JPH0690406A - Solid-state image pickup element - Google Patents

Abstract

PURPOSE:To prevent unnecessary electric charge from being not completely discharged in the vertical blanking period at the time of sweeping out unnecessary electric charge in vertical transfer registers through a horizontal driving register with respect to the CCD solid-state image pickup element. CONSTITUTION:With respect to the solid-state image pickup element provided with plural photodetectors arranged in a matrix, vertical transfer registers corresponding to respective columns of these photodetectors, and a horizontal transfer register, the vertical overflow function (refer to potential state 18) is given to the horizontal transfer register 4, and unnecessary electric charge in vertical transfer registers is discharged to an output part from the horizontal transfer register 4, and the quantity of electric charge exceeding the quantity of electric charge handled by the horizontal transfer register out of unnecessary electric charge is discharged to the substrate side through the vertical overflow function.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image pickup device such as a CCD image sensor.

[0002]

2. Description of the Related Art As a CCD solid-state image pickup device, a FIT (frame interline transfer) type CCD solid-state image pickup device is known. This FIT type CCD solid-state image pickup device has a plurality of light receiving elements (pixels) arranged in a matrix and a vertical transfer register having a CCD structure corresponding to each vertical column of the light receiving elements, and the image pickup section. Each of the vertical transfer registers has a plurality of vertical transfer registers corresponding to each vertical transfer register, and a horizontal transfer register disposed below the storage unit. After being read out to the transfer register, it is once transferred to the accumulating unit, and then the signal charge is transferred from the accumulating unit to the horizontal transfer register for each line, transferred in the horizontal transfer register, and the signal is output from the output unit. To be done.

Signal reading of the FIT type CCD solid-state image pickup device generally includes field reading and frame reading.

Field reading is as shown in FIG.
The signal of two light receiving elements (pixels) 6 that are continuous in the vertical direction.
Vertical transfer of signal charge once in 1/60 second (1 field)
Read to register, mix in vertical transfer register and drop
This is a read method that performs direct transfer. In the first field
Line Y₁And Y₂, Line Y₃And Y_FourTwo recipients
The signal charges of the optical signal are added, and in the second field, the light charges are added.
Y₂And Y₃, Line Y_FourAnd Y_Five, ... Two light-receiving elements
The signal charges of the child are added. Figure 8: Field reading
It shows the spatial spread of the signal in motion,₁Is
First field, E ₁Indicates the second field. Fee
The characteristic of the field readout is the time taken to sample the signal.
Since it is 1/60 second, the dynamic resolution is high,
The signal charges for two pixels in the vertical direction are mixed.
Therefore, the vertical resolution is reduced.

For frame reading, as shown in FIG.
This is a readout method in which the signal charges of every other light receiving element (pixel) 6 are read out and transferred once every 1/30 second (one frame). That is, the signal charges of the light receiving elements 6 on the lines Y ₁ , Y ₃ , Y _5, ... Are read in the first field, and the lines Y ₂ , Y ₄ , Y _{6 ,.}
The signal charge of the light receiving element 6 is read out. FIG. 11 shows the spatial spread of the signal in the frame read operation. O ₂ shows the first field and E ₂ shows the second field. In this frame reading, since the signal charges of each pixel are not mixed, the vertical resolution does not deteriorate, but on the other hand, the reading is done once every 1/30 second, so for a fast-moving subject. An afterimage called a frame afterimage appears.

On the other hand, in order to improve the vertical resolution of the FIT type CCD solid-state image pickup device, a third read operation method has been proposed in which the read operation is performed in the intermediate operation between the field read and the frame read. In the third read operation method, as shown in FIG. 5, the photosensing elements on the odd and even lines have a difference in sensitivity, which is inverted for each field, and the signal charges of the photosensors 6 on two lines are added. It is then read out. In FIG. 5, the exposure time of one light receiving element 6 is set to 1/60 seconds, and the exposure time of the other light receiving element is set to a shorter time, for example, 1/120 seconds, and signal charges of both light receiving elements 6 are added and read.

That is, in the first field, the exposure time of the light receiving elements on the odd lines is 1/120 seconds, and the exposure time of the light receiving elements on the even lines is 1/60 seconds, so that the lines Y ₁ and Y ₂ ,
The signal charges of the two light receiving elements Y ₃ and Y ₄ , ... Are added, and in the second field, the exposure time of the light receiving elements of the odd lines is set to 1/60 seconds, and the exposure time of the light receiving elements of the even lines is set to 1 / 120 seconds as lines Y ₂ and Y ₃ , Y ₄ and Y ₅ ,
The signal charges of the two light receiving elements are added. In this way, the frame afterimage does not appear in order to read in 1/60 seconds, and the component of the signal obtained by mixing two vertically continuous pixels is dominated by the pixel having an exposure time of 1/60 seconds. As a result, the state where the signals of two pixels are not mixed is approached, and the vertical resolution is improved. FIG. 6 shows the spatial spread of the signal in this read operation.
O ₃ indicates the first field and E ₃ indicates the second field.

By the way, in the FIT type CCD solid-state image pickup device, the unnecessary charges discarded in the vertical transfer register before reading the original signal charges must not be mixed with the original signal charges. In a normal operation, an operation called high-speed sweep-out transfer is performed to discharge unnecessary charges in the vertical transfer register before reading and performing the operation. Heretofore, various methods have been used to discharge this unnecessary charge.

[0009]

As a method of discharging the unnecessary charges in the vertical transfer register, for example, the unnecessary charges are discharged to the horizontal transfer register side, and the horizontal transfer register performs the horizontal transfer at a normal speed or faster. There is a method of discharging to the output side.

However, in the case of this method, if the amount of unnecessary charges discharged to the horizontal transfer register is too large and the amount of charges handled by the horizontal transfer register is exceeded, the unnecessary charges can be sufficiently transferred by the horizontal transfer register. . If the unnecessary charge is within the amount of charge handled by the horizontal transfer register, the time required to discharge it is one scan line period (the time required to transfer from end to end of the horizontal transfer register). However, in this discharging operation, unnecessary charges larger than the amount of charges handled by the horizontal transfer register may be transferred to the horizontal transfer register. In that case, in the horizontal transfer register,
In the scan line period, the discharge is insufficient and requires a lot of time. If this discharge is not completed within the vertical blanking period, unnecessary charges that cannot be completely discharged will be mixed into the video signal.

In order to avoid this, there is also a method in which a drain portion (smear drain) is provided below the horizontal transfer register and unnecessary charges that cannot be handled by the horizontal transfer register are discharged to this drain portion. in this way,
(A) Since the drain part is provided near the horizontal transfer register, the potential of the drain part becomes deep, which may cause breakdown. (B) Horizontal transfer for complete discharge to the drain part. There is a problem that a gate needs to be provided between the register and the drain portion, and the number of necessary clock pulses increases.

In addition, as a method for discharging unnecessary charges in the vertical transfer register, a method is provided in which a drain section is provided on the side opposite to the output section side of the horizontal transfer register and the horizontal transfer register is reversely transferred to discharge unnecessary charges. Alternatively, there is also a method in which the vertical transfer register is reversely transferred and a drain part is provided on the upper side of the imaging unit (the side opposite to the horizontal transfer register) to discharge unnecessary charges. However, these methods also have the same problems as described above.

On the other hand, when there is a signal charge that exceeds the amount of charge handled by the horizontal transfer register during normal signal charge transfer (so-called large light amount), the surplus charge overflows in the horizontal direction and the screen flow. May occur.

In view of the above-mentioned point, the present invention makes it possible to discharge excess charges and properly transfer charges in the horizontal transfer register even when charges exceeding the handled charge amount are transferred to the horizontal transfer register. A solid-state imaging device is provided.

[0015]

According to the present invention, a plurality of light receiving elements 6 arranged in a matrix, a vertical transfer register 7 corresponding to each column of the light receiving elements 6, and a horizontal transfer register 4 are provided.
In the solid-state image sensor having the above, the horizontal transfer register 4 has a vertical overflow function, and the vertical transfer register 7
Is transferred from the horizontal transfer register 4 to the output unit 5, and the charge exceeding the amount of charge handled by the horizontal transfer register 4 is discharged to the substrate side through the vertical overflow function.

Further, according to the present invention, a plurality of light receiving elements 6 arranged in a matrix, a vertical transfer register 7 corresponding to each column of the light receiving elements 6 and a horizontal transfer register 4 are provided. In the solid-state imaging device configured to add and read the signal charges of the light receiving elements 6 of two lines which match each other, the horizontal transfer register 4 is provided with a vertical overflow function so that unnecessary charges in the vertical transfer register 4 are removed from the horizontal transfer register 4. In addition to being discharged to the output unit 5, unnecessary charges exceeding the amount of charges handled by the horizontal transfer register 4 among the unnecessary charges are discharged to the substrate side via the vertical overflow function.

In the above solid-state image pickup device, the sensitivity ratio of the light receiving elements 6 of two adjacent lines can be set to 1: 1/2.

Further, it is possible to make the light receiving element 6 between two adjacent lines have a sensitivity difference by the electronic shutter operation.

Further, the unnecessary charges in the vertical transfer register 7 are discharged within the vertical blanking period.

[0020]

In the present invention, by providing the horizontal transfer register with the vertical overflow function, even if an excessive amount of charge exceeding the amount of charge to be handled is transferred to the horizontal transfer register, the overflow function is provided to the extent that the amount of charge to be handled exceeds. The charges are discharged to the substrate side through the horizontal transfer register, and only the charges less than the handled charge amount are transferred in the horizontal direction in the horizontal transfer register, so that the unnecessary charges are completely swept out or the screen flow at the time of a large amount of light is prevented. Etc. are possible.

Further, in the present invention, the horizontal transfer register is provided with a vertical overflow function so that unnecessary charges in the vertical transfer register are discharged from the horizontal transfer register to the output section, and at the same time, unnecessary charges in the horizontal transfer register are handled. By discharging the charge exceeding the amount toward the substrate via the vertical overflow function, even if the amount of unnecessary charge exceeds the amount handled by the horizontal transfer register, it can be completely discharged, and the unnecessary charge is transferred horizontally. It does not remain in the register. Therefore, the video signal and the unnecessary charges do not mix.

In the operation of adding and reading the signal charges of the two light receiving elements having a difference in sensitivity, when the sensitivity ratio of the two light receiving elements is set to 1: 1/2, signal reading is properly performed.

Further, by using the electronic shutter operation, it is possible to easily make a difference in sensitivity.

Since the discharge of the unnecessary charges can be completed within the vertical blanking period, the unnecessary charges are not mixed with the video signal.

[0025]

Embodiments of the solid-state image pickup device according to the present invention will be described below with reference to the drawings.

FIG. 1 shows the case of application to a FIT type CCD solid-state image pickup device. In the figure, 1 is a CCD according to this example.
The solid-state image pickup device is shown as a whole, 2 is its image pickup unit, 3 is a storage unit, 4 is a horizontal transfer register having a CCD structure, and 5 is an output unit connected to the final stage of the horizontal transfer register 4.

The image pickup section 2 arranges a large number of light receiving elements 6 to be pixels in a matrix and transfers the signal charges of the light receiving elements 6 to one side of each vertical column of the light receiving elements in the vertical direction.
A vertical transfer register 7 having a CD structure is arranged.

The storage unit 3 is arranged below the image pickup unit 2 in the vertical direction, and is for temporarily storing the signal charges generated in the image pickup unit 2, and has a one-to-one correspondence with each vertical transfer register 7 of the image pickup unit 2. Similarly, a plurality of vertical transfer registers 8 of CCD structure
To have.

Vertical transfer register 7 and storage unit of the image pickup unit 2
The vertical transfer registers 8 of 3 are all driven by, for example, 4 phases.
Pulse φIM₁, ΦIM₂, ΦIM₃, ΦIM_FourAnd φST₁, Φ
ST₂, ΦST₃, ΦST_Four4 phase drive system controlled by
The four transfer units having transfer electrodes are set to 1 bit.
is doing. In the vertical transfer register 7 of the image pickup unit 2, φIM ₁
And φIM₂Transfer section to which is applied and φIM₃And φ
IM_FourThe two transfer units to which the
Is formed to correspond to.

The horizontal transfer register 4 employs a two-phase drive system controlled by two-phase drive pulses φH ₁ and φH _{2. As} shown in FIG. 2, the insulating film 12 is formed on the semiconductor substrate 11.
The first storage section St ₁ , the first transfer section Tr ₁ , the second storage section St _2, and the second transfer section Tr ₂ each having a transfer electrode 11 formed through
A bit is formed, and one bit is formed so as to correspond to one vertical transfer register 8.

Each light receiving element 6 of the image pickup section 2 is constructed to have a vertical overflow function for overflowing the signal charges to the substrate side, and at the time of exposure, the potential state shown by the solid line 15 in FIG. Are accumulated and excess charges overflow to the substrate side beyond the potential barrier section 16. At the same time, the substrate potential is changed by the electronic shutter pulse applied during the exposure period, the potential state shown by the broken line 17 in FIG. 4 is established, and the charges accumulated up to that point are discharged to the substrate side, and accumulated in the subsequent exposure time. It has an electronic shutter function for reading out only the generated signal charges.

However, in this example, the potential distribution in the depth direction is set to the state of the solid line 18 in FIG. 3 especially when the storage unit St ₁ (or St ₂ ) is in the ON state. The structure is such that electric charges that exceed the potential barrier portion (so-called overflow portion) 19 overflow to the substrate side, that is, a structure having a vertical overflow function.

In this case, the potential when the storage unit St ₁ (or St ₂ ) in FIG. 2 is in the ON state (high potential level) is φ min, and the transfer unit Tr ₁ (or Tr) is
₂ ) the potential is φ max, the height of the potential barrier between them is φ bar _1, and as shown in FIG. 3 (potential diagram on the line AA in FIG. 2), the storage unit St
₁ (or St ₂ ) depth barrier 1
When the potential of 9 is φOF and the height of the potential barrier between them is φbar ₂ , it is set so that the relation of φmin <φOF <φmax φbar ₂ <φbar ₁ is satisfied.

Next, the operation of the above CCD solid-state image pickup device will be described.

During the vertical blanking period, unnecessary charges in the vertical transfer register 7 are discharged, signal charges are read from the light receiving element 6 to the vertical transfer register 7, signal charges are transferred from the image pickup section 2 to the storage section 3, and the like. A series of operations is performed.

That is, before reading the signal charge of the light receiving element 6 to the vertical transfer register 7, the unnecessary charge in the vertical transfer register 7 is discharged to the vertical transfer register 7 of the image pickup unit 2 and the vertical transfer register 8 of the storage unit 3 at high speed. Apply a pulse to transfer to the horizontal transfer register 4 at high speed, and
The contents are transferred and discharged to the output unit 5.

When unnecessary charges are transferred to the horizontal transfer register 4, any charges exceeding the amount of charges handled by the horizontal transfer register 4 among the unnecessary charges are transferred to the substrate by the vertical overflow function as shown by the potential distribution in FIG. Discharged to the side. Therefore, the horizontal transfer register 4 transfers unnecessary charges less than the handled charge amount, and the discharge of the unnecessary charges from the vertical transfer register 8 to the horizontal transfer register 7 is completed during the time required to discharge the unnecessary charges. 1 scan line time (the time required to transfer from end to end of the horizontal transfer register). Therefore, even if the amount of unnecessary charges is equal to or more than the amount of charges handled by the horizontal transfer register, the horizontal transfer register 4 can complete the discharge in one horizontal scanning period.

Next, the read pulse causes the signal charge of the light-receiving element 6 to pass through the read gate to the vertical shift register 7.
After being read by the vertical transfer registers 7 and 8, a high-speed transfer pulse is applied to the vertical transfer registers 7 and 8 and the vertical transfer registers 7 and 8 accumulate the data in the storage unit 3.
Transferred to.

Then, in each horizontal blanking period, the signal charges for each horizontal line from the storage unit 3 are transferred to the horizontal transfer register 4.
Transferred to. The signal charge of one horizontal line transferred to the horizontal transfer register 4 is horizontally transferred in the horizontal transfer register 4 and output from the output unit 5.

On the other hand, the pixel reading operation is performed by the above-mentioned third reading method in which the signal charges of two vertically adjacent pixels having a difference in sensitivity are added and read.

In this example, as described with reference to FIG. 6, of the light receiving elements 6 of the upper and lower two lines, the exposure time of the light receiving element 6 of one line is ⅙, which is the same as in the normal field reading.
0 seconds, the exposure time of the light receiving elements on the other line is set to 1/120 seconds by operating the electronic shutter, and the sensitivity difference between the pixels on both lines is set to 1: 1/2. The signal charges are added in the vertical transfer register 7. Then, the groups for addition in the odd field and the even field are alternately changed and output.

According to the above configuration, of the unnecessary charges transferred to the horizontal transfer register 4 during the high-speed sweeping of the unnecessary charges in the vertical transfer register 7 before reading the signal charges, the charges handled by the horizontal transfer register are included. The charge exceeding the amount overflows to the substrate side and is discharged, and only the charge less than the handled charge is transferred in the horizontal transfer register 7 and discharged from the output unit 5. Therefore, there is a problem in performing the above reading operation. It is possible to completely prevent unnecessary electric charges that would otherwise remain in the horizontal transfer register.

That is, the discharge of the unnecessary charges can be completed within the vertical blanking period, and it is possible to prevent the unnecessary charges from being mixed into the effective video signal.

Further, during normal signal charge transfer, even if there is a signal charge that exceeds the amount of charge handled by the horizontal transfer register 4, the excess charge does not overflow in the horizontal direction, so that it can occur when the amount of light is large. It is possible to prevent a so-called screen flow having a certain characteristic.

In addition, in the read operation in which the signal charges of the two pixels having the sensitivity difference are added and read, the upper and lower two
The ratio of pixel sensitivity is 1: 1/2 (ie 1/60 seconds: 1
/ 120 seconds), the signal reading can be properly operated.

Further, by utilizing the electronic shutter operation, it is possible to easily make a difference in sensitivity.

In the above example, the sensitivity ratio of the upper and lower two pixels is 1 :.
Although it has been set to 1/2, the sensitivity ratio is not limited to this, and can be set to any sensitivity ratio.

The present invention can also be applied to a FIT type CCD image pickup device which performs field reading and frame reading operations.

Further, in the above example, the horizontal transfer register having the vertical overflow function of the present invention is applied to the FIT type CCD solid state image pickup device, but it is also applied to the interline transfer (IT) type CCD solid state image pickup device. be able to.

[0050]

According to the present invention, in the solid-state image pickup device, when the unnecessary charge in the vertical transfer register before reading the signal charge is discharged through the horizontal transfer register, the unnecessary charge exceeds the amount of charge handled by the horizontal transfer register. Also in this case, all the particles can be discharged within the vertical blanking period without being left in the horizontal transfer register. Therefore, it is possible to prevent unnecessary charges from being mixed into the effective video signal.

In addition, during normal signal charge transfer, even if there is a signal charge that exceeds the amount of charge handled by the horizontal transfer register, the excess charge does not overflow in the horizontal direction, so there is a possibility that it will occur when there is a large amount of light. There is a screen flow that can be prevented.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an example of a FIT type CCD solid-state imaging device according to the present invention.

FIG. 2 is a diagram showing a cross section and a potential of a horizontal transfer register.

FIG. 3 is a potential diagram on the line AA of FIG.

FIG. 4 is a potential diagram used to explain an electronic shutter operation.

FIG. 5 is an explanatory diagram of a third read operation.

FIG. 6 is a diagram showing a spatial spread of a signal in the read operation of FIG.

FIG. 7 is an explanatory diagram of a field read operation.

8 is a diagram showing a spatial spread of a signal in the field read operation of FIG.

FIG. 9 is an explanatory diagram of a frame reading operation.

10 is a diagram showing a spatial spread of a signal in the frame read operation of FIG.

[Explanation of symbols]

 1 FIT CCD solid-state imaging device 2 imaging unit 3 storage unit 4 horizontal transfer register 5 output unit 6 light-receiving device 7, 8 vertical transfer register

Claims (5)

[Claims] 1. A plurality of light receiving elements arranged in a matrix, and a vertical transfer register corresponding to each column of the light receiving elements,
In a solid-state imaging device having a horizontal transfer register, the horizontal transfer register is provided with a vertical overflow function,
The charges from the vertical transfer register are transferred from the horizontal transfer register to the output section, and the charges exceeding the amount of charges handled by the horizontal transfer register are discharged to the substrate side through the vertical overflow function. A solid-state image sensor having the above-mentioned structure. 2. A plurality of light receiving elements arranged in a matrix, and a vertical transfer register corresponding to each column of the light receiving elements,
Adjacent two with a horizontal transfer register and different sensitivity
In a solid-state imaging device configured to add and read out signal charges of light receiving elements of a line, the horizontal transfer register is provided with a vertical overflow function, and unnecessary charges in the vertical transfer register are transferred from the horizontal transfer register to an output section. A solid-state image pickup device, characterized in that unnecessary charges exceeding the amount of charges handled by the horizontal transfer register among the unnecessary charges are discharged to the substrate side through the vertical overflow function. 3. The solid-state imaging device according to claim 2, wherein the sensitivity ratio of the light receiving elements of two adjacent lines is set to 1: 1/2. 4. The solid-state image pickup device according to claim 2, wherein a light receiving element between two adjacent lines is provided with a sensitivity difference by an electronic shutter operation. 5. The solid-state image pickup device according to claim 2, wherein unnecessary charges in the vertical transfer register are discharged within the vertical blanking period.