JPH04364681A - Solid-state image pickup device - Google Patents

Abstract

PURPOSE:To improve a range in an output level in which the SN ratio of a standard output level is improved and gradation is reproduced with respect to the solid-state image pickup device used for a video camera. CONSTITUTION:A charge stored and photoelectric-converted at a photoelectric conversion element 8 for a time of N/(N+1) of one field period is given to a charge transfer gate 9 and read to a vertical charge transfer section 10 from the photoelectric conversion element 8 by using a read pulse. An output charge Qs is saturated by an incident luminous quantity A and the output charge remains Qs at a luminous quantity more than the luminous quantity A. A 2nd storage operation is immediately started after the charge is read by a 1st storage operation. The charge is subjected to photoelectric conversion for a time of N/(N+1) of one field period by the 2nd storage operation and the charge stored in the photoelectric conversion element 8 is read to the vertical charge transfer section 10 from the photoelectric conversion element 8 by using a read pulse given to the charge transfer gate 9. Since the storage time in the 2nd storage operation is 1/N in comparison with the time in the 1st storage operation, an incident luminous quantity B at saturation is the luminous quantity being a multiple of N of the saturation incident luminous quantity A in the 1st storage operation.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state imaging device used in video cameras and the like.

0002

2. Description of the Related Art In recent years, solid-state imaging devices used in video cameras and the like have improved in performance and are now being used in broadcast cameras.

An example of a conventional solid-state imaging device will be described below with reference to the drawings. (FIG. 3) is a structural diagram showing the structure of a conventional solid-state imaging device. In (Figure 3),
1 is a photoelectric conversion element, 2 is a charge transfer gate, 3 is a vertical charge transfer section, 4 is a charge storage section, 5 is a horizontal charge transfer section, 6 is an output stage, and 7 is an output terminal. Incident light that enters the photoelectric conversion element 1 is photoelectrically converted into signal charges, which are accumulated in the photoelectric conversion element 1 for a period of one field.

During the vertical blanking period, a read pulse is applied to the charge transfer gate 2, and the charges accumulated in the photoelectric conversion element 1 are read out to the vertical charge transfer section 3. Thereafter, within the vertical blanking period, the charges in the vertical charge transfer section 3 are transferred at high speed to the storage section 4, and in the next field, they are sequentially transferred to the horizontal charge transfer section 5 to the output stage 6 and the output terminal 7.
It is output as an output signal through.

FIG. 2 shows photoelectric conversion characteristics representing the relationship between the amount of incident light and the amount of output charge of a conventional solid-state imaging device. In conventional solid-state imaging devices, the amount of incident light and the amount of output charge are proportional, and as the amount of incident light increases, the amount of output charge also increases. However, the output charge amount is saturated at a certain amount of incident light A, and the output charge amount becomes constant at a higher amount of incident light.

Therefore, in a video camera, this amount of incident light A
Gradation reproduction is not possible with stronger incident light. When designing a video camera, it is necessary to determine the standard amount of light that provides the white level of the output signal. In general, in video cameras, in order to reproduce gradation even in high-brightness areas that are 4 to 6 times brighter than the standard light amount, the standard light amount A' of the video camera is set to the saturated light amount A of the solid-state image sensor.
It is set at 1/4 to 1/6 of that.

[0007]

[Problems to be Solved by the Invention] However, with the above configuration, in order to reproduce gradations up to N times the standard light amount with a video camera, the standard light amount must be set to 1/N times the saturated light amount of the solid-state image sensor. It is necessary to Since the amount of incident light and the amount of output charge of a solid-state image sensor are proportional, the amount of output charge at standard light amount is 1 of the amount of output charge at saturated light amount of the solid-state image sensor.
/N.

Since the SN ratio is proportional to the square root of the output charge amount, the SN ratio at standard light intensity is 1/√N of the SN ratio at saturated light intensity.
The problem arises that. This also means that when trying to improve the S/N ratio at standard light intensity, the ratio N of the maximum incident light intensity that can reproduce gradation when using the same solid-state image sensor to the standard light intensity must be reduced. Occur.

[0009]

[Means for Solving the Problems] In order to solve the above problems, the present invention provides a first accumulation operation in which the element is saturated with a specific amount of incident light in a solid-state image sensor, and a first accumulation operation in the first accumulation operation. A second accumulation operation in which the element is saturated with an amount of incident light different from the amount of incident light is performed within a unit accumulation time, and the signal obtained in the first accumulation operation and the signal obtained in the second accumulation operation are combined. The added signal is used as an output signal per unit accumulation time.

0010

[Operation] The first accumulation operation uses up to the saturation output charge of the solid-state image sensor to obtain a signal up to the standard light intensity, and the second accumulation operation obtains a signal of a high brightness area brighter than the standard light intensity, and each signal is Since the added signal is used as the output signal, the output charge amount at standard light intensity is larger than the saturated output charge amount of the solid-state image sensor, and the S/N ratio at standard light intensity is at least as high as the S/N ratio at the saturated light intensity of the solid-state image sensor. By changing the ratio of the saturated light amount of the second accumulation operation and the saturated light amount of the first accumulation operation,
It is possible to change the range of incident light that can reproduce gradations with respect to the standard light amount.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A solid-state imaging device according to a first embodiment of the present invention will be described below with reference to the drawings. (FIG. 1) is a structural diagram showing the structure of a solid-state imaging device of the present invention. (Fig. 1), 8 is a photoelectric conversion element, 9 is a charge transfer gate,
10 is a vertical charge transfer section, 11 is a charge storage section, 12 is a horizontal charge transfer section, 13 is an output stage, and 14 is an output terminal. This structure is the same as that of a conventional FIT type solid-state image sensor, but the structure is such that the maximum amount of accumulated charge in the vertical charge transfer section 12 is twice the maximum amount of accumulated charge in the photoelectric conversion element 8. .

In the photoelectric conversion element 8, N/ of one field period is
The charges accumulated through photoelectric conversion for a period of (N+1) are read out from the photoelectric conversion element 8 to the vertical charge transfer section 10 by a read pulse applied to the charge transfer gate 9. Here, N is a constant greater than 1. A graph showing the relationship between the amount of incident light and the amount of output charge obtained by the first accumulation operation is shown in (a) of FIG. 4 by a dashed line. (Figure 4) (a)
When the amount of incident light is A, the output charge amount becomes Qs and saturates, and when the amount of light exceeds that amount, the output charge amount remains constant at Qs.

[0013] Immediately after the charges resulting from the first accumulation operation are read out, the second accumulation operation begins. Charges photoelectrically converted for a time of 1/(N+1) of one field period by the second accumulation operation and accumulated in the photoelectric conversion element 8 are transferred from the photoelectric conversion element 8 to the vertical charge transfer section by a read pulse given to the charge transfer gate 9. 10. The accumulation time in the second accumulation operation is 1/N of the accumulation time in the first accumulation operation.

A graph showing the relationship between the amount of output charge obtained by the second accumulation operation and the amount of incident light is shown by a chain double-dashed line in FIG. 4(b). Since the accumulation time in the second accumulation operation is 1/N compared to the first accumulation operation, the amount of incident light B at the time of saturation in (Fig. 4) (b) is (Fig. 4) (a). The light amount is N times the saturated incident light amount A during operation.

A graph showing the relationship between time and the amount of charge accumulated in the photoelectric conversion element 8 when the amount of incident light is A is shown by the dashed-dotted line (FIG. 5) (a), and when the amount of incident light is B The relationship between time and the amount of charge accumulated in the photoelectric conversion element 8 is shown by the two-dot chain line (FIG. 5) (b), and the timing of the read pulse is shown in (FIG. 5) (c).

In the incident light amount A (FIG. 5(a)), the charge inside the photoelectric conversion element 8 increases with time during the first accumulation operation, and the first accumulation operation starts at the same time as the photoelectric conversion element 8 is saturated. At the end, the charge in the photoelectric conversion element 8 is read out, and the second
The accumulation operation begins. In the second accumulation operation, the accumulation time is 1/N of the accumulation time of the first accumulation operation, so the amount of charge accumulated in the second accumulation operation is 1/N of the amount of charge accumulated in the first accumulation operation. Become.

In the incident light amount B (FIG. 5) (b), the photoelectric conversion element 8 becomes saturated after a while after the first accumulation operation starts. After the first accumulation operation is completed, the charges in the photoelectric conversion element 8 are read out, and the second accumulation operation begins. Incident light amount B
Since the amount of light is N times the amount of incident light A, in this case, the photoelectric conversion element 8 is saturated even in the second accumulation operation.

In the vertical charge transfer section 10, the charges obtained by the first accumulation operation and the charges obtained by the second accumulation operation are added together. The charges added in this manner are transferred to the charge storage unit 1 at high speed within the vertical blanking period.
1, the signals are sequentially transferred to the horizontal charge transfer section 12 and outputted as output signals through the output stage 13 and the output terminal 14.

A graph showing the relationship between the amount of output charge obtained by adding the charges obtained by the first accumulation operation and the charges obtained by the second accumulation operation in the vertical charge transfer section 10 and the amount of incident light is shown below. (Figure 4) (c) is shown by a solid line. (FIG. 4) The relationship between the amount of incident light and the amount of output charge shown in (c) is the photoelectric conversion characteristic of the solid-state imaging device in this example.

(FIG. 4) (c), the output charge amount increases proportionally until the amount of incident light is A, and when the amount of incident light is A, the saturated output charge amount Qs of the photoelectric conversion element 8 becomes (1+N)/
It becomes N times. Even after the amount of incident light exceeds A, the output charge amount increases proportionally, although the slope changes, and becomes twice the saturated output charge amount Qs of the photoelectric conversion element 8 when the amount of incident light is B.

In the solid-state image pickup device of this embodiment, the output charge is not saturated until the amount of incident light reaches B, which is N times the amount of incident light A at which the photoelectric conversion element 8 is saturated, so that tone reproduction can be performed up to the amount of incident light B. In the conventional method, the standard incident light amount was set to 1/N of the incident light amount A at which the solid-state image sensor is saturated in order to reproduce gradation up to a light amount N times the standard light amount, but by using the solid-state image sensor of the present invention, While the standard amount of incident light is kept at the saturated amount of incident light A of the element, gradations can be reproduced up to a light amount N times that of the standard state.

The standard output charge amount of the conventional solid-state imaging device is 1/N of the saturation output charge amount of the element, whereas the standard output charge amount of the solid-state imaging device of this embodiment is 1/N of the saturation output charge amount of the solid-state imaging device. Since it is (1+N)/N times the output charge amount, the output charge amount in the standard state of the solid-state imaging device of this embodiment is (N+1) of the output charge amount in the standard state of the conventional solid-state imaging device.
) will be doubled. Since the SN ratio of a solid-state imaging device is proportional to the square root of the output charge amount, the solid-state imaging device of this embodiment can increase the SN ratio in a standard state by √N times or more compared to a conventional solid-state imaging device.

In this embodiment, in the graph showing the relationship between the amount of incident light and the amount of output charge shown in FIG. 4(c), the slope differs with respect to the standard amount of incident light A. As a result, signals in high-brightness areas that are brighter than the standard amount of incident light are compressed, and it seems that unnaturalness appears in the output image. However, even in cameras using conventional solid-state imaging devices, such compression is performed by the knee correction circuit included in the process circuit in the signal processing section of the camera, and there is no problem at all in practice.

In this embodiment, the accumulation time in the first accumulation operation and the accumulation time in the second accumulation operation are determined based on the time of one field. In the case of an imaging device that is driven regardless of time, the accumulation time can be determined based on the time of one field or more.

Furthermore, in this embodiment, the signal obtained in the first accumulation operation and the signal obtained in the second accumulation operation are added inside the solid-state image sensor, but by using a memory or the like, the signal obtained in the second accumulation operation is added digitally outside the element. A similar effect can be obtained by adding the signals together to obtain an output signal. A solid-state imaging device according to a second embodiment of the present invention will be described below with reference to the drawings. (FIG. 6) is a block diagram showing the configuration of the solid-state imaging device of the present invention. (Fig. 6), 15 is an optical lens, 16 is an aperture, 17 is an aperture drive unit, 1
8 is a solid-state image sensor drive circuit, 19 is a solid-state image sensor, 20
is the output terminal. The solid-state imaging device used in the solid-state imaging device is the same as that used in the first embodiment.

This structure is almost the same as that of a conventional FIT type solid-state image sensor, but as shown in FIG. 3, the maximum amount of accumulated charge in the vertical charge transfer section 10 is twice that of the photoelectric conversion element 8. It is structured so that

In the photoelectric conversion element 8, 1/1 of one field period
The charges accumulated through photoelectric conversion for two hours are read out from the photoelectric conversion element 8 to the vertical charge transfer section 10 by a read pulse applied to the charge transfer gate 9. A graph showing the relationship between the amount of incident light passing through the optical lens 15 and entering the aperture 16 and the amount of output charge obtained by the first accumulation operation is shown in (
It is shown by the dashed line in Figure 7) (a). (FIG. 7) (a) When the amount of incident light is A, the output charge amount becomes Qs and saturates, and when the amount of light exceeds that amount, the output charge amount remains constant at Qs.

At the same time as the charges resulting from the first accumulation operation are read out, the solid-state image sensor drive circuit 18 sends a drive pulse to the aperture drive section 17, and the aperture drive section 17 causes the aperture 16 to control the amount of light incident on the solid-state image sensor 19. It is closed so that the amount of incident light becomes 1/N of the amount of incident light in the first accumulation operation. Here N
is a constant greater than 1.

Immediately thereafter, the second accumulation operation begins. The charges photoelectrically converted and accumulated for 1/2 of one field period in the second accumulation operation are read out from the photoelectric conversion element 8 to the vertical charge transfer section 10 by a read pulse applied to the charge transfer gate 9. The amount of output charge obtained by the second accumulation operation and the aperture 1 through the optical lens 15
A graph showing the relationship between the amount of incident light incident on 6 (Figure 7) (
b) Indicated by a chain double-dashed line.

Compared to the first accumulation operation, in the second accumulation operation, the diaphragm is closed so that the amount of incident light incident on the solid-state image sensor 19 is 1/N, so (FIG. 7) (b) The amount of incident light B when saturated is (Fig. 7) (a).
The light amount is N times the saturated incident light amount A in the accumulation operation.

A graph showing the relationship between the time when the amount of incident light is A and the amount of charge accumulated in the photoelectric conversion element 8 is shown by the dashed-dotted line (FIG. 8) (a), and the time when the amount of incident light is B is shown in (a) of FIG. The relationship between the amount of charge accumulated in the photoelectric conversion element 8 and the amount of charge accumulated in the photoelectric conversion element 8 is shown by the two-dot chain line (FIG. 8) (b), and the timing of the read pulse is shown in (FIG. 8) (c).

In the incident light amount A (FIG. 8) (a), the charge inside the photoelectric conversion element 8 increases with time during the first accumulation operation, and the first accumulation operation ends at the same time as the element becomes saturated, and the photoelectric conversion element 8 is terminated at the same time as the element becomes saturated. The charge within the conversion element 8 is read out. In the second accumulation operation, the amount of incident light that enters the solid-state image sensor 19 is 1/N of the amount of incident light in the first accumulation operation, so the amount of charge accumulated in the second accumulation operation is accumulated in the first accumulation operation. It becomes 1/N of the amount of charge.

In FIG. 5(b) showing the amount of incident light B, the photoelectric conversion element 8 becomes saturated after a while after the first accumulation operation starts. When the first accumulation operation is completed, the charges in the photoelectric conversion element 8 are read out. Since the incident light amount B is N times the incident light amount A, in this case, the photoelectric conversion element 8 is saturated even in the second accumulation operation.

In the vertical charge transfer section 10, the charges obtained by the first accumulation operation and the charges obtained by the second accumulation operation are added. The charges added in this manner are transferred to the charge storage section 11 at high speed within the vertical blanking period.
After being transferred to the horizontal charge transfer section 12, the charges are transferred to the solid-state image sensor 19 through the output stage 13 and the output terminal 14.
is output as the output signal.

It is obtained by adding the amount of incident light passing through the optical lens 15 and entering the aperture 16, the charge obtained by the first accumulation operation in the vertical charge transfer section 10, and the charge obtained by the second accumulation operation. A graph showing the relationship between the output charge amount and the output charge amount is shown in (c) of FIG. 7 as a solid line.

In (c) of FIG. 7, the output charge amount increases proportionally until the amount of incident light is A, and when the amount of incident light is A, the saturated output charge amount Qs of the photoelectric conversion element 8 becomes (1+N)/
It becomes N times. Even after the amount of incident light exceeds A, the output charge amount increases proportionally, although the slope changes, and becomes saturated at twice the saturated output charge amount Qs of the photoelectric conversion element 8 when the amount of incident light is B.

In the solid-state image pickup device of this embodiment, the output charge is not saturated until the amount of incident light reaches B, which is N times the amount of incident light A at which the photoelectric conversion element 8 is saturated, so that gradation reproduction can be performed up to the amount of incident light B. In the conventional method, the standard incident light amount was set to 1/N of the incident light amount A that saturates the element in order to reproduce gradation up to a light amount N times the standard light amount, but by using the solid-state imaging device of the present invention, the standard While keeping the amount of incident light at the saturation amount of incident light A of the element, gradations can be reproduced up to a light amount N times that of the standard state.

In contrast to the standard output charge amount of the conventional solid-state imaging device, which is 1/N of the saturation output charge amount of the element, the standard output charge amount of the solid-state imaging device of this embodiment is the saturation output charge of the element. Since the output charge amount is (1+N)/N times the amount, the output charge amount in the standard state of the solid-state imaging device of this embodiment is (N+1) times or more the output charge amount in the standard state of the conventional solid-state imaging device. Since the SN ratio of a solid-state imaging device is proportional to the square root of the output charge amount, the solid-state imaging device of this embodiment can increase the SN ratio in a standard state by √N times or more compared to a conventional solid-state imaging device.

In this embodiment, the accumulation time in the first accumulation operation and the accumulation time in the second accumulation operation are determined based on the time of one field. In the case of an imaging device that is driven regardless of time, the accumulation time can be determined based on the time of one field or more.

Further, in this embodiment, the amount of light incident on the solid-state image pickup device was changed using an aperture, but it may also be changed by inserting a filter such as an ND filter.

Furthermore, in this embodiment, the signal obtained in the first accumulation operation and the signal obtained in the second accumulation operation are added inside the solid-state image sensor, but they can be digitally added outside the element by using a memory or the like. A similar effect can be obtained by adding together to obtain an output signal.

[0042]

Effects of the Invention In a solid-state image sensor, there is a first accumulation operation in which the element is saturated with a specific amount of incident light, and a second accumulation operation in which the element is saturated with an amount of incident light different from the amount of incident light in the first accumulation operation. an accumulation operation is performed within a unit accumulation time, and a signal obtained by adding the signal obtained in the first accumulation operation and the signal obtained in the second accumulation operation is used as an output signal per unit accumulation time. Therefore, in the first accumulation operation, it is possible to obtain a signal up to the standard light intensity by using up to the saturation output charge of the image sensor, and in the second accumulation operation, it is used to reproduce the gradation of a high-brightness area that is brighter than the standard light intensity. I can get a signal.

Therefore, the SN ratio at the standard light amount can be increased to at least the SN ratio at the saturated light amount of the solid-state image sensor, and furthermore, the range of incident light that can reproduce gradation can be freely changed.

[Brief explanation of the drawing]

FIG. 1 is a structural diagram of an example of a conventional solid-state imaging device.

FIG. 2 is a graph of photoelectric conversion characteristics showing the relationship between the amount of incident light and the amount of output charge of a conventional solid-state imaging device.

FIG. 3 is a structural diagram showing the structure of a solid-state imaging device according to a first embodiment of the present invention.

FIG. 4 is a graph showing the relationship between the amount of incident light and the amount of output charge of the solid-state imaging device according to the first embodiment of the present invention.

FIG. 5 is a graph showing the relationship between time and the amount of charge accumulated in a photoelectric conversion element in the solid-state imaging device according to the first embodiment of the present invention.

FIG. 6 is a block diagram showing the configuration of a solid-state imaging device according to a second embodiment of the present invention.

FIG. 7 is a graph showing the relationship between the amount of incident light and the amount of accumulated charge in a solid-state imaging device according to a second embodiment of the present invention.

FIG. 8 is a graph showing the relationship between time and the amount of charge accumulated in a photoelectric conversion element in a solid-state imaging device according to a second embodiment of the present invention.

[Explanation of symbols]

1 Photoelectric conversion element 2 Charge transfer gate 3 Vertical charge transfer section 4 Charge storage section 5 Horizontal charge transfer section 6 Output stage 7 Output terminal 8 Photoelectric conversion element 9 Charge transfer gate 10 Vertical charge transfer section 11 Charge storage section 12 Horizontal charge transfer section 13 Output stage 14 Output terminal 15 Optical lens 16 Aperture 17 Aperture drive section 18 Solid-state image sensor drive circuit 19 Solid-state image sensor 20 Output terminal

Claims (8)

[Claims] 1. In a solid-state image sensor, a first accumulation operation that saturates the element with a specific amount of incident light;
A second accumulation operation in which the element is saturated with an amount of incident light different from the amount of incident light in the accumulation operation is performed within a unit accumulation time, and the signal obtained in the first accumulation operation and the second accumulation operation are
A solid-state imaging device characterized in that a signal obtained by adding together signals obtained in the accumulation operation is used as an output signal per unit accumulation time. 2. The solid-state imaging device includes a solid-state imaging device that performs photoelectric conversion and outputs a signal according to incident light, and an optical system that forms an image of the incident light on a photoelectric conversion surface of the solid-state imaging device.
The solid-state imaging device according to claim 1, further comprising an aperture mechanism that changes the amount of incident light incident on the solid-state imaging device. 3. In the solid-state image sensor, the first accumulation operation and the second accumulation operation are performed within a unit accumulation time, and assuming that the aperture value of the aperture mechanism is constant, the accumulation time in the first accumulation operation; 3. The solid-state imaging device according to claim 2, wherein the accumulation times in the second accumulation operation are different. 4. In the solid-state image sensor, the first accumulation operation and the second accumulation operation are performed within a unit time, and the accumulation time of the first accumulation operation and the accumulation time of the second accumulation operation are respectively 3. The aperture value of the aperture mechanism in the first accumulation operation is different from the aperture value of the aperture mechanism in the second accumulation operation. Solid-state imaging device. Claim 5: The signal obtained in the first accumulation operation and the second
3. The solid-state imaging device according to claim 2, wherein the signals obtained by the accumulation operations are added together inside the solid-state imaging device. 6. The solid-state image sensor is a so-called frame interline transfer type solid-state image sensor that includes a light receiving section, a storage section, and an output section, and the charge accumulated by the first accumulation operation is transferred to the vertical charge transfer section in the light receiving section. A second accumulation operation is performed after reading out the charge from the first accumulation operation, and the charge accumulated by the second accumulation operation is read out to the vertical charge transfer section in which the charge from the first accumulation operation is still held. 6. The solid-state imaging device according to claim 5, wherein the charge obtained in the first accumulation operation and the charge obtained in the second accumulation operation are added together. 7. The solid-state imaging device according to claim 1, wherein the output signal per unit accumulation time is output as a signal corresponding to the time of one field determined by a television system. 8. The solid-state imaging device according to claim 1, wherein the output signal per unit accumulation time is output as a signal corresponding to a time period for a plurality of fields determined by a television system.