JPH11346334A - Solid-state image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image with excellent quality with an extended dynamic range by preventing an image from being floated in white in the case that an object with high luminance is photographed where photosensing pixels with high sensitivity are saturated. SOLUTION: An S/H circuits 29, 30 and a subtractor 4 detect charges of high sensitivity signal charges obtained by photosensing pixels with high sensitivity, the high sensitivity output signals are given to a logarithmic amplifier 36, in which the signals are reflected on a level of a reset pulse ϕRG2 so as to vary a clip level of the high sensitivity signal charge depending on a level of the reset pulse ϕRG2 and the clip level is decreased when the charges of the high sensitivity signal charges are increased.

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 and, more particularly, to a CCD (Charge Co.) which realizes a wide dynamic range using a plurality of types of photosensitive pixels having different photoelectric sensitivity characteristics.
upled Device) Related to solid-state imaging devices.

[0002]

2. Description of the Related Art In a CCD solid-state imaging device, the signal output is saturated after signal charges photoelectrically converted and accumulated in each photosensitive pixel (photoelectric conversion element) overflow from the pixel. Can not be used. Therefore,
The dynamic range with respect to the light input is narrow. For example, when an image of a person standing at the window is taken from the indoor side, the person becomes black.

Therefore, as one of means for expanding the dynamic range, a plurality of two-dimensionally arranged photosensitive pixels adjacent to each other are grouped, and the photoelectric sensitivity characteristics of the photosensitive pixels in each group are made different from each other. There is a CCD solid-state imaging device in which signal charges of different photosensitive pixels are simultaneously read out to a charge transfer unit and added (see Japanese Patent Application Laid-Open No. 3-117281).

[0004]

However, in the above-described CCD solid-state imaging device having a wide dynamic range, a high-luminance subject whose saturation of a photosensitive pixel having a higher photoelectric sensitivity characteristic (hereinafter referred to as a high-sensitivity pixel) is saturated. When the image is captured, the captured image of the subject becomes a white floating image, and there is a problem that a high-quality image with an expanded dynamic range cannot be obtained.

If the sensitivity of a photosensitive pixel having a lower photoelectric sensitivity characteristic (hereinafter referred to as a low-sensitivity pixel) is extremely reduced so that the photosensitive pixels having different photoelectric sensitivity characteristics do not saturate at the same time, the sensitivity of a high-sensitivity pixel is reduced. There is a large difference between the light amount range in which the tone can be obtained and the light amount range in which the gradation can be obtained with the low-sensitivity pixels. As a result, the so-called insensitive light amount range that cannot be detected by either the high-sensitivity pixels or the low-sensitivity pixels is widened. There was a problem. Regarding this problem, it is possible to narrow the insensitive light amount range by making the sensitivity of the high-sensitivity pixel relatively close to that of the low-sensitivity pixel, but in such a case, the amount of expansion of the dynamic range decreases. A new problem arises.

[0006]

According to a first aspect of the present invention, there are provided a plurality of types of photosensitive pixels having different photosensitivity characteristics, and the photoelectric sensitivity characteristics of the signal charges obtained by the plurality of types of photosensitive pixels are included. The high-sensitivity signal charge obtained by the photosensitive pixel having the higher sensitivity is clipped at a predetermined clip level, and the low-sensitivity signal obtained by the photosensitive pixel having the lower photoelectric sensitivity characteristic is compared with the high-sensitivity signal charge after clipping. In a solid-state imaging device configured to add charges, a high-sensitivity charge amount detection unit that detects a charge amount of a high-sensitivity signal charge obtained by a photosensitive pixel having a higher photoelectric sensitivity characteristic, and the high-sensitivity charge amount detection unit And a clip level varying means for varying the clip level in accordance with the amount of charge detected by the method.

In the solid-state imaging device having the above structure, the charge amount of the high-sensitivity signal charge obtained by the photosensitive pixel having the higher photoelectric sensitivity characteristic is detected by the high-sensitivity charge amount detecting means, and the charge amount is determined in accordance with the detected charge amount. Since the clip level changing means changes the clip level, for example, by performing a process of lowering the clip level when the charge amount of the high-sensitivity signal charge is large, when a very high-luminance subject is imaged, Of the high-sensitivity signal charge of
The ratio of the low-sensitivity signal charge to the charge amount after the addition can be increased.

According to the present invention, there is provided a photosensitive pixel having a plurality of types of photosensitive pixels having different photoelectric sensitivity characteristics, and of a signal charge obtained by the plurality of types of photosensitive pixels, a photosensitive pixel having a higher photoelectric sensitivity characteristic. Is clipped at a predetermined clip level, and a low-sensitivity signal charge obtained by a photosensitive pixel having a lower photoelectric sensitivity characteristic is added to the high-sensitivity signal charge after clipping. A low-sensitivity signal amount detecting means for detecting a low-sensitivity signal charge amount obtained by a photosensitive pixel having a lower photoelectric sensitivity characteristic, and a charge amount detected by the low-sensitivity charge amount detecting means. And a low-sensitivity exposure time varying means for varying the exposure time of the photosensitive pixel having the lower photoelectric sensitivity characteristic.

In the solid-state imaging device having the above configuration, the charge amount of the low-sensitivity signal charge obtained by the photosensitive pixel having the lower photoelectric sensitivity characteristic is detected by the low-sensitivity charge amount detecting means, and the charge amount is determined according to the detected charge amount. Since the low-sensitivity exposure time varying means changes the exposure time of the photosensitive pixel having the lower photoelectric sensitivity characteristic, for example, when the amount of the low-sensitivity signal charge is large, the exposure of the photosensitive pixel having the lower photoelectric sensitivity characteristic is performed. By shortening the time, it is possible to prevent saturation of signal charges when capturing an image of a high-luminance subject, and conversely, when the amount of low-sensitivity signal charges is small, the photosensitive pixels with lower photoelectric sensitivity characteristics By increasing the exposure time, it is possible to increase the sensitivity when capturing a low-luminance subject.

According to a third aspect of the present invention, there are provided a plurality of types of photosensitive pixels having different photoelectric sensitivity characteristics, and a photosensitive pixel having a higher photoelectric sensitivity characteristic among signal charges obtained by the plurality of types of photosensitive pixels. Is clipped at a predetermined clip level, and a low-sensitivity signal charge obtained by a photosensitive pixel having a lower photoelectric sensitivity characteristic is added to the high-sensitivity signal charge after clipping. Charge detection means for detecting the charge amount of the high-sensitivity signal charge obtained by the photosensitive pixel having the higher photoelectric sensitivity characteristic, and the charge amount detected by the high-sensitivity charge amount detection means. And a high-sensitivity exposure time varying means for varying the exposure time of the photosensitive pixel having the higher photoelectric sensitivity characteristic.

In the solid-state imaging device having the above structure, the charge amount of the high-sensitivity signal charge obtained by the photosensitive pixel having the higher photoelectric sensitivity characteristic is detected by the high-sensitivity charge amount detecting means, and the charge amount is determined according to the detected charge amount. Since the high-sensitivity exposure time varying means changes the exposure time of the photosensitive pixel having the higher photoelectric sensitivity characteristic, for example, when the amount of the high-sensitivity signal charge is large, the exposure of the photosensitive pixel having the higher photoelectric sensitivity characteristic is performed. By shortening the time, it is possible to prevent saturation of signal charges when capturing a high-luminance subject.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram of a CCD solid-state imaging device to which the present invention is applied. FIG.
, An imaging unit (imaging area) 11 includes a plurality of photosensitive elements 12 that are two-dimensionally arranged in a vertical and horizontal direction on a semiconductor substrate, convert incident light into signal charges having a charge amount corresponding to the light amount, and accumulate the signal charges. And a plurality of vertical transfer units 13 provided along the vertical direction of each of the plurality of photosensitive elements 12. This imaging unit 1
In FIG. 1, the plurality of photosensitive pixels 12 are classified into a pixel group 12o of an odd line and a pixel group 12e of an even line. As will be described later, the pixel group 12o of the odd line and the pixel group 12e of the even line alternate in a field unit. A high-sensitivity signal charge (hereinafter, high-sensitivity signal charge) and a low-sensitivity signal charge (hereinafter, low-sensitivity signal charge) are obtained.

The plurality of vertical transfer units 13 are composed of a set (packet sequence) of packets provided in a one-to-one correspondence with each photosensitive pixel 12, and three transfer electrodes are provided on a transfer channel of each packet. 14-1, 14-2 and 14-3 are arranged in the transfer direction. These three transfer electrodes 14-
Among the 1, 14-2 and 14-3, for example, the middle transfer electrode 1
Reference numeral 4-2 also functions as a readout gate electrode for reading out signal charges from the photosensitive element 12. Then, the vertical transfer unit 13
Phase vertical transfer pulses φV1, φV2a, φV2b, φV
3 is driven for transfer.

The four-phase vertical transfer pulses φV1 and φV2
a, φV2b, φV3, the vertical transfer pulse φV1,
φV3 is applied to the transfer electrodes 14-1 and 14-3 of each packet, respectively, and the vertical transfer pulse φV2a is applied to the transfer electrode 14-2 of the packet corresponding to the pixel group 12e of the even line.
The vertical transfer pulse φV2b is applied to the odd-numbered pixel group 12
The voltage is applied to the transfer electrode 14-2 of the packet corresponding to o. Here, since the transfer electrode 14-2 also serves as a read gate electrode, the vertical transfer pulses φV2a, φV
2b takes three values of a low level, an intermediate level and a high level, and a high level pulse among them is a read pulse. Note that the difference between the vertical transfer pulses φV2a and φV2b lies in the difference in the generation timing of the read pulse.

A horizontal transfer unit 15 is disposed below the image pickup unit 11 in the drawing, adjacent to the end of the plurality of vertical transfer units 13 in the transfer direction. The horizontal transfer unit 15 is driven by two-phase horizontal transfer pulses φH1 and φH2. At the end of the horizontal transfer unit 15 in the transfer direction, a charge detection unit 16 having, for example, a floating diffusion amplifier configuration, which detects a signal charge transferred by the horizontal transfer unit 15, converts the signal charge into a signal voltage, and outputs the signal voltage. Is provided.

The charge detecting section 16 has a FD (floating diffusion) section 19 and an RD (reset drain) section 20, and a reset having two reset gate electrodes 21-1 and 21-2 arranged in tandem between them. And a gate section 22, and can perform a clip operation on signal charges in the FD section 19.

In the charge detection section 16 having such a configuration, R
A predetermined reset drain voltage Vrd is applied to the D section 20. In addition, two reset gate electrodes 21-1,
Reset pulses φRG1 and φRG2 are applied to 21-2, respectively. Then, the horizontal transfer unit 15 to the FD unit 1
The signal charge transferred to 9 is subjected to clip processing and addition processing in the FD section 19, is converted into a signal voltage, and is output to the outside via the buffer 24.

As described above, CC having a wide dynamic range
A D solid-state imaging device is configured. Four-phase vertical transfer pulses φV1, φV2a, φV2 for driving the vertical transfer unit 13
b, φV3, two-phase horizontal transfer pulses φH1, φH2 for driving the horizontal transfer unit 15, two reset pulses φRG1, φRG2 for driving the charge detection unit 16, and a shutter pulse φSUB applied to the substrate, respectively. Generated by generator 25. When the shutter pulse φSUB is applied to the substrate, a so-called electronic shutter operation of sweeping out all signal charges accumulated in the photosensitive pixels 12 to the substrate is realized.

Next, a method of driving the CCD solid-state imaging device having the above configuration will be described.

In the image pickup section 11, for example, a plurality of types of photosensitive sensitivity characteristics are made different by changing the exposure time of a photosensitive pixel such as a pixel exposed only during a scanning period and a pixel exposed only during a blanking period. Using the photosensitive pixel 12, a high-sensitivity signal charge is transmitted from a photosensitive pixel having a higher photoelectric sensitivity characteristic (hereinafter, a high-sensitivity pixel), and a low-sensitivity signal is transmitted from a photosensitive pixel having a lower photoelectric sensitivity characteristic (hereinafter, a low-sensitivity pixel). I try to get a charge. Incidentally, in FIG. 1, for easy understanding, high-sensitivity signal charges are schematically indicated by large circles and low-sensitivity signal charges are schematically indicated by small circles.

First, the operation of the imaging unit 11 will be described with reference to the timing chart of FIG. In the even-numbered field, when a readout pulse rises in the vertical transfer pulse φV2a at time t11, the high-sensitivity signal charge of the pixel group 12e of the even-numbered line photoelectrically converted in the vertical effective video period is read out to the vertical transfer unit 13. After the high-sensitivity signal charges are read, the signal charges in all the pixels are swept away by the substrate by applying the shutter pulse φSUB to the substrate at time t12.

Thereafter, photoelectric conversion is performed again in the vertical blanking period. When a readout pulse is generated in the vertical transfer pulse φV2b at time t13 during the vertical blanking period, the odd line photoelectrically converted during the vertical blanking period is output. The low-sensitivity signal charges of the pixel group 12o of the vertical transfer unit 1
3 is read. After the low-sensitivity signal charge is read,
By applying the shutter pulse φSUB to the substrate again at time t14, the signal charges in all the pixels are swept away by the substrate, and thereafter, the photoelectric conversion operation of the odd field is started.

With the above operation, the high-sensitivity signal charges and the low-sensitivity signal charges are alternately arranged in the vertical transfer unit 13. The vertical transfer operation of the vertical transfer unit 13 causes the high-sensitivity signal charges and the low-sensitivity signal charges to be paired with the horizontal transfer unit 1.
5 is transferred. Thus, the high-sensitivity signal charges and the low-sensitivity signal charges are alternately arranged in the horizontal transfer unit 15. After that, the horizontal transfer operation of the horizontal transfer unit 15 causes the high-sensitivity signal charges and the low-sensitivity signal charges to alternately change the FD of the charge detection unit 16.
It is transferred to the unit 19. The operation of the charge detection unit 16 will be described later in detail.

When an odd field is entered and a read pulse rises in the vertical transfer pulse φV2b at time t15, high-sensitivity signal charges of the pixel group 12o of the odd line photoelectrically converted in the vertical effective video period are read out to the vertical transfer unit 13. . After the high-sensitivity signal charges have been read, the shutter pulse φSUB is applied to the substrate at time t16,
The signal charges in all the pixels are swept away to the substrate.

Thereafter, photoelectric conversion is performed again in the vertical blanking period. When a readout pulse rises in the vertical transfer pulse φV2a at time t17 during the vertical blanking period, the even-numbered lines photoelectrically converted during the vertical blanking period are output. Low-sensitivity signal charges of the pixel group 12e of the vertical transfer unit 1
3 is read. After the low-sensitivity signal charge is read,
By applying the shutter pulse φSUB to the substrate again at time t18, the signal charges in all the pixels are swept away by the substrate. The above-described series of operations are repeatedly executed in field units.

Next, the operation of the charge detector 16 will be described with reference to the timing chart of FIG. 3 and the potential diagram of FIG.

First, reset pulses φRG1, φRG2
Is a high (H) level period T11 is a reset operation period. In this reset operation period T11, both potentials below the reset gate electrodes 21-1 and 21-2 are deepened, so that the FD portion 19 The charges are swept away by the RD unit 20, and a reset operation is performed.

Subsequently, when the reset pulse φRG2 transitions from a high level to a low (L) level, the potential below the reset gate electrode 21-2 becomes shallow. The storage capacitance of the FD section 19 is determined by the height of the potential barrier below the reset gate electrode 21-2. Since the storage capacitance of the FD unit 19 has a variation (saturation unevenness) in the saturation signal amount of each pixel of the imaging unit 11, the reset pulse φRG2 has a minimum saturation signal amount in the variation.
Is set to a low level value.

When the reset pulse φRG1 is at a high level,
A period T12 during which the reset pulse φRG2 is at a low level is a clipping operation period. In this clipping operation period, the high-sensitivity signal charges obtained when the incident light amount saturates the pixels having high photoelectric sensitivity characteristics are transferred to the horizontal transfer unit 15. Is transferred to the FD region 19, the signal charge amount exceeds the potential barrier below the reset gate electrode 21-2, and the excess charge is swept away by the RD section 20,
A clip operation is performed.

Subsequently, when the reset pulse φRG1 transitions from a high level to a low level, the low level value is set lower than the low level value of the reset pulse φRG2. The lower potential becomes shallower than the potential below the reset gate electrode 21-2.

A period T13 in which both the reset pulses φRG1 and φRG2 are at a low level is an addition operation period. In this addition operation period, a low-sensitivity signal charge is transferred to the FD section 19, thereby clipping the high-sensitivity signal. The charge and the low-sensitivity signal charge are added. Thereafter, the reset operation period T11 is entered again, and thereafter, a series of operations of a reset operation, a clip operation, and an addition operation are repeatedly performed.
As a result, the dynamic range of the output signal in the CCD solid-state imaging device can be expanded, and an output signal in which unevenness in the saturation signal amount of the pixel is eliminated can be obtained.

FIG. 5 is a block diagram showing an embodiment of the solid-state imaging device according to the present invention. In the figure, the output (OUT) of the CCD image sensor 26 is S / H (sample hold).
The signals are sampled by the circuits 27, 28, 29, 30, 31, 32. The S / H circuit 27 has a sampling pulse φSHP and the S / H circuit 28 has a sampling pulse φSHP.
The SHD2 and S / H circuit 29 output a sampling pulse φSH
The P, S / H circuit 30 has a sampling pulse φSHD1,
The S / H circuit 31 supplies sampling pulses φSHD1, S /
The H circuit 32 samples the output (voltage) of the CCD element 26 with the sampling pulse φSHD2.

In the operation timings shown in FIGS. 3 and 4, S / S by the sampling pulse φSHP is used.
The sample timing of the H circuits 27 and 29 is the reset operation period (T11), the sample timing of the S / H circuits 30 and 31 by the sampling pulse φSHD1 is the clip operation period (T12), and the sampling timing of the S / H circuits 28 and 32 by the sampling pulse φSHD2. The sample timing is set in the addition operation period (T13).

The output of the S / H circuit 27 is the non-inverting (+) input of the subtractor 33, and the output of the S / H circuit 28 is
3 is the inverted (-) input. As a result, the output signal from the subtractor 33 becomes an output signal (addition output signal) having a voltage level corresponding to the added charge amount obtained by adding the low-sensitivity signal charge to the high-sensitivity signal charge after clipping, and is treated as a video signal. It is.

On the other hand, the output of the S / H circuit 29 is
, And the output of the S / H circuit 30 is
4 is the inverted input. As a result, the output signal from the subtractor 34 becomes an output signal (high-sensitivity output signal) having a voltage level corresponding to the charge amount of the high-sensitivity signal charge after clipping. The amount can be detected.

Further, the output from the S / H circuit 31 is
5, and the output of the S / H circuit 32 is the inverted input of the subtractor 35. As a result, the output signal from the subtractor 35 is a charge amount obtained by taking the difference between the charge amount of the high-sensitivity signal charge after clipping and the above-mentioned added charge amount, that is, a voltage level output corresponding to the charge amount of the low-sensitivity signal charge. Since the signal is a signal (low-sensitivity output signal), the amount of low-sensitivity signal charge can be detected from the output signal.

Here, the output signal (high-sensitivity output signal) of the subtractor 34 is input to the logarithmic amplifier 36. The logarithmic amplifier 36 has an operational amplifier 36a and a transistor 36b. The output of the subtractor 34 is input to the non-inverting input of the operational amplifier 36a via the resistor R1. On the other hand, a reference potential is applied to the inverting input of the operational amplifier 36a by the resistor R2 and the variable resistor 36c, and the potential level can be adjusted by the variable resistor 36c. A transistor 36b is provided in a feedback system between the output side of the operational amplifier 36a and the non-inverting input side.

The logarithmic amplifier 36 includes an operational amplifier 36
The voltage level of the high-sensitivity output signal serving as the non-inverting input of a is logarithmically amplified. The output of the logarithmic amplifier 36 is superimposed on the signal line of the reset pulse φRG2 between the timing generator 25 and the CCD image sensor 26. Capacitors C1 and C2 are provided on the signal lines of the reset pulses φRG1 and φRG2, respectively.
Further, a combined resistance of the variable resistor R3 and the resistor R4 is superimposed on the signal line of the reset pulse φRG1, and the variable resistor R3
The level of the reset pulse φRG1 can be adjusted by changing the resistance value of the reset pulse φRG1.

On the other hand, the output signal (low-sensitivity output signal) of the subtractor 35 is input to the exposure time calculator 37. The exposure time calculator 37 calculates the exposure time of the low-sensitivity pixel according to the voltage level of the output signal of the subtractor 35 based on the voltage level. The calculation result in the exposure time calculator 37 is given to the timing generator 25.

In the above configuration, first, the logarithmic amplifier 36
The output signal amplified by the
Between the reset pulse φRG and the CCD image sensor 26
2 signal lines. Thereby, reset pulse φRG generated from timing generator 25
The level of 2 changes according to the voltage level of the output signal of the logarithmic amplifier 36 superimposed on the wiring line. More specifically, the logarithmic amplifier 36
Of the reset pulse .phi.RG2 at the time of the reset operation increases accordingly.

Here, the clip level of the high-sensitivity signal charge in the charge detection section 16 is determined by the low level value of the reset pulse φRG2 applied to the reset gate electrode 21-2. That is, when the low level value of the reset pulse φRG2 is increased, the potential under the reset gate electrode 21-2 at the time of the clipping operation becomes deeper.
The charge amount of the high-sensitivity signal charges stored in the FD section 19 is reduced accordingly. As a result, the clip level of the high-sensitivity signal charge drops from the level shown in FIG. 6A to the level shown in FIG. 6B, and accordingly, the knee point of the CCD output characteristic also drops.

Thus, by adopting a circuit configuration for lowering the clip level when the amount of high-sensitivity signal charges is large as in the present embodiment, an image of a high-luminance subject in which high-sensitivity pixels are saturated can be taken. In this case, it is possible to reduce the accumulated charge amount of the high-sensitivity signal charges during the clip operation and increase the proportion of the low-sensitivity signal charges in the signal charges obtained by the subsequent addition operation. In addition, by passing the high-sensitivity output signal through the logarithmic amplifier 36 as described above, the knee point of the output characteristic due to the clipping operation is logarithmically increased with an increase in the amount of incident light on the high-sensitivity pixel (the amount of the high-sensitivity signal charge). Can be lowered.

As a result, even when a high-luminance subject in which the high-sensitivity pixels are saturated is imaged, the low-sensitivity signal charges obtained by the low-sensitivity pixels greatly contribute to the output signal of the CCD solid-state imaging device. Thus, an output signal corresponding to the amount of incident light can be obtained. Therefore, the phenomenon in which the high-sensitivity pixels are saturated and the captured image floats white can be effectively prevented,
It is possible to obtain a high-quality image with an expanded dynamic range. Further, by passing the high-sensitivity output signal through the logarithmic amplifier 36, it becomes possible to logarithmically change the output signal of the CCD solid-state imaging device with respect to the light amount.

Further, since the knee point of the CCD output characteristic can be controlled by the DC voltage value, the circuit of the feedback system can be easily formed, and the feedback period can be shortened as much as possible. This makes it possible to control the knee point in each photosensitive pixel or in a minute area.

The subtracter 3 corresponding to the low-sensitivity output signal
5 is input to the exposure time calculation unit 37, the exposure time calculation unit 37 calculates the exposure time according to the output level (voltage level) of the subtractor 35, and gives the calculation result to the timing generator 25. Can be Then, in the timing generator 25, when the voltage level of the low-sensitivity output signal is low (when the amount of the low-sensitivity signal charge is small), the shutter pulse φSUB that determines the exposure time of the low-sensitivity pixel is controlled. The exposure time of the low-sensitivity pixel is increased, and when the voltage level of the low-sensitivity output signal is high (when the amount of the low-sensitivity signal charge is large), the exposure time of the low-sensitivity pixel is reduced.

More specifically, as shown in FIG. 7, the accumulation amount of the signal charge in the low-sensitivity pixel generally varies from the rising timing of the shutter pulse φSUB to the vertical transfer pulse φSUB after the read pulse rises in the vertical transfer pulse φV2a. It is determined by the period Tf until the read pulse rises at φV2b. Then, another shutter pulse φSUB is added between the shutter pulse φSUB and the vertical transfer pulse φV2b, and the position (rising timing) of the added shutter pulse φSUB is changed to control the exposure time of the low-sensitivity pixel. I do. Thus, for example, when the additional pulse φSUB rises at the position shown in the figure, the exposure time of the low-sensitivity pixel becomes Ta, and when the additional pulse φSUB rises at the position shown in the figure, the exposure time of the low-sensitivity pixel becomes Is limited to Tb shorter than Ta.

Thus, when the luminance distribution of the subject is high and the amount of low-sensitivity signal charges increases, the exposure time of the low-sensitivity pixels is reduced to prevent saturation of the signal charges, and the luminance distribution of the subject is low. When the charge amount of the low-sensitivity signal charge decreases, the sensitivity can be increased by increasing the exposure time of the low-sensitivity pixel. It is possible to obtain an image having a clear contrast both indoors and outdoors without blackout or overexposure.

Further, as means for preventing the saturation of the accumulated charges in the high-sensitivity pixels, the output signal of the subtractor 34, which becomes the high-sensitivity output signal, is supplied to the exposure time calculating section 37, where the level of the high-sensitivity output signal is adjusted. A configuration in which the exposure time is calculated and the exposure time of the high-sensitivity pixel is controlled by the same method (electronic shutter method) as described above may be employed.

In this configuration, when an image of a high-brightness subject in which the high-sensitivity pixels are saturated is taken, an increase in the amount of the high-sensitivity signal charges is caused by applying an electronic shutter to the exposure of the high-sensitivity pixels. By shortening the time, the phenomenon that the high-sensitivity signal charge is saturated can be prevented, and the high-sensitivity signal can be optimized.

In the above embodiment, the operation of clipping the high-sensitivity signal charge and the operation of adding the high-sensitivity signal charge after clipping and the low-sensitivity signal charge are performed inside the device have been described. The same applies to those performed by an external circuit.

[0051]

As described above, according to the first aspect of the present invention, the high-sensitivity charge amount detecting means for detecting the amount of the high-sensitivity signal charge obtained by the photosensitive pixel having the higher photoelectric sensitivity characteristic. And a clip level varying means for varying a clip level according to the charge amount detected by the high-sensitivity charge amount detection means, so that the high-sensitivity signal detected by the high-sensitivity charge amount detection means is provided. When the amount of charge is large, the clip level for clipping the high-sensitivity signal charge is reduced by the clip level varying means, thereby preventing a phenomenon in which the captured image floats white even when a high-luminance subject is imaged. It is possible to obtain a high quality image with a wide dynamic range.

According to the second aspect of the present invention, a low-sensitivity charge detecting means for detecting a low-sensitivity signal charge obtained by a photosensitive pixel having a lower photoelectric sensitivity characteristic, and the low-sensitivity charge Low-sensitivity exposure time varying means for varying the exposure time of the photosensitive pixel with the lower photoelectric sensitivity characteristic in accordance with the amount of charge detected by the amount detection means, When the charge amount is large, the exposure time of the photosensitive pixel with the lower photoelectric sensitivity characteristic is shortened, and when the charge amount of the low-sensitivity signal charge is small, the exposure time of the photosensitive pixel with the lower photoelectric sensitivity characteristic is lengthened. Thus, it is possible to obtain a high-quality image free from underexposure and overexposure.

According to the third aspect of the present invention, there is provided a high-sensitivity charge detecting means for detecting a high-sensitivity signal charge obtained by a photosensitive pixel having a higher photoelectric sensitivity characteristic. High sensitivity exposure time varying means for varying the exposure time of the photosensitive pixel having the higher photoelectric sensitivity characteristic in accordance with the amount of charge detected by the quantity detection means. When the high-sensitivity signal charge detected by the means has a large amount of charge, the high-sensitivity exposure time varying means shortens the exposure time of the photosensitive pixel having the higher photoelectric sensitivity characteristic to capture a high-luminance subject. However, it is possible to prevent a photosensitive pixel having a higher photoelectric sensitivity characteristic from being saturated, and to obtain a high-quality image.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a CCD solid-state imaging device to which the present invention is applied.

FIG. 2 is a timing chart of a vertical transfer pulse.

FIG. 3 is a timing chart of a reset pulse.

FIG. 4 is a potential diagram for explaining a reset operation, a clip operation, and an addition operation of a signal charge.

FIG. 5 is a block diagram illustrating an embodiment of a solid-state imaging device according to the present invention.

FIG. 6 is an output characteristic diagram of light quantity-signal voltage according to the embodiment of the present invention.

FIG. 7 is a timing chart illustrating specific means for varying the exposure time of a photosensitive pixel.

[Explanation of symbols]

12 (12e, 12o): photosensitive pixel, 19: FD (floating diffusion) section, 20: RD (reset drain) section, 21-1, 21-2: reset gate electrode, 24: buffer, 25: timing generator,
26: CCD imaging device, 27 to 32: S / H (sample hold) circuit, 33 to 35: subtractor, 36: logarithmic amplifier, 37: exposure time calculator

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[Procedure amendment]

[Submission date] September 8, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0046

[Correction method] Change

[Correction contents]

More specifically, the accumulation time of the signal charge in the low-sensitivity pixel is usually from the rising timing of the shutter pulse φSUB after the read pulse rises to the vertical transfer pulse φV2a, as shown in FIG. It is determined by the period Tf until the read pulse rises at φV2b. Then, another shutter pulse φSUB is added between the shutter pulse φSUB and the vertical transfer pulse φV2b, and the position (rising timing) of the added shutter pulse φSUB is changed to control the exposure time of the low-sensitivity pixel. I do. Thus, for example, when the additional pulse φSUB rises at the position shown in the figure, the exposure time of the low-sensitivity pixel becomes Ta, and when the additional pulse φSUB rises at the position shown in the figure, the exposure time of the low-sensitivity pixel becomes Is limited to Tb shorter than Ta.

Claims (3)

[Claims] 1. A high-sensitivity signal obtained by a photosensitive pixel having a higher photoelectric sensitivity characteristic among a plurality of types of photosensitive pixels having different photoelectric sensitivity characteristics among signal charges obtained by the plurality of types of photosensitive pixels. In the solid-state imaging device, the charge is clipped at a predetermined clip level, and the low-sensitivity signal charge obtained by the photosensitive pixel having the lower photoelectric sensitivity characteristic is added to the high-sensitivity signal charge after the clipping. High-sensitivity charge detection means for detecting the amount of high-sensitivity signal charge obtained by the photosensitive pixel having the higher photoelectric sensitivity characteristic; and the clip according to the charge detected by the high-sensitivity charge detection means. A solid-state imaging device comprising: a clip level varying unit that varies a level. 2. A high-sensitivity signal obtained by a photosensitive pixel having a higher photoelectric sensitivity characteristic among a plurality of types of photosensitive pixels having different photoelectric sensitivity characteristics, among signal charges obtained by the plurality of types of photosensitive pixels. In the solid-state imaging device, the charge is clipped at a predetermined clip level, and the low-sensitivity signal charge obtained by the photosensitive pixel having the lower photoelectric sensitivity characteristic is added to the high-sensitivity signal charge after the clipping. A low-sensitivity-charge-amount detecting unit that detects a charge amount of a low-sensitivity signal charge obtained by the photosensitive pixel having the lower photoelectric sensitivity characteristic, and, in accordance with the charge amount detected by the low-sensitivity-charge-amount detecting unit, A solid-state imaging device comprising: a low-sensitivity exposure time varying unit that varies an exposure time of a photosensitive pixel having a lower photoelectric sensitivity characteristic. 3. A high-sensitivity signal obtained by a photosensitive pixel having a higher photoelectric sensitivity characteristic among a plurality of types of photosensitive pixels having different photoelectric sensitivity characteristics among signal charges obtained by the plurality of types of photosensitive pixels. In the solid-state imaging device, the charge is clipped at a predetermined clip level, and the low-sensitivity signal charge obtained by the photosensitive pixel having the lower photoelectric sensitivity characteristic is added to the high-sensitivity signal charge after the clipping. A high-sensitivity charge amount detection unit that detects a charge amount of a high-sensitivity signal charge obtained by the photosensitive pixel having the higher photoelectric sensitivity characteristic, and, according to the charge amount detected by the high-sensitivity charge amount detection unit, A solid-state imaging device comprising: a high-sensitivity exposure time varying unit that varies an exposure time of a photosensitive pixel having a higher photoelectric sensitivity characteristic.