JPH06178212A - Output correction device in dark state for solid-state image pickup element - Google Patents

Abstract

PURPOSE:To obtain the dark state output correction device capable of correcting a dark state output with high accuracy and comparatively simple configuration. CONSTITUTION:The device is provided with a memory 2 storing in advance dark state output data of valid picture elements of a solid-state image pickup element 1 and light interruption dummy picture element data, a D/A converter 4 converting the dark state output data of the memory 2 sequentially into an analog signal synchronously with a picture element output of the solid-state image pickup element 1, a control means 3 comparing a light shield dummy picture element signal in operation of the solid-state image pickup element 1 with the light shield dummy picture element data stored in the memory 2 and controlling a reference voltage of the D/A converter 4 and a differential amplifier 5 subtracting the dark state output from a picture element signal of the solid-state image pickup element 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dark-state output correction apparatus for a solid-state image pickup device capable of correcting the dark-time output of each pixel included in a pixel signal of the solid-state image pickup device.

[0002]

2. Description of the Related Art Conventional solid-state image pickup devices include charge-coupled devices (abbreviated as CCD),
Alternatively, a static induction transistor (Static Ind.
uction Transistor: abbreviated as sIT) or charge modulation device (abbreviated as Charge Modulation Device: CMD)
There is one in which the unit pixels are arranged in a matrix.

In an apparatus for reproducing an image by an image sensor using such a solid-state image pickup device, it is known that a dark output produced when light is blocked changes with temperature and storage time.

[0006] Conventionally, a measure has been made to remove only the dark output generated in the solid-state image pickup device and extract only the true image signal. For example, as a first example thereof, Japanese Patent Laid-Open No. 59-59
As described in Japanese Patent Laid-Open No. 19483, the value of the dark output generated in the solid-state image sensor is stored in advance as a function of temperature and storage time, and the output signal generated in the solid-state image sensor at the time of image input is stored in advance as a function of temperature and storage time. Among the stored dark outputs, there is a method of subtracting a dark output value that reacts to the temperature and the accumulation time at the time of image input to remove the dark output generated in the solid-state image sensor at the time of image input.

A second example is Japanese Patent Laid-Open No. 63-263.
As shown in Japanese Patent No. 881 publication, a dark output of a solid-state image pickup device at a certain constant environmental temperature in a dark state and at a constant accumulation time is detected, and then the environmental temperature is detected by a temperature detecting means for each image input operation. There is a method of measuring the accumulation time with a time measuring means and correcting the dark output amount from the environmental temperature and the accumulation time.

[0006]

The first conventional example described above is a method for detecting the temperature and the accumulation time and correcting the dark output based on the result, so that the temperature output for dark output correction is corrected. The detection means is required, the temperature of the semiconductor substrate inside the solid-state image pickup device cannot be accurately detected from the outside, and the dark output of the solid-state image pickup device is doubled every time the temperature rises by about 8 ° C. However, there is a problem that the calculation for correction becomes complicated.

Further, in the above-mentioned second conventional example, in order to detect the correction data for correcting the dark output of the solid-state image sensor, it is necessary to provide a means for darkening the light receiving portion of the solid-state image sensor, Further, similar to the first conventional example, a temperature detecting means for detecting the temperature is required and the temperature is corrected, so that there is a problem that the calculation becomes complicated.

The present invention has been made in order to solve the above problems, and provides a dark-state output correction apparatus for a solid-state image pickup device, which has a relatively simple structure and is capable of highly accurate dark-time output correction. The purpose is to

[0009]

In order to achieve the above object, according to the invention corresponding to claim 1, dark output data of effective pixels of a solid-state image sensor and dark output data of light-shielding dummy pixels are stored in advance. And a D / A converter that sequentially converts the dark output data of the memory into an analog signal in synchronization with the pixel signal output of the solid-state image sensor.
Based on the output of the comparing means for comparing the light-shielding dummy pixel signal during the operation of the solid-state image sensor and the light-shielding dummy pixel data stored in the memory,
And a control means for controlling the reference voltage of the D / A converter.

In order to achieve the above object, according to the invention according to claim 2, a memory in which dark output data of effective pixels of the solid-state image pickup device and data obtained by adding a plurality of light-shielding dummy pixel signals are stored in advance, A D / A converter that sequentially converts the dark output data of the memory into an analog signal in synchronization with the pixel signal output of the solid-state imaging device;

Comparing means for comparing a plurality of light-shielding dummy pixel signals with the averaged plurality of light-shielding dummy pixel data stored in the memory when reading out the pixel signals of the solid-state image pickup device; Based on the output of the comparison means,
And a control means for controlling the reference voltage of the D / A converter.

[0012]

According to the invention corresponding to claim 1, the light-shielding dummy pixel data stored in advance in the memory is compared with the light-shielding dummy pixel signal during the operation of the solid-state image pickup device, and the D / A converter is based on the comparison result. Since the reference voltage is controlled, it is possible to highly accurately correct the dark output with a relatively simple configuration.

According to a second aspect of the present invention, when the pixel signals of the solid-state image pickup device are read out, a plurality of light-shielding dummy pixel signals and a plurality of added and averaged light-shielding dummy pixels stored in advance in the memory are added. Since the data is compared and the reference voltage of the D / A converter is controlled based on the comparison result, the correction of the dark-time output with a relatively simple configuration and higher accuracy than that of claim 1 is achieved. You can

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of the present invention, which is configured as follows. A dark output memory 2 in which dark output data of effective pixels and light-shielding dummy pixel data at a certain temperature and a certain storage time of the solid-state image sensor 1 are stored in advance, and a memory 2 in synchronization with a pixel signal output of the solid-state image sensor 1. A D / A converter 4 for sequentially converting the dark output data into an analog signal;

A differential amplifier 5 for subtracting the output of the D / A converter 4 from the image signal of the solid-state image pickup device 1 and an A / D converter 7 for converting the output of the differential amplifier 5 into a digital signal.
And an image memory 6 for storing the data of the A / D converter 7, and a central processing unit (CPU: control means of the present invention) 3 for controlling the reference voltage of the D / A converter 4. The light-shielding dummy pixel signal during the operation of the solid-state imaging device 1 is compared with the light-shielding dummy pixel data stored in the memory 2, and D is calculated based on the result.
The reference voltage of the / A converter 4 is controlled.

In such a structure, when the pixel signal of the solid-state image pickup device 1 is read, the dark output data corresponding to the output pixel is output from the dark output memory 2.
After converting to an analog signal by the D / A converter 4,
The differential amplifier 5 subtracts the dark output from the pixel signal of the solid-state image sensor 1. The output of the differential amplifier 5 is converted into a digital signal by the A / D converter 7 and then stored in the image memory 6. At this time, if the dark output stored in the dark output memory 2 does not match the dark output of the solid-state image sensor 1, this correction method is invalid.

Therefore, in FIG. 1, the CPU 3
Input the dark output of the light-shielding dummy pixel from the dark output memory 2 and the dark output of the light-shielding dummy pixel of the solid-state image sensor 1 from the image memory 6 so that the both dark output levels match. It is configured to control the reference voltage of the D / A converter 4.

Generally, a pixel of a solid-state image pickup device includes an effective pixel for inputting a pixel and a dummy pixel not used for image input. Among the dummy pixels, a light-shielding dummy pixel in which a light receiving portion of the pixel is shielded is shielded. Since it is included and driven at the same temperature and storage time as the effective pixel, it can be used as a monitor for dark output. In the example of FIG. 1, since the light-shielding dummy pixels are driven under the same conditions as the image input effective pixels, if the dark output level of the effective pixels is k times, the dark output level of the light shielding dummy pixels is also k. Therefore, by matching the dark output level of the light-shielding dummy pixel stored in the dark output memory 1 with the dark output level of the light-shielding dummy pixel of the solid-state image sensor 2, the effective pixel is also highly accurately dark. Time output can be obtained and can be realized by highly accurate dark time output correction.

FIG. 2 is a block diagram showing the first embodiment of the present invention. The dark output memory 9 stores dark output data of each pixel at a certain temperature of the CCD 10 at a certain accumulation time, receives an address signal of the dark output data stored from the timing generator 8, and outputs it as an address signal. Output the corresponding dark output data. The D / A converter 12 converts the dark output data into an analog signal and inputs it to the differential amplifier 13. Further, the CCD 10 is driven by the drive pulse from the timing generator 8, and C
The image projected on the light receiving surface of the CD 10 is converted into an electric signal and input to the differential amplifier 13. The differential amplifier 13 is C
The dark output is subtracted from the image signal of the CD 10. The output of the differential amplifier 13 is converted into digital data by the A / D converter 15 and stored in the image memory 14. CP
U11 inputs the output level of the light-shielding dummy pixel of the CCD 10 stored in the image memory 14 and the output level of the light-shielding dummy pixel of the CCD 10 stored in the dark-time output memory 9, and compares both levels. Then, the reference voltage of the D / A converter 12 such that the two levels match is calculated, and the reference voltage is output to the D / A converter 12.

The operation of the first embodiment thus constructed will be described below. The dark output level of the CCD 10 changes depending on the temperature and the storage time. Further, since the dark output level of the CCD 10 differs depending on each pixel, it is necessary to perform correction for each pixel in order to perform highly accurate dark output correction.

For this reason, in the first embodiment, the dark output level of each pixel at a certain temperature and a certain storage time is stored in the dark output memory 9 as a reference value of the dark output level and is actually stored. The image is input once under the condition that the image is input by the CCD 10. Then, the CPU 11
The dark output of the light-shielding dummy pixel of the CCD 10 stored in the dark output memory 9 is input and the CCD 10 is actually used.
The dark output of the light-shielding dummy pixel when the image is input is input from the image memory 14. Since the light-shielding dummy pixel and the effective pixel are always driven under the same condition, the dark output ratio of the light-shielding dummy pixel and the effective pixel is always constant. Therefore, the CPU 11 inputs the dark output level of the light-shielding dummy pixel stored in the dark output memory 9 and the dark output level of the light-shielding dummy pixel stored in the image memory 14, and compares the both dark output levels. However, by controlling the reference voltage of the D / A converter 12 so that both dark output levels match, the dark output levels of all the pixels output from the D / A converter 12 become
Since the output coincides with the dark output included in the output signal 10, the dark output can be precisely corrected.

FIG. 3 is a block diagram showing a second embodiment of the present invention. The CCD 17 is driven under predetermined conditions by the drive pulse of the timing generator 16. CCD17
The output signal of is continuously output in the order of the light-shielding dummy pixel signal and the effective pixel signal. Sample hold circuit 19
Receives a timing pulse from the timing generator 16 and sets the light shielding dummy pixel signal level of the CCD 17 to CC.
D17 is sampled for each scan and held. The signal held by the sample hold circuit 19 is subjected to predetermined voltage amplification by the amplifier 20, and then used as a reference voltage for the D / A converter 21.
1 is supplied. The memory 18 stores the dark output of each pixel of the CCD 17 at a certain temperature and a certain storage time, and outputs the dark output data corresponding to the address signal from the timing generator 16 to the D / A converter 21. The D / A converter 21 converts the dark output data into an analog signal, which is input to the differential amplifier 22 and C
The dark output included in the image signal output from the CD 17 is subtracted. C stored in memory 18
In the dark output data of the CD 17, the dark output data of other pixels are similarly proportionally converted and stored so that the data of the light-shielding dummy pixel serving as the reference becomes the specified value D _OB ,
When the reference voltage of the D / A converter 21 is V _DAREF , the dark output voltage V _OBREF of the light-shielding dummy pixel output from the D / A converter 21 is represented by V _OBREF = D _OB × V _DAREF (1) .

As described in the first embodiment, the dark output V of the light-shielding dummy pixel output from the D / A converter 21.
_OBREF and light-shielding dummy pixel V output from CCD 17
D / A converter 2 to match the _OBOUT level
The reference voltage V _{DAREF of} 1 may be controlled. V _OBREF = V _DAREF (2) Therefore, from the equations (1) and (2), the D / A converter 2
The reference voltage V _{DAREF of} 1 is _expressed by the equation (3). V _DAREF = 1 / D _OB × V _OBOUT (3) From the equation (3), the amplification factor of the amplifier 20 may be 1 / D _OB .

With the above configuration, the CCD
The output of the light-shielding dummy pixel, which is the reference of the dark output, is sampled every 17 scans, and the dark output of the effective pixel is corrected based on the output, so that changes in temperature and storage time can be dealt with in real time. Moreover, it is possible to accurately correct the dark output.

FIG. 2 shows the third embodiment of the present invention.
Although the configuration is the same as that of the embodiment of FIG. 2, the following points are different from the second embodiment. That is, CP
U11 calculates an appropriate charge accumulation time according to the conditions such as the light receiving surface of the CCD 10 and the like, and the timing generator 8
Is added to control the charge storage time of the CCD 10. It is known that the dark output of the CCD 10 is proportional to the accumulation time. Also, CPU1
1 is a D / A converter 1 when changing the charge storage time
The reference voltage of 2 is also changed according to the change amount of the charge storage time.

With this configuration, the CCD 1
When the charge accumulation time of 0 becomes k times, the dark output level of each pixel of the CCD 10 also becomes k times. Therefore, the reference voltage of the D / A converter 12 is made k times to correct the dark output level. By multiplying by, it is possible to accurately correct the dark output. Therefore, according to the third embodiment, not only the change in the dark output due to the temperature change of the CCD 10 but also the change in the storage time of the CCD 10 can be quickly and accurately handled.

Next, a fourth embodiment will be described with reference to FIG. FIG. 4 is a diagram in which, for example, the contents stored in advance in the dark output memory 9 of the embodiment of FIG. 2 are changed as follows for the reason described below. In the figure,
φ1 is a CCD charge transfer clock, and φR is a reset pulse. FIG. 4A shows the case of the first embodiment of FIG. 2, in which a reset pulse φR is output for each pixel signal and
Driving is performed so as to output a pixel signal. However, since the dark output of one pixel is very small and it is difficult to measure accurately, the D / A converter 1
An error is likely to occur in the calculation of the reference voltage of 2.

Therefore, in this embodiment, as shown in FIG. 4B, the reset pulse φR is thinned out in the light-shielding dummy pixel portion, and the combined dark output of a plurality of light-shielding dummy pixels is taken out as a CCD output signal. By combining the dark output of a plurality of pixels, the signal level becomes relatively large and the levels of each pixel are averaged, so that it is possible to perform accurate measurement, and the reference voltage of the D / A converter is also calculated accurately. Therefore, it is possible to perform more accurate dark output correction.

[0029]

According to the present invention, the dark output of each pixel included in the output signal of the solid-state image pickup device can be corrected with high precision by a simple structure without requiring temperature detecting means. A dark output correction device for a solid-state image sensor can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a dark-state output correction apparatus for a solid-state image sensor according to the present invention.

FIG. 2 is a block diagram showing a first embodiment of a dark-state output correction apparatus for a solid-state image sensor according to the present invention.

FIG. 3 is a block diagram showing a second embodiment of the dark-time output correction apparatus for a solid-state image sensor according to the present invention.

FIG. 4 is a block diagram for explaining a fourth embodiment of the dark-state output correction apparatus for a solid-state image sensor according to the present invention.

[Explanation of symbols]

1 ... Solid-state imaging device, 2 ... Dark output memory, 3 ... CPU
(Central processing unit), 4 ... D / A converter, 5 ... Differential amplifier, 6 ... Image memory, 7 ... A / D converter.

Claims (2)

[Claims] 1. A memory in which dark output data of effective pixels of a solid-state image sensor and dark output data of light-shielding dummy pixels are stored in advance, and a dark signal of the memory is synchronized with a pixel signal output of the solid-state image sensor. D / that sequentially converts the output data to analog signals
An A converter, a comparison unit that compares the light-shielding dummy pixel signal during the operation of the solid-state imaging device with the light-shielding dummy pixel data stored in the memory, and the D / A converter based on the output of the comparison unit. And a control unit for controlling the reference voltage of the solid-state image pickup device. 2. A memory in which dark output data of effective pixels of a solid-state image sensor and data obtained by adding a plurality of light-shielding dummy pixel signals are stored in advance, and in synchronization with a pixel signal output of the solid-state image sensor, D / that sequentially converts dark output data to analog signals
A converter, and a comparing unit that compares a plurality of light-shielding dummy pixel signals when reading the pixel signal of the solid-state image sensor with the averaged plurality of light-shielding dummy pixel data stored in the memory. A dark-state output correction apparatus for a solid-state image sensor, comprising: a control unit that controls the reference voltage of the D / A converter based on the output of the comparison unit.