JPS605681A - Method and apparatus of solid-state image pickup - Google Patents

Abstract

PURPOSE:To improve the contrast by controlling the conduction/nonconduction of a leakage switch provided to each of a photo sensing element by means of a control signal so as to attain high speed photographing without any shutter. CONSTITUTION:Each of the photo sensing elements 8 arranged in a matrix is provided with the switch 13 leaking a charge generated by the photoelectric effect. The image pickup time is set optionally by controlling the conductive/ nonconductive state of the leakage switch 13 by means of the control signal.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a solid-state imaging device and an imaging method.

Conventional Structures and Their Problems Recently, solid-state imaging devices consisting of a photodiode matrix and various scanning elements have been developed and are being used in portable video cameras and the like. The scanning element is CCD (Charge Coupled D
evice), BBD (Bucket Brigade)
Device), MOS shift register, etc. are used. FIG. 1 shows a block diagram of a conventional interline CCD solid-state imaging device for a video camera. It consists of photodiodes 1 arranged in a matrix, a large number of CCD lines 2 arranged in the vertical direction, one row of CCD lines 3 arranged in the horizontal direction, transfer gates 4, and the like.

The photodiode 1 detects an image signal proportional to the exposure amount in the form of an electric charge, and the transfer gate 4 simultaneously detects the C signal attached to each photodiode 4 on a one-to-one basis.
The charge corresponding to the image signal is sent to the CD charge well, transferred by the vertical transfer clock 5 and the horizontal transfer clock 6, and after amplification, the image signal is sequentially taken out from the output terminal 7. The time sequence of image transfer in this conventional example is shown in the second example.
As shown in the figure. The upper pulse waveform is a signal applied to the transfer gate 4, and its period Th is one frame time.

Section A is the first frame shooting time, B is the photodiode signal of the fourth frame signal is active) C is the first frame transfer time, D is the second frame shooting time, E is the sending time of the second frame signal, F is the second frame signal transfer time,
g is the third frame imaging time.

The solid-state imaging device shown in FIG. 1 was developed for use in industrial or consumer TV images, and there is a limit to the imaging speed (minimum exposure time) due to the scanning frequency of the TV. In other words, the frame period of a standard TV picture is 1
/30 seconds. If the number of scanning lines is 525 trees, the horizontal scanning period will be 6.35×10 −5 seconds. Increase the number of horizontal images to 50
If it is 0, the clock period for horizontal scanning is 6.3
5x10-5/500-0.127 microseconds, converted to frequency, is 7.87 MHz. This is close to the limit of the clock frequency of the scanning device mentioned above. Therefore, the minimum exposure time for such an imaging device is approximately 1/
It is considered to be 30 seconds. If you reduce the image quality, you can increase the speed a little more, but with conventional methods, it is difficult to achieve both image quality and shooting speed. The exposure time of 1/30 second is longer than that of a general optical camera. When the subject is a moving body, the image taken with a video camera appears to flow. When viewed as both images of a moving object or as a still image, or when viewed time-lapse, the image becomes blurred and unclear. This is a particularly big drawback in the case of still image video cameras that can not only be viewed on a cathode ray tube, but can also make hard copies. For example 1/500 second or 1/
A video camera that can take pictures at a fast shutter speed (exposure time) such as 1000 seconds is desired.

However, as mentioned above, in conventional solid-state imaging devices, the exposure time and scanning time for photographing are the same, so the minimum value of the exposure time is determined by the minimum possible value of the scanning time.
High-speed photography is difficult unless used in conjunction with a mechanical shutter.

In addition, conventionally, when photographing a bright subject, both sides become white and contrast cannot be obtained, so a means for measuring the brightness of the subject is provided separately from the solid-state imaging device.
At present, the overflow drain electrode S1 and the overflow gate electrode S2 shown in the figure are controlled to prevent a decrease in contrast.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a solid-state imaging device capable of high-speed imaging without a mechanical shutter, and an imaging method capable of obtaining images with good contrast with a simple configuration.

Structure of the Invention The solid-state imaging device of the present invention includes photosensitive elements arranged in a matrix, transfer gates connected to each of the photosensitive elements, a CCD for vertical scanning, and a CCD for horizontal scanning, and a CCD connected to each of the photosensitive elements. The present invention is characterized in that a leak switch and a leak electrode are provided, and the leak switch is made conductive during unnecessary exposure time to inhibit charge accumulation in the photosensitive element.

Furthermore, the imaging method of the present invention prohibits the loading of a charge on the photosensitive element with a leak switch connected to each exposure element in a conductive state during the unnecessary exposure time, and uses the leakage current during the unnecessary exposure time to open the aperture device. It is characterized by controlling the rate.

The leak switch is made up of TFTs (field effect transistors) in high density, one electrode (source electrode) of which is connected to each active electrode, and the drain electrodes of the TFTs are commonly connected to act as a photocurrent leak electrode. becomes. Further, the gate electrodes of the TFTs are connected in common, and a control signal is applied to keep the FETs in a non-conducting state only for the necessary exposure time. Due to the action of this leak switch, only the image signal generated by the photosensitive element during the required exposure time is sent through the transfer gate to the charge well of the CCD in one-to-one correspondence with the photosensitive element.
The D function allows an image signal to be obtained from the output terminal. Note that the magnitude of leakage current is proportional to the brightness of the entire image, so by controlling the aperture diameter of the aperture using this current, it is possible to simplify the configuration and obtain images with good contrast. It is something.

DESCRIPTION OF THE EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. Third
The figure is a block diagram of a solid-state imaging device according to the present invention. 8
is a photodiode for light detection, 9 is a CCD for vertical transfer, and 10 is a CCD for horizontal transfer.
, 11 is a transfer gate FET whose gate electrodes are commonly connected to a transfer gate signal terminal 1.
Connected to 2. Reference numeral 13 denotes an FET for leaking optical signals during unnecessary photographing time, the sources of which are connected to the respective electrodes of the photodiodes 8 in one-to-one correspondence, and the drains thereof are commonly connected to the leak electrode terminal 14. Further, the gate electrodes of the FETs 13 are connected in common to a leak control electrode terminal 5 for controlling the imaging time. 16 is a video output amplifier, and 17 is a voltage conversion circuit that generates an aperture control signal using leakage current and is composed of an operational amplifier.

This imaging device operates as follows. When photographing, a desired power supply voltage is applied to the power supply terminal, and the leak electrode terminal 14 is installed. In preparation before photographing, an active signal is applied to the leak control electrode terminal 15 to turn the leak FET 13 into a conductive state and to completely discharge the optical signal charge of the photodiode 8. Furthermore, an inactive signal is applied to the transfer gate 12. is added to keep the transfer gate FET 11 in a non-conductive state. Next, an inactive signal is applied to the leak control electrode terminal 15 for a desired photographing time (exposure time) to make the leak FET 13 non-conductive.

During this time, a charge proportional to the optical signal is stored in the photodiode 8. Next, a Noah signal is applied to the transfer gate 12 to turn on the transfer gate FET 11 and transfer the optical signal charge from the photodiode 8 to the C
to the charge wells in the CD. At the end of transmission, an inactive signal is applied to the transfer gate 12 to make the transfer gate FET 11 non-conductive, and then the COD transfer lock 1819 transfers the optical signal charge vertically and horizontally to obtain an image signal from the output terminal.

FIG. 4 shows the time sequence of imaging and signal charge transfer. The timing of imaging is determined by the timing of the leak gate pulse and the transfer gate pulse, and can be arbitrarily limited, and can be made shorter than one frame transfer time. For example, fast photographing of 1/500 second or 1/1000 second is also possible.

Charge transfer is determined by a transfer gate pulse and a transfer clock.

In FIG. 4, 1 is the first frame imaging time, II is the fourth frame signal transfer time, III is the second frame imaging time, and IV is the second frame transfer time.

By controlling the FET as a leak switch in this manner, the imaging and transfer times can be set independently, allowing high-speed imaging. Here, since the magnitude of the leakage current is proportional to the brightness of the entire image, by controlling the aperture diameter of the aperture using this leakage current, the exposure amount can be automatically adjusted without providing a separate light detection means. can be done.

In the above embodiment, the photodiode 8 is used as the photosensitive element, but any element having a photoelectric conversion function can be used for the same purpose; for example, a phototransistor may be used. Furthermore, although a field effect transistor is used as the leak switch, a bipolar transistor can also be used.

Effects of the Invention As described above, the solid-state imaging device of the present invention includes a switch for leaking charges generated by the photoelectric effect in each of the photosensitive elements arranged in a matrix,
Since the conducting or non-conducting state of this leak switch can be controlled with a control signal and the imaging time can be arbitrarily set, high-speed imaging is possible without a mechanical shutter, and a moving subject can be clearly imaged. It is also effective for still image cameras.

Further, according to the imaging method of the present invention, since the aperture diameter of the comparison switch is controlled according to the magnitude of the current of the leak switch,
The configuration is simple and images with good contrast can be obtained.

[Brief explanation of the drawing]

Figure 1 is a diagram of a conventional solid-state dance statue neck! Ti
EndPage: 3 Figure 2 is a time sequence diagram of imaging and transfer in Figure 1, Figure 3 is a block diagram of the main parts of a solid-state imaging device in an embodiment of the present invention, and Figure 4 is a diagram of imaging and signals in Figure 3. FIG. 3 is a time series diagram of charge transfer. 8...Photodiode, 9...Vertical transfer CCD, 1
0...Horizontal transfer (CCD), 11...Transfer gate FFT, 12...Transfer gate signal terminal, 13...FET for leak switch, 14...Leak electrode terminal, 15...Leak control Electrode terminal, 16.
...Video output amplifier, 17...Leak current-voltage conversion circuit, I...1st frame imaging interval, II...1st
Frame signal transfer time, III...second frame imaging time, IV...second frame transfer time

Claims (1)

[Claims] 1. Photosensitive elements arranged in a matrix, transfer gates connected to each of the photosensitive elements, and C for vertical scanning.
In addition to providing a CD and a horizontal scanning CCD, a leak switch and a leak electrode connected to each of the photosensitive elements are provided, and the leak switch is made conductive during unnecessary exposure time to prohibit charge accumulation in the photosensitive element. Solid-state imaging device. 2. During the unnecessary exposure time, the leak switch connected to each photosensitive element is turned on to prohibit charge accumulation in the photosensitive element,
An imaging method in which an aperture ratio of a diaphragm device is controlled by a leakage current during the unnecessary exposure time.