JPS5919493A - Image pickup device - Google Patents

Abstract

PURPOSE:To improve the color reproducibility and sensitivity, by controlling the storage time at each part corresponding to each color filter of an image pickup means depending on a respective color filter. CONSTITUTION:Charges stored in a photodiode section 14 are absorbed in a drain via a clear line 122 by outputting a clear pulse with shift registers 111, 112. An output in response to the amount of charges discharged during the period until being scanned with a readout scanning after the clear operation is obtained at an output terminal 20. The color filters are arranged on the photodiode section 14. The timing of the output of the clear pulse is changed depending on each filter and the storage time at each part corresponding to each color filter is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved imaging device having excellent color reproducibility, sensitivity, etc.

BACKGROUND OF THE INVENTION A solid-state imaging device used in a conventional television broadcasting camera must have a resolution comparable to that of the imaging electron tube used in current television broadcasting. For this reason, approximately 50
A photoelectric conversion element of about 0 (vertical) x 400 (horizontal) pixels,
A switch for selecting (x, y) coordinates corresponding to each photoelectric conversion element, and approximately 500 stages of X-scanning circuits and X-scanning circuits for opening and closing the switches are required. Therefore, it is usually manufactured using MO8 large-scale integrated circuit technology, which is relatively easy to achieve high integration. FIG. 1 is a diagram illustrating the outline of such a solid-state imaging device, and 11 is a horizontal scanning direction NM for selecting the X position.
, 12 is a vertical scanning circuit for Y position selection. 13 is a vertical switch MOS transistor (hereinafter abbreviated as MO8T) that is opened and closed by the vertical scanning pulse from the circuit 12.
, 14 is a photodiode using the source junction of MO8Tt3, and 15 is a vertical signal output line commonly connected to the drains of MO8T13. 16 is a horizontal scanning circuit 1
MO8T for a horizontal switch is opened and closed by a horizontal scanning pulse from 1, and its drain is connected to a horizontal signal output line 17, and its source is connected to a vertical signal output line 5. Reference numeral 18 denotes a photodiode drive voltage source (video voltage source) connected to the horizontal signal output line 17 via a resistor 19. Also, 20
is a signal output terminal. The two horizontal and vertical scanning circuits sequentially open and close MO8T switches 16 and 13 to transfer the photocurrent from the two-dimensionally arranged photodiodes to the resistor 19.
read through. Since the signal from each photodiode corresponds to the optical image projected thereon, the video signal can be extracted by the above operation. A feature of this type of solid-state imaging device is that an MO8T source for switching can be used for photoelectric conversion, and a FiMOS T shift register can be used for a scanning circuit.

Therefore, it is usually relatively easy to achieve high integration, and the MO8 large-scale integrated circuit technology is used as an example of the pixel structure shown in FIG. In FIG. 2, 23 is an N-type semiconductor substrate on which photoelectric conversion elements, scanning circuits, etc. are integrated;
24 is a well of a P-type semiconductor region formed on an N-type semiconductor substrate. Further, 13 is a vertical switch MO8T having a gate electrode 25 to which a vertical scanning pulse from the vertical scanning circuit 12 is applied. Reference numeral 26 designates the source of MO8'P13, which is a heavily doped N-type impurity region, and constitutes the photodiode 14 by its junction with the P-type well. 27 is M
This is the drain of O8'l'13, is a high concentration N-type impurity region, and is connected to the conductor layer 28 which becomes the vertical signal output line 15. One end of the output line 28 (15), to which the drains of a plurality of switch MO8Ts are connected in common, is connected to a horizontal switch MO8T16 that opens and closes in response to horizontal scanning pulses from the horizontal scanning circuit 11, and
The other end of 6 is connected to a horizontal signal output line 17. The uncircumcised well 24 and substrate 23 are typically fixed at ground voltage (OV) (the PN junction between the well and the substrate may be reverse biased). Further, 291.292.degree. 293 is an insulating film, and a Sin film is usually used.

The photodiode charged with the target voltage vv1 by scanning is discharged (Δvv) according to the amount of light incident during the frame period, and the switch MO8T13 is charged in the next scanning.
．． When 16 becomes conductive, a charging current flows to charge this discharged amount.

This charging current is connected to a resistor 19 connected to a target power source 18.
A video signal can be obtained at the output terminal 20.

In such conventional solid-state imaging devices, in order to compensate for the lack of blue sensitivity, the pixel cells corresponding to the blue filter are made larger than other pixel cells, or the aperture pitch of the red and green filters is changed by using a light-shielding layer, etc. Methods such as making the aperture pitch narrower than the aperture pitch of This method causes a moiré phenomenon due to a change in the spatial sampling pitch of the subject image, and also causes a decrease in the sensitivity of the solid-state imaging device. Another method has been to shift the spectral characteristics of a blue filter toward longer wavelengths in order to improve the sensitivity of the blue signal, but this has the disadvantage that color reproduction deteriorates. Also, as a way to eliminate the above-mentioned drawbacks in the signal processing system, it is possible to match the red and green signal levels to the blue signal level, but in this case, the sensitivity of the entire solid-state imaging device becomes the blue sensitivity level, which has poor sensitivity. There is a drawback.

Solid-state imaging devices usually require an operation called white balance before taking a picture. That is, since the sensitivity of blue, red, and green differs depending on the color temperature of the light source at the time of photography, the white balance must be adjusted depending on the light source, for example, under fluorescent lights, during the day, or on cloudy days. Then, adjust the white balance by photographing a normal white object.JG, 33
Match the sensitivity of. For this purpose, in the past, a color temperature correction filter was provided, and a sensitivity adjustment circuit was also provided in the signal processing system to achieve perfect white balance, which resulted in a complicated configuration.

The present invention provides an imaging device that can overcome the drawbacks of the prior art, and is characterized by providing an imaging means that can easily control the accumulation time of pixels corresponding to each color of a color filter. It's about doing.

For this purpose, the main feature is that a charge clear gate is provided for each pixel.

Further, the embodiment of the present invention is characterized in that the accumulation time of pixels corresponding to each color of the color filter is controlled to vary depending on each color of the color filter.

This makes it possible to obtain an imaging device with excellent color reproducibility and high sensitivity.

Other features are indicated throughout the drawings and the following description.

The present invention will be described in detail below based on Examples.

FIG. 3 is a diagram showing an embodiment of a semiconductor device suitable for the imaging apparatus of the present invention, and FIG. 4 is a sectional view of a main part of the device shown in FIG.

In addition, 1st. The same components as in FIG. 2 are given the same reference numbers.

ill, 112. are shift registers for clear selection at the X and X positions, respectively, and l13 is a horizontal switch MO that is opened and closed by the horizontal clear pulse from the register 111.
The S transistors (MO8T) 122 and 115 are a common wiring.

Reference numeral 116 is an MO8T that opens and closes according to a vertical clear pulse, and is connected to the positive side of the source Fi power supply 18.

The two horizontal and vertical clear selection shift registers sequentially open and close the MO8Ts 116 and 113 to clear the photocurrent from the two-dimensionally arranged photodiodes.

Note that an MO8T shift register may be used as the shift register.

In FIG. 4, 113 is a horizontal MO8 switch,
It has a gate electrode 125 to which a clear pulse from a clear register l11 is applied at the position. MO8T1
The source of No. 3 is common to the source of 26HMO8Tl13. Reference numeral 127 denotes a drain of MO8Trt3, which causes charges to flow into the horizontal clear line 122 via an electrode 128.

One end of the clear line 122 is connected to the MO8T switch 116, and the MO8T switch 116 is opened and closed by a clear pulse from the X position clear register 112.

Further, the drain of MO8Tl16 is connected to the positive terminal of the power supply 18.

With this structure, according to this embodiment, the charge accumulated in the photodiode section 14 is absorbed into the drain via the clear line 122 by outputting a clear pulse from the shift register Ill, 112. After this clearing operation, the photodiode charged to the target voltage is discharged according to the amount of light incident on it during the readout scan until it is output. 19, and a corresponding video signal can be obtained at the output terminal 20.

Next, an embodiment of an imaging apparatus to which an imaging means having a charge clearing function as described above is applied will be described below.

FIG. 5 is a schematic diagram of the solid-state image sensor shown in FIG.
It was set at 6. The symbol A471n indicates the number assigned to the pixel cell.

FIG. 6 is a diagram showing an example of a color filter provided on the solid-state image sensor of FIG.
A red transmission filter (几) is placed on the pixel cell of
n2. An is a green transmission filter (G), An3. A
n6 corresponds to the blue transmission filter.

FIG. 7 is a timing diagram illustrating the operation of the solid-state image sensing device of FIG. 5 equipped with the above-mentioned color filter. In FIG. 7, P, , P, 2. P, . . . P, 6 (omitted in the figure) are pixel cells Al l , Al1 . AHB...
・A6. FIG. 4 is a timing chart of pulses related to charge clearing, photoelectric conversion, and information charge reading corresponding to the above.

In the figure, TR, 'I'G, T, are the photoelectric conversion periods of the pixel cells corresponding to each color filter, To is the information charge readout period for reading out the information charges accumulated in the pixel cells, and TcRlTcG, TcB are the periods of the pixel cells. This charge clearing period is used to control the gradient so that the photoelectric conversion period TCR+TCG+TCB can be freely set by clearing the cells.

In FIG. 7, the periods of 'I'CR and TcG are the same, so the photoelectric conversion period IIRI TG is the same period.

TcB is set to a shorter period than TCR+TCG, and the reason for this is that solid-state imaging devices are made of silicon and usually have very poor blue sensitivity. That is, in order to compensate for the lack of blue sensitivity, it is necessary to make the photoelectric conversion period TH, longer than TR1TG in the pixel cell corresponding to the blue filter.

As a result, the sensitivities of R, G, and H become the same, resulting in an image with good color reproduction.

It should be noted that the present invention is limited to improving blue sensitivity, and may be used as long as it corrects the spectral sensitivity of the imaging means.

FIG. 8 is a block diagram of a signal processing system when the information charge readout signal line is a single line, that is, for single-line readout.

Figure 9 shows information charge readout 1. FIG. 2 is a block diagram of a signal processing system in the case of multi-line signal lines, that is, multi-line readout.

In FIG. 8, the solid-state image sensor 100 has a clock circuit 11.
The drive is controlled by 0. Part of that timing is the 7th
In this example, the solid-state image sensor l is the timing shown in the figure.
The output of oo is a point sequential signal and 17It, , , G, ,
,B,, ,几8. ... (Each All, A
It corresponds to pixel cells of 111 AIB + A14... ) is obtained. In this case, as mentioned above, if the photoelectric conversion periods of 1 and 00 are the same, and the photoelectric conversion period of B is longer than R1 (1), the dark current component included in the dot sequential signal is 1. In this embodiment, as a countermeasure against this problem, the memory 140 allows the memory 140 to transfer It,
The dark current components corresponding to 0- and H are memorized, and the process circuit 120 is synchronized with the clock circuit 110 Calano Hals.
1c, the dark current component is subtracted from the point sequential signal. Further, in the process circuit 120, the point sequential signals 1t,
The signal is separated into G and B signals and subjected to general process processing such as γ correction.
It is converted into a C signal.

Further, in FIG. 8, a signal W B P i-j is a white balance control signal sent from the process circuit 120 to the clock circuit 110. That is, WBP is It, G, obtained from the solid-state image sensor 100 when photographing a white object.
The photoelectric conversion period TR,
It works to adjust TG and TH. Directly, it is sufficient to control the charge clear period TCR+TCGvTcB. In this case, there is no time limit for the charge clearing interval as long as it is a period in which the charges in the pixel cells can be completely cleared. However, in order to improve sensitivity, it is desirable to control the machine for as short a period as possible.

The signal WBP is output every time a white balance set switch (not shown) is operated, and the previous white balance state is maintained until the support switch is operated again.

Therefore, in this embodiment, the accumulation time of the B signal is controlled according to the color temperature of the subject, and the optimum imaging sensitivity can be obtained according to the photographing situation.

In the case of FIG. 9, it is R because it is a multi-line readout.

Since the G and B signals are processed independently, the memory circuit shown in FIG. 8 is no longer necessary. i.e. It, G and B
This is because, although the dark current components are different, these dark current components are isometrically canceled if the signal from the optical black pixel cell (black reference) is clamped.

As mentioned above, by using an image sensor that can independently control charge accumulation and charge clearing, it is possible to easily adjust the sensitivity of R, G, and H, and therefore the color filters) t, G,
Since H can be given ideal spectral characteristics, color reproducibility is very good and the sensitivity of the imaging device is improved.

Further, according to the present invention, the sensitivity can be adjusted by adjusting the storage timing, so there is no need to provide a variable gain circuit or the like in the analog signal processing circuit. It is also advantageous that there is no need to use a color temperature correction filter to adjust the white balance, and the cost is low.

In the above embodiment, by providing a 1/C clear gate for each pixel of the X-Y address type image sensor, the accumulation time of each pixel can be reduced! I'll say that, but 'r
If reading is performed in v synchronization, another reading is performed within the l field interval, and this readout output is discharged, a clear gate becomes unnecessary. It goes without saying that such a configuration may be used as the LH to perform the storage control according to the color of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a conventional MO8 type solid-state imaging device, FIG. 2 is a partial structural diagram of FIG. 1, and FIG. 3 is a diagram showing an example of a solid-state imaging device equipped with a clearing mechanism according to the present invention. Figure 4 is the third
FIG. 5 is a schematic diagram of a solid-state image sensor that does not provide a detailed explanation of the present invention; FIG. 6 is a diagram showing an example of a color filter; and FIG. 7 provides a detailed explanation of the present invention. FIG. 8 shows an embodiment of an imaging apparatus using a single-line readout type image pickup element, and FIG. 9 shows an embodiment of an image pickup apparatus using a multi-line readout type image pickup element. 11...X position read register, 12...X position read register, 111...X position clear register, 112...X position clear register. Patent applicant Canon Co., Ltd.

Claims (3)

[Claims] (1) An imaging means having a photoelectric conversion function, a color filter arranged in front of the imaging means and consisting of an array of multiple types of color filters, and an accumulation time in each part of the imaging means corresponding to each color filter. and a control means for controlling the color filters according to the respective color filters. (2) The imaging apparatus according to claim 1, wherein the control means controls the accumulation time of each portion so as to correct the spectral sensitivity of the imaging means. (3) The control means controls the accumulation time of each portion so that a predetermined primary color signal is obtained at the same level for a white image.
).