JP5135613B2 - Image sensor and imaging apparatus using the same - Google Patents

Description

  The present invention relates to an image sensor and an image pickup apparatus using the same, and more particularly to an image sensor used in a field such as remote sensing and an image pickup apparatus using the same.

  2. Description of the Related Art In recent years, a large number of image sensors have been developed in which a large number of pixels (photodetectors) are arranged in an array on a semiconductor substrate and a signal charge readout circuit and an output amplifier are provided on the same substrate. In remote sensing, an image sensor in which pixels are arranged in a one-dimensional array is mounted on an artificial satellite or the like, and a two-dimensional image of the ground surface is photographed by making the direction perpendicular to the pixel array coincide with the traveling direction of the satellite. In order to improve the image resolution, it is desirable to make the pixel pitch as small as possible. However, if the pixel pitch is reduced, the amount of light incident on the pixel is reduced by the amount that the area of the pixel is reduced, and the S / N deteriorates.

  As a clever means for improving the S / N, a TDI (Time Delay and Integration) image sensor has been developed. The TDI system is a CCD (Charge Coupled Devices) image sensor readout system that improves S / N by synchronizing the charge transfer timing with the movement timing of the subject image. As the CCD, an FFT (Full Frame Transfer) type CCD which is a two-dimensional image sensor is used. In the case of remote sensing, the TDI operation can be realized by matching the charge transfer speed in the vertical direction of the CCD with the moving speed of the satellite. When the M-stage TDI operation is performed by the vertical CCD, the accumulation time is effectively M times, so that the sensitivity is improved M times and the S / N is improved to √M times.

  In the TDI type image sensor, so-called bidirectional TDI is proposed in which the charge transfer direction is switched between the forward direction and the reverse direction (see, for example, Patent Document 1). In this image sensor, the number of TDI stages can be switched by controlling the switching position between the forward direction and the reverse direction in the charge transfer direction by a vertical transfer clock applied from the outside.

JP 11-298805 A

  However, in remote sensing, if it is attempted to photograph a plurality of points sequentially while moving at high speed, it is difficult to match the moving direction of the subject image with the vertical direction of the pixel array. If an angle shift occurs in both directions, the image resolution is significantly degraded. For this reason, conventionally, it is necessary to perform imaging after controlling the attitude of the satellite to match both directions, and the number of points that can be photographed is limited.

  The TDI image sensor disclosed in Patent Document 1 switches the charge transfer direction in two ways, but the charge transfer direction is limited to only the forward direction and the reverse direction. Therefore, with this image sensor, it is not possible to compensate for the angular deviation between the moving direction of the subject image and the vertical direction of the pixel array, and it is not possible to significantly increase the number of imaging points.

  Therefore, a main object of the present invention is to provide an image sensor capable of obtaining a high image resolution even when the moving direction of the subject image does not coincide with the vertical direction of the pixel array.

  The image sensor according to the present invention includes a pixel array including a plurality of pixel blocks arranged in the vertical direction. Each pixel block includes a plurality of pixels arranged in the horizontal direction. The odd-numbered pixel block and the even-numbered pixel block are shifted in the horizontal direction by a predetermined distance so that each pixel of each pixel block faces two pixels of the next-stage pixel block. The image sensor is further provided between each two adjacent pixel blocks, and the signal charge from each pixel of the preceding pixel block is transferred to any of the two pixels of the next pixel block facing the pixel. A charge distribution unit for selectively transmitting to one of the pixels is provided.

  In the image sensor according to the present invention, a plurality of pixel blocks are arranged in the vertical direction, and the odd-numbered pixel blocks and the even-numbered pixel blocks are arranged so that each pixel of each pixel block faces two pixels of the next-stage pixel block. The pixel blocks are horizontally displaced by a predetermined distance, a charge distribution unit is provided between each adjacent two pixel blocks, and signal charges from each pixel of the previous pixel block are transferred to the two pixel blocks of the next pixel block. This is selectively transmitted to one of the pixels. Therefore, even when the moving direction of the subject image does not coincide with the vertical direction of the pixel array, the signal charge transfer direction can be made coincident with the moving direction of the subject image, and a high image resolution can be obtained.

1 is a block diagram illustrating a configuration of a TDI image sensor according to Embodiment 1 of the present invention. It is a figure which shows the principal part of the TDI system image sensor shown in FIG. 3 is a time chart showing the operation of the charge distribution unit shown in FIG. 2. FIG. 3 is a diagram illustrating an operation of a charge distribution unit illustrated in FIG. 2. FIG. 10 is another diagram showing the operation of the charge distribution unit shown in FIG. 2. FIG. 10 is still another diagram illustrating the operation of the charge distribution unit illustrated in FIG. 2. FIG. 10 is still another diagram illustrating the operation of the charge distribution unit illustrated in FIG. 2. It is a block diagram which shows the structure of the imaging device by Embodiment 2 of this invention.

[Embodiment 1]
The TDI image sensor according to Embodiment 1 of the present application is formed on the surface of a silicon substrate, and includes a pixel array 1 as shown in FIG. The pixel array 1 includes n (where n is an integer of 2 or more) pixel blocks BK1 to BKn arranged in the vertical direction (vertical direction in FIG. 1). Each pixel block BK includes a plurality of pixels 2 arranged in a plurality of rows (three rows in FIG. 1) and a plurality of columns. The plurality of pixels 2 in each pixel row are arranged in the horizontal direction (left-right direction in FIG. 1) at a predetermined pixel pitch. The plurality of pixels 2 in each pixel column are arranged in the vertical direction (vertical direction in FIG. 1) at a predetermined pixel pitch. Each pixel 2 generates an amount of charge corresponding to the incident light intensity. The signal charge generated in each pixel 2 is sequentially transferred to the pixel 2 on the downstream side (lower side in FIG. 1) in the column direction.

  The pixels 2 of the odd-numbered pixel blocks BK1, BK3,... And the pixels 2 of the even-numbered pixel blocks BK2, BK4,... Are shifted from each other in the horizontal direction by a half pitch of the pixel pitch. . Therefore, each pixel 2 in the last pixel row of each pixel block BK is opposed to two pixels 2 in the first pixel row of the next pixel block (lower side in FIG. 1).

  In addition, charge distribution units CS1 to CSn-1 are provided between the pixel blocks BK1 to BKn, respectively. Each charge distributing unit CS converts the signal charge from each pixel 2 in the last row of the previous pixel block BK to one of the two corresponding pixels 2 in the first pixel row in the next pixel block BK. Selectively transfer to pixel 2.

  Further, a charge storage unit 3, a horizontal CCD 4, and an output amplifier 5 are provided adjacent to the final pixel block BKn. When light enters the pixel 2, an amount of electric charge corresponding to the incident light intensity is generated in the pixel 2. The signal charge generated in the pixel 2 passes through the pixel block BK and the charge distribution unit CS alternately, and is transferred in the vertical direction (downward in FIG. 1) toward the charge storage unit 3, and then from the charge storage unit 3. It is transferred to the horizontal CCD 4, further transferred in the horizontal direction (right direction in FIG. 1) by the horizontal CCD 4, and output from the output amplifier 5.

  FIG. 2 is a diagram showing a main part of the TDI type image sensor shown in FIG. In FIG. 2, for simplification of the drawing, seven pixel blocks BK1 to BK7 and six charge distribution units CS1 to CS6 are shown. In each pixel block BK, only one pixel row is shown. In FIG. 2, a rectangular area surrounded by a thick frame line corresponds to one pixel 2, and a horizontally long band-shaped area surrounded by a thick frame line corresponds to one charge distribution unit CS.

  A plurality of (three in FIG. 2) vertical transfer electrodes (polysilicon gates) 6 are commonly provided in the pixel row of each pixel block BK. Each vertical transfer electrode 6 extends in the horizontal direction, and the three vertical transfer electrodes 6 are arranged adjacent to each other in the vertical direction. Each charge distribution unit CS is provided with two distribution electrodes (polysilicon gates) 7 corresponding to the respective pixels 2. In other words, each charge distribution unit CS is provided with twice as many distribution electrodes 7 as the pixels 2 belonging to one pixel row. The plurality of distribution electrodes 7 of each charge distribution unit CS are arranged at a pitch of half the pixel pitch in the horizontal direction.

  In FIG. 2, the shaded area is the vertical transfer channel 8 formed in the silicon substrate. The vertical transfer channel 8 is formed below the three vertical transfer electrodes 6 corresponding to each pixel 2 in each pixel block BK. The vertical transfer channel 8 corresponding to each pixel 2 is separated from the vertical transfer channel 8 corresponding to the pixel 2 adjacent in the horizontal direction. Further, the vertical transfer channel 8 is formed below the sorting electrode 7 corresponding to each sorting electrode 7 in each charge sorting unit CS. The vertical transfer channel 8 corresponding to each distribution electrode 7 is connected to the vertical transfer channel 8 corresponding to the pixel 2 in the previous stage and the subsequent stage.

  In addition, input pins P1 to P3 are provided in common to the pixel blocks BK1 to BK7. The first (first top in FIG. 2) vertical transfer electrode 6 of each pixel block BK is connected to the input pin P <b> 1 through the contact hole 10 and the metal wiring 11. The second vertical transfer electrode 6 of each pixel block BK is connected to the input pin P2 via the contact hole 10 and the metal wiring 11. The third vertical transfer electrode 6 of each pixel block BK is connected to the input pin P3 through the contact hole 10 and the metal wiring 11. Clock signals φT1 to φT3 are externally applied to the input pins P1 to P3, respectively.

  Further, input pins P11a to P16a are provided corresponding to the odd-numbered distribution electrodes 7 of the charge distribution units CS1 to CS6, respectively, and input pins P11b corresponding to the even-numbered distribution electrodes 7 of the charge distribution units CS1 to CS6, respectively. To P16b are provided. The odd-numbered sorting electrode 7 of each charge sorting section (for example, CS1) is connected to the corresponding input pin (in this case P11a) via the contact hole 12 and the metal wiring 13. Even-numbered sorting electrodes 7 of each charge sorting section (for example, CS1) are connected to corresponding input pins (in this case, P11b) through contact holes 12 and metal wirings 13. Clock signals φL1 to φL6 can be externally applied to the input pins P11a to 16a, respectively. Clock signals φR1 to φR6 are externally applied to the input pins P11b to 16b, respectively.

  FIG. 3A is a time chart showing the waveforms of the clock signals φT1 to φT3, φR, and φL when the charges are distributed to the right, and FIG. 3B is a clock signal φT1 to φT3 when the charges are distributed to the left. It is a time chart which shows the waveform of (phi) R and (phi) L. The clock signals φT1 to φT3, φR (or φL) are the same as the vertical transfer clock signal supplied to the four-phase drive CCD, but the way of supplying the clock signal depends on whether the charge is transferred to the left or right by the charge distribution unit CS. Is different. That is, when distributing the charge to the right in FIG. 2, the clock signal φR is activated and the clock signal φL is fixed to the “L” level, and when distributing the charge to the left in FIG. The clock signal φR is fixed to “L” level while being activated.

  Next, the charge transfer operation of this image sensor will be described. In a CCD, a potential well is formed in a transfer channel below a transfer electrode to which an “H” level signal is applied, and signal charges are accumulated in the potential well. In FIG. 3A, when the clock signals φT1 and φT2 are both set to the “H” level, a potential well is formed in the vertical transfer channel 8 below the first and second vertical transfer electrodes 6 of each pixel block BK. The signal charge is accumulated in the potential well.

  Next, when the clock signals φT2 and φT3 are both set to the “H” level, a potential well is formed in the vertical transfer channel 8 below the second and third vertical transfer electrodes 6 of each pixel block BK. As the signal moves, the signal charge moves. Next, when the clock signals φT3 and φR are both set to the “H” level, the vertical transfer channel below the third vertical transfer electrode 6 of each pixel block BK and the even-numbered distribution electrodes 7 of the charge distribution unit CS. 8, a potential well is formed. At this time, since the clock signal φL is fixed at the “L” level, no potential well is formed under each odd-numbered distribution electrode 7 of the charge distribution unit CS. Accordingly, the signal charges move below the third vertical transfer electrode 6 of each pixel block BK and the even-numbered distribution electrodes 7 of the charge distribution unit CS.

  Next, when both the clock signals φR and φT1 are set to the “H” level, the vertical transfer channel below the even-numbered distribution electrodes 7 of the charge distribution unit CS and the first vertical transfer electrode 6 of each pixel block BK. 8, a potential well is formed, and the signal charge moves as the potential well moves. When the drive clock shown in FIG. 3A is given by the above series of transfer operations, the signal charge generated in the pixel 2 is transferred to the lower right pixel 2 via the charge distributing unit CS.

  Similarly, in FIG. 3B, when the clock signals φT1 and φT2 are both set to the “H” level, the potential is applied to the vertical transfer channel 8 below the first and second vertical transfer electrodes 6 of each pixel block BK. A well is formed, and signal charges are accumulated in the potential well.

  Next, when the clock signals φT2 and φT3 are both set to the “H” level, a potential well is formed in the vertical transfer channel 8 below the second and third vertical transfer electrodes 6 of each pixel block BK. As the signal moves, the signal charge moves. Next, when the clock signals φT3 and φL are both set to the “H” level, the vertical transfer channel below the third vertical transfer electrode 6 of each pixel block BK and the odd-numbered distribution electrodes 7 of the charge distribution unit CS. 8, a potential well is formed. At this time, since the clock signal φR is fixed at the “L” level, no potential well is formed under each even-numbered distribution electrode 7 of the charge distribution unit CS. Therefore, the signal charge moves below the third vertical transfer electrode 6 of each pixel block BK and the odd-numbered distribution electrodes 7 of the charge distribution unit CS.

  Next, when both of the clock signals φL and φT1 are set to the “H” level, the vertical transfer channel below each odd-numbered distribution electrode 7 of the charge distribution unit CS and the first vertical transfer electrode 6 of each pixel block BK. 8, a potential well is formed, and the signal charge moves as the potential well moves. When the drive clock shown in FIG. 3B is given by the above series of transfer operations, the signal charge generated in the pixel 2 is transferred to the lower left pixel 2 via the charge distributing unit CS.

  The clock signals φR and φL are set independently for each charge distribution unit CS. Depending on how the clock signals φR1 to φR6 and φL1 to φL6 are combined, the charge transfer direction (angle) when performing the TDI transfer can be changed.

  4 to 7 are diagrams showing a charge transfer method of the TDI image sensor shown in FIGS. 4 to 7, nine pixel blocks BK1 to BK9 and eight charge distribution units CS1 to CS8 are shown for the sake of simplicity. In each pixel block BK, only two pixel rows are shown.

  In FIG. 4, clock signals φR1, φL2, φR3, φL4, φR5, φL6, φR7, and φL8 are input to the charge distributing units CS1 to CS8, respectively. Clock signals φL1, φR2, φL3, φR4, φL5, φR6, φL7, and φR8 are all fixed at the “L” level. In this case, the charge distribution units CS1 to CS8 distribute the signal charges from the preceding pixel blocks BK1 to BK8 to the right, left, right, left, right, left, right, and left, respectively. For this reason, the signal charge moves while meandering through the path indicated by the arrow in FIG. 4, and the transfer direction of the signal charge is the vertical direction of the pixel array 1 (downward direction in FIG. 4) as a whole.

  In FIG. 5, clock signals φR1, φR2, φL3, φR4, φR5, φL6, φR7, and φR8 are input to the charge distributing units CS1 to CS8, respectively. Clock signals φL1, φL2, φR3, φL4, φL5, φR6, φL7, and φL8 are all fixed at the “L” level. In this case, the charge distribution units CS1 to CS8 distribute the signal charges from the preceding pixel blocks BK1 to BK8 to the right, right, left, right, right, left, right, and right, respectively. In this case, since the distribution is performed twice on the right and once on the left, the signal charge transfer direction as a whole is diagonally lower right in FIG.

  In FIG. 6, clock signals φR1 to φR3, φL4, φR5 to φR7, and φL8 are input to the charge distributing units CS1 to CS8, respectively. Clock signals φL1 to φL3, φR4, φL5 to φL7, and φR8 are all fixed at “L” level. In this case, the charge distribution units CS1 to CS8 distribute the signal charges from the preceding pixel blocks BK1 to BK8 to the right, right, right, left, right, right, right, and left, respectively. In this case, since the distribution is performed three times to the right and one time to the left, the transfer direction of the signal charge is diagonally lower right in FIG. 6 as much as the frequency of distribution in the right direction is higher.

  In FIG. 7, clock signals φR1 to φR8 are input to the charge distributing units CS1 to CS8, respectively. Clock signals φL1 to φL8 are all fixed at “L” level. In this case, the charge distribution units CS1 to CS8 all distribute signal charges from the preceding pixel blocks BK1 to BK8 to the right. In this case, since the distribution to the right is repeated, the transfer direction of the signal charge is diagonally lower right in FIG. The arrows in FIGS. 4 to 7 represent the charge transfer paths, and the angle at which the transfer direction is bent in the order of FIGS. 4 to 7 increases. Although FIGS. 4 to 7 show the case where the transfer direction is bent to the right, the transfer direction is bent to the left if the symbols R and L indicating the clock signal are interchanged.

  In the first embodiment, the pixel array 1 is divided into a plurality of pixel blocks BK, a charge distribution unit CS is provided between each two adjacent pixel blocks BK, and signal charges from the pixels 2 of the preceding pixel block BK are provided. Is selectively transmitted to one of the two pixels 2 of the pixel block BK at the next stage. Therefore, even when the moving direction of the subject image does not coincide with the column direction of the pixel array 1, the signal charge transfer direction can be made coincident with the moving direction of the subject image, and a high image resolution can be obtained.

  In general, visible image sensors include a front-side incident type sensor that uses light from a subject incident from the front side of the element, and a back-side incident type sensor that allows light to enter from the back side of the element. The TDI image sensor according to the first embodiment of the present invention can be applied to both front-illuminated and back-illuminated sensors. However, when a large number of metal wirings to the charge distributing unit CS are required, a larger pixel aperture ratio can be obtained by using the back-illuminated type.

[Embodiment 2]
FIG. 8 is a block diagram showing a configuration of an imaging apparatus according to Embodiment 2 of the present invention. In FIG. 8, the imaging apparatus includes a TDI image sensor 20, a control circuit 21, and a detection device 22. The TDI image sensor 20 is the same as the TDI image sensor shown in FIGS. The detection device 22 detects the moving direction of the subject image projected on the pixel array 1 of the TDI image sensor 20. As a method of detecting the moving direction of the subject image, a method of calculating from the information on the moving direction of the satellite and the direction of the imaging system obtained from a gyro sensor or the like, or another two-dimensional image sensor installed on the focal plane of the imaging system There is a method of using image information.

  The control circuit 21 generates clock signals φT1 to φT3, φR, and φL based on the detection result of the detection device 22, and matches the movement direction of the subject image projected on the pixel array 1 and the charge transfer direction (angle). Let In addition, when the charge is transferred obliquely downward, the control circuit 21 finely adjusts the cycle of the clock signals φT1 to φT3 when the transfer direction bend is large (see FIGS. 5 to 7). Reduces resolution degradation. In this case, when the charge is transferred in the vertical direction (see FIG. 4), the transfer cycle may be set to T / cos θ, where T is the vertical transfer cycle and θ is the bending angle in the transfer direction.

  In the second embodiment, even when the moving direction of the subject image as the satellite travels does not coincide with the column direction of the pixel array 1, the transfer direction of the signal charge can be matched with the moving direction of the subject image. Deterioration can be prevented. As a result, when a plurality of points are to be photographed sequentially, it is not necessary to make the moving direction of the subject image completely coincide with the vertical direction of the pixel array 1, so that the required accuracy for the attitude control of the satellite is relaxed and the points can be photographed. The number of increases significantly.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  1 pixel array, 2 pixels, 3 charge storage unit, 4 horizontal CCD, 5 output amplifier, 6 vertical transfer electrode, 7 distribution electrode, 8 vertical transfer channel, 10, 12 contact hole, 11, 13 metal wiring, 20 TDI image Sensor, 21 control circuit, 22 detector, BK pixel block, CS charge distribution unit, P input pin.

Claims (4)

A pixel array including a plurality of pixel blocks arranged in a vertical direction,
Each pixel block includes a plurality of pixels arranged in a horizontal direction,
The odd-numbered pixel block and the even-numbered pixel block are arranged so as to be shifted in the horizontal direction by a predetermined distance so that each pixel of each pixel block faces two pixels of the next-stage pixel block.
Further, provided between each two adjacent pixel blocks, signal charges from each pixel in the previous pixel block are transferred to one of the two pixels in the next pixel block facing the pixel. An image sensor comprising a charge distribution unit for selectively transmitting. A plurality of charge distribution units,
The image sensor according to claim 1, wherein each charge distribution unit operates independently of other charge distribution units. An image sensor according to claim 2;
A detection device for detecting a moving direction of a subject image projected on the pixel array;
An image pickup apparatus comprising: a control circuit that controls each charge distribution unit so that a moving direction of the subject image and a signal charge transfer direction in the pixel array coincide with each other based on a detection result of the detection apparatus.   The imaging device according to claim 3, wherein the control circuit controls a transfer rate of the signal charge according to a transfer direction of the signal charge.

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