JPH05122615A - Signal read-out processing system for solid-state image pickup element - Google Patents

Abstract

PURPOSE:To provide a signal read-out processing system for a solid-state image pickup element capable of following up the change of dark time fixed pattern noise (FPN) due to change of temperature, etc., stably suppressing the dark time FPN. CONSTITUTION:After a signal corresponding to photoelectric charge during one frame period is read out of a solid-state image pickup element 1, a signal at dark time is read out immediately after resetting or while resetting the stored electric charge for the next one frame period, amplified by an amplifier 6, converted into a digital signal by an A/D converter 7 and fetched in a memory 8. The signal in the photoelectric charge fetched in the memory 8 and the dark time signal are converted into analog signals by D/A converters 9 and 10 and subtracted by a subtractor 11 to output video signals in which the dark time FPN is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal read-out processing system for a solid-state image pickup device which can follow a change in dark fixed pattern noise due to a temperature change and the like and can always stably suppress the dark fixed pattern noise. ..

[0002]

2. Description of the Related Art Conventionally, a photoelectric conversion function and amplification of accumulated electric charge,
Static induction transistor (abbreviated as SIT) and charge modulation device (Charge Modulation Device) that have read and reset functions.
In order to cancel fixed pattern noise (hereinafter abbreviated as FPN) peculiar to the image sensor in a device that reproduces an image by an image sensor that uses an internal amplification type photoelectric conversion element such as CMD) as a unit pixel. Further, storage means such as a frame memory is provided, FPN is stored for each pixel in the storage means, and from the image information obtained from each pixel of the image sensor, the FPN corresponding to the pixel is stored.
An FPN suppressing means for subtracting PN to obtain an image signal is required.

FIG. 4 shows a conventional FP used in an image reproducing apparatus using such an internal amplification type image sensor.
It is a block block diagram of N suppression means. Image sensor 10
The image signal output from 2 is amplified by the amplifier circuit 103 and converted into digital data by the A / D converter 104. The digital data becomes dark FPN data of each pixel when light is blocked by the shutter 101 arranged in front of the image sensor 102. At this time, switch 10
5 is connected to the a side, and the FPN data is sequentially stored in the frame memory 106. After the end of accumulation for one frame period,
If the switch 105 is connected to the b side and the shutter 101 is opened, the image signal due to the photocharges sent to the A / D converter 104 after the opening is A / D converted and stored in the frame memory 106 by the subtractor 107. The FPN data that has been subjected to repeated subtraction processing is input to the D / A converter 108 as data in which the FPN has been canceled, D / A converted, and output as an output video signal.

FIG. 5 is a block diagram showing another configuration example of the conventional FPN suppressing means. In this configuration example, a light signal line memory 112 and a dark signal line memory 113 formed of a capacitor array are provided in a solid-state image sensor 111, and a light receiving unit 11 is provided.
Line signal memory for bright signals that corresponds to each pixel in the horizontal blanking period of the image signal generated by the photocharge of one horizontal pixel column
The data is simultaneously transferred to and held in the 112 capacity columns. After transferring the signal by photocharge to the bright signal line memory 112,
In the same horizontal blanking period, the same horizontal pixel column is reset at the same time, and the dark signal (FPN) is simultaneously transferred to and held in the capacitance column of the dark signal line memory 113 corresponding to each pixel. Next, in the horizontal scanning period, both the signals from the bright signal line memory 112 and the dark signal line memory 113 are sequentially read out at the same time, and the external subtractor 115 subtracts the dark signal from the signal due to the photocharges to suppress the dark FPN. It is designed to output a video signal.

[0005]

By the way, in the conventional FPN suppressing means shown in FIG. 4, the FPN data at the time of darkness is stored in the frame memory 106 in advance, and the darkness is detected from the image signal corresponding to the photocharge. Since the video signal is output by subtracting the FPN at the time
When N changes, there is a problem that the change cannot be followed and the FPN cannot always be suppressed stably.

Further, in the conventional FPN suppressing means shown in FIG. 5, since two line memories have to be arranged in the solid-state image pickup device, the structure of the solid-state image pickup device is complicated, the chip area is increased, and the solid-state image pickup is performed. There is a problem that the number of output signal lines from the element becomes two. This is a fatal problem in applications where the chip area and mounting space are limited, for example, when mounted on the tip of an endoscope for use. Furthermore, there is a problem that the FPN suppressing effect does not become large as a whole, because the variation of the capacitance column corresponding to each pixel forming the line memory causes a new variation of the signal level, that is, a new FPN.

The present invention has been made in order to solve the above-mentioned problems of the conventional FPN suppressing means of the internal amplification type solid-state image pickup device, and prevents the increase of the chip area due to the line memory, etc. It is an object of the present invention to provide a signal readout processing method of an internal amplification type solid-state imaging device which can follow the change of the FPN and constantly suppress the FPN in the dark.

[0008]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a signal readout of a solid-state image pickup device in which an internal amplification type photoelectric conversion element is used as a unit pixel and the unit pixel is arranged in a matrix. In the processing method, a signal corresponding to the photocharge is read out by a normal operation during one frame period, and then a signal in the absence of photocharge is read out immediately after or while resetting the accumulated charge during the next one frame period. An external circuit subtracts a signal in the absence of photocharge from a signal corresponding to photocharge.

In the signal read processing system thus constructed, every time a signal corresponding to the photocharge of one frame is read, the signal of one frame immediately after that is read out and subtracted. , The signal from which the FPN has been removed is output. Therefore, even when the dark FPN is suppressed in real time and the dark FPN changes due to a temperature change or the like, the change immediately follows the change and the dark FPN is always stable.
A signal that suppresses is obtained.

According to this signal read processing method,
Since it is not necessary to provide a line memory in the solid-state imaging device, it is possible to prevent an increase in the chip area of the device due to the addition of the line memory and the generation of new FPN due to the variation in the capacity of the line memory.

A method is conceivable in which a signal corresponding to the photocharge is read out for each horizontal pixel column and a signal immediately after that is read out in the absence of the photocharge, and the subtraction process is performed.
In this case, since the double speed scanning means is required, in the present invention, the signal corresponding to the photocharge and the signal in the absence of the photocharge are read out and subtracted on a frame-by-frame basis as described above. .. As a result, the double speed scanning means is not required, and it is sufficiently applicable for still image use.

[0012]

EXAMPLES Next, examples will be described. FIG. 1 is a block configuration diagram of a signal read processing device for explaining an embodiment of a signal read processing system according to the present invention. In the figure, reference numeral 1 is a solid-state image sensor, which is a light receiving portion 2 formed by arranging internal amplification type pixels such as SIT and CMD in a matrix, and a vertical portion for selecting a pixel row in the horizontal direction of the light receiving portion 2. It is composed of a scan shift register 3 and a horizontal scan shift register 5 for selecting a vertical signal line of the light receiving section 2 via a horizontal scan switch 4. Then, after the signal corresponding to the photocharge is read for one frame period, the signal is read for the next one frame period immediately after or while resetting the accumulated charge.

Reference numeral 6 is an amplifier for amplifying the signal read out through the horizontal scanning switch 4 of the solid-state image pickup device 1. The signal amplified by the amplifier 6 is A / D converted by the A / D converter 7. It is D-converted and taken into the memory 8. Reference numerals 9 and 10 are D for D / A converting the signal corresponding to the photocharges stored in the memory 8 and the signal in the absence of the photocharges, respectively.
The respective signals D / A-converted by the D / A converters 9 and 10 by the / A converter are input to the subtractor 11 where they are subtracted and output as an output video signal. Reference numeral 12 is a memory control unit that controls the operation of the memory 8.

Next, the operation of the signal read-out processing device thus constructed will be described. FIG. 2 is a timing chart showing the signal waveform of each part for explaining this operation. First, a signal corresponding to photocharge is read from the solid-state image sensor 1 for one frame period. In the next one frame period, the signal is read out immediately after resetting the accumulated charge or while resetting. This corresponds to reading the dark signal.

The internal amplification type image pickup device generates an FPN due to variations in characteristics of a transistor that amplifies accumulated charges. The dark signal is read out when the dark current is zero (hereinafter, in this sense). (Used) is also read. Since the dark current has been suppressed to a very small value recently and can be ignored under the normal use condition of a solid-state image pickup device, the dark FPN means that it is caused by variations in transistor characteristics. .. The dark FPN exists at a constant level irrespective of the amount of light, and is superposed in an offset manner on the signal corresponding to the first read photocharge.

The signal due to the photocharge and the dark signal are shown in FIG.
As shown by the signal waveform of A, the frame sequential signal A is read out. It should be noted that FIG. 2 shows the m-1 to m + 4th signals. The frame sequential signal A read in this way is amplified by the amplifier 6,
The signal is converted into a digital signal by the / D converter 7 and stored in the memory 8.

Next, by controlling the phase of the memory read pulse by the memory control unit 12, a signal B due to photocharge is generated.
And the signal C in the dark. Here, since the signal B due to photocharge and the dark signal C are frame-sequential, a frame having no corresponding signal is interpolated by the signal of the previous frame. Next, the signal B due to photocharge and the signal C at dark are respectively
A / A converters 9 and 10 perform D / A conversion and input to the subtractor 11,
By subtracting the dark signal C from the signal B due to photocharges, a dark FPN-suppressed video signal D is obtained. Here, the same video signal is output for two frames,
It does not pose any problem for small-motion applications. The dark signal C changes depending on the temperature characteristics, but the change in a short time of several frame periods (1/30 × N seconds) can be ignored.

In the present embodiment, in the (m + 1) th frame, the dark signal of the mth frame is subtracted from the signal of the photocharges of the (m + 1) th frame.
The dark signal of (m-2) or (m + 2) may be subtracted. Further, if the average value of the dark signal of several frames is calculated and subtracted, random noise can be reduced.

Next, a processing method for non-interlaced reading will be described with reference to FIG. The signal corresponding to the photocharge in one frame period and the dark signal immediately after or while resetting the accumulated charge in the next one frame period are the frame sequential signals as shown by the signal waveform of A in FIG. It is read out as A, converted into a digital signal, and stored in the memory 8. Next, as in the case of interlaced reading, the phase of the memory reading pulse is controlled by the memory control unit 12 to separate it into the signal B due to photocharge and the dark signal C. Here, since the signal due to photocharge and the dark signal are frame-sequential, a frame without a signal is interpolated with the signal of the previous frame. Then D /
By A-converting and subtracting the dark signal C from the signal B resulting from the photocharge by the subtracter 11, a dark FPN-suppressed video signal D is obtained.

In the above embodiment, the signal read from the memory is D / A converted and then arithmetically processed. However, the same operation and effect can be obtained by performing the arithmetic processing and then D / A conversion. That is clear.

In the above embodiment, the A / D converter, the memory, the D / A converter, etc. are constructed as external circuits. However, it is common to digitize the video camera to improve its function and performance. Since it is possible to share the parts for those uses, there is no cost problem in implementation.

[0022]

As described above on the basis of the embodiments,
According to the present invention, even when the dark FPN is suppressed in real time and the dark FPN changes due to temperature change or the like,
Immediately following the change, a signal in which the FPN during darkness is suppressed can always be obtained stably.

Further, since it is not necessary to provide a line memory in the solid-state image pickup device, it is possible to prevent the increase of the chip area of the device due to the addition of the line memory and the generation of new FPN due to the variation in the capacity of the line memory. Further, it is possible to obtain a video signal from which the FPN has been removed in the dark without requiring a double speed scanning mechanism or the like.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of a signal read processing device for explaining an embodiment of a signal read processing system according to the present invention.

FIG. 2 is a timing chart showing signal waveforms for explaining the operation of the embodiment shown in FIG.

FIG. 3 is a timing chart showing signal waveforms for explaining the operation in the case of non-interlaced reading in the embodiment shown in FIG.

FIG. 4 is a block configuration diagram showing a configuration example of a conventional FPN suppressing means.

FIG. 5 is a block configuration diagram showing another configuration example of the conventional FPN suppressing means.

[Explanation of symbols]

 1 Solid-state image sensor 2 Light receiving part 3 Vertical scanning shift register 4 Horizontal scanning switch 5 Horizontal scanning shift register 6 Amplifier 7 A / D converter 8 Memory 9, 10 D / A converter 11 Subtractor 12 Memory control part

Claims (1)

[Claims] 1. A signal readout processing system for a solid-state image pickup device, comprising internal amplification type photoelectric conversion elements as unit pixels, wherein the unit pixels are arranged in a matrix, and a signal corresponding to photocharge is generated by a normal operation during one frame period. After reading
In the next one frame period, immediately after resetting the accumulated charge or while resetting, the signal in the state without photocharge is read, and the signal in the state without photocharge is subtracted from the signal corresponding to the photocharge in the external circuit. A signal readout processing method for a solid-state image sensor, characterized in that