1. Field of the Invention
One disclosed aspect of the embodiments relates to a solid-state imaging device, an imaging system, and a copier, used in a copier, an image scanner, and the like.
2. Description of the Related Art
In recent years, reduction of the pixel size tends to be required for solid-state imaging devices with an increase in the number of pixels with improvement of the resolution. As a technology to respond to the reduction of the pixel size, a pixel sharing technology as described in Japanese Patent Application Laid-Open No. 9-46596 is known. In Japanese Patent Application Laid-Open No. 9-46596, a circuit of and after a floating diffusion is shared by a plurality of pixels (photodiodes), so that the reduction of the pixel size is achieved.
A solid-state imaging device of an embodiment is a solid-state imaging device configured to be relatively scanned in a first direction with respect to an original copy, and including: a plurality of cells; and a memory, wherein each of the plurality of cells includes a first photoelectric conversion unit configured to convert light into electric carriers and accumulate the electric carriers, and a second photoelectric conversion unit arranged in the first direction with respect to the first photoelectric conversion unit, and configured to convert light into electric carriers and accumulate the electric carriers, the memory is provided common to the first and second photoelectric conversion units, and holds the electric carriers accumulated by each of the first and second photoelectric conversion units, or signals based on the electric carries, and an interval of the first and second photoelectric conversion units of one cell of the plurality of cells in the first direction is {n+(b/a)}×x, where a is a period from when the first and second photoelectric conversion units terminate an electric carrier accumulation to when the first and second photoelectric conversion units perform the electric carrier accumulation again and next terminate the electric carrier accumulation, b is a gap of timing at which the electric carrier accumulation of the first and second photoelectric conversion units is terminated, n is an integer of 1 or more, and x is an interval of the first photoelectric conversion unit of the one cell of the plurality of cells, and the first photoelectric conversion unit of another cell adjacent to the one cell in a second direction perpendicular to the first direction.
Further features of the disclosure will become apparent from the following description of exemplary embodiments (with reference to the attached drawings).
However, when the technology of Japanese Patent Application Laid-Open No. 9-46596 is applied to a line sensor used in a copier or the like, the following problems are caused. In the technology described in Japanese Patent Application Laid-Open No. 9-46596, a plurality of pixel signals is read out by a single readout circuit. Therefore, readout timing of pixels that share the floating diffusion is different. That is, among the pixels that share a memory, which holds electric carriers accumulated by each of a plurality of photoelectric conversion units or signals based on the electric carriers, timing at which electric carrier accumulation is terminated is shifted. Accordingly, a gap is caused in imaging positions, which causes a decrease in image quality such as deterioration of a fixed-pattern noise and degradation of the resolution represented by color degrading.
An objective of an embodiment is to provide a solid-state imaging device, an imaging system, and a copier, which can decrease the fixed-pattern noise and the color degrading caused by the gap of timing at which the electric carrier accumulation is terminated.
One disclosed feature of the embodiments may be described as a process which is usually depicted as a timing chart or timing diagram. A timing diagram may illustrate the timing relationships of several entities, such as signals, events, etc. Although a timing diagram may describe the operations as a sequential process, some operations may be performed in parallel or concurrently. In addition, unless specifically stated, the order of the operations or timing instants may be re-arranged. Furthermore, the timing or temporal distances may not be scaled or depict the timing relationships in exact proportions.
At time t4, the pulses pres and ptx1 becomes a high level, the reset transistor 105 and the transfer transistor 103 are ON, and the photodiode 101 and the floating diffusion vfd are reset to the power source potential vdd. At time t5, the pulse ptx1 becomes a low level, the transfer transistor 103 is OFF, and the reset of the photodiode 101 is terminated. At the same time, the solid-state imaging device is relatively scanned with respect to an original copy, and the electric carrier accumulation period of the next row of the photodiode 101 is started. Following that, the pulse pres becomes a low level, and the reset transistor 105 is OFF.
At time t6, the pulse ptx2 becomes a high level, the transfer transistor 104 is ON, and transfer of the electric carriers from the photodiode 102 to the floating diffusion vfd is started. At time t7, the pulse ptx2 becomes a low level, the transfer transistor 104 is OFF, and the transfer of the electric carriers from the photodiode 102 to the floating diffusion vfd is terminated. The time t7 means the end of the electric carrier accumulation period of the photodiode 102. The period before the time t7 is the electric carrier accumulation period in which the photodiode 102 converts the incident light into the electric carriers, and accumulates the electric carriers. The amplification transistor 106 outputs a voltage according to the electric carriers of the floating diffusion vfd to the output terminal vout through the selection transistor 107.
At time t8, the pulses pres and ptx2 become a high level, the reset transistor 105 and the transfer transistor 104 are ON, and the photodiode 102 and the floating diffusion vfd are reset to the power source potential vdd. At time t9, the pulse ptx2 becomes a low level, the transfer transistor 103 is OFF, and the reset of the photodiode 102 is terminated. At the same time, the solid-state imaging device is relatively scanned with respect to the original copy, and the electric carrier accumulation period of the next row of the photodiode 102 is started.
Following that, the processing of the time t1 and subsequent steps is repeated. One period of the above operation (for example, a period from the time t3 to the next time t3) is a. That is, the period a is a readout period of the electric carriers of the photodiodes 101 and 102. Further, a gap between the electric carrier accumulation end time t3 of the photodiode 101 and the electric carrier accumulation end time t7 of the photodiode 102 is a gap b of timing at which the electric carrier accumulation of the photodiodes 101 and 102 is terminated. The gap b of the timing at which the electric carrier accumulation of the photodiodes 101 and 102 is terminated is also a gap between the electric carrier accumulation start time t5 of the photodiode 101 and the electric carrier accumulation start time t9 of the photodiode 102.
Next, characteristics of image reading using the solid-state imaging device (line sensor) will be described. In the line sensor, imaging positions are shifted between the photodiodes 101 and 102 due to the physical gap (regular interval) y of imaging positions on an original image, of pixels corresponding to the photodiodes 101 and 102. Therefore, in a typical line sensor, a function to correct the gap of the imaging positions with respect to the output images of the photodiodes 101 and 102 may be provided. When the line sensor or the original copy is being moved in the sub-scanning direction, a positional relationship between the photodiodes 101 and 102 is always maintained constant. Therefore, the imaging positions of the pixels on the same time are shifted by the amount corresponding to the interval y. When y is an integral multiple of the pixel pitch x in the main scanning direction (y=n×x, n is an integer of 1 or more), the gap between the imaging positions can be decreased if images are synthesized after being shifted by n×x rows in correction by the processing circuit of a following stage. However, when a gap is caused between the imaging positions of the photodiodes 101 and 102 due to the gap b of the timing at which the electric carrier accumulation of the photodiodes 101 and 102 is terminated, this gap is remained as a component that cannot be removed in the above correction. To be specific, when an imaging range in the readout period a corresponds to the pixel pitch x in the main scanning direction on one-to-one basis, the gap between the imaging positions of the photodiodes 101 and 102 can be expressed by (b/a)×x. A gap of the imaging positions is caused between the photodiodes 101 and 102 by the gap. Note that, here, the electric carrier accumulation period is determined by the pulses ptx1, ptx2, and pres. That is, the gap b of the timing at which the electric carrier accumulation of the photodiodes 101 and 102 is terminated is a gap of operation timing of the transfer transistors 103 and 104, and the reset transistor 105.
Therefore, in the present embodiment, the pixel pitch y in the sub-scanning direction is shifted by the gap (b/a)×x. With the gap of the imaging positions caused due to the shift, the gap of the imaging positions caused due to the gap of timing at which the electric carrier accumulation at the time of sharing pixels is terminated is decreased, whereby the image quality is improved. That is, the pixel pitch y is set to satisfy the relationship expressed by the following formula (1).
y={n+(b/a)}×x (1)
Note that, under the conditions of use of a copier or the like using a real line sensor, there is influence of an aberration and the like that an optical member such as a lens has, as a factor to cause the gap of the imaging positions described above. When considering the influence, a variable c is added to the formula (1), as expressed by the following formula (2).
y={n+(b/a)+c}×x (2)
Here, an absolute value of c is supposed to be a value from 0.1 to 0.15, both inclusive. However, in the present embodiment, y is not changed according to the variable c. Although depending on the specification, the period a and the gap b becomes b/a=0.2 where a=100 μs, and b=20 μs. Effect to reduce the influence of the image gap is substantial by the correction of this b/a.
Further, the pixel cell 110 is not limited to the configuration of two pixel sharing of
y12={n+(b12/a)}×x (3)
y23={n+(b23/a)}×x (4)
Further, a pixel cell 110 having the pixel pitch y (y12, y23) in the sub-scanning direction of an integral multiple of the pixel pitch x in the main scanning direction may be included, depending on operating conditions of the pixels. An example thereof will be described with reference to
Because it is not necessary for the pixel pitch ymr to consider the gap of the imaging positions from a point that the pixel signals of the photodiodes PD_M and PD_R are not used in the same image, the pixel pitch ymr can be set to an integral multiple of the pixel pitch x in the main scanning direction, as expressed by the following formula (5).
ymr=n×x (5)
From a point that the timing of the electric carrier accumulation of the photodiodes PD_R and PD_G coincides with each other according to
yrg=n×x (6)
It is necessary to shift the pixel pitch ygb by the amount corresponding to the gap b of the timing at which the electric carrier accumulation of the photodiodes PD_G and PD_B is terminated, according to
ygb={n+(b/a)}x (7)
As described above, in the present embodiment, the pixel cell 110 having a pixel pitch in the sub-scanning direction of an integral multiple of the pixel pitch x in the main scanning direction can be included depending on the operating conditions of the pixels. By appropriately setting the pixel pitch in the sub-scanning direction, a favorable image with a decreased fixed-pattern noise can be obtained, the noise being caused by the gap of the timing at which the electric carrier accumulation is terminated.
y=(b/a)×x (8)
A pixel pitch y of the present embodiment is different from the first embodiment, and becomes a pixel pitch of when a variable n is 0 in the formula (1), as expressed by the formula (8), and thus the variable n disappears. When considering the first and second embodiments, the variable n of the formula (1) is an integer of 0 or more. When sharing two pixels arrayed in the main scanning direction, by setting the pixel pitch y, like the formula (8), a favorable image with a decreased fixed-pattern noise can be obtained, the noise being caused by a gap of timing at which electric carrier accumulation is terminated. In the present embodiment, in consideration of influence of an aberration and the like that an optical member such as a lens has, a variable c may be added to the formula (8), as expressed by the following formula (9). Here, an absolute value of c is supposed to be a value from 0.1 to 0.15, both inclusive.
y={(b/a)+c}×x (9)
Note that, in the first and second embodiments, examples have been described, in which the memory that holds the electric carriers accumulated by the first and second photoelectric conversion units is a floating diffusion. As another example, the memory may hold the signal, which is output by the amplification transistor 106, based on the electric carriers accumulated by the first and second photoelectric conversion units. That is, the memory is shared by the first and second photoelectric conversion units, and may just have a configuration to hold the electric carriers accumulated by the first and second photoelectric conversion units or the signals based on the electric carriers.
Note that the interval x is the distance between the center of gravity of the photodiode 101 of the pixel cell 110 and the center of gravity of the photodiode 101 included in the adjacent pixel cell 110. As another example, a distance between a left end of the photodiode 101 included in the pixel cell 110 and a left end of the photodiode 101 include in the adjacent pixel cell 110 may be employed as the interval x. Similarly, a distance between a right end of the photodiode 101 included in the pixel cell 110 and a right end of the photodiode 101 included in the adjacent pixel cell 110 may be employed as the interval x.
Further, the interval y is the distance between the center of gravity of the photodiode 101 of the pixel cell 110 and the center of gravity of the photodiode 102 included in the same pixel cell 110. As another example, a distance between an upper end of the photodiode 101 included in the pixel cell 110 and an upper end of the photodiode 102 included in the same pixel cell 110 may be employed as the interval y. Similarly, a distance between a lower end of the photodiode 101 included in the pixel cell 110 and a lower end of the photodiode 102 included in the same pixel cell 110 may be employed as the interval y.
The optical unit 810 that is an optical system such as a lens focuses light from an object on a pixel array 100 of the imaging device 1000, and forms an image of the object. Note that the optical unit 810 can be deleted. The imaging device 1000 outputs a signal according to the light focused on the pixel array 100 at timing based on a signal from the timing control circuit unit 850. The signal output from the imaging device 1000 is input to the video signal processing circuit unit 830 that is a video signal processing unit. The video signal processing circuit unit 830 performs processing such as analog-digital (AD) conversion for the output signal of the imaging device 1000 according to a method determined by a program and the like. A signal generated by the processing in the video signal processing circuit unit 830 is output to the recording/communication unit 840 as image data. The recording/communication unit 840 outputs a signal for forming an image to the reproduction/display unit 870. A moving image and a still image are reproduced and displayed in the reproduction/display unit 870. Further, the recording/communication unit 840 inputs the signal from the video signal processing circuit unit 830, and performs communication with the system control circuit unit 860. In addition, the recording/communication unit 840 performs an operation to record the signal for forming an image on a recording medium (not illustrated).
The system control circuit unit 860 centrally controls the operation of the imaging system 800, and controls driving of the optical unit 810, the timing control circuit unit 850, the recording/communication unit 840, and the reproduction/display unit 870. Further, the system control circuit unit 860 includes a storage device (not illustrated) that is a recording medium, for example, and records programs and the like necessary for controlling the operation of the imaging system 800 in the storage device. Further, the system control circuit unit 860 supplies a signal that switches a drive mode according to an operation of the user, for example. Specific examples include change of a row to be read or a row to be reset, change of a field angle associated with electronic zooming, shift of a field angle associated with an electronic image stabilizing function, and the like. The timing control circuit unit 850 controls drive timing of the imaging device 1000 and the video signal processing circuit unit 830 based on the control of the system control circuit unit 860 as a control unit.
Note that all of the above-described embodiments are mere specific examples for implementing the embodiments, and the technical scope of the disclosure should not be construed by these embodiments in a limited manner. That is, the disclosure can be implemented in various forms without departing from the technical idea or the principal characteristics of the disclosure.
A fixed-pattern noise or color degrading in the sub-scanning direction caused due to the gap of timing at which the electric carrier accumulation of the first and second photoelectric conversion units is terminated can be decreased.
While the disclosure has been described with reference to exemplary embodiments, it is to be understood that the disclosure is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2014-008802, filed Jan. 21, 2014, which is hereby incorporated by reference herein in its entirety.
Number | Date | Country | Kind |
---|---|---|---|
2014-008802 | Jan 2014 | JP | national |