JPH07322148A - Solid-state image pickup device and its driving method - Google Patents

Abstract

PURPOSE:To prevent the increase of a dark current to improve the picture quality for high-sensitivity image pickup by performing the high-speed vertical transfer operation only in the vertical fly-back time, when signal electric charge is read out, but inhibiting this operation in the other vertical fly-back time at the time of high-sensitivity image pickup to suppress the generation of heat due to high-speed transfer. CONSTITUTION:A read pulse and a high-speed transfer pulse out of driving pulses are outputted from a read pulse generating circuit 4 and a high-speed transfer pulse generating circuit 5 respectively. Output timings of the read pulse and the high-speed transfer pulse are controlled in accordance with storage time setting by a control circuit 6. This storage time setting means setting or the sensitivity mode and the sensitivity magnification. The control circuit 6 can turn off the high-speed transfer pulse generating circuit 5 to inhibit the generation of the high-speed transfer pulse at a prescribed timing at the time of high-sensitivity image pickup. Consequently, the frequency in occurrence of the high-speed transfer pulse is reduced to 1/N in the N-fold high-sensitivity image pickup mode, and thereby, heat generation due to high-speed transfer is reduced to 1/N.

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 using a charge storage type image pickup device, and more particularly to a high-speed transfer type solid-state image pickup device and a driving method thereof.

[0002]

2. Description of the Related Art In a solid-state image pickup device such as a CCD, a smear phenomenon is apt to occur when a high-intensity portion is present on an image pickup screen, and the image quality is remarkably low. In order to suppress this phenomenon, FI
A high-speed vertical transfer method is generally adopted in the T (frame interline transfer) structure.

FIG. 3 is a schematic diagram showing a planar structure of a FIT type CCD image pickup device. As shown in the figure, photosensitive parts 101 made of photodiodes are arranged in an area, and a vertical transfer part 102 made of a CCD is provided for each vertical line. The signal charge accumulated in the photosensitive section 101 is
After being read by the vertical transfer unit 102 for each vertical line, it is transferred at high speed and stored in the memory unit 103. And C
The image pickup signal is sequentially read by the horizontal transfer unit 104 including a CD through the amplifier 105 for each horizontal line.

FIG. 4 is a timing chart showing an example of a driving method in a conventional solid-state image pickup device. In a period in which the vertical synchronizing signal is rising, that is, a vertical retrace line period, first, before the read pulse, unnecessary charges in the vertical transfer unit 102 are discharged by the high-speed transfer pulse _{PHS of} 1 MHz. Then, the photosensitive member 101 is read by the read pulse.
The accumulated charge of is transferred to the vertical transfer unit 102. Then 1
The vertical transfer unit 102 uses the high-speed transfer pulse P _{HS of} MHz.
Signal charges are transferred from the memory unit 103 to the memory unit 103 at high speed. The signal charges transferred to the memory unit 103 are sequentially read for each horizontal line according to the horizontal synchronization pulse.

By the way, in such a CCD image pickup device, it is possible to adjust the amount of charge accumulated in each photosensitive portion 101 by changing the interval of the read pulse. For example, the read pulse interval is 1/60 second to 1/30
When switching to seconds, the number of frames per second is halved, but the charge storage time is doubled, so that the image sensor can be operated in the high sensitivity mode.

[0006]

However, in the above-mentioned conventional method, the high-speed transfer pulse is supplied to the CCD image pickup device every vertical blanking period regardless of the normal sensitivity mode and the high sensitivity mode. There is a problem that the temperature rises, the dark current increases, and the image quality deteriorates. In particular, in the high sensitivity mode, the dark current also increases in proportion to the accumulation time, so that the deterioration of image quality becomes a serious problem.

For example, in the case of a 2-inch CCD image pickup device of 1-inch format, the load capacity of the vertical transfer section is large, and therefore, when high-speed transfer is performed at 1 MHz, 300
Power of about mW is consumed, and a part of the power becomes heat to raise the temperature of the element.

An object of the present invention is to provide a solid-state image pickup device which suppresses an increase in temperature and improves image quality during high-sensitivity image pickup, and a driving method thereof.

[0009]

A solid-state image pickup device according to the present invention is of a system in which signal charges of a charge storage type image pickup device are vertically transferred at high speed and read out during a vertical retrace period, and read out for reading out signal charges. An accumulation time setting means for setting the accumulation time of the signal charge by generating a pulse, a high-speed pulse generation means for generating a high-speed pulse for high-speed vertical transfer, and a high-speed pulse only for generating a read pulse. Other than that, it is characterized by comprising control means for inhibiting the generation of high-speed pulses.

Further, according to the driving method of the present invention, in a solid-state image pickup device capable of performing normal image pickup or high-sensitivity image pickup by controlling the length of the accumulation time of the charge storage type image pickup element, a vertical retrace line is provided during normal image pickup. The high-speed vertical transfer of the accumulated charge of the charge storage type image sensor is performed for each period, and the high-speed vertical transfer of the accumulated charge is performed only during the vertical retrace period of the period corresponding to the length of the accumulation time during high-sensitivity imaging. Characterize.

[0011]

In normal imaging, high-speed vertical transfer is performed in each vertical blanking period in order to suppress vertical smear, and signal charges are read out. However, in high-sensitivity imaging, countermeasures against smear are considered unnecessary, so signal charges are read out. High-speed vertical transfer is performed only during the vertical retrace line period, and high-speed vertical transfer operation is prohibited during other vertical retrace line periods. Thereby, heat generation due to high-speed transfer can be suppressed.

[0012]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a block diagram of a solid-state image pickup device for realizing the signal reading method according to the present invention. In the figure, the CCD image pickup device 1 is a FIT type C shown in FIG.
This is a CD image pickup device, and its image pickup signal is subjected to predetermined processing by the video signal processing circuit 2 and output as a video signal.

The CCD image pickup device 1 performs the above-mentioned signal charge reading operation by the drive pulse from the drive circuit 3.
That is, the drive pulse includes a high speed transfer pulse, a read pulse, a vertical sync pulse, a horizontal sync pulse, and other necessary pulses.

The read pulse among the drive pulses is output from the read pulse generating circuit 4, and the high speed transfer pulse is output from the high speed transfer pulse generating circuit 5. The output timing of the read pulse and the high-speed transfer pulse is controlled by the control circuit 6 according to the accumulation time setting. The accumulation time setting means setting of the sensitivity mode and the sensitivity magnification. Furthermore,
The control circuit 6 can turn off the high-speed transfer pulse generation circuit 5 at a predetermined timing during high-sensitivity imaging, and can inhibit high-speed pulse generation.

FIG. 2 is a timing chart showing an embodiment of the signal reading method according to the present invention.

First, at the time of normal image pickup, the accumulation time is 1/60
The control circuit 6 generates a read pulse in the same 1/60 second cycle as the vertical synchronizing signal in the vertical blanking period, and further generates the high-speed transfer pulse shown in FIG. And the high-speed vertical transfer of signal charges. Thereby, the smear phenomenon can be effectively suppressed.

At the time of high sensitivity imaging, for example, the accumulation time is 1 /
When set to 20 seconds, high-sensitivity imaging that is three times that in the normal mode is performed. At that time, the control circuit 6 turns off the high-speed transfer pulse generation circuit 5 so as to prohibit the generation of the high-speed transfer pulse during the vertical blanking period during which the read pulse is not output.
Set to F. That is, as shown in FIG. 2, the high-speed transfer pulse is only output at a 1/20 second cycle like the read pulse, and is output at a 1/60 second cycle every vertical blanking period as in the conventional case. There is no such thing. This is because the smear phenomenon does not become a problem because the subject is dark at the time of high-sensitivity imaging.

Therefore, in the N times high-sensitivity imaging mode, the frequency of high-speed transfer pulses is 1 / N, and the amount of heat generated by high-speed transfer is also reduced to 1 / N. The higher the magnification of high sensitivity, the lower the amount of heat generation, and therefore the image quality of a dark object is improved.

[0020]

As described in detail above, the solid-state image pickup device and the driving method according to the present invention suppress the temperature rise of the image pickup device by performing the high-speed vertical transfer only during the vertical retrace line period during which the signal charges are read out. Therefore, it is possible to prevent an increase in dark current and improve the image quality during high-sensitivity imaging.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of a solid-state imaging device for realizing a signal reading method according to the present invention.

FIG. 2 is a timing chart showing an embodiment of a signal reading method according to the present invention.

FIG. 3 is a schematic diagram showing a planar structure of a FIT type CCD image pickup device.

FIG. 4 is a timing chart showing an example of a conventional signal reading method.

[Explanation of symbols]

 1 CCD image pickup device 2 video signal processing circuit 3 CCD drive circuit 4 read pulse generation circuit 5 high speed transfer pulse generation circuit 6 control circuit

Claims (3)

[Claims] 1. A solid-state image pickup device of a type in which signal charges of a charge storage type image pickup device are vertically transferred at a high speed during a vertical retrace period to read the signal charges by generating a read pulse for reading the signal charges. A storage time setting means for setting a storage time, a high speed pulse generation means for generating a high speed pulse for performing the high speed vertical transfer, a high speed pulse only when the read pulse is generated, and a high speed pulse otherwise. A solid-state imaging device comprising: a control unit that prohibits the generation of pulses. 2. A solid-state image pickup device capable of performing normal image pickup or high-sensitivity image pickup by controlling the length of the accumulation time of the charge storage type image pickup device, wherein a read pulse for reading the accumulated charge of the image pickup device is provided. Read pulse generating means for generating, high-speed pulse generating means for generating high-speed pulse for performing high-speed vertical transfer of the accumulated charge, and high-speed vertical transfer of the accumulated charge for reading every accumulated vertical charge during the normal imaging A control means for controlling the read pulse and the high speed pulse so that the high-speed vertical transfer of the stored charge is performed only during the vertical retrace period of the cycle corresponding to the length of the storage time during the high-sensitivity imaging. A solid-state imaging device characterized by the above. 3. A driving method of a solid-state image pickup device capable of performing normal image pickup or high-sensitivity image pickup by controlling a storage time length of a charge storage type image pickup element, wherein at the time of the normal image pickup, every vertical blanking period. At the time of the high-sensitivity imaging, the accumulated charge of the charge-accumulation-type image sensor is read at a high speed, and the accumulated charge is read at a high-speed vertical transfer only during a vertical retrace period of a period corresponding to the length of the accumulation time. A method for driving a solid-state imaging device, comprising: