JP3161302B2 - Image sensor and image reading device using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a charge transfer type image sensor having an array of photoelectric conversion elements and a charge transfer device for receiving and transferring charges from each element of the array on a semiconductor substrate.

[0002]

2. Description of the Related Art FIG.
A one-dimensional image sensor having a structure as shown in FIG. This conventional sensor has a one-dimensional array 2 of a large number of photoelectric conversion elements (for example, photodiodes) formed on a semiconductor substrate, and a transfer array is provided on one side of the photodiode array 2 along the array 2. A gate 4 and a charge transfer register (eg, a CCD register) 6 are formed, and on the other side, similarly along the array 2,
A gate 8 and a drain 10 are formed. here,
Since the gate 8 functions to limit the time for sensing an image like a shutter of a camera, it is hereinafter referred to as a shutter gate.

[0003] Such a one-dimensional image sensor is widely used for reading an original by, for example, a flatbed type image scanner or an original reading section of a copying machine or a facsimile machine. In these apparatuses, the one-dimensional image sensor sequentially reads the image of each line from left to right on the document surface while optically scanning the document surface from top to bottom. While scanning the document surface from top to bottom,
The shutter gate 8 repeats an operation of opening at the first half of each cycle and closing at the second half of the cycle. Also,
In synchronization with this, the transfer gate 4 also repeats the operation of opening for a short time immediately before the shutter gate 8 opens.

In the period when the shutter gate 8 is open,
All charges generated in each photodiode of the array 2 according to the amount of received light are discharged to the drain 10. That is, the image is not sensed. In the subsequent period in which the shutter gate 8 is closed, charges corresponding to the amount of received light are accumulated in each diode. That is, the image of the line is sensed during this period. Thereafter, when a predetermined charge accumulation period elapses,
The transfer gate 4 is opened, and the charges stored in the diode array 2 are transferred to the CCD register 6 in parallel. Thereafter, the shutter gate 8 repeats the above-mentioned opening / closing operation again, and the electric charge of the next line is accumulated in the diode array 2, while the CCD register 6 sequentially outputs the electric charge received earlier while serially transferring it to the subsequent stage.

[0005]

One problem with the conventional image sensor is that serial transfer of charges by the CCD register 6 takes time. That is, an image scanner or a copying machine is provided with a one-dimensional image sensor having a necessary number of photodiodes so that a document having the maximum size in its specifications can be read at the highest optical resolution. For example, to read an 8.5 inch line at an optical resolution of 600 dpi,
A sensor with a net of 5100 photodiodes is required. As can be seen from the above description with reference to FIG. 1, the conventional one-dimensional image sensor reads one line each time.
The charges of all the photodiodes are transferred in parallel to the CCD register 6 and output serially from the CCD register 6. The CCD register 6 cannot receive the next line of electric charge unless all the electric charges received from the array 2 are output. Therefore, for example, 51
In a sensor having 00 photodiodes, 5100 charges must be serially transferred by the CCD register 6 for each line. This means that in FIG. 1B, N needs to be 5100 or more.

[0006] This is true whether the document size is large or small. That is, a narrow document (that is,
Even when reading a document with a short line length), all charges read from the range of the maximum document width exceeding the width of the document must be serially transferred by the CCD register. It takes about the same amount as the widest document. As a result, even when the document size is reduced, the entire reading time is not reduced as much as the reduction rate of the area.

[0007] A similar problem exists in a two-dimensional image sensor. That is, in the two-dimensional image sensor, the one-dimensional image sensors as described above are arranged in a large number of columns, and the charges output from those columns are serially transferred to the columns by an additional charge transfer register arranged vertically. Is what you do. Even in such a two-dimensional image sensor, there is a transfer time problem in the same manner as described above regarding the charge transfer in the charge transfer registers of each column and the additional charge transfer registers.

Accordingly, it is an object of the present invention to provide a charge transfer type image sensor in which the transfer of an image charge in an area in a short time is completed according to the size of the area to be read.

[0009]

In the image sensor of the present invention, an additional gate and a drain are formed adjacent to the charge transfer register. When this additional gate opens, the charge in the charge transfer register is drained to the additional drain and the charge transfer register is emptied. Therefore,
When the size of the area to be read is small, unnecessary charges outside the above-mentioned area remaining in the charge transfer register are opened by opening an additional gate when only the charge in the range covering the area is output from the charge transfer register. It can be discharged at a stretch. Therefore, those unnecessary charges do not need to be further serially transferred on the charge transfer register.
Since the next reading operation is immediately performed, the image reading time is reduced.

An image reading apparatus according to the present invention includes the image sensor having the above-described configuration, and a driving device for the image sensor. The driving device drives the charge transfer register within a range of the number of clock signals required to output charges corresponding to an image to be read from the charge transfer register, and all charges to be read from the charge transfer register are output. When finished, open the trimming gate. As a result, unnecessary charges remaining in the charge transfer register are immediately discharged to the trimming drain, so that the read operation can be immediately started.

[0011]

FIG. 2 shows a planar structure of a one-dimensional image sensor according to an embodiment of the present invention. This image sensor is for color reading, and has three modules 20R, 2R for reading three primary color components of red (R), green (G) and blue (B), respectively.
0G and 20B are provided on a single semiconductor substrate. These modules 20R, 20G, 20B are R, G,
B are arranged closely adjacent to each other in the order of B.

The individual modules 20R, 20G, 20B
Are basically the same. Therefore, taking the module 20R for R as an example, there is a one-dimensional array 22R of a large number of photodiodes, and a transfer gate 24R and a CCD register 26R are formed on one side of the array 22R along the array 22R. On the other side, a shutter gate 28R and a drain 30R are similarly formed along the array 22R. The configuration up to this point is the same as that of the conventional one shown in FIG.
The difference from the conventional configuration is that an additional gate 32R is formed along the CCD register 26R on the side opposite to the transfer gate 24R of the CCD register 26R. And this additional gate 32R
It is adjacent to the drain 30G of the adjacent G module 20G. This additional gate 32R is connected to C
Unnecessary charges in the CD register 26R are drained at once.
Since it has a function of discharging to 0G, that is, a function of trimming unnecessary charges, it is hereinafter referred to as a trimming gate.

The structure of the G module 20G is the same as described above, and the trimming gate 32G is adjacent to the drain 30B of the B module 20B. The B module 20B has the same basic configuration, but further includes an additional drain 3 adjacent to the trimming gate 32B.
0A is formed. This additional drain 30A
This is for discharging unnecessary charges in the CCD register 26B of the B module 20B.

FIG. 3 is a timing chart showing signals for driving each module of the one-dimensional image sensor. FIG. 4 shows the energy level of each part of the module at each stage of driving. Since all the modules are driven in the same manner, the operation of the R module 20R will be described here as an example.

In FIG. 3, a transfer gate (T
G) The signal is at a high level for a predetermined period at a fixed period (section (D) in FIG. 3). At this time, the transfer gate 24R opens only during the high level, and all the charges accumulated in the photodiode array 22R are transferred in parallel to the CCD register 26R. The state of the energy level is shown in FIG.

During the period from the fall of the TG signal to the next fall, the shutter signal goes to a high level and a low level.
R is opened, and the electric charge accumulated in the photodiode array 22R flows to the drain 30R to empty the electric charge. FIG.
(A) shows the state of the energy level at this time, and corresponds to (A) in FIG.

Next, the shutter gate 28R is closed while the TG signal is at the low level, and charges corresponding to the amount of received light are accumulated in the photodiode array 22R only while the shutter gate 28R is closed. This is performed in the section of FIG. 3B, and the state of the energy level at that time is as shown in FIG. 4B.
However, this indicates a stage in the middle of accumulation.

In sections (A) and (B) of FIG. 3, the CCD register 2 is synchronized with a high-frequency clock signal (CLK).
The charges in 6R are serially transferred along the register 26R, and are sequentially output from the CCD register 26R. At this time, the CLK signal is output by the number of photodiodes corresponding to the line length to be read. For example, if there are 5100 net photodiodes in the array 22R so that the maximum line length of 8.5 inches can be read at the highest resolution of 600 dpi, the original size is small and, for example, from the first to the 2,000th photodiode. When the line length of the document is covered by the range of the photodiodes, only 2000 signals are output, and only the first to 2,000th charges are stored in the CCD register 2.
6R, the unnecessary charges of the 2001 or higher number are C
It remains in the CD register 26R.

Thereafter, the trimming signal goes high for a predetermined time width, and the trimming gate 32R is opened only during the high level. The energy level at this time is shown in FIG. This corresponds to FIG. As shown here, the unnecessary charges remaining in the CCD register 26R are simultaneously discharged to the drain 30G, and the CCD register 26R is emptied instantly. Thus, unnecessary charges are erased from the CCD register 26R at once,
The time required to serially transfer them is saved, and the system immediately enters the reading operation of the next line. As a result, when the document size is small, the line reading time (that is, the period of the TG signal) can be reduced according to the line length, and high-speed image reading can be performed.

FIG. 5 shows a configuration of an image scanner 50 using the one-dimensional image sensor 20 as described above. The read command from the host computer 52 is received by the image processing control unit 56 through the interface circuit 54. The read command includes data (for example, the coordinates of the origin of the rectangular read area, the length of the vertical and horizontal sides, and the like) specifying which area on the document table (not shown) is to be read. The image processing control unit 56 determines T based on the data.
The period and the number of outputs of the G signal, and the number of outputs of the CLK signal in each period are determined. Here, assuming that the origin of the platen is the upper left corner of the platen and that the image sensor 20 travels from top to bottom on the platen, the number of output CLK signals in each cycle is the left side of the platen. Is determined by the number of photodiodes covering the distance from the to the right side of the reading area (that is, the line length to be read), and the cycle of the TG signal is also determined accordingly (however, no matter how short the line length is,
The period is not shorter than the lower limit of the period required to secure the charge accumulation period necessary to obtain sufficient sensitivity and the time required to move from one line to the next line).
The number of output TG signals is determined by the number of lines covering the length of the vertical side from the upper side to the lower side of the reading area, and is a function of the reading resolution and the length of the vertical side.

When the cycle and the number of outputs of the TG signal and the number of outputs of the CLK signal in each cycle are determined in this manner, the image processing control unit 56 sends a drive command based on the determination to the drive signal generation circuit 58. give. The drive signal generation circuit 58 generates the TG signal and the CLK signal at the timing shown in FIG. 3 according to the cycle and the number of outputs of the TG signal determined by the image processing control unit 56 and the number of outputs of the CLK signal in each cycle. , A shutter signal, a trimming signal and the like are supplied to the image sensor 20. Thus, the reading operation as described above is performed.

The electric charge output from the CCD register of the image sensor 20 is converted into an analog voltage signal corresponding to the electric charge at an output stage of the sensor 20, and is converted into an analog voltage signal by the A / D converter 6.
0 is given. The A / D converter 60 captures an analog voltage signal from the sensor 20 in synchronization with an output timing from the sensor 20 by a synchronization signal from the drive signal generation circuit 58, and converts the analog voltage signal into a multi-bit digital code. This digital code is sent to the image processing controller, where the well-known digital image processing to be performed by the scanner is performed, and the resulting digital image data is returned to the host computer 52.

While a preferred embodiment of the present invention has been described above, the present invention can be implemented in various other modes. For example, in the above embodiment, adjacent modules share one drain for one shutter and another for trimming, but they share the drain for both shutters, And 2 for trimming
One drain may be provided for each module.
In each module, the shutter gate and the shutter drain are not necessarily required. When the shutter gate and the drain for the shutter are removed, each module includes, as in the module 20B for B in FIG.
A new drain for trimming may be provided, or an adjacent module may share one drain for trimming. Further, the embodiment like the module for B in FIG. 2 can be implemented independently and used as an image sensor for monochromatic reading. Also, the charge transfer element does not necessarily have to be a CCD,
Other types may be used. Further, the above-described one-dimensional image sensors can be arranged in a large number of rows and implemented as a two-dimensional image sensor. In the case of a two-dimensional image sensor, an additional charge transfer register for serially transferring charges output from a large number of one-dimensional image sensors is provided, and a trimming gate and a drain are also provided for this additional charge transfer register. Can be.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a conventional one-dimensional image sensor.

FIG. 2 is a plan view showing a one-dimensional image sensor according to one embodiment of the present invention.

FIG. 3 is a timing chart showing signals for driving each module of the one-dimensional image sensor of FIG. 2;

FIG. 4 is a diagram showing the energy level of each part of the module at each stage of driving the sensor of FIG. 2;

FIG. 5 is a block diagram showing a configuration of an image scanner 52 using the sensor of FIG. 2;

[Explanation of symbols]

 20 One-dimensional image sensor 20R, 20G, 20B Each color module 22R, 22G, 22B Photodiode register 24R, 24G, 24B Transfer gate 26R, 26G, 26B CCD register 28R, 28G, 28B Shutter gate 30R, 30G, 30B, 30A Drain 32R , 32G, 32B trimming gate

Claims (4)

(57) [Claims] 1. An image sensor having a charge transfer register for transferring a large number of charges representing a read image, comprising: a trimming gate formed adjacent to the charge transfer register; and a trimming gate formed adjacent to the trimming gate. An image sensor comprising: a formed trimming drain. 2. The image sensor according to claim 1, wherein a one-dimensional array of photoelectric conversion elements for generating the electric charge, a shutter gate formed adjacent to one side of the array, and an adjacent to the shutter gate. An image sensor further comprising a shutter drain formed as described above. 3. A color image sensor comprising a plurality of modules arranged adjacent to each other for reading a plurality of color components, wherein each of said modules stores a number of charges representing a corresponding color component of an image. A one-dimensional array of photoelectric conversion elements to be generated, a charge transfer register that receives the charge from the array and serially transfers the charge, a shutter gate formed adjacent to one side of the array, and a shutter gate adjacent to the shutter gate. A shutter drain formed in the above manner; a trimming gate formed adjacent to the charge transfer register; and a trimming drain formed adjacent to the trimming gate. Characterized in that the shutter drain also serves as the other trimming drain. Jisensa. 4. An image reading apparatus comprising an image sensor and a driving device for the image sensor, wherein the image sensor comprises: a charge transfer register for transferring a large number of charges representing an image; A driver for outputting a charge corresponding to an image to be read from the charge transfer register, the trimming gate having a trimming gate formed adjacently; and a trimming drain formed adjacent to the trimming gate. Means for driving the charge transfer register within a required number of clock signals; and unnecessary charges in the charge transfer register when all charges corresponding to the image area to be read have been output from the charge transfer register. Means for opening the trimming gate in order to discharge the liquid to the trimming drain Image reading apparatus characterized by having a.