JPH0670240A - Solid state image pickup element - Google Patents

Abstract

PURPOSE:To improve the S/N of a solid state image pickup element for still pictures. CONSTITUTION:An image pickup area 2 is provided together with a storing area 3 which temporarily stores the signal charge received from the area 2, a 1st horizontal transfer register part 4 which is provided between both areas 2 and 3, and a 2nd horizontal transfer register part 5 which is provided at the side opposite to the part 4. Then the signal charge of a single frame of the area 3 and the signal charge of the next frame of the area 2 are outputted through both registers 4 and 5, and these two output signals are added together.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image pickup device having an image pickup area and a storage area.

[0002]

2. Description of the Related Art Recently, there is an increasing demand for an electronic still camera using a CCD solid-state image pickup device for image input to a computer or for news reports. When considering the above applications, C
It is said that the number of pixels required for a CD solid-state image sensor is at least 1 million. On the other hand, it is desirable that the size of the CCD solid-state image pickup device is small in consideration of cost and portability. That is, what is desired for the CCD solid-state image sensor is a small number of pixels.

[0003]

By the way, when developing a device in the above-mentioned direction, that is, a CCD solid-state image pickup device, the biggest problem is optical shot noise. This is because the optical shot noise is a physical phenomenon and cannot be solved by the progress of process technology.

In the CCD solid-state image pickup device, the signal-to-shot noise ratio S / N is when the signal amount is Q _S.

[0005]

[Equation 1] Given in.

The decrease in Q _S due to the miniaturization and the increase in the number of pixels of the CCD solid-state image sensor leads to the deterioration of the S / N of the optical shot noise, as can be seen from the equation (1). Optical shot noise S /
Although N is not a specific numerical value as to how acceptable N is, it is a fact that N is close to the allowable limit.

For random noise such as shot noise, it is effective to add a plurality of times and take the average value, but a recording medium such as a frame memory is required, and the system becomes large-scale and complicated. there is a possibility.

In view of the above points, the present invention adds signals without using an external storage device such as a frame memory,
Provided is a solid-state image sensor capable of improving the S / N of an output signal from the solid-state image sensor.

[0009]

A solid-state image pickup device according to the present invention includes an image pickup region 2 having a plurality of light receiving portions 6, a storage region 3 for temporarily storing signal charges of the image pickup region 2, and an image pickup region 2.
And the first horizontal transfer register unit 4 arranged between the storage area 3 and the storage area 3.
And a second horizontal transfer register unit 5 arranged on the opposite side of the storage region 3 from the first horizontal transfer register unit 4, and the signal charge e ₂ of the imaging region 2 and the signal charge e of the storage region 3 are included. ₁ is output through the first and second horizontal transfer register sections 4 and 5, respectively, and the two output signals are added.

Further, the solid-state image pickup device according to the present invention includes an image pickup region 2 having a plurality of light receiving portions 6, a storage region 3 for temporarily storing signal charges of the image pickup region 2, and a space between the image pickup region 2 and the storage region 3. The first horizontal transfer register section 4 is provided and the second horizontal transfer register section 5 is provided on the opposite side of the storage area 3 from the first horizontal transfer register section 4. set by the electronic shutter, and outputs the signal charges e ₁ of the signal charges e ₂ the storage region 3 of the imaging region 2 through the respective first and second horizontal transfer registers 4 and 5, adds the two output signals To configure.

The image pickup area 2 and the storage area 3 can be constructed by a frame interline transfer system structure.

The image pickup area 2 and the storage area 3 can be constructed by a frame transfer type structure.

[0013]

In the present invention, the first horizontal transfer register section 4 is arranged between the imaging area 2 and the storage area 3, and the second horizontal transfer register section 4 is provided on the opposite side of the storage area 3 from the first horizontal transfer register section 4.
The horizontal transfer register section 5 of FIG. 2 is arranged, and the signal charges e ₁ and e ₂ of _one field and the next field are simultaneously output through the first and second horizontal transfer register sections 4 and 5, and these two output signals are output. By adding, the signal output is doubled, while the optical shot noise is doubled, and the S / N of the output signal for a still image is improved.

Further, according to the present invention, the amount of light received during the light receiving period is set by the electronic shutter so that the amount of signal charge in one field in the storage region 3 and the amount of signal charge in the next field in the imaging region 2 are completely eliminated. Can be the same.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the case where the present invention is applied to a CCD solid-state image pickup device of a frame interline transfer system. In the figure, 1 indicates the entire CCD solid-state image sensor, 2
Is an image pickup area, 3 is a storage area for temporarily storing signal charges in the image pickup area 2, 4 is a first horizontal transfer register section having a CCD structure, and 5 is a second horizontal transfer register section having a CCD structure. .

The image pickup area 2 has a plurality of light receiving portions 6 arranged in a matrix and CCs arranged on one side of each row of the light receiving portions 6.
It is configured to have a vertical transfer register unit 7 having a D structure. The storage area 3 is composed of a plurality of vertical transfer register units 7 in the imaging area 2.
The vertical transfer register unit 8 having a plurality of CCD structures is provided corresponding to the above.

The first horizontal transfer register section 4 is provided between the image pickup area 2 and the storage area 3, and the second horizontal transfer register section 5 is located at the lower end of the storage area 3, that is, the first horizontal transfer. It is provided on the opposite side of the register unit 4. First and second output units 9 and 10 are connected to the final stages of the first and second horizontal transfer register units 4 and 5, respectively, and the output units 9 and 10 are connected to an adder circuit 11.

Next, the operation of the solid-state image pickup device 1 will be described with reference to FIGS. 2 and 3.

First, as shown in FIG. 2A, photoelectric conversion is performed in each light receiving portion 6 by the first light reception 12, and the signal charge e ₁ of _one frame is accumulated in each light receiving portion 6.

Next, as shown in FIG. 2B, the signal charge e ₁ of the light receiving portion 6 is read out to the vertical transfer register portion 7 in the vertical blanking period.

Next, as shown in FIG. 2C, the vertical transfer register is
The signal charge e read to the star unit 7 ₁The vertical blanket
Across the first horizontal transfer register unit 4 within the ringing period
High-speed transfer to the vertical transfer register unit 8 of the storage area 3,
(So-called frame transfer), one frame of the storage area 3
Signal charge e₁Is stored once.

Next, as shown in FIG. 3D, in the image pickup area 2, photoelectric conversion is performed in each light receiving section 6 by the second light reception 13, and the signal charge e ₂ of the next frame is received in each light receiving section 6.
Accumulate in.

Next, as shown in FIG. 3E, the signal charge e ₂ of the light receiving section 6 is read out to the vertical transfer register section 7.

Next, as shown in FIG. 3F, the signal charges e ₁ in the storage area 3 are sequentially read line by line to the second horizontal transfer register section 5 (so-called line transfer), and at the same time, the above-mentioned 1 frame is read. and the signal charges e ₂ of the synchronous read the horizontal transfer register portion 4 of the signal charges e ₂ forward as soon as each line of the following frame read to the vertical transfer register portion 7 of the imaging area 2 (so-called Line transfer). Next, the signal charges e ₂ and e ₁ are transferred in the first and second horizontal transfer register units 4 and 5, respectively, and after the signals of one field and the next field are simultaneously output through the respective output units. , Both output signals are added by the adder circuit 11 and output.

In the above operation, if the object is not moving at the time of the first light reception 12 of FIG. 2A and the second light reception 13 of FIG. 3D, the signal charge e ₂ of the next frame in the imaging area ₂ And the signal charge e ₁ of one frame in the storage region 3 is exactly the same. That is, the same signal is detected at the first output unit 9 and the second output unit 10. By adding these outputs by the external circuit, that is, the adder circuit 11, a double signal output is obtained.

On the other hand, since randomly generated noise such as optical shot noise is only √2 times, the S / N of the output of the solid-state image pickup device 1 of this example is the solid-state image pickup of the normal frame interline transfer system. Random noise is twice as large as that of the element, and an improvement of about 3 dB can be achieved.

FIG. 4 shows a timing chart. Here, the timing of reading all pixels is shown. In this timing chart, the amount of light received for the first time and the amount of light received for the second time are made the same by using the electronic shutter. That is, in the first light receiving period, the electronic shutter pulse P ₁ is given by the time t _1, it until the charge is exhausted, the time t ₂ from a later time t ₁ is given read pulse P ₂
The light receiving time and hence the light receiving amount are set in the period up to. The signal charge e accumulated in the light receiving portion 6 according to the amount of light received during this period
₁ is read to the vertical transfer register unit 7 at time t ₂ .
Then, the signal charge e ₁ is frame-transferred to the storage region 3 by the clock voltage φ _VF for frame transfer.

[0029] Then, the electronic shutter pulse P ₁ at time t ₃ is provided at the second round of the light receiving period, similarly received time period from time t ₃ to time t ₄ when read pulse P ₂ is applied, thus receiving The amount is set, and the signal charge amount e ₂ accumulated during this period is read out to the vertical transfer register unit 7 at time t ₄ . Then, by the line transfer clock voltage φ _VL , both signal charges e ₂ and e _{1 in the} image pickup area 2 and the storage area 3 are line-transferred to the first and second horizontal transfer register sections 4 and 5, respectively, for horizontal transfer. The clock voltage φ _H causes the horizontal transfer register units 4 and 5 to be transferred to the output unit side. The amount of light received at the first time and the amount of light received at the second time are mutually different by making the light receiving time from time t ₁ to t ₂ and the light receiving time from time t ₃ to t _{4 the} same by the electronic shutter pulse P _1. Can be matched equally, and the signal charges e ₁ and e of _one frame and the next frame
_{The two} charges can be matched.

On the other hand, at the time of frame transfer, the signal charge e ₁ is transferred across the first horizontal transfer register section 4. In order to improve the transfer at this time, the following structure can be adopted. For example, the bias potential of at least the first horizontal transfer register unit 4 is set to an intermediate level between the high level and the low level of the clock voltage φ _VF applied to the vertical transfer register units 7 and 8 (shown by the dotted line 14 in FIG. 4). Or storage area 3
Is made deeper than that of the imaging region 2. As this method, the clock voltage of the vertical transfer register section may be made different between the storage region 3 and the imaging region 2 or a potential difference may be created by ion implantation.

The frame transfer shown in FIG. 4 may be line transfer if there is no problem such as smear or dark current. However, in that case, the time taken to capture the image becomes slightly longer.

According to the embodiment described above, temporarily stores the first signal charges e ₁ frame into the storage area 3, the signal charges e ₁ and the signal charges of the next frame of the image pickup area 2 e ₂ and the second Also, the S / N of the output signal from the CCD image pickup device is output without using an external storage device such as a frame memory by outputting the signal through the first horizontal transfer register units 5 and 4 and adding and outputting by the adder circuit 11. Can be improved.
That is, the S / N ratio of the CCD image pickup device for still images can be improved.

In the above example, the present invention is applied to the CCD solid-state image pickup device of the frame interline transfer system. However, as shown in FIG. 5, in addition, as shown in FIG.
6, and in that case also, the first horizontal transfer register unit 4 is arranged between the imaging region 17 and the accumulation region 18,
The second horizontal transfer register section 5 is arranged below the storage area 18, and the output sections 9 and 10 of the first and second horizontal transfer register sections 4 and 5 are connected to the adder circuit 11. . Also in this case, the S / N of the output signal can be improved as in the above example.

[0034]

According to the present invention, by adding signals without using an external storage device such as a frame memory,
The S / N of the output signal from the solid-state image sensor can be improved. It is possible to improve the S / N in a so-called solid-state image pickup device for still images. In the present invention, the solid-state image pickup device itself can be miniaturized, and is suitably applied to, for example, an image input to a computer or an electronic still camera using the solid-state image pickup device for news.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of a solid-state image sensor according to the present invention.

FIG. 2 is an operation explanatory diagram (1).

FIG. 3 is an operation explanatory diagram (2).

FIG. 4 is a timing chart diagram according to the present invention.

FIG. 5 is a configuration diagram of another embodiment of the solid-state image sensor according to the present invention.

[Explanation of symbols]

1 frame interline transfer type CCD solid-state image sensor 2, 17 imaging area 3, 18 storage area 6 light receiving section 4, 5 horizontal transfer register section 7, 8 vertical transfer register section 9, 10 output section 11 adder circuit 12, 13 light receiving section e ₁ , e ₂ signal charge 16 frame transfer CCD solid-state image sensor

Claims (4)

[Claims] 1. An image pickup area having a plurality of light receiving sections, a storage area for temporarily storing signal charges of the image pickup area, a first horizontal transfer register section arranged in the image pickup area, and the storage area. A second horizontal transfer register section disposed on the opposite side of the first horizontal transfer register section of the storage area, and the signal charge of the imaging area and the signal charge of the storage area are respectively supplied to the first horizontal transfer register section. And a second horizontal transfer register section for outputting and adding the two output signals. 2. An image pickup area having a plurality of light receiving sections, a storage area for temporarily storing signal charges of the image pickup area, and a first horizontal transfer register section arranged between the image pickup area and the storage area. A second horizontal transfer register section arranged on the opposite side of the first horizontal transfer register section in the accumulation area, and the amount of light received in the light receiving period is set by an electronic shutter; And a signal charge of the storage area is output through the first and second horizontal transfer register sections, respectively, and the two output signals are added together. 3. The solid-state image pickup device according to claim 1, wherein the image pickup region and the storage region have a frame interline transfer system structure. 4. The solid-state image pickup device according to claim 1, wherein the image pickup region and the storage region have a frame transfer type structure.