JPH07122722A - Image pickup device - Google Patents

Abstract

PURPOSE:To control the shapes of false patterns by providing adjacent sweeping switches which sweep part of charges of photodetectors to charge transferring elements which are different from the charge transfer elements to which the charges of the photodetectors are transferred. CONSTITUTION:TG1 and TG2 are maintained in opened states at the charge overflowing timing. Overflowing charges flow into the charge transferring element between adjacent false lateral patterns P1 and P3 after passing over the potential across an adjacent sweeping switch and photodetector reading-out switch which is lower than the potential in the charge transfer element in the transferring direction. When ordinary transfer is performed after the above- mentioned series of operations, the lateral false patterns P1, P2, and P3 are generated as oversaturation patterns. The saturation patterns can be changed to such arbitrary patterns as the cross patterns, etc., by adjusting the correlation between the potential obtained when the adjacent sweeping switches and the potential obtained when the charge transfer elements are set in the state of barrier.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art FIG. 4 shows an example of a conventional image pickup apparatus. The charge transfer device 2 is composed of a charge-coupled device that transfers charges one-dimensionally from the top to the bottom of the figure, and is composed of a light receiving device 1 and a read switch 3 for transferring signal charges from the light receiving device to the charge transfer device. The unit pixels 7 are arranged in a two-dimensional array. The charge coupled device has a portion 3 to which the read switch is connected and a non-connection portion 4. An image sensor having this structure is called an interline image sensor.

[0003]

In an image pickup device using an interline image sensor, the amount of signal charges transferred from the light receiving element is set so as not to exceed the held charge limit of the charge transfer element. When the signal charges exceeding the above limit are transferred from the light receiving element, they are mixed with the signals of the adjacent unit pixels separated by the 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 the unit pixels in the vertical direction are called Q1 and Q3. Q1
To Q3 are connected to the same charge transfer element. Now, consider a situation in which a charge amount exceeding the held charge limit is transferred from the light receiving element of Q2 to the charge transfer element. The state of the potential of the charge transfer element in this situation is shown in FIG. The charges exceeding the holding limit are mixed in Q1 and Q3. That is, as shown in FIG. 5B, a vertical false pattern is generated. The length of the linear pseudo pattern depends on the ratio between the amount of charge transferred from the light receiving element and the holding limit.

In the image pickup device, the amount of electric charge generated in 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. In order to prevent the generation of harmful false patterns, the function of overflow drain is added to each light receiving element to discard the generated charge that exceeds the holding limit of the charge transfer element, or the reset voltage is adjusted to adjust the charge capacity of the light receiving element. By limiting the charge, the charge is not transferred to the charge transfer element beyond the holding limit. However, in order to realize the overflow drain function, the lateral overflow drain has a problem that the sensitivity is lowered due to the reduction of the effective light receiving element area in the unit pixel. Further, since the vertical overflow drain structure is sensitive to the structure of the detector, it requires a strictly controlled manufacturing process. When the reset voltage is adjusted, the dynamic range and sensitivity characteristics of the light receiving element itself are deteriorated.

As described above, in the conventional image pickup apparatus, the assumed maximum amount of generated charges does not exceed the holding limit of the charge transfer element to prevent the generation of the vertical line false pattern which is a harmful false pattern. I had a problem I had to do.

[0006]

According to the present invention, a light receiving element is arranged adjacent to a charge transfer element for transferring charges in a one-dimensional direction, and a read switch for reading out charges from the light receiving element to the charge transfer element is connected. In an imaging device using an image sensor in which sub-pixels are arranged in a two-dimensional array, the charge of the light receiving element is partially swept 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 device comprising an adjacent sweep switch, and in the image pickup device, after starting signal charge transfer to a charge transfer device via the readout switch, and at a charge transfer device. Before the operation is started, the adjacent sweep switch is opened, and the charge exceeding the amount of charge held in the charge transfer element is transferred to the read 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 the location where the charge is oversaturated by using the harmful false pattern, which in turn leads to charge transfer due to charge oversaturation. It is also possible to prevent the functional deterioration of the element.

[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 the first embodiment of the present invention. The unit pixel 7 is provided with an adjacent sweep switch 6 in addition to the structure of the interline image sensor shown in FIG. The driving method and operation will be described with reference to FIG. The applied voltage to the V1, V4, TG1, and TG3 gate electrodes in FIG. 1 is shown in FIG. 2 (a), and the channel potential thereof is shown in FIG. 2 (b). The other electrodes V3 and V2 are V
It is an inversion voltage of 1, V4. In the first embodiment, an example of interlaced reading is used, but TG2 and TG4 are shown in FIG.
The field shown in (a) (this field is called the first field) is always at the L (low) level, and the second field has the same pulse waveform as in FIG. 2 (a). Figure 2
The potential distributions of AA ′ and BB ′ (FIG. 1) at the respective timings of and of (a) are shown by a solid line and a broken line in FIG. 2 (c). For the purpose of explanation, FIG. 2 (c) shows P2.
The light receiving element of the unit pixel (see FIG. 2D) is a (see FIG.
(C)-) is generated and held, and P1
And the situation where the charge amount of the light receiving element of P3 is 0 (zero) was set. Further, in this setting, the charge amount a exceeds the holding limit of the charge transfer element. At the timing of, since both TG1 and TG3 are in the closed state, the charge a is P
It is held in the second light receiving element. After t [seconds] after opening TG1, TG3 becomes open. This delay time is set as a waiting time so that the formation of potential distribution and the movement of charges can follow the pulse voltage application. Adjacent sweep switch (TG
By making 3) open, it is possible to move the charge of the light receiving element to the charge transfer element without distortion within the required charge amount range. In this embodiment, the charge amount b at the timing of is equal to a. However, because of the above setting,
That is, the amount of charges in b exceeds the holding limit of the charge transfer element, and charges overflow from the potential well during the transfer operation. Let this overflow timing. As shown in FIG. 2A, TG1 and TG3 maintain the open state at the timing when the charges overflow. For this reason,
As shown in (c), the overflowed charge passes over the potentials of the adjacent sweep switch and the light-receiving element reading switch, which are lower than the potential barrier in the transfer direction in the charge transfer element, and in the adjacent charge transfer elements of P1 and P3. Flow into. When normal transfer is performed after this series of operations, horizontal false patterns (P1, P2, P3) are generated as the oversaturation pattern shown in FIG.

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

(Embodiment 2) A second embodiment of the present invention is shown in FIG.
Shown in. The difference from the first embodiment is that the applied voltage is different from the part to which the adjacent sweep switch 5 is connected.
Since the connecting portion is different, a supersaturation pattern different from that of the first embodiment can be obtained.

(Embodiment 3) In the above-mentioned two embodiments, the read switch and the adjacent sweep switch have the same channel potential characteristics, but by adopting different characteristics, 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 characteristics of the adjacent sweep switch are shallower (pinning potential) and higher (pinning applied voltage) than the characteristics of the read switch, respectively. This image sensor has a T shown in FIG.
A trapezoidal voltage similar to G1 is applied. When the slope of the rising portion of TG1 is loosened, the time change of the channel potential of each part is equivalent to that of TG3 shown in FIG. 2A, which rises later than TG1. The delay time can be controlled by the rising slope of the trapezoidal wave. Further, by setting the driving waveform of V1 to V4 to be a ternary pulse, it is possible to control the timing when the charge transfer element overflows.

In the above example, a charge coupled device (CCD) is used as a charge transfer device, but a charge swept device (CSD) can be similarly realized.
It is difficult to define the saturation level in CSD, but when a large amount of charge enters the charge transfer element, it is necessary to increase the number of additional transfer pulses in order to flow all the charge spread in the CSD in the transfer direction, and the transfer frequency is high. The problem becomes significant. The present invention can reduce the burden of additional transfer.

[0013]

In the image pickup device according to the present invention, when supersaturated charges exceeding the transfer charge holding limit of the charge transfer element are generated in the light receiving element, the supersaturation pattern can be selected. In particular, when the position of the object is being detected, the cross-saturation pattern is used so that the position detection function is not impaired even during oversaturation. As described above, since the problem of loss of function even at the time of oversaturation can be reduced, the degree of freedom in setting the sensitivity characteristics and the dynamic range of the light receiving element can be increased.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a driving method of the image pickup apparatus according to the first embodiment of the present invention.

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

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

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

[Explanation of symbols]

1 Light receiving element 2 Charge transfer element 3 Read switch connection section of charge transfer element 4 Read switch non-connection section of charge transfer element 5 Read switch 6 Adjacent sweep switch 7 Unit pixel V1, V2, V3, V4 Charge transfer element The electrode name.

Claims (2)

[Claims] 1. A two-dimensional array of unit pixels in which a light receiving element is arranged adjacent to a charge transfer element for transferring charges in a one-dimensional direction and connected by a read switch for reading out charges from the light receiving element to the charge transfer element. In an image pickup device using the image sensor arranged in, the adjacent sweep switch for partially sweeping 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. 2. The amount of charge held in the charge transfer element is opened by opening the adjacent sweep switch after starting the signal charge transfer to the charge transfer element via the read switch and before starting the transfer operation in the charge transfer element. 2. The image pickup apparatus according to claim 1, wherein the charge exceeding the amount is transferred to the charge transfer element connected to the adjacent sweep switch via the read switch and the light receiving element.