JPS61127278A - Automatic exposure electronic camera - Google Patents

Abstract

PURPOSE:To control always accurately the quantity of exposure to obtain still picture signals of optimum S/N by providing an electrode which detects that a certain quantity of or more electric charge is stored in each picture element of a solid-state image pickup element and reading out the signal electric charge from the image pickup element when the variance of the potential of the detecting electrode exceeds a certain value. CONSTITUTION:When a shutter button 12 is depressed, a shift pulse FS is generated to discharge the stored electric charge stored in picture elements 21. Thereafter, a shutter is opened. The electric charge proportional to the quantity of incident light is stored in each picture element 21, and the electric charge of picture elements in a high luminance part is flowed to a detecting electrode 26 after the elapse of a certain time; and when the quantity of this electric charge reaches a prescribed value, an output VF of an amplifier 27 is higher than a comparison voltage Vref of a voltage comparator 28, and the output of the voltage comparator 28 is changed from '0' to '1', and this output state is held by a latch circuit 29. The shutter is closed by this latch output VR to generate the shift pulse FS, and the signal electric charge is prevented from being flowed into the detecting electrode 26. Next, clock pulses phiV and phiH are supplied to a vertical transfer part 23 and a horizontal transfer part 24 to read out the image pickup output from an output part 25.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an electronic camera that captures and records a still I7 image using a solid-state image pickup device, and particularly relates to its I77J1 optical system.

[Technical background of the invention and its problems]

C0D-? Imaging devices using solid-state image sensors such as MO8 have already begun to be put into practical use as video cameras for capturing moving images, but recently so-called electronic cameras that use solid-state image sensors to capture still images have been introduced. Attention has been paid.

In the case of a video camera, the exposure time of the photosensitive surface is usually constant f61/30 seconds, which corresponds to one frame of television.

On the other hand, electronic cameras, like conventional cameras using film, are required to be able to vary the exposure time over a wide range from several seconds to about 171,000 seconds.

For this reason, exposure time control and signal readout timing, which were not problems with video cameras, have become important issues.

That is, if the exposure time is shorter than the appropriate exposure time, the charge due to the incident light is small, so the ratio to the noise charge decreases, and only an image with a poor SIN can be reproduced. On the other hand, if the exposure time is longer than the normal exposure time, excess charge will occur in each photosensitive area, and the reproduced image will be white in areas where the incident light is above a certain level.9. In addition, excess charge leaks to other pixels, causing pluming. In other words, accurately controlling the exposure time is essential to obtaining the best image.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an automatic exposure electronic camera that controls the shutter or readout timing so that the exposure time is always optimal, so that still images with good S/N ratio can be obtained.

[Summary of the invention]

In this invention, each image J of a solid-state image sensor is provided with an electrode that detects when a charge of a certain level or more is accumulated. When the change exceeds a certain value, the image pickup device reads out the signal charge (if it has a shutter, closes the shutter) and records it.

〔Effect of the invention〕

According to this invention, there is no need for any special exposure measurement means, and the readout timing (
Since the X light amount is always controlled accurately regardless of changes in external temperature, wavelength of incident light, etc., a still image signal with an optimum S/N ratio can be obtained.

[Embodiments of the invention]

FIG. 1 shows the configuration of an electronic camera according to an embodiment of the present invention.

In the figure, light 1 from the subject is transmitted through the imaging lens 2 and the aperture 93.
, the shutter 5, etc., and are guided to the solid-state image sensor 6. The shutter 5 is not necessarily required.

As the solid-state image sensor 6, for example, a known interline transfer CCD1 image element as shown in FIG. 2 is used.

This image sensor has a photosensitive surface n formed by arranging pixels 21 consisting of photoelectric conversion elements such as photodiodes in a two-dimensional manner, and accumulates charges in each pixel 21 in accordance with the amount of human light t. Shift pulse FS i from the second lick direct transfer section 23
The electrical signal is then transferred to the horizontal transfer section and output from the output circuit as an electrical signal.

Charge transfer is performed by applying a clock pulse φV to the vertical transfer section 23 and a clock pulse φV to the horizontal transfer section 23. An excess charge detection electrode j is provided in this image sensor.

When a charge of a certain value or more is accumulated in the pixel 21, the excess charge flows into the detection@@26. This excess charge is collected from all the pixels and generates a voltage change called VOFD. FIG. 3 shows a schematic diagram of an example of the cross-sectional structure of one pixel section. A CPM layer 32 is formed on the Nil silicon layer, and furthermore, a photoelectric conversion section 31, a vertical transfer section 31, and an n-type layer 1- which becomes an excess charge detection electrode are formed.

Form.

The imaging operation when using the imaging device with the above configuration will be described using the timing chart of FIG. 5.

First, press the shutter button 12 and the shift button (Lus FS
is generated, and the accumulated charge accumulated in the pixel 21 is swept out and discarded to the outside by the vertical and horizontal transfer sections - then the shutter opens. Charge proportional to the incident light jk begins to accumulate in each pixel 21. After a certain period of time has elapsed, the electric charge of the pixel in the area where the incident light intensity is high (high 4 degree area) will change to the detection electrode (-
It starts to flow in. The charge is amplified by each amplifier. 26
When the nine aerosol loads reach a predetermined amount, the output Vr of the amplifier I becomes higher than the comparison voltage Vra1 of the voltage comparator υ, and the output of the voltage comparator 44 changes from the 10 m state to the "1" state and that change. is held in the p''1'' state by the latch circuit 29. This two-way output VRi closes the shutter and generates a shift pulse FS, and lowers the voltage of the control gate im that controls the charge flowing into the sensor electrode so that the signal charge does not flow into the detection electrode A.

Next is Qiao Zhi Transfer Department. Valley clock pulses φ and φ are supplied to the horizontal transfer section 24, and the imaging output is read out from the output circuit 6, converted into a recording signal by the signal processing circuit 8, and written to the recording medium 10.

In this way, the charge accumulated in each pixel can be increased as much as possible, and an image signal with a good S/N ratio can always be obtained.

Ma7'2:, 3J! ! There are times when you want to create a virtual image of the dark areas even if the white areas are blown out. At this time, you can change the control voltage VOFG that controls the charge flowing into the excess charge detection circuit, or change the reference voltage of the voltage comparator (-) to obtain an arbitrary start-up timing (shutter one hour). It is possible.

Although the above example uses a shutter, the shutter is not necessarily required if all pixel charges are transferred simultaneously (and the duty shift register is also transferred twice).

In addition, in the example of Fig. 3, the excess load detection abrasive pole is provided in a plane, but as shown in Fig. 4, an n-p-n structure is created in the vertical direction to detect changes in the substrate potential and perform timing fill@. is also possible.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the configuration of an electronic camera related to this invention, Figure 2 is a diagram conceptually showing the configuration of a solid-state image sensor in this embodiment, Figures 3 and 4 are This is an example of a cross-sectional view of one pixel portion in Fig. 2. Fig. 5 is a timing chart of the continuous operation in the same embodiment. 1... Subject light 2... Continuous image lens 3...
Aperture 95... Shutter 6... Solid-state image sensor 1
2... Shutter button Calm... Pixel n... Photosensitive surface A... Excessive abrasive load detection, etc. n... Amplifier A... Pressure comparator 4... Latch circuit agent Patent attorney Rule close yI! i Yu (and 1 other person) Figure 1 Figure 2 Figure An 7 C) Be 1-7 Figure 3 Figure 4

Claims (7)

[Claims] (1) In an electronic camera that captures and records still images using a solid-state image sensor having a photosensitive surface configured by two-dimensionally arranging pixels that accumulate charges according to incident photoelectricity, the pixels of the solid-state image sensor An automatic exposure electronic camera characterized in that an electrode is provided for detecting that a certain amount of charge has been accumulated, and a signal from the pixel is read out when a change in the potential of the electrode exceeds a certain value. (2) Claim 1 characterized in that it has a shutter and closes this shutter at the same time as reading starts.
Auto-exposure electronic camera as described in Section 1. (3) The automatic exposure electronic camera according to claim 1, characterized in that the potential of the excess charge detection electrode is set to a constant value at the same time as readout is started to prevent charges from flowing out to the detection electrode during readout. (4) The automatic exposure electronic camera according to claim 1, wherein the sensitivity of excessive charge detection is controlled by biasing the voltage of the detection electrode to a constant value. (5) A control electrode is provided to control the amount of charge flowing into the excess charge detection electrode, and the sensitivity of excess charge detection is controlled by the voltage applied to the electrode.
Auto-exposure electronic camera as described in Section 1. (6) The potential of the excess charge detection electrode is amplified and compared with a reference potential using a voltage comparator, and when the potential becomes larger than the reference potential, a latch circuit is triggered and reading is started by the output of the latch circuit. Auto-exposure electronic camera according to scope 1. (7) The automatic exposure electronic camera according to claim 1 or 6, characterized in that the readout start timing is changed by changing the reference potential.