JPS58187081A - Solid-state image pickup device and its drive method - Google Patents

Abstract

PURPOSE:To eliminate the fixed pattern due to the difference between threshold values of transfer and discharge gates, by reading out signals at each field and passing the excluded signal charges through the same transfer gate both for the exclusion and transfer. CONSTITUTION:Before reading out the signal charges stored in odd number of photoelectric conversion elements 1, 3..., the signal charges stored in even number of photoelectric conversion elements 2, 4... are transferred to a charge transfer element train 6 through a transfer gate 5 and excluded to a charge absorbing region 7 through a gate 9. In forming the 2nd field by reading out the signal charge stored in the even number photoelectric conversion elements 2, 4,..., first the signal charges stored in the odd number photoelectric conversion elements 1, 3... are transferred to the charge transfer element train 6 through the transfer gate 5, and the signal charges of the odd number of the elements 1, 3... transferred to the train 6 are excluded to the charge absorbing region 7 through the gate 9.

Description

[Detailed description of the invention] The present invention relates to a solid-state imaging device and a method for driving the same.

Generally, in solid-state imaging devices, interlaced scanning is performed in order to improve resolution1, but the present invention aims to improve the problems of interlaced scanning.

The drawbacks of the conventional solid-state imaging device using the interline transfer method COD will be described below as an example.

FIG. 1 shows the main parts of a solid-state imaging device having an interline transfer method COD. The operation of this solid-state imaging device is to first transfer the signal charges accumulated in the odd-numbered photoelectric conversion elements 1, 3, etc. to the charge transfer element array 6 through the transfer gate 6, and output a signal for one field. . Next, the signal charges accumulated in the even-numbered photoelectric conversion elements 2, 4, . . . are transferred to the charge transfer element array 6 to output signals for the next one field.

When such a conventional driving method of a solid-state imaging device is used, the signal charges forming the first field and the second field are the odd-numbered photoelectric conversion elements 1: 3, . . . , respectively.
These are signal charges stored in even-numbered photoelectric conversion elements 2, 4, . . . , and since these charges are adjacent to each other and independent, an image with good resolution can be obtained. Furthermore, when focusing on one photoelectric conversion element, two fields are read out once, so the time required to integrate the signal charges is twice as long as when reading out each field. In other words, the standard television system (
According to the NTS C method, the integration time is 16.7 milliseconds when reading out each field, whereas it is 33 milliseconds in the interlaced scanning described in -. Such a driving method is called a frame accumulation method.

However, such conventional driving methods for solid-state imaging devices have the following drawbacks.

In other words, since the signal charge continues to be integrated during the integration time,
If the object is a stationary object, the integration time may be long, but if the object is a moving object, a phenomenon similar to the blurring of the object that occurs when photographing a moving object at a slow shutter speed will occur.

This phenomenon is called equivalent afterimage.

As a method for reducing this equivalent afterimage, there is a driving method called field accumulation method.To explain this method using FIG. 1, first, photoelectric conversion elements 2 and 1 and 4 are 3, the signal charge of the even-numbered photoelectric conversion element and the signal charge accumulated in the odd-numbered photoelectric conversion element above it are mixed and read out, and in the second feed/read, the signal charge of the photoelectric conversion element is read out. This is a driving method of a solid-state imaging device in which signal charges accumulated in the photoelectric conversion elements of the number 2 and 3, 4 and 5, etc. and the odd numbered photoelectric conversion elements below are mixed and read out.

In this driving force method, since each photoelectric conversion element is read out in one field jσ, the integration time is a sufficient time (16.7 milliseconds) as in the frame accumulation method, and the equivalent afterimage is reduced. However, the signal charges that make up the first field and the second field' use signal charges stored in the same photoelectric conversion element, and only change the signal charges that are mixed as a pair, so the resolution is worse than that of the frame accumulation method. There is a problem where you can only get images.

In order to eliminate the drawbacks of the field accumulation method and the frame accumulation method as described above, i2i et al.
... is transferred to the charge transfer unit 6 through the transfer gate 6, and then a voltage is applied to the excess charge discharge gate 8 adjacent to the photoelectric conversion element 2, thereby converting the signal charge to the even-numbered photoelectric conversion element 2. , 4... are discharged to the charge absorption region 7 adjacent to the excess charge υ1 output gate 8, and in the next second field, the even-numbered photoelectric conversion elements 2, 4... After transferring the signal charge to the charge transfer unit 6, by applying a voltage to the excess charge discharge gate 8, the signal load accumulated in the odd-numbered optical conversion elements 1, 3, etc. is transferred to the charge absorption region. There is a drive method for discharging to.

However, in this driving method, when the charge of the photoelectric conversion element 71j is discharged to the charge absorption region 7, BBD transfer is performed in which charge remains in the photoelectric conversion element. comes out.

For this reason, a fixed pattern appears on the image due to variations in the threshold value IE pressure, which is a fatal flaw for practical use.

The present invention eliminates the above-mentioned drawbacks of the conventional solid-state imaging device, which maintains the high resolution of the frame accumulation method, achieves low equivalent afterimages of the field accumulation method, and does not produce fixed patterns due to differences in gate threshold values. The present invention also provides a method for driving the same.

A solid-state imaging device and a driving method thereof according to an embodiment of the present invention will be described below. FIG. 2 is a diagram showing essential parts of a solid-state imaging device in an embodiment of the present invention.

The device consists of 1°2 photoelectric conversion elements arranged in 11 rows.
3. 4..., a charge transfer element array 6 that transfers signal charges accumulated in the photoelectric conversion element, and a charge absorption region 7, and between the charge transfer element array 6 and the charge absorption region 7. This serves as the gate electrode 9. In addition, in FIG. 2, the same parts as in FIG. 1 showing the conventional example are given the same numbers. A feature of this device is that it has a gate electrode 9 between the charge transfer element array 6 and the charge absorption region 7.

To explain the driving method of the device, first, when reading signal charges accumulated in odd-numbered photoelectric conversion elements 1, 3, . . . to form a first field, the odd-numbered photoelectric conversion elements 1 , 3..., before reading and hanging the signal charges accumulated in the even-numbered photoelectric conversion elements 2, 4..., first transfer the signal charges accumulated in the even-numbered photoelectric conversion elements 2, 4... to the charge transfer element array 6 through the transfer gate 6, The signal charges of the even-numbered photoelectric conversion elements 2 4 . . . transferred to the charge transfer element array 6 are discharged to the charge absorption region 7 through the gate electrode 9 . When reading out the signal charges accumulated in the even-numbered photoelectric conversion elements 2, 4... to form the second field, the signal charges accumulated in the even-numbered photoelectric conversion elements 2, 4... Before reading out signal charges, the signal charges accumulated in the odd-numbered photoelectric conversion elements 1, 3, etc. are first transferred to the charge transfer element array 6 through the transfer gate 6, and the odd-numbered photoelectric conversion elements transferred to the charge transfer element array 6 are The signal charges of the photoelectric conversion elements 1, 3, . . . are discharged to the charge absorption region 7 through the data 1 electrode 9.

According to this driving method of the solid-state imaging device, the signals 3' accumulated in each light 1F conversion element 1 + 2 + 3 + 4... are read out or discharged for each field, so the integration time is The time is 16.7 milliseconds, and the equivalent afterimage is the same as that of the field accumulation method.The signal charges used to configure the first and second fields are still generated by independent photoelectric conversion elements 1. 2. as in the frame accumulation method.
Since the signal charge accumulated in 3+4... is used,
The same resolution as the frame accumulation method can be obtained. Furthermore, since the same transfer gate 6 as in the case of transfer is used when discharging signal charges, the fixed pattern caused by the difference in threshold values of the transfer and discharge gates is eliminated.

Since the discharge from the charge transfer element array 6 to the charge absorption region 7 through the gate electrode 9 is a complete transfer, it is not affected by the threshold value as in BBD transfer. A fixed pattern due to variations in the threshold value does not occur.

Next, the solid-state imaging device of the present invention and its driving method will be explained in more detail using the solid-state imaging device of FIG. 3 and the clock pulse chart 1 of FIG. 4. Figure 3 shows four transfer element rows.
1 is a diagram showing the main parts of a solid-state imaging device according to an embodiment of the present invention when configured with phases φ1. φ2. φ3. φ4 is a clock pulse applied to the charge transfer element;
The clock pulse φ8 applied to the gate electrode 9 is used to discharge charges from the charge transfer element to the charge absorption drain 7.
is the clock pulse applied to

To explain the driving method of this device, a high voltage is simultaneously applied to φ3 and φPT during the period B in FIG. Forward. Next, by applying a positive voltage to the charge transfer element and lowering the rtf pressure of the charge transfer element, the signal charge of the `+L charge transfer element array 6 is discharged to the `llLll loading region 7. Thereafter, by applying a high pressure to φ1, φ, and T, the signal charges accumulated in the photoelectric conversion elements 1, 3, and so on are transferred to the charge transfer element array 6.The operation of period B in FIG. 4 ends. After that, by applying a pulse of the fourth period [C, 1 (1 (+: ■ transfer transfer element - 1 column 6 internal charge) is transferred in the charge transfer element column 6 in order to extract it as a signal output.

In period C in FIG. 4, signal charges accumulated in the photoelectric conversion elements 1, 3, . . . are transferred to the charge transfer element array 6 by simultaneously applying a high voltage to φ1, φ, and T. Next φ8
By applying a high voltage to the charge transfer element array 6, the signal charges in the charge transfer element array 6 are discharged to the charge absorption region 7. After that, φ1 and φ,
By applying a high voltage to T, the photoelectric conversion elements 2 and 4
... is transferred to the charge transfer element array 6. After the operation of period C in FIG. 4 is completed, E in FIG.
By adding the period and period A in FIG. 4, charges are transferred within the charge transfer element array 6 and read out.

In this example, the fixed Pakuun ratio for the saturated signal was 60 dB or more, and an extremely excellent ratio could be achieved.

According to the solid-state imaging device and its driving method of the present invention described above, it is possible to maintain the high resolution of the frame accumulation method and achieve low equivalent afterimages of the field accumulation method. (This eliminates the conventional fixed pattern as there is no effect of fluctuations in the f41 value of the ¥ bar.
Industrial utility value (tn is large.

[Brief explanation of drawings]

FIG. 1 is an enlarged view of main parts of a conventional solid-state imaging device, FIG. 2 is an enlarged view of a retaining part of a solid-state imaging device according to an embodiment of the present invention, and FIG.
The figure is an enlarged view of the main parts of a solid-state image sensor using an array of four-phase charge transfer elements to further specifically explain the solid-state image sensor according to the embodiment of the present invention, and FIG. 4 is an enlarged view of the solid-state image sensor shown in FIG. 3. FIG. 1.3...Odd numbered photoelectric conversion element, 2,4...
... Even numbered photoelectric conversion elements, 6 ... Transfer gate, 6 ... Transfer element row, 7 ... Charge series region, 8 ... Charge Discharge gate, 9...
Gate electrode, 1o...Channel stopper. Name of agent: -11F Rido Toshio Nakao and 1 other person
Figure 1 Figure 2 Figure 3 Figure 4

Claims (2)

[Claims] (1) comprising photoelectric conversion elements arranged in a matrix, a charge transfer element row that transfers signal charges accumulated in the photoelectric conversion elements, and a charge absorption region, the charge transfer element row and the charge absorption region; A solid-state imaging device characterized in that a gate electrode is provided between the regions. (2) comprising photoelectric conversion elements arranged in a matrix, 11 charge transfer columns for transferring signal charges accumulated in the photoelectric conversion elements, and a charge absorption region, the charge transfer element columns and the charge absorption region; In a method for driving a solid-state imaging device in which a gate electrode is provided between a region and a region, a signal charge accumulated in a first photoelectric conversion element group consisting of photoelectric conversion elements in every row of the photoelectric conversion elements is , transferred to the charge transfer element, further opened the gate electrode to discharge the charge to the charge absorption region, and then transferred to a second photoelectric conversion element group consisting of photoelectric conversion elements in a different row from the first photoelectric conversion element group. The accumulated signal charge was read out, and then the signal charge accumulated in the second photoelectric conversion element group was transferred to the charge transfer element array, and subsequently the gate electrode was opened and discharged to the nIJ charge absorption region. A method for driving a solid-state imaging device, comprising: thereafter reading signal charges accumulated in the first photoelectric conversion element group.