JP2616672B2 - Imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging device.

[0002]

2. Description of the Related Art An example of a conventional imaging apparatus is shown in FIG. It comprises a charge transfer element 2 composed of a charge-coupled element for transferring charges in a one-dimensional direction from the top to the bottom of the figure, a light receiving element 1, and a readout switch 3 for transferring signal charges from the light receiving element to the charge transfer element. Unit pixels 7 are arranged in a two-dimensional array. The charge-coupled device has a portion 3 to which the readout switch connects and a non-connection portion 4. An image sensor having this structure is called an interline image sensor.

[0003]

In an image pickup apparatus using an interline image sensor, the amount of signal charges transferred from a light receiving element is set so as not to exceed the limit of the charge held by the charge transfer element. When a signal charge exceeding the limit is transferred from the light receiving element, it is mixed with a signal of an adjacent unit pixel separated by a low potential barrier. This will be specifically described with reference to FIG. FIG. 5B shows an image area formed by arranging unit pixels in a two-dimensional array. As shown in the figure, one unit pixel is called Q2, and its unit pixels in the vertical direction are called Q1 and Q3. Q1
To Q3 are connected to the same charge transfer element. Here, a situation is considered in which an amount of charge exceeding the retained charge limit has been transferred from the light receiving element of Q2 to the charge transfer element. FIG. 5A shows the state of the potential of the charge transfer element in this situation. Charges exceeding the retention limit are mixed into Q1 and Q3. That is, as shown in FIG. 5B, a vertical false linear pattern occurs. The length of the linear false pattern depends on the ratio between the amount of charge transferred from the light receiving element and the holding limit.

In an image pickup apparatus, the amount of electric charge generated by the light receiving element depends on the amount of light emitted from the outside. Many signal charges are generated under strong irradiation light. The external irradiation light cannot be controlled by the imaging device itself. To prevent the generation of harmful false patterns, the overflow drain function is added to each light receiving element to discard generated charges that exceed the holding limit of the charge transfer element, or the charge capacity of the light receiving element is adjusted by adjusting the reset voltage. To prevent the charge from being transferred to the charge transfer element beyond the holding limit. However, in order to realize the overflow drain function, the horizontal overflow drain has a problem that the sensitivity is reduced due to a decrease in the effective light receiving element area in a unit pixel. Further, since the vertical overflow drain structure is sensitive to the structure of the detector, a strictly controlled manufacturing process is required. When adjusting the reset voltage, the dynamic range and sensitivity characteristics of the light receiving element itself are deteriorated.

As described above, in the conventional image pickup apparatus, the generation of the vertical line false pattern, which is a harmful false pattern, is prevented by preventing the assumed maximum generated charge amount from exceeding the holding limit of the charge transfer element. Had a problem that had to be.

[0006]

According to the present invention, a light receiving element is arranged adjacent to a charge transfer element for performing one-dimensional charge transfer, and is connected by a read switch for reading charges from the light receiving element to the charge transfer element. In an image pickup device using an image sensor in which unit pixels are arranged in a two-dimensional array, the charge of a light receiving element is partially swept out to an adjacent charge transfer element different from the charge transfer element to which the charge of the light receiving element is transferred. An image pickup apparatus comprising an adjacent sweeping switch, and in the above image pickup apparatus, after starting signal charge transfer to a charge transfer element via the readout switch, and by the charge transfer element Before starting the operation, the adjacent sweeping switch is opened, and the charge corresponding to the amount of charge retained in the charge transfer element exceeds the readout switch and the light receiving element. An imaging apparatus characterized by to transfer the adjacent sweep the charge transfer device which is connected to the switch. With this configuration, it is possible to control the shape of the false pattern, so that it is possible to detect a supersaturated portion of the charge using the harmful false pattern, and, consequently, charge transfer due to the supersaturation of the charge. It is also possible to prevent the function of the element from being deteriorated.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the drawings.

(Embodiment 1) FIG. 1 is a block diagram of a first embodiment of the present invention. The unit pixel 7 includes an adjacent sweeping switch 6 in addition to the configuration of the interline image sensor shown in FIG. The driving method and operation will be described with reference to FIG. FIG. 2A shows the voltage applied to the gate electrodes V1, V4, TG1, and TG3 in FIG. 1, and FIG. 2B shows the channel potential. The other electrodes V3 and V2 are V
1, the inverted voltage of V4. The first embodiment is an example of interlaced reading, but TG2 and TG4 are shown in FIG.
In the field shown in FIG. 2A (this field is referred to as a first field), the level is always L (low) level, and the second field has a pulse waveform similar to that shown in FIG. FIG.
The potential distribution of AA 'and BB' (FIG. 1) at each timing of (a) is shown by a solid line and a broken line in FIG. 2 (c). For the sake of explanation, FIG.
The light receiving element of the unit pixel (see FIG.
(C)-) charge is generated and held, and P1
And the situation where the charge amount of the light receiving element of P3 is 0 (zero). Further, in this setting, it is assumed that the charge amount a exceeds the holding limit of the charge transfer element. Since the TG1 and TG3 are both closed at the timing of, the electric charge a becomes P
2 are held in the two light receiving elements. TG3 is opened after t [sec] after TG1 is opened. This delay time is set as a waiting time for the formation of a potential distribution and the movement of charges to follow the pulse voltage application. After this delay time, the adjacent sweeping switch (TG)
By setting 3) to the open state, it is possible to move the charge of the light receiving element to the charge transfer element without distortion within a necessary charge amount range. In this embodiment, the charge amount b at the timing is equal to a. However, according to the above setting, a
That is, the charge amount of b exceeds the holding limit of the charge transfer element, and the charge overflows from the potential well during the transfer operation. Assume this overflow timing. As shown in FIG. 2A, TG1 and TG3 maintain the open state at the timing when the charge overflows. Therefore, FIG.
As shown by (c), the overflowed charges pass over the potentials of the adjacent sweeping switch and the light-receiving element readout switch, which are lower than the potential barrier in the transfer direction in the charge transfer element, and pass through the adjacent charge transfer elements of P1 and P3. Flow into After the series of operations, when a normal transfer is performed, a horizontal false pattern (P1, P2, P3) is generated as a supersaturated pattern shown in FIG.

The supersaturation pattern can be made into an arbitrary pattern such as a cross pattern by adjusting the relative relationship between the potential of the adjacent sweeping switch in the open state and the potential of the charge transfer element in the barrier state. When the center position of the target is detected, the cross-oversaturation pattern can be sufficiently used.

(Embodiment 2) FIG. 3 shows a second embodiment of the present invention.
Shown in The difference from the first embodiment is that the voltage applied to the portion to which the adjacent sweeping switch 5 is connected is different.
Since the connection portion is different, a supersaturation pattern different from that of the first embodiment is obtained.

(Embodiment 3) In the above two embodiments, the read switch and the adjacent sweeping switch have the same channel potential characteristics. However, by making the characteristics different, a common drive pulse is applied to both. It is also possible. In this example, the pinning potential and the pinning applied voltage of the channel potential characteristic of the adjacent sweeping switch are shallower (pinning potential) and higher (pinning applied voltage), respectively, than the characteristics of the readout switch. This image sensor is provided with T in FIG.
A trapezoidal voltage similar to that of G1 is applied. If the slope of the rising portion of TG1 is made gentler, the time variation of the channel potential of each section is equivalent to that TG3 shown in FIG. 2A rises later than TG1. The delay time can be controlled by the rising slope of the trapezoidal wave. Further, when the driving waveforms of V1 to V4 are ternary pulses, the timing at which the charge transfer element overflows can be controlled.

In the above example, a charge-coupled device (CCD) is used as the charge transfer device. However, a charge-swept device (CSD) can be similarly realized.
Although it is difficult to define the saturation level in the CSD, if a large amount of charge enters the charge transfer element, it is necessary to increase an additional transfer pulse in order to cause all of the spread charge in the CSD to flow in the transfer direction. Problem becomes remarkable. According to the present invention, the burden on the additional transfer can be reduced.

[0013]

According to the image pickup apparatus of the present invention, when a supersaturated charge exceeding the transfer charge holding limit of the charge transfer element is generated in the light receiving element, the supersaturation pattern can be selected. In particular, when the position of the object is detected, the cross-oversaturation pattern is used, so that the function of position detection is not impaired even during oversaturation. As described above, the problem of impairing the function even at the time of supersaturation can be reduced, so that the sensitivity characteristic of the light receiving element and the freedom of setting the dynamic range can be increased.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an image sensor of an imaging apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a driving method of the imaging device according to the first embodiment of the present invention.

FIG. 3 is a configuration diagram of an image sensor according to a second embodiment of the present invention.

FIG. 4 is a configuration diagram illustrating an example of a conventional imaging device.

FIG. 5 is a schematic diagram for explaining a problem of a conventional imaging device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Light receiving element 2 Charge transfer element 3 Charge transfer element read switch connection part 4 Charge transfer element read switch non-connection part 5 Read switch 6 Adjacent sweeping switch 7 Unit pixel V1, V2, V3, V4 Charge transfer element This is the electrode name.

Claims (2)

(57) [Claims] 1. A two-dimensional array of unit pixels in which a light receiving element is arranged adjacent to a charge transfer element for performing one-dimensional charge transfer and connected by a readout switch for reading out the charge from the light receiving element to the charge transfer element. In the imaging apparatus using the image sensor arranged in the above, an adjacent sweeping switch for partially sweeping out the charge of the light receiving element to an adjacent charge transfer element different from the charge transfer element to which the charge of the light receiving element is transferred is provided. An imaging device characterized by the above-mentioned. 2. An adjacent sweeping switch is opened after starting signal charge transfer to a charge transfer element via a readout switch and before starting a transfer operation in the charge transfer element, and the amount of charge held in the charge transfer element 2. The imaging apparatus according to claim 1, wherein the charge exceeding the threshold value is transferred to the charge transfer element connected to the adjacent sweeping switch via the readout switch and the light receiving element.