode 4r are transferred to the saving electrode 4l. At time t19, the shift gate 11 is returned from 3 V to 1 V, the saving electrode 4l is changed from 5 V to 1 V, the shift gate 12l is changed from 0 V to 3 V, and the signals charges of G are respectively returned to their original horizontal transfer electrode 5l.
Similarly to the operations described so far, for the signal charges of the right photosensitive pixel 3r of R as well, at time t20 to t25, a transfer passage can be secured by moving and saving the present signal charges to the saving electrode 4l and the transfer of the present signal charges can be then carried out by use of the present transfer passage.
As described in the above-mentioned two operations, between the photosensitive pixel lines 2 and 3 and the horizontal transfer electrodes 5 and 6, there is provided the saving and storage part 4 consisting of the two saving electrodes 4r and 4l, and the signal charges of R under exposure are taken out once into the saving and storage part 4 to thereby secure a transfer passage for transfer of the signal charges of G after exposed, which makes it possible to read out the signal charges of G through the photosensitive pixels of R under exposure. Also, by transferring in both directions the signal charges of R taken out during the exposure thereof to thereby return them to their original photosensitive pixel lines, the exposure operation can be continued. Further, this saving and storage part 4 can be used also when the signal charges of R are transferred to the horizontal transfer electrode 6 through the horizontal transfer electrode 5 of G being transferred in the horizontal direction. This makes it possible to control or shift the color exposure phase timings from one another, which has been difficult according to the prior art. Due to this, it is possible to prevent the color registration correction performance from being lowered when the scanning density in the sub-scanning direction is varied, which scanning density variation is used for a magnification varying mode in a digital color copying machine. Further, in this manner, since the registration correction of decimal portions can be made with high accuracy, there is eliminated the need that the gap between the photosensitive pixel lines should be the integer multiple of the pixel pitch, which in turn makes it possible to set the gap between the pixel lines in less than 2 lines (for example, the pixel line gap can be set at 1.5 lines).
In each block of the present image sensor, as shown in FIG. 8, a shift gate SHG for reading out the signal charges of G is interposed between the photosensitive pixel line 22 of G and the photosensitive pixel line 23 of R, while a shift gate SHR for reading out the signal charges of R is interposed between the photosensitive pixel line 23 of R and the saving and storage part 24. Here, the signal charges of the G photosensitive pixel line 22 situated in the center of the three color lines are read out through the photosensitive pixel line 23 of R.
The saving and storage part 24 comprises a first transfer electrode line and a second transfer electrode line. Also, the first and second transfer electrode lines both include stages necessary to transfer the even and odd signal charges of the two colors R and G to horizontal transfer electrodes 25-28, and also they include two systems, that is, A and B systems of electrodes T1A, T1B, T2A and T2B, respectively. And between the first and second transfer electrode lines, there is interposed a shift gate SHT which can be operated in linking with the second transfer electrode line T2A of the A system. Also, at the respective terminal points of the first and second transfer electrode lines, there are provided drains D which are used to discharge excessive dark output components. The second transfer electrode line T2B is used to carry the signal charges to the horizontal transfer electrodes 25-28 forming the two systems of the two colors R and G which are respectively located in front of the drains D.
First, a description will be given of an operation to feed the signal charges of the photosensitive pixels to the first transfer electrode with reference to FIG. 9(b). In this case, with the first transfer electrode line T1A set at H, the shift gate SHR is changed from L to H. The signal charges of R are read out according to the potential gradient into the portion of the first transfer electrode line where the electrode T1A is located. At the same time, if the shift gate SHG is changed from L to H, then the signal charges of G are also read out through the photosensitive pixels of R into the portion of the first transfer electrode line where the electrode T1A is located.
Further, referring to the signal charges that are read out into the first transfer electrode T1A, as shown in FIGS. 9(c) and 9(d), the first transfer electrode T1A of the A system is changed in the order of H, L and H, and the first transfer electrode T1B of the B system is fixed at a level between H and L of the first transfer electrode T1A of the A system so that this level can operate as a virtual phase, whereby the signal charges read into the first transfer electrode T1A can be transferred to the right (the side that is near the horizontal transfer electrode) sequentially. When transferred down to the drains D in the final stage, the signal charges (dark output portions) can be discharged here from the drains D.
FIG. 10 is an explanatory view of variations in the potential distribution of the second transfer electrode line as well as an operation to transmit the signal charges of the photosensitive pixels to the second transfer electrode line. FIG. 10(a) shows the structure of a sensor, and FIGS. 10(b) and 10(c) show the drive signals of the respective electrodes and variations in the drive signals. In the second transfer electrode line, as shown in FIGS. 10(b) and 10(c), the second transfer electrodes T2B of the B system are changed in the order of H, L and H, and one horizontal transfer electrodes φ1 is changed in the order of L, H and L, whereby the signal charges can be sequentially transferred to the right (that is, in the direction of the horizontal transfer electrodes). At this time, the second transfer electrodes T2A of the A system are fixed at L. And the potential level of the second transfer electrode line when the second transfer electrodes T2A of the A system is set at L is set at a level between H and L of the second transfer electrodes T2B of the B system, so that they can operate as a virtual phase similarly to the first transfer electrodes T1B of the B system.
Next, a description will be given below of an operation to transfer the signal charges in the horizontal direction within the saving and storage part. FIG. 11 is an explanatory view of variations in a potential distribution within the saving and storage part when the signal charges are transferred in the horizontal direction as well as an operation to transfer the signal charges in the horizontal direction within the saving and storage part. FIGS. 11(a) shows the structure of a sensor, and FIGS. 11(b)-11(f) respectively show the drive signals of the respective electrodes and variations in the potential distribution. First, in a potential section C shown in FIG. 11(a), there is shown a portion of the first transfer electrode line into which signal charges read out in parallel from two even and odd systems of read pixels are transferred. This is a part of the first transfer electrode line in which the transfer electrodes are closely connected with each other. The signal charges of the pixel line are read into the two mutually adjoining transfer electrodes of the first transfer electrodes T1A. Then, as shown in FIGS. 11(b) and 11(c), if the first transfer electrodes T1A are changed in the order of L, H and L, then the signal charges are transferred to the right sequentially. Then, in accordance with meandering of the first transfer electrode, the signal charges that have been transferred to the right are transferred downwardly as shown in FIG. 9.
FIGS. 11(d) and 11(f) show variations in the potential distribution in the potential section D in FIG. 11(a) which are caused by the states of the drive signals. This part is used to move in parallel a group of signal charges under transfer through the first transfer electrode line to the second transfer electrode line. First, the signal charges existing on the first transfer electrode side (on the right side) when the second transfer electrodes T2A are at L can be transferred to the second transfer electrode side (to the left side) by varying the second transfer electrodes T2A from L to H. In other words, since the second transfer electrodes T2A are changed from L to H, by means of a potential gradient which is produced by varying the potentials of the second transfer electrodes T2A and shift gate SHT to H at the same time, the signal charges can be transferred in parallel between the two transfer electrode lines.
First, a description will be given below of how to take out the R signal charges during the exposure period with reference to FIG. 12. In FIG. 12, time t10 designates a state in which the exposure of G is ended and R is under exposure. If the exposure of G is completed, then, first, at time t11, by turning the R shift gate SHR and first transfer electrode line T1A to H, the signal charges of the two pixels of R can be transferred to the adjoining first transfer electrode line. Next, at time t12 and t13, the first transfer electrode line T1A is driven to vary in the order of L, H and L, while the signal charges of R are transferred sequentially through the first transfer electrode line T1A and reach the 4th stage/6th stage of the first transfer electrode line. Further, at time t14, by driving the second transfer electrode line T2A to H, the signal charges of R are transferred to the second transfer electrode line and, at time t15, by driving the second transfer electrode line T2A, the signal charges of R are stored and held in the 1st stage/3rd stage of the second transfer electrodes.
Next, a description will be given below of how to take out the signal charges of G. In FIG. 13, time t20 shows the same state as time t15. First, at time t21, by driving the shift gate SHG of G, shift gate SHR of R and first transfer electrode line T1A to H respectively, the signal charges of G of two pixels are transferred through the interiors of the R photosensitive pixel line to the adjoining first transfer electrode line. At time t22 and t23, by driving the first transfer electrode line T1A to vary in the order of L, H, L, H, L, H and L, the signal charges of G are transferred through the first transfer electrode line sequentially and reach the 8th stage/10th stage of the first transfer electrode line. Further, at time t24, by driving the second transfer electrode line T2A to H, the signal charges of G are transferred to the second transfer electrode line and, at time t25, by driving the second transfer electrode line T2A to L, the signal charges of G are stored and held in the 5th stage/7th stage of the second transfer electrodes.
Next, a description will be given below of an operation to be performed at a time point when the remaining exposure of R is completed with reference to FIG. 14. In FIG. 14, time t30 shows a state in which the exposure of R after time t25 is continued and the signal charges are stored in the R pixel line. If the remaining exposure of R is ended, first, at time t31, by driving the shift gate SHR of R and first transfer electrode line T1A to H respectively, the signal charges of R of two pixels are transferred to the adjoining first transfer electrode line. Next, at time t32 and t33, by driving the first transfer electrode line T1A to vary in the order of L, H and L, the signal charges of R are transferred through the first transfer electrode line sequentially and reach the 4th stage/6th stage of the first transfer electrode line. Further, at time t34, by driving the second transfer electrode line T2A into H, the signal charges of R are transferred to the second transfer electrode line and are added to the signal charges of a first half section of the exposure period. At time t35, by driving the second transfer electrode line T2A to L, the signal charges of R are stored and held in the 1st stage/3rd stage of the second transfer electrodes. In this state, the signal charges of both R and G corresponding to one exposure period are stored in the second transfer electrodes.
Next, a description will be given below of an operation to deliver the signal charges stored in the second transfer electrodes to the horizontal transfer electrodes with reference to FIG. 15. In FIG. 15, time t40 shows a state in which, after the state of time t35, the signal charges of one line of the horizontal transfer electrodes have been read out completely. During a period of t41 to t45, by fixing the second transfer electrode lines T2A and φ2 at L respectively and also by driving the second transfer electrode lines T2B and φ1 in the mutually opposing phases, the signal charges are sequentially transferred and are then set at the respective positions of the four lines of horizontal transfer electrodes.
Concretely, as in FIG. 17 which shows one block of the present image sensor, there is interposed between the photosensitive pixel 42 of G and the photosensitive pixel 43 of R a shift gate 52 which is used to transfer the signal charges of G and, between the photosensitive pixel 43 of R and a storage part 45, there is interposed a shift gate 53 which is used to transfer not only the signal charges of R but also the signal charges of G transferred through the shift gate 52 to the R photosensitive pixel 43. Out of the signal charges of G and R transferred from the photosensitive pixels 42 and 43 to the storage electrode of the storage part 45, the signal charges of G are guided through a shift gate 54 to the horizontal transfer electrode 46 of G; and, the signal charges of R are guided through a shift gate 54 to the horizontal transfer electrode 46 of G, after then, the signal charges are further guided through a shift gate 55 to the storage electrode of a storage part 47 and are still further guided through a shift gate 56 to the horizontal transfer electrode 48 of R. And the signal charges of G guided to the horizontal transfer electrode 46 by means of the above operations are converted to time series signals and are then read out by the horizontal transfer electrodes of φ1Gand φ2G, while the signal charges of R guided to the horizontal transfer electrode 48 of R are converted into time series signals and are then read out by the horizontal transfer electrodes of φ1R and φ2R.
In FIG. 18, time t0 stands for a timing when the horizontal transfer of the signal charges of G is completed. At this time, the exposure of the photosensitive pixel line of G is almost completed, while the photosensitive pixel line is on the way of the exposure period thereof. First, during period t1, if the shift gates 54 and 56 are turned on, then the signal charges of R within the storage part 45 as well as the signal charges of R within the storage part 47 are moved in the potential increasing direction along the potential gradient, so that they are respectively transferred to φ1G of the horizontal transfer electrode 46 of G and φ1R of the horizontal transfer electrode 48 of R. Next, during period t2, if the shift gates 53 and 55 are turned on, then the signal charges of R within the photosensitive pixel line 43 of R and the signal charges of R within φ1G of the horizontal transfer electrode 46 of G are respectively transferred to the storage parts 45 and 47. After period t2, the exposure of the photosensitive pixel line 42 of G is ended completely.
Next, during period t3, if the shift gates 52, 54 and 56 are turned on, then the signal charges of G within the photosensitive pixel line 42 of G are transferred to the photosensitive pixel line 43 of R, the signal charges of R within the storage part 45 are transferred to φ1G of the horizontal transfer electrode 46 of G, and the signal charges of R within the storage part 47 are transferred to φ1R of the horizontal transfer electrode 48 of R. In this operation, in φ1R of the horizontal transfer electrode 48 of R, the signal charges of R just before the signal charges transferred during period t1 are combined with the signal charges of R transferred during period t3. Next, during period t4, if the shift gates 53 and 55 are turned on, then the signal charges of G within the photosensitive pixel line 43 of R are transferred to the storage part 45, while the signal charges of R within φ1G of the horizontal transfer electrode 46 of G are transferred to the storage part 47. Further, during period t5, if the shift gate 54 is turned on, then the signal charges of G within the storage part 45 are transferred to φ1G of the horizontal transfer electrode 46 of G.
Next, a description will be given below of a specific structure and operation timings of the present embodiment with reference to FIGS. 21-24. FIGS. 21 and 22 respectively show plane structures of a four-pixel portion of the image sensor shown in FIG. 20, in which only the G-Even/R photosensitive pixel line side of the image sensor is shown. In these figures, a circle and a triangle respectively indicate signal charges accumulated, and as the signal charges increase, the mark changes in the order of a small triangle, a large triangle, and a circle. Signal charges are accumulated similarly in the Green-Odd pixels, but a description thereof will be omitted to avoid unduly complicating the figures. Circles, triangles, and arrows show movement of signal charges at time t0-t9. Reference characters SHG, SHR1/2 and the like are control lines which are used to drive the respective gate electrodes that are shown in these figures, while φ1 and φ2 are respectively 2φ clock control lines which can be used in common for the respective horizontal transfer CCD registers of G-Even, R-Odd and R-Even. Here, FIG. 23 is a time chart which shows the operation timings of the respective electrodes, and the above-mentioned respective control lines are used to generate and control pulses at the timings shown in the time chart.
At time t3, following the temporary saving of the signal charges of R-Even, the signal charges of G-Even pass through the R photosensitive pixel and, therefore, the signal charges of G produce a mixed color for the R photosensitive pixel. The degree of the mixed color is determined by a ratio of a pulse width at time t3 with respect to the read cycle Ts of one line of the CCD. Normally, since the pulse width at time t3 is 1-2 μsec, while the cycle Ts is in the order of 400 μsec even in a high-speed copying machine, the mixed color ratio is in the order of 0.25-0.5%, which has little influence on the quality of an image formed. Also, in order to reduce the influence of a mixed color, for example, in the case of an RGB system, B may be allotted to the intermediate pixel line of the three photosensitive pixel lines. This is because the color B is least sensitive when it is measured according to a spectral luminous efficiency for the human eyes, that is, hard to perceive. In addition, in the case of a copying machine, a Y (yellow) signal (Y is a complementary color to B) is produced from a B signal, and the color Y is also less sensitive to the human eyes and is not noticeable.
Next, at time t4, the signal charges of G-Even of the nth line are transferred to the φ1 side of the intermediate register 66. In this case, the R-Even signal charges are transferred to TG so that the R signal charges of the nth line that have been continuously held in the intermediate register 67 of R since the time t0 can be distributed to the Odd/Even 2φ signals.
At time t5 and t6, the signal charges of R-Even that have been saved and are being exposed are returned back to the photosensitive pixel line 63 of R and, at the same time, the G-Even signal charges of the nth line are transferred to the horizontal transfer CCD register 71 of G-Even. Here, the reverse transfer of the signal charges is carried out, that is, the signal charges are transferred reversely from the horizontal transfer CCD register 71 of G-Even to the intermediate register 66 of G-Even as well as from the intermediate register 66 of G-Even to the photosensitive pixel line 63 of R. This reverse transfer will be discussed in detail afterwards. Also, the R signal charges of the nth line are also distributed into Odd and Even and are then transferred to the respective φ1 sides of Odd and Even, respectively.
At time t7, φ1 and φ2 start their complementary drive operations and the signal charges of G-Even of the nth line as well as the signal charges of R-Odd and R-Even of the nth line start to be transferred in the horizontal direction at the same time and with the same phase. At time t8, since the exposure period of R of the (n+1)th line is ended, by driving the gate electrode SHR1/2 to H, the R signal charges of the (n+1)th line are transferred from the R photosensitive pixel line 63 to the intermediate register 66 of G. At this time, in the G photosensitive pixel line 63, the signal charges of the (n+1)th line are still in the exposure period. At time t9, in the R photosensitive pixel line 63, the exposure period of an (n+2)th line is already started and thus the operation as it is returned to the state of time t0.
Next, a description will be given below of the internal structure of a register which is structured so as to perform the above-mentioned transfer operation in both directions. FIG. 24 is a vertical direction section view of a register formed on an N-type Si substrate and corresponding to one pixel, in which the electric field potentials of the respective parts of the register are also shown. In this electric field potential view, a solid line designates a case in which a voltage to be applied to the respective gate electrodes is of a L (low) level, and a dotted line stands for a case in which the applied voltage is set in the H level and the potentials are lowered. As the polarity of the signal charge, an electron carrier dominates, that is, the polarity of the signal charge is a negative polarity and, in FIG. 24, the signal charge always flows in a positive direction in which the potential is lowered. A register, which is arranged so as to perform the transfer operation in both directions, is located just below the gate electrode STG1/2 and, with the potential level thereof set in the applied voltage L level, the register is situated in the more negative direction than the adjoining photosensitive pixel line (Red PD) 63 and the horizontal CCD register 71 of G-Even. This potential level at the applied voltage L level depends on the thickness or impurity density of an N layer formed within a P-well in FIG. 24. The potential level of an N-type semiconductor becomes an N- type and is thus increased in level by increasing the impurity density thereof, while it becomes an N+ type and is thus decreased in level by decreasing the impurity density thereof. Therefore, in the present embodiment, other registers are formed as N-, whereas the intermediate register 66 of G-Even just below the gate electrode STG1/2 is formed as N+. As a result, a potential which is one stage higher in level than the adjoining registers can be formed just below the gate electrode STG1/2.
In FIG. 28, a pulse generation part 134 is a part into which a reference clock signal CK1 is input from a given oscillator and also which, in accordance with outputs from a group of comparators 137, generates a signal S1 for determining the stop periods of clock pulses φ1 and φ2, a signal S2 for determining the H/L of the stop periods of the clock pulses φ1 and φ2, shift pulses SH-- G, SH-- B and SH-- R, a data valid signal, and a synchronous grounding signal at given timings, respectively. On the other hand, a pulse generation part 135 is used to generate horizontal transfer clock pulses φ1 and φ2 as well as reset pulses RS1 and RS2 in accordance with the signals that are output from the pulse generation part 134. A counter 136 is used to count a twofold cycle clock CK2 obtained by frequency dividing the reference clock signal CK1 into one half in accordance with a line signal LINE input from outside, and output the count value to the comparators 137. To the comparators 137 are connected registers 138 respectively which are used to set the count values that are compared by the comparators 137. The registers 138 are structured such that signals are input into them from a CPU (not shown) and the set values can be rewritten properly as the need arises. A sync detection circuit 140 is used to detect a sync relationship between the line signal LINE, reference clock CK1 and twofold cycle clock CK2.
Next, a description will be given below of an operation to generate the shift pulses SH-- G, SH-- B and SH-- R, horizontal transfer clock pulses φ1 and φ2, and reset pulses RS1 and RS2 by the above-structured timing generation circuit 121.
First, in the present timing generation circuit, the counter 136 counts the number of pulses of the twofold cycle clock CK2 at the fall timing of the line signal LINE input from outside. Here, the line signal LINE is a signal asynchronous with the reference clock CK1 and, in a digital color copying machine, there is normally used a signal which is synchronous with a timing signal of a polygon scanner of a laser print part. Therefore, due to the fact that the line signal LINE is a signal asynchronous with the twofold cycle clock CK2, the value to be counted by the counter 136 from a certain line signal LINE to a next line signal LINE varies. In view of this, it is necessary to determine a delay pixel by use of the count value. After the line signal LINE falls and the twofold cycle clock CK2 falls, a timing signal S1 is made to fall at a timing when the reference clock CK1 falls for the first time and the twofold cycle clock CK2 is masked by the timing signal S1, thereby providing a signal which can be used to set the stop period in the horizontal transfer clock pulse φ1.
Here, the reason why, for the line signal LINE, the reference of operation of the image sensor is determined in synchronization with the twofold cycle clock CK2 is to prevent the operation of the horizontal transfer clock of one line from being unfinished. That is, if the reference of the operation of the image sensor is synchronized with the reference clock CK1, then even when the horizontal transfer clock φ1 is at H, there is a possibility that the signal S1 for setting the stop period in the horizontal transfer clock φ1 can rise. This in turn raises a possibility that the final pulse width of the horizontal transfer clock φ1 can be reduced to one half. In the normal use of the image sensor, in a period which extends from the falling of the above-mentioned line signal LINE to the falling of the signal S1, the reading out of the image signal has been completed. Therefore, the occurrence of the horizontal transfer clock having such a half width has no influence on the normal use of the image sensor. However, in the use of the present embodiment of the invention, since there is a possibility that an operation to read out the signals of R and the like can be continued even during the above period, the occurrence of the horizontal transfer clock having such a half width has an influence on the read image data. This is the reason why the signal S1 for setting the stop period in the horizontal transfer clock φ1 is set in such a manner that it is synchronous with the twofold cycle clock CK2.
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