JP2000146527A - Image sensing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the saturation of a signal level and to obtain a better linearity by providing over flow drains(OFDs) and over flow gate(OFG) switches on a CCD image sensing device. SOLUTION: A push-broom scanning sensing apparatus 1 which is mounted on an artificial satellite for example, scans the surface of the ground, and obtains two-dimensional picture images, is provided with OFDs 9 which correspond to each line of photoelectric converting elements 1 and discharge signal charges from the photoelectric elements 1 outside without transferring them to CCDs 2, and OFG switches 10 which transfer the signal charges from the photoelectric elements 1 to the OFDs 9. And a signal light forms an image on a CCD image sensing element 11 by an optical system 5, and the image of a target moves on the CCD element 11 in accordance with the movement of the apparatus. The photoelectric elements 1 are exposed while the target image moves one pitch, and within that exposed time the OFG switches 10 operate in accordance with a set time by an OFG switch driver 12, and generated charges are discharged to the OFDs 9 during that time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a push-bloom scanning type imaging apparatus capable of obtaining a two-dimensional image by scanning the ground surface while traveling over the ground surface at a constant speed, and more particularly to an artificial satellite mounted on the satellite. And suppressing the saturation of the level of the image signal when the ground surface is imaged.

[0002]

2. Description of the Related Art FIG. 4 is a conceptual diagram showing the principle of a push-bloom scanning type imaging device mounted on an artificial satellite for acquiring a two-dimensional image. In the figure, reference numeral 17 denotes an artificial satellite equipped with a push-bloom scanning imaging device, A denotes the direction of movement of the satellite, 18 denotes the observation field of view of the push-bloom scanning imaging device, 19 denotes the ground surface, and 20 denotes the push-bloom scanning imaging device. Is a one-dimensional image on the ground surface obtained by one scan,
Reference numeral 21 denotes a two-dimensional image on the ground obtained as the satellite advances. The image acquired by the push bloom scanning type imaging apparatus in one scan is one-dimensional as shown in FIG. 4, but a two-dimensional image can be obtained by using the motion of the satellite.

FIG. 5 is a block diagram showing one embodiment of a conventional push-bloom scanning type imaging apparatus. In the figure, reference numeral 1 denotes a photoelectric conversion element which is arranged two-dimensionally to form a plurality of rows and columns, and detects signal light from an object to be observed and converts it into an electric signal.
Correspond to each column of the photoelectric conversion elements 1 and are provided in parallel with the traveling direction of the device, and transfer a charge of an output signal from the photoelectric conversion element 1 of each column in a column direction to a first CCD (Cha).
rge Coupled Device), 3 is located at the last stage of the first CCD 2 and is provided with a second CCD provided in a direction perpendicular to the traveling direction of the device, 4 is a photoelectric conversion element 1 and the first CCD 2 , A CCD image pickup device having a second CCD 3, 5 an optical system for introducing signal light to the CCD image pickup device 4, 6 a first CCD driver for driving the first CCD 2, 7 for driving the second CCD 3 A second CCD driver 8 is an image processing device, and B is an arrow indicating the traveling direction of the device.

Next, the operation will be described. In the above configuration, the signal light is imaged on the CCD image pickup device 4 by the optical system 5. At this time, when the apparatus moves in the direction indicated by arrow B in FIG. 5, the target image moves on the CCD image sensor 4 in the direction opposite to the direction of arrow B. The movement direction indicated by arrow B coincides with the movement direction A of the satellite shown in FIG. Now, consider a state in which a target image is located on the photoelectric conversion element 1. The charge generated by the photoelectric conversion element 1 is integrated while the target image moves by one pitch of the photoelectric conversion element 1,
The data is read out to the charge transfer cells in the second row of the adjacent first CCD 2. Next, the target image is the photoelectric conversion element 1 in the second row.
, The charge generated by the photoelectric conversion element 1 is similarly integrated while the target image moves by one pitch of the photoelectric conversion element 1, and is read out to the charge transfer cell on the second row of the adjacent first CCD 2. . At this time, the charges read out to the charge transfer cells in the first row are transferred to the charge transfer cells in the second row first, so that the photoelectric conversion elements 1 in the first row and the second row are transferred. Are added on the charge transfer cells in the second row. By continuously performing the above operations, the charges generated by the photoelectric conversion elements 1 for the number of rows are added on the first CCD 2 while the target image moves on the CCD image pickup device 4. The added charges are input to the second CCD 2 and read out to obtain a one-dimensional image signal. Further, a two-dimensional image signal is obtained by scanning in the traveling direction by the movement of the apparatus itself.

The above operation is performed by TDI (Time Delay)
& Integration). Note that the signal level S of the image signal output is represented by “Equation 1”. In Equation 1, H is the illuminance of the signal light, R is the sensitivity of the photoelectric conversion element 1, Ti is the exposure time, M is the number of rows of the photoelectric conversion element 1, and K is a constant.

[0006]

(Equation 1)

The signal level S is proportional to the product of the illuminance H of the signal light, the sensitivity R of the photoelectric conversion element 1, the exposure time Ti, and the number M of rows of the photoelectric conversion element 1 according to "Equation 1".

[0008]

The conventional device is configured as described above, and by using the TDI operation,
Since the charges generated in the photoelectric conversion elements 1 can be integrated by M for the number of rows, a large signal level can be obtained even when the illuminance of the signal light is small, as shown in "Equation 1". However, when the illuminance of the signal light is large, the charge is
There is a disadvantage that the charge is saturated on the charge transfer cells of the first CCD 2 or the second CCD 3 and the linearity with respect to the illuminance of the signal light of the signal level cannot be obtained.

The present invention has been made to solve such a problem, and an object of the present invention is to provide an imaging apparatus capable of suppressing signal level saturation.

[0010]

According to a first aspect of the present invention, an imaging apparatus includes an OFD (Over Flow Drain) and an OFD.
Set G (Over Flow Gate) switch to CCD
Provided on the image sensor, OFD switch open / close time is OFD
By controlling with a switch driver, the exposure time Ti shown in "Equation 1" is substantially reduced, and a means for suppressing the saturation of the signal level is provided.

In the second invention, the wiring corresponding to the OFD, the OFG switch, the row direction, and each OFG switch is C
By providing an OFG switch selection circuit on the CD image sensor and further opening and closing the OFG switch in units of switches arranged in the row direction, the number M of rows of the photoelectric conversion element 1 shown in "Equation 1" is increased. Is substantially reduced, and means for suppressing the saturation of the signal level is provided.

In the third aspect of the present invention, the first photoelectric conversion element is provided in parallel with the traveling direction of the device, corresponding to each column of the photoelectric conversion elements, and transfers the charge of the output signal from the photoelectric conversion element in each column in the column direction. By providing wiring corresponding to each CCD cell on the CCD image pickup device, and further providing a CCD selection circuit so that the transfer operation of the first CCD can be controlled in units of cells arranged in the row direction. , The number M of rows of the photoelectric conversion elements 1 shown in "Equation 1" is substantially reduced, and means for suppressing the saturation of the signal level is provided.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a diagram showing an example of the embodiment of the present invention, wherein 1 to 3 and 5 to 8 are the same as those of the conventional embodiment. Reference numeral 9 corresponds to each row of the photoelectric conversion elements 1, in order to discharge the electric charge of the output signal from the photoelectric conversion element 1 to the outside without transferring it to the first CCD 2 at a position parallel to the traveling direction of the device. The provided OFD and 10 are provided between the photoelectric conversion element 1 and the OFD 9 and transfer the charge of the output signal from the photoelectric conversion element 1 to the OFD 9.
OFG switch for transferring to 9; 11 for photoelectric conversion element 1
, A first CCD 2, a second CCD 3, and the OFD
Reference numeral 9 denotes a CCD image pickup device provided with the OFG switch 10, and reference numeral 12 denotes an OFG switch driver for driving the OFG switch 10.

Next, the operation will be described. In the above configuration, the signal light is imaged on the CCD image sensor 11 by the optical system 5. At this time, when the apparatus moves in the direction indicated by the arrow B in FIG. 1, the target image moves on the CCD image sensor 11 in a direction opposite to the direction of the arrow B. Now, consider a state in which the target image approaches the photoelectric conversion element 1 in the first row. The charges generated by the photoelectric conversion element 1 are exposed while the target image moves by one pitch of the photoelectric conversion element 1. The exposure time is assumed to be Ti. Within the exposure time Ti, OF
When the OFG switch driver 12 is set to open the G switch 10 only during the time To (To ≦ Ti), the electric charge generated in the photoelectric conversion element 1 is discharged to the OFD 9 during the time To. The charge integrated with Ti-To for the remaining time after the OFG switch 10 is closed is the adjacent first CC.
The data is read out to the charge transfer cells in the first row of D2. Next, when the target image reaches the photoelectric conversion element 1 in the second row, the charge generated by the photoelectric conversion element 1 is integrated with the target image for the time Ti-To in the same manner as in the first row, and the adjacent image is obtained. 1 CCD2
In the second row of charge transfer cells. At this time, the charges read out to the charge transfer cells in the first row are transferred to the charge transfer cells in the second row first, so that the photoelectric conversion elements 1 in the first row and the second row are transferred. Generated charge is the second
The addition is performed on the charge transfer cells in the row. By continuously performing the above operations, the charges generated by the photoelectric conversion elements 1 for the number of rows are added on the first CCD 2 while the target image moves on the CCD image sensor 11.

After addition, the output of each column is
Is input to the transfer cell of the CCD 3 and is read out. The above operation is performed by the CCD image sensor 11. The subsequent operation is the same as that of the conventional device.

Next, a signal level obtained by the device according to the embodiment will be described. Photoelectric conversion element 1
Is equivalent to that of the conventional device and has the same illuminance of the signal light, the signal level output from the present device is expressed by "Equation 2".

[0017]

(Equation 2)

Comparing "Equation 1" and "Equation 2", it can be seen that the signal level of the device obtained in one example of this embodiment is reduced by (Ti-To) / Ti times that of the conventional device.

Further, the saturation level of the first CCD 2 or the second CCD 3 of the device shown in one example of this embodiment is equal to the saturation level of the first CCD 2 or the second CCD 3 of the conventional device. If so, the illuminance range of the signal light that can maintain the linearity of the device obtained in an example of this embodiment is Ti / (Ti-T
o) It turns out that it improves twice.

Embodiment 2 FIG. 2 is a diagram showing an example of the embodiment of the present invention, wherein 1 to 3, 5 to 10, and 12 are the same as the example of the first embodiment. Reference numeral 13 denotes a photoelectric conversion element 1, a first CCD 2, a second CCD 3, and an OFD
9 and a CCD image pickup device having an OFG switch 10 individually wired to a row-direction switch. An OFD 14 can open and close the OFG switches individually in a row-direction arrangement.
This is a G switch selection circuit.

Next, the operation will be described. In the above configuration, the number of arrays of the photoelectric conversion elements 1 in the row direction is assumed to be M, and the OF of the first row to the Nth (N ≦ M) row is assumed.
The G switch is always opened by the OFG switch selection circuit 14, while the OFG in the (N + 1) th row to the Mth row is
The switch shall always be set to the closed state.
Assuming that the target image moves in the same manner as in the example of the first embodiment, all the charges generated in the photoelectric conversion elements 1 in the first to Nth rows are discharged to the OFD 9, and the adjacent first C
It is not read out to the charge transfer cell of CD2. On the other hand,
The exposure time Ti in the photoelectric conversion elements 1 in the + 1st to Mth rows
All the charges generated within are read out to the charge transfer cells of the adjacent first CCD 2.

Through such an operation, the signal finally added on the charge transfer cells of the first CCD 2 in the (N + 1) th to Mth rows is output from the device.

Next, the signal level obtained by the device according to the embodiment will be described. Photoelectric conversion element 1
Is equivalent to that of the conventional apparatus and has the same illuminance of the signal light, the signal level output from the present apparatus is expressed by "Equation 3".

[0024]

(Equation 3)

Comparing "Equation 1" and "Equation 3", it can be seen that the signal level of the device obtained in an example of this embodiment is reduced by (MN) / M times that of the conventional device.

Further, the saturation level of the first CCD 2 or the second CCD 3 of the device shown in one example of this embodiment is equal to the saturation level of the first CCD 2 or the second CCD 3 of the conventional device. If so, it can be seen that the illuminance range of the signal light, which can maintain the linearity of the device obtained in an example of this embodiment, is improved by M / (M-N) times as compared with the conventional device.

Embodiment 3 FIG. 3 is a diagram showing an example of the embodiment of the present invention, wherein 1 to 3 and 5 to 8 are the same as the example of the first embodiment. 15 is a photoelectric conversion element 1;
A CCD image pickup device including a first CCD 2 and a second CCD 3, and a CCD selection switch 16 capable of controlling the transfer operation of the first CCD 2 in units of cells arranged in the row direction.

Next, the operation will be described. In the above configuration, the number of arrays of the photoelectric conversion elements 1 in the row direction is assumed to be M, and the first CCD 2 from the first row to the Nth (N ≦ M) row is operated by the CCD selection switch 16. In the OFF state, on the other hand, the first CCD in the (N + 1) th to Mth rows
2 is set to ON. Assuming that the target image moves in the same manner as in the example of the first embodiment, the charges generated in the photoelectric conversion elements 1 in the first to Nth rows are transferred to the charge transfer cells of the adjacent first CCD 2. Is read,
It is not transferred to the next row of charge transfer cells. On the other hand, the Nth
The charges generated in the photoelectric conversion elements 1 in the first to Mth rows are read out to the charge transfer cells of the adjacent first CCD 2 and added on the charge transfer cells.

Through such an operation, finally, a signal added on the charge transfer cells of the first CCD 2 in the (N + 1) th row to the Mth row is output from the device.

Next, a signal level obtained by the apparatus according to the embodiment will be described. Photoelectric conversion element 1
Is the same as that of the conventional apparatus and the illuminance of the signal light is the same, the signal level output from the present apparatus is expressed by "Equation 3" as in the second embodiment. That is, it can be seen that the signal level of the device obtained in an example of this embodiment is reduced by (MN) / M times as compared with the conventional device.

Further, the saturation level of the first CCD 2 or the second CCD 3 of the device shown in an example of this embodiment is equal to the saturation level of the first CCD 2 or the second CCD 3 of the conventional device. Then, it can be seen that the illuminance range of the signal light, which can maintain the linearity of the device obtained in an example of this embodiment, is improved by M / (M−N) times compared to the conventional device.

[0032]

As described above, according to the first invention, O
FD and OFG switches are provided on the CCD
By controlling the opening / closing time of the G switch by the OFD switch driver, the saturation of the signal level can be suppressed, so that there is an effect that sufficient linearity can be obtained even when the illuminance of the signal light is large.

According to the second invention, OFD and OF
By providing wiring corresponding to the G switch and the row direction and each OFG switch on the CCD image pickup device, and providing the OFG switch selection circuit so that the opening and closing of the OFG switch can be performed in units of switches arranged in the row direction. Since the saturation of the signal level can be suppressed, sufficient linearity can be obtained even when the illuminance of the signal light is large.

Further, according to the third aspect of the present invention, the electric charge of the output signal from the photoelectric conversion element of each column is provided in the column direction corresponding to each column of the photoelectric conversion element and provided in parallel with the traveling direction of the device. The wiring corresponding to each cell of the first CCD to be transferred is C
The signal level saturation can be suppressed by providing a CCD selection circuit provided on the CD imaging device and further providing a CCD selection circuit so that the transfer operation of the first CCD can be controlled in units of cells arranged in the row direction. Therefore, there is an effect that sufficient linearity can be obtained even when the illuminance of the signal light is large.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a second embodiment of the present invention.

FIG. 3 is a diagram showing a third embodiment of the present invention.

FIG. 4 is a diagram showing a concept of a push-bloom scanning type imaging device mounted on an artificial satellite for obtaining a two-dimensional image.

FIG. 5 is a diagram showing a configuration of a conventional push-bloom scanning type imaging apparatus.

[Explanation of symbols]

1 photoelectric conversion element, 2 first CCD, 3 second CC
D, 4 CCD image sensor, 5 optical system, 6 first CC
D driver, 7 second CCD driver, 8 image processing device, 9 OFD, 10 OFG switch, 11 CCD
Image sensor, 12 OFG switch driver, 13 CC
D imaging device, 14 OFG switch selection circuit, 15 CCD imaging device according to the third invention, 16 CCD selection switch, 17 artificial satellite, 18 observation field of view, 19 ground surface,
20 One-dimensional image on the ground, 21 Two-dimensional image on the ground, A satellite's motion direction, B device's traveling direction.

Claims (3)

[Claims] 1. A photoelectric conversion element which is arranged two-dimensionally to form a plurality of rows and columns, detects signal light from an object to be observed and converts it into an electric signal, and corresponds to each column of said photoelectric conversion element. , A first CC that is provided in parallel with the traveling direction of the device and transfers the charge of the output signal from the photoelectric conversion element in each column in the column direction.
D (Charge Coupled Device),
A second CCD positioned at the last stage of the first CCD and provided in a direction orthogonal to the traveling direction of the device, a position corresponding to each row of the photoelectric conversion elements and parallel to the traveling direction of the device; OFD (Over Fl) provided for discharging the charge of the output signal from the photoelectric conversion element to the outside.
ow drain), an OFG (Over Flow) provided between the photoelectric conversion element and the OFD and having a function of transferring a charge of an output signal from the photoelectric conversion element to the OFD and adjusting an exposure time of the photoelectric conversion element. Gat
e) a CCD image sensor having a switch, an optical system for introducing signal light to the CCD image sensor, and the first CCD
A first CCD driver for driving the second CCD and the second CCD
, A second CCD driver for driving the OFG switch, and a second CCD driver for driving the OFG switch.
An image pickup apparatus comprising: an image processing apparatus that performs A / D conversion of an image signal output from a CD. 2. A photoelectric conversion element which is arranged two-dimensionally to form a plurality of rows and columns, detects signal light from an object to be observed, and converts the signal light into an electric signal, and corresponds to each column of the photoelectric conversion element. , A first CC that is provided in parallel with the traveling direction of the device and transfers the charge of the output signal from the photoelectric conversion element in each column in the column direction.
D (Charge Coupled Device),
A second CCD positioned at the last stage of the first CCD and provided in a direction orthogonal to the traveling direction of the device, a position corresponding to each row of the photoelectric conversion elements and parallel to the traveling direction of the device; The charge of the output signal from the photoelectric conversion element,
OFD provided for discharging to the outside (Over F
low Drain), the photoelectric conversion element and the OFD
And an OFG (Over Flow Ga) having a function of transferring the charge of the output signal from the photoelectric conversion element to the OFD and adjusting the exposure time of the photoelectric conversion element.
te) a CCD image sensor having a switch, an optical system for introducing signal light into the CCD image sensor, and the first CC
D, a first CCD driver for driving D,
D, a second CCD driver for driving the OFG switch, an OFG switch driver for driving the OFG switch,
An OFG switch selection circuit for selecting the drive to the switch corresponding to each row by an external command and setting the exposure time of the selected photoelectric conversion element to 0, and the A of the image signal output from the second CCD. An image pickup apparatus comprising: an image processing apparatus that performs / D conversion. 3. A photoelectric conversion element which is arranged two-dimensionally to form a plurality of rows and columns, detects signal light from an object to be observed and converts it into an electric signal, and corresponds to each column of the photoelectric conversion element. , A first CC that is provided in parallel with the traveling direction of the device and transfers the charge of the output signal from the photoelectric conversion element in each column in the column direction.
D (Charge Coupled Device),
A second CCD that is located at the last stage of the first CCD and that is provided in a direction orthogonal to the traveling direction of the device;
A CD imaging device, an optical system for introducing signal light into the CCD imaging device, and a first CCD for driving the first CCD
A driver and a CCD selection switch for selecting the driving of the first CCD corresponding to each row by an external command, and restricting the transfer of electric charges in the selected CCD, and driving the second CCD. An imaging apparatus comprising: a second CCD driver; and an image processing device that performs A / D conversion of an image signal output from the second CCD.