JPH05260391A - Solid-state image pickup element - Google Patents

Abstract

PURPOSE:To obtain the solid-state image pickup device in which a dynamic range depending on a charge quantity processed by a vertical charge transfer section is expanded without deteriorating a sensor sensitivity. CONSTITUTION:In the still picture use camera system having a mechanical shutter in front of a light receiving section of a CCD solid-state image pickup element 10, a signal charge as to a video image stored in a photosensor 1 is read to a vertical register 3 for plural number of times and the signal voltage based on the signal charge by plural number of times is synthesized by signal processing systems 12, 13, 14. The dynamic range of the CCD solid-state image pickup element 10 depending on the processed charge quantity of the vertical register 3 is expanded.

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,
In particular, the present invention relates to a solid-state image pickup device suitable for use in a still image camera system having a means for limiting the exposure time such as a mechanical shutter.

[0002]

2. Description of the Related Art FIG. 4 shows an example of the structure of an interline transfer type CCD solid-state image pickup device. In the figure, photosensors (light receiving portions) 1 which are two-dimensionally arranged in pixel units and photoelectrically convert incident light into signal charges and accumulate the signal charges, and photosensors 1 arranged in each vertical column of the photosensors 1 and through a read gate 2 An imaging region 4 is configured by a vertical register (vertical charge transfer unit) 3 that vertically transfers the read signal charges.

The vertical register 3 transfers the signal charges read from the photosensor 1 to a horizontal register (horizontal charge transfer section) 5 in a cycle of one horizontal scanning period. Horizontal register 5
Horizontally transfers the signal charges for one scanning line transferred from the vertical register 3. At the output end of the horizontal register 5, a charge detection unit 6 composed of, for example, a floating diffusion amplifier is arranged. The charge detection unit 6 detects the signal charge transferred by the horizontal register 5 and converts it into a signal voltage. Then, the pixel signals corresponding to the signal charges accumulated in each photosensor 1 are output in time series.

In such a CCD solid-state image pickup device, its dynamic range is determined by the amount of charge handled by the vertical register 3 (or horizontal register 5). Therefore, when a signal charge that exceeds the amount of charge handled in each transfer register 3 and 5 is input from the photo sensor 1, normal transfer cannot be performed, and thus the CCD solid-state image sensor cannot output a normal image signal. ..

For this reason, the photosensor 1 is provided with an overflow drain structure for discharging excess charges. For example, in a photo sensor with a vertical overflow drain structure, the vertical overflow barrier is controlled by the impurity concentration distribution in the sensor section and the voltage applied to the substrate section to determine the amount of charge that can be accumulated in the sensor section. ing.

This charge amount is set so as not to exceed the charge amount handled by the vertical register 3 even when light having the maximum intensity in the use range enters the sensor section. In other words, if the vertical register 3 has more charge to be handled, more signal charge can be stored in the sensor unit. Further, if the vertical register 3 is not limited in the amount of electric charges handled, it should be possible to store more signal charges in the sensor section even in terms of its area.

[0007]

By the way, the present CC
The D solid-state image sensor has a drawback that its dynamic range is lower than that of a silver plate photograph. Especially when a CCD solid-state image sensor is used for recording a still image, the low dynamic range is fatal. To increase the dynamic range, the amount of charge handled by the vertical register 3 may be increased. However, the amount of charge handled by the vertical register 3 largely depends on the width thereof, and widening the width simultaneously narrows the sensor opening. Become. When the sensor opening is narrowed, the sensitivity of the photo sensor 1 is lowered, which causes a problem in device characteristics.

The present invention has been made in view of the above points, and a solid-state image pickup device capable of expanding the dynamic range determined by the amount of charges handled by the vertical charge transfer section without lowering the sensor sensitivity. The purpose is to provide.

[0009]

A solid-state image pickup device according to the present invention is a solid-state image pickup device used in a camera system having means for limiting an exposure time. A solid-state image sensor having a charge transfer unit for sequentially transferring the signal charges accumulated in the image pickup unit and a charge detection unit for detecting the signal charges transferred by the charge transfer unit and converting the signal charges into a signal voltage; Based on the signal charge of the final read while storing a signal voltage based on the signal charge of each time read in multiple times and a drive circuit that drives the read signal charges to be read out to the charge transfer unit in multiple times. And a signal processing circuit for combining the signal voltage and an image output.

Further, the solid-state image pickup device according to the present invention is provided with a light receiving section which is two-dimensionally arranged in pixel units, a charge transfer section for sequentially transferring signal charges accumulated in the light receiving section, and a charge transfer section provided in the middle of the charge transfer section. Stored in the light receiving section, and a solid-state image sensor having a storage section for temporarily storing the signal charge transferred by the charge transfer section and a charge detection section for detecting the signal charge transferred by the charge transfer section and converting the signal charge into a signal voltage. The read signal charge is divided into a plurality of times and read out to the charge transfer section, and the read signal charge of each time is accumulated in the accumulation section and is driven so as to be transferred while being combined with the signal charge of the final read. And a drive circuit.

[0011]

In the still image camera system having a means for limiting the exposure time such as a mechanical shutter, the signal charge for one image accumulated in each light receiving portion of the solid-state image pickup device is divided into a plurality of times to the charge transfer portion. By reading out and synthesizing the signal voltage based on the signal charges of the plurality of times in the signal processing system, the dynamic range of the solid-state imaging device determined by the charge amount handled by the charge transfer unit can be expanded.
In addition, since it is not necessary to increase the amount of charge handled by the charge transfer unit, the opening area of the sensor opening that is influenced by the width of the vertical register can be maintained, and thus the sensitivity is not reduced.

In addition, another storage section is provided in the middle of the charge transfer section in the solid-state image pickup device, the signal charges read out from the light receiving section in a plurality of times are temporarily stored in this storage section, and the stored charges are finally stored. Although it is necessary to increase the amount of charge handled by the transfer unit of the combined signal charge by combining it with the signal charge for reading, the amount of charge handled by the vertical charge transfer unit in the imaging area can remain the same, thus reducing sensor sensitivity. The dynamic range of the solid-state imaging device, which is determined by the amount of charges handled by the vertical charge transfer unit, can be expanded without performing the above.

[0013]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a configuration diagram showing an embodiment of the present invention, and shows a case where the present invention is applied to an interline transfer type CCD solid-state image sensor used in a still image camera system having a mechanical shutter for limiting an exposure time. The CCD solid-state image pickup device 10 has the same structure as the conventional one, and the front shutter (not shown) is arranged on the front surface of the light receiving portion thereof.

In the figure, a timing generator 7 outputs a clock pulse V for driving the vertical register 3 in four phases.
and φ ₁ ~Vφ _4, the clock pulses H.phi ₁ for driving the horizontal register 5 2 phases, various timing signals such as H.phi ₂ is generated. Of these various timing signals, clock pulses H.phi ₁ of 2 phases for the clock pulse Vφ ₁ ~Vφ ₄ and the horizontal drive of the four-phase for vertical driving, H.phi
₂ is supplied to the vertical register 3 and the horizontal register 5 via the drive circuit 8, respectively.

Four-phase clock pulse V for vertical driving
Of φ _{1 to} Vφ ₄ , the first-phase clock pulse Vφ ₁ and the third-phase clock pulse Vφ ₃ each take three levels of high level, intermediate level, and low level, and the high-level pulse is the photosensor. It is used as a read pulse of the signal charge from 1. Further, in the present invention, the amount of signal charge read from the photosensor 1 to the vertical register 3 at a time is limited, and the peak value of the read pulse is set according to the number of times of reading in order to read the signal charge in a plurality of times. The drive circuit 8 controls the peak value so as to raise it stepwise.

The output signal of the charge detector 6 is digitized by the A / D converter 12 after passing through the sample hold (S / H) circuit 11, and each signal before the final read is read out in the memory 13 in a plurality of readings. Memorized in. Then, the signal from the final read is supplied to the combining circuit 14,
By being combined with each signal stored in the memory 13 up to that point, it is derived as a pixel signal by signal charge for one image accumulated in the photo sensor 1.

Next, the operation when the signal charges accumulated in the photosensor 1 are divided into a plurality of times and read out to the vertical register 3 will be described with reference to FIG. First, in a state (a) in which the shutter arranged on the front surface of the light receiving unit is closed and the CCD solid-state image sensor 10 is not exposed to light, photoelectric conversion is not performed in the photosensor 1, and therefore the photosensor 1 receives a signal. No charge is stored.

Next, the shutter is opened, and the image pickup area of the CCD solid-state image pickup device 10 starts to be irradiated with light, and at the same time, the signal charge starts to be accumulated in the photosensor 1 by photoelectric conversion according to the incident light amount (b). After a certain exposure time, the shutter is closed, the generation of the signal charge in the photo sensor 1 is finished, and the signal charge is accumulated in the photo sensor 1. At this time, if the signal charge accumulated in the photosensor 1 is within the amount of charge handled by the vertical register 3,
The signal charge in the photo sensor 1 may be read into the vertical register 3 as usual.

However, if the signal charge accumulated in the photosensor 1 is larger than the amount of charge handled by the vertical register 3, all the signal charges in the photosensor 1 are not read out at once, and the vertical register 3 is sufficiently discharged. Only the amount (a part of the signal charge) that can be transferred is read (b). In order to read only part of this signal charge from the photosensor 1, as described above, the peak value of the read pulse (Vφ ₁ or Vφ ₃ ) of the signal charge from the photosensor 1 should be set lower than that during normal reading. Good.

A part of the signal charge read out to the vertical register 3 is vertically and horizontally transferred in the same manner as in the normal transfer, and converted into a signal voltage in the charge detection unit 6. This signal voltage, after passing through the sample hold circuit 11, is A /
It is digitized by the D converter 12 and stored in the memory 13. At this time, unread signal charges are accumulated in the photo sensor 1 (d).

After that, the remaining signal charges in the photosensor 1 are read to the vertical register 3, and the read signal charges are vertically and horizontally transferred in the same manner as in the above case.
This signal charge is converted into a signal voltage by the charge detection unit 6,
After passing through the sample hold circuit 11 and the A / D converter 12, the signal voltage is supplied to the combining circuit 14 and is combined with the signal voltage stored in the memory 13, and is output as a video signal by the signal charge accumulated in the photo sensor 1. It

As described above, the signal charges for one image accumulated in the photosensor 1 are read out to the vertical register 3 in plural times, and the signal voltage based on the separately read out signal charges is combined in the signal processing system. By doing so, it is possible to expand the dynamic range of the CCD solid-state imaging device 10 which is determined by the amount of charge handled by the vertical register 3. Moreover, since it is not necessary to increase the amount of charges handled by the vertical register 3, the opening area of the sensor opening that depends on the width of the vertical register 3 can be maintained, and therefore the sensor sensitivity does not decrease.

In this example, the case where the signal charge accumulated in the photosensor 1 is read out to the vertical register 3 in two times has been described. However, the amount of signal charge that can be accumulated in the photosensor 1 is described. From the relationship between the amount of charge handled by the vertical register 3 and the vertical register 3, the reading from the photosensor 1 to the vertical register 3 is not limited to two times and may be performed in three or more times.

FIG. 3 is a CCD showing another embodiment of the present invention.
It is a block diagram of a solid-state image sensor. In the present embodiment, instead of converting the signal charges read out from the photosensor 1 to the vertical register 3 a plurality of times into the signal voltage after being converted into the signal voltage in the signal processing system as in the case of the above embodiment, the vertical register 3 is combined. In the middle of 3, the storage unit 15 is provided corresponding to each photosensor 1 in the imaging region 4, the storage unit 15 is temporarily stored, and the stored charge is combined with the signal charge of the final read. There is.

According to this structure, although the amount of charge handled in each of the vertical register 3'and the horizontal register 5 in the storage region 16 needs to be increased, the amount of charge handled in the vertical register 3 in the image pickup region 4 can remain unchanged. The dynamic range of the CCD solid-state imaging device 10 can be expanded without lowering the sensor sensitivity.

In each of the above-mentioned embodiments, the case where the invention is applied to the CCD solid-state image pickup device of the interline transfer system has been described. However, the present invention is not limited to this, and the present invention is a CCD of the frame interline transfer system. It is similarly applicable to a solid-state image sensor.

[0027]

As described above, according to the present invention,
In a still image camera system having a mechanical shutter on the front surface of the light receiving unit of the solid-state image sensor, the signal charges of one image accumulated in each light-receiving unit of the solid-state image sensor are read out to the charge transfer unit in a plurality of times. By combining the signal voltage based on the signal charges of multiple times in the signal processing system, the dynamic range of the solid-state imaging device, which is determined by the charge amount handled by the charge transfer unit, can be expanded, and the charge handled by the charge transfer unit can be expanded. Since it is not necessary to increase the amount, it is possible to maintain the opening area of the sensor opening that depends on the width of the vertical register, and thus the sensor sensitivity does not decrease.

Further, another storage section is provided in the middle of the charge transfer section in the solid-state image pickup device, the signal charges read out from the light receiving section in a plurality of times are temporarily stored in this storage section, and the stored charges are finally stored. Since it is necessary to increase the amount of charge handled by the transfer unit of the combined signal charge by combining it with the signal charge for reading, the amount of charge handled by the vertical register in the imaging area can remain the same. Therefore, the dynamic range of the solid-state image pickup device can be expanded without any decrease.

[Brief description of drawings]

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

FIG. 2 is a cross-sectional view of a photo sensor, a read gate, and a vertical register for explaining a signal charge read operation from the photo sensor.

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

FIG. 4 is a configuration diagram of an example of an interline transfer type CCD solid-state imaging device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensor 3 Vertical register 4 Imaging area 5 Horizontal register 7 Timing generator 10 CCD solid-state imaging device 12 A / D converter 13 Memory 14 Compositing circuit 15 Storage section 16 Storage area

Claims (2)

[Claims] 1. A solid-state imaging device for use in a camera system having means for limiting an exposure time, comprising: a light-receiving section that is two-dimensionally arranged in pixel units; and a charge that sequentially transfers signal charges accumulated in the light-receiving section. A solid-state imaging device having a transfer section and a charge detection section for detecting the signal charge transferred by the charge transfer section and converting the signal charge into a signal voltage; and dividing the signal charge accumulated in the light receiving section into a plurality of times. A drive circuit that drives the charge transfer unit to read out, and a signal voltage based on the signal charge of each time read out a plurality of times is stored while being combined with the signal voltage based on the signal charge of the final read out to obtain an imaging output. A solid-state imaging device comprising a signal processing circuit. 2. A solid-state imaging device for use in a camera system having means for limiting an exposure time, comprising: a light-receiving section that is two-dimensionally arranged in pixel units, and a charge that sequentially transfers signal charges accumulated in the light-receiving section. A transfer unit, a storage unit provided in the middle of the charge transfer unit for temporarily storing the transferred signal charge, and a charge detection for detecting the signal charge transferred by the charge transfer unit and converting the signal charge into a signal voltage. A solid-state imaging device having a unit, and reading the signal charges accumulated in the light receiving unit into the charge transfer unit in a plurality of times, and accumulating the read signal charges at each time in the accumulation unit and accumulating the accumulated signal charges. A solid-state imaging device comprising: a drive circuit that drives to transfer electric charges while combining the electric charges with signal charges for final reading.