JPH04301982A - Solid-state image pickup device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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 relates to a technique that is effective for use in, for example, a device having a long exposure mode such as night vision photography.

0002

2. Description of the Related Art A TSL type MOS type solid-state image sensor is well known. This solid-state image sensor is provided with an optical black that blocks light from a photodiode section formed at the peripheral end of the scanning area. DC reproduction is performed using the readout signal obtained by scanning this optical black portion as a reference potential. Regarding such a TSL type MOS type solid-state image sensor, there is Japanese Patent Application Laid-Open No. 63-37781.

0003

[Problem to be Solved by the Invention] The present inventor has proposed a method for performing long-time exposure and high-sensitivity photography by temporarily stopping the scanning of the solid-state image sensor at the boundary between fields or frames. Thought. It has been found that in this case, the period of the horizontal optical black portion formed by the light-shielded pixel cells is extremely short, causing a problem in that accurate DC reproduction cannot be performed. An object of the present invention is to provide a solid-state imaging device that enables good DC reproduction while performing a long exposure mode. The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

0004

[Means for Solving the Problems] A brief overview of typical inventions disclosed in this application is as follows. In other words, a solid-state image sensor is used that is equipped with a scanning circuit that outputs signals from a plurality of pixel cells arranged in a two-dimensional manner in time series, and when in long exposure mode, the pixel cells formed in the vertical optical black section are used. After performing a scanning operation, video signals from the scanning area are outputted in time series.

[0005]

According to the above-described means, since signals are output from pixels that have been shielded from light for a relatively long period of time by scanning the vertical optical black portion, good DC reproduction by the clamp circuit is possible.

【Example】

FIG. 1 shows a block diagram of an embodiment of a solid-state imaging device according to the present invention. Solid-state image sensor M
The ID is not particularly limited, but may be a MOS type solid-state image sensor. The read signal output from the solid-state image sensor MID is amplified by a preamplifier. This amplified signal has switching noise removed by a low-pass filter LPF, and is input to a clamp circuit that performs DC regeneration. The video signal VD passed through this clamp circuit undergoes necessary signal processing by a signal processing circuit (not shown) and is converted into, for example, an image signal for television.

As shown in FIG. 2, among the two-dimensionally arranged pixel cells constituting the imaging surface of the solid-state image sensor, the pixel cells in the shaded areas in the figure have a surface made of an aluminum film or the like. A light shielding film is provided to form an optical black portion. In the light-shielded pixel cells, no photoelectric conversion operation is performed, so the reset level (black level) is output as is. DC reproduction is performed by setting the read signal from the pixel cell in the optical black portion to the black level.

In this embodiment, the following scanning operation is performed in order to realize the long exposure mode of the solid-state image sensor. The drive circuit is added with a function of temporarily stopping the horizontal scanning operation and vertical scanning operation of the solid-state image sensor MID. Specifically, the vertical scanning pulse and the horizontal scanning pulse are stopped at a certain point, and the period of time is added as the accumulation time of the pixel cell, thereby realizing the long exposure mode. Thereby, for example, night vision photography such as microscopic photography in which illumination light cannot be used can be realized.

In the long exposure mode as described above,
When scanning is started from the beginning A of the imaging surface, reading from the pixel cells that are shielded from light for only a very short time from the horizontal optical black portion is performed. The clamp circuit that performs DC regeneration has the following configuration. As shown in FIG. 1, the transistor Q2 is turned on by a clamp pulse generated corresponding to the scanning period of the optical black portion. By turning on the transistor Q2, a reference voltage (a constant DC voltage VR) is applied to the other electrode of the capacitor C. A video signal is output to one electrode of the capacitor C through the low-pass filter LPF and transmitted to one electrode of the capacitor C. Therefore, the black level output from the solid-state image sensor MID during the scanning period of the optical book section is
used for charging. In other words, the DC voltage that is the difference between the black level from the pixel cell and the reference voltage VR is stored in the capacitor C. Since scanning is stopped in the long exposure mode, the DC voltage held in the capacitor C changes relatively greatly due to leakage current and the like. Therefore, as described above, the black level is supplied from the horizontal optical black portion for only a very short time, making it impossible to perform the DC reproduction described above.

In this embodiment, in the long exposure mode, as shown in FIG. 2, the horizontal and vertical scanning is temporarily stopped at the left end point D, which is 1H below the point B where the reading of the pixel cells in the scanning area is completed. to be paused. This long-time exposure including the pause time allows the pixel cells to perform a highly sensitive photoelectric conversion operation. And when reading it,
The scanning operation resumes from point D where it was temporarily stopped. That is, during the scan from point D to the final point E of the vertical optical black section, the black level from the shaded pixel cell is output. Thereby, even if the capacitance value of the capacitor C of the clamp circuit is made relatively large, a DC voltage corresponding to the difference voltage between the black level and the DC voltage VR can be set in the capacitor C.

[0011]Then, the drive circuit returns to the top A of the imaging plane and performs scanning to read out the pixel cells in the scanning area, and in synchronization with this, sets the clamp pulse to a low level and turns off the transistor Q2. let By the scanning operation of the scanning area, the video signal corresponding to the photoelectric conversion signal formed by the photodiode of the pixel cell is superimposed on the DC voltage accumulated in the capacitor C, and is passed through the emitter follower output transistor Q1 of the clamp circuit. Output. After the 1H readout, the black level from the horizontal optical black portion is read out again to correct leakage of the capacitor C during the 1H scanning period. Since such a clamp operation during the scanning period corrects leakage during the 1H period, even a very short black level readout is sufficient.

FIG. 3 shows a schematic waveform diagram of an example of a readout signal in the long exposure mode in this embodiment. When reading from the pixel cells in the scan area is completed, scanning is stopped at that point. This results in
During this time, nothing is output from the solid-state image sensor as shown by the dotted line in the figure. In scanning in the next frame or field, optical black is output in response to the start of scanning from point D to point E(A). This optical black output provides a corresponding DC voltage to the capacitor of the clamp circuit. Therefore, the video signal to be output next is output as a video signal containing a DC voltage based on the optical black.

The effects obtained from the above embodiments are as follows. (1) Using a solid-state image sensor equipped with a scanning circuit that outputs signals from multiple pixel cells arranged two-dimensionally in time series, pixels formed in the vertical optical black area are used in long exposure mode. By performing a scanning operation at the end of the cell and then outputting video signals from the scanning area in time series, it is possible to perform long exposure mode and output signals from pixels that have been shielded from light for a relatively long period of time. Therefore, the effect that good DC regeneration by the clamp circuit becomes possible can be obtained. (2) According to (1) above, the long exposure mode and DC reproduction are possible by the driving method using the driving circuit without changing the configuration of the solid-state image sensor itself. Therefore, it is possible to obtain a solid-state imaging device having both the normal photographing mode and the long exposure mode.

[0014] The invention made by the present inventor has been specifically explained based on examples, but the present invention is not limited to the above-mentioned examples, and can be modified in various ways without departing from the gist thereof. Needless to say. For example, horizontal and vertical shift registers may be completely stopped in operation, or the frequency of their scanning pulses may be slowed down sufficiently compared to normal, so that they can be considered to be in a substantially dormant state. Good too. The solid-state image sensor is MO
In addition to the S type, any type may be used as long as it outputs the black level from the light-shielded pixel cell as described above and is used for DC reproduction. The present invention can be widely used in solid-state imaging devices using solid-state imaging elements such as those described above.

[0015]

Effects of the Invention A brief explanation of the effects obtained by typical inventions disclosed in this application is as follows. In other words, a solid-state image sensor is used that is equipped with a scanning circuit that outputs signals from a plurality of pixel cells arranged in a two-dimensional manner in time series, and when in long exposure mode, the pixel cells formed in the vertical optical black section are used. By first performing a scanning operation and then outputting video signals from the scanning area in chronological order, signals can be output from pixels that have been shielded from light for a relatively long period of time while performing long exposure mode. Good DC regeneration is possible using the clamp circuit.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a solid-state imaging device according to the present invention.

FIG. 2 is a screen configuration diagram for explaining an example of a read operation of the solid-state imaging device shown in FIG. 1;

FIG. 3 is a schematic waveform diagram showing an example of a read signal from a solid-state image sensor used in the present invention.

[Explanation of symbols]

MID...solid-state image sensor, LPF...low-pass filter, P
D...Pixel array, VSR...Vertical shift register, ITG
...Interlace gate circuit, DV...drive circuit, HSR...
Horizontal shift register.

Claims (2)

[Claims] Claim 1: A solid-state image sensor equipped with a scanning circuit that outputs signals from a plurality of pixel cells arranged in a two-dimensional manner in time series, and a solid-state image sensor formed in a vertical optical black part in a long exposure mode. What is claimed is: 1. A solid-state imaging device comprising: a drive circuit having a function of forming a drive pulse that outputs a video signal from a scan area in time series after performing a scan operation of a pixel cell. 2. The driving circuit stops the scanning operation at a certain point immediately after scanning the pixel cells in the scanning area of the solid-state image sensor in the long exposure mode, and performs scanning in the next field or frame. 2. The solid-state imaging device according to claim 1, wherein pixel cells in the vertical optical black portion are scanned by starting the scanning operation from the stopped position.