JP2525646B2 - Driving method for solid-state imaging device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for driving a solid-state image sensor, and particularly to a method for driving a solid-state image sensor suitable when applied to an electronic still camera.

(Prior Art) Conventionally, when a solid-state image sensor is applied to an electronic still camera, a subject is imaged in a sequence as shown in FIG.

That is, the element is read out immediately before the shutter operation, the dark charge accumulated in the element is swept out, the subject image is exposed by opening the shutter to accumulate the charge, and when the shutter is closed, The image signal of the subject is being read.

Of the above sequences, the dark charge sweep mode is
It is performed at the same time when the camera power is turned on, and is repeated until immediately before the shutter operation. As a result, a decrease in S / N due to the mixture of dark charges is always prevented, and a good image signal can be obtained.

(Problems to be Solved by the Invention) However, when only one shot to be photographed needs to be recorded as in an electronic still camera, it is not necessary to repeatedly execute the sweep operation before opening the shutter.

Further, in the video camera, it is necessary to drive the element to set the angle of view even at the time of monitoring, but in the electronic still camera, if the element is placed in a driving state before the photographing and the sweeping operation is performed, power consumption increases. .

Note that the present inventors have already proposed a solid-state image sensor in which the vertical charge transfer unit has a photoelectric conversion function itself at the same time as charge transfer and can improve both sensitivity and resolution when applied to an electronic still camera. did.

In this solid-state imaging device, a color filter of one color is arranged on the vertical charge transfer section, and a color filter of two colors is arranged in the photosensitive area so that image signals of three colors are output in a frame sequential manner. It is provided.

When such a field-sequential output solid-state image sensor is applied to an electronic still camera, the solid-state image sensor can sweep out signal charges of each color all at once in one field period in a charge sweep mode. ,convenient.

The object of the present invention has been made based on the above circumstances, and provides a method for driving a solid-state imaging device, which can reduce power consumption when applied to an electronic still camera and can improve both resolution and sensitivity. Especially.

(Means for Solving the Problems) The above object of the present invention is to provide a photosensitive region including at least a plurality of light receiving elements, a vertical charge transfer unit attached to each vertical column of the light receiving elements, and a horizontal charge transfer unit. In this case, the vertical charge transfer section can not only transfer the charge formed by the light receiving element but also perform photoelectric conversion by itself, and in the vertical charge transfer section, one of the three primary colors or complementary colors can be used. A color filter that forms a color signal and that forms the remaining two color signals in the light receiving element is arranged, and the signal charge of each color formed by exposing the photosensitive region and the vertical charge transfer unit for a predetermined period by the shutter operation. In the method of driving the solid-state image sensor that outputs the frame sequentially, the first operation is performed by the standby mode before the shutter operation and the trigger signal issued by the shutter operation. When the device is driven for the first time, all the charges formed in the light receiving element and the vertical charge transfer section are swept out all at once, and the shutter is opened and the charge transfer clock is synchronized with the completion of sweeping out the charges. In the exposure / accumulation mode in which signals are stopped and charges are accumulated, and after the shutter is closed, the signal charges in the vertical charge transfer unit are first read out to the outside via the horizontal charge transfer unit, and then 1 corresponding to one color of the light receiving element. This is achieved by a method for driving a solid-state image pickup device, which is characterized in that a signal for a screen and then a signal for one screen corresponding to another color are sequentially read out in a frame-sequential manner.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic configuration diagram of a solid-state image pickup device to which the present invention is applied, and this device outputs color image signals of R, G, B3 primary colors in a frame sequential manner.

In the figure, a light receiving unit 10 is attached to each photosensitive region 14 formed of a group of light receiving cells formed by photoelectric conversion elements arranged in a vertical direction as shown by a dotted rectangle, and each vertical row of the photosensitive regions 14. Multiple photosensitive areas formed from photosensitive transfer area 15
14 and photosensitive transfer areas 15 are alternately provided in the horizontal direction (left and right direction in the figure).

On the surface of each light receiving cell in the photosensitive area 14, green and blue filters indicated by symbols G and B are alternately arranged in the vertical direction.

The photosensitive transfer area 15 is composed of transfer cells corresponding to each light receiving cell of the photosensitive area 14 as shown by a dotted rectangle in the figure, and each transfer cell has a photoelectric conversion function and operates mutually. Therefore, it has a function of transferring signal charges downward. That is, the photosensitive transfer area 15 is composed of a self-operation type imaging device.

On the surface of the photosensitive transfer area 15, red filters indicated by a symbol R are arranged in a stripe shape. On the output side of the light receiving unit 10, a horizontal charge transfer unit 11 composed of a horizontal CCD is arranged via a transmission gate Tg, and an output amplifier 12 for reading out signal charges by a drive signal φs is arranged at the output end thereof. There is.

 FIG. 2 shows the configuration of the light receiving section 10.

A plurality of polysilicon transfer electrodes 18 and 19 extending in the horizontal direction are provided in the photosensitive transfer region 15 under the filter R, and the charges are moved downward by two-phase driving (φV _{1 to} φV ₂ ). Transfer sequentially. On the other hand, the surface of the light-receiving cell below the filters G and B in the photosensitive area 14 is not provided with the transfer electrodes 18 and 19 opened. Instead, on each photosensitive area 14, a third electrode is provided along the vertical direction. A thin polysilicon electrode 20 is provided.

Further, although not shown in the figure, a fixed potential barrier is formed between the light receiving cell surrounded by the channel stopper indicated by the dotted line and the transfer cell forming the photosensitive transfer area 15. The signal charges are provided so as not to be transferred to the light receiving cells.

That is, in the light receiving cell and the transfer cell in which the potential well moves up and down with the potential barrier as a boundary,
The light-receiving cell is provided with a voltage φp by the third thin polysilicon electrode 20 at the time of charge storage and is provided deeper than the barrier to store signal charges, and is provided at a level lower than the barrier at the time of charge transfer. Is field-shifted to the transfer cell.

On the other hand, the transfer cell is provided so that the potential level does not become lower than the barrier even during charge transfer, where the potential well is shallower than during storage.

Further, in the solid-state imaging device, a long wavelength light (color R) filter is arranged on the photosensitive transfer region, and the signal charge formed by the long wavelength light filter is arranged on the photosensitive region. The signal charges formed by the filters for the medium wavelength light (color G) and the short wavelength light (color B) are read first.

This is because the long-wavelength optical signal charges largely leak light and diffuse carriers generated in the deep portion of the substrate, and have a great influence on other light receiving cells.

FIGS. 3 to 5 show driving timings when the solid-state image pickup device is applied to an electronic still camera, and the driving method of the device according to the present invention will be described.

As is apparent from FIG. 3, the driving sequence of the device when applied to the electronic still camera is composed of a standby mode, a sweep mode, an exposure / accumulation mode and a read mode.

The standby mode represents a state in which the power of the camera is not turned on, and accordingly, the solid-state image sensor is not driven and the photographing is not performed.

One of the features of the present invention is that the photographing operation is started only when the photographer operates the shutter means in this state to start driving the element.

That is, when the shutter button is operated, the element is driven with a slight delay with the trigger signal generated by this operation, and the sweep mode is executed.

In the sweep mode, the dark charges generated in the photosensitive transfer area 15 and the photosensitive area are collectively transferred and simultaneously transferred from the vertical charge transfer section 15 to the horizontal charge transfer section 11. Therefore, the signal charges of the colors G and B under the photosensitive area 14 are the same as those in the third area shown in FIG.
The electrode 20 is provided at the “L” level, and the transfer electrodes 18 and 19 of the corresponding light receiving cells are provided at the “H” level according to the respective timings, so that the field shift is simultaneously performed, and the force generated in the photosensitive transfer area 15 is generated. It is vertically transferred together with the signal charge of R, further horizontally transferred, and swept out.

When all the dark charges in the light receiving unit 10 have been swept out, the shutter of the camera is opened in synchronization with this point and the camera shifts to the exposure / accumulation mode.

The exposure / accumulation mode is performed by opening the shutter only for a predetermined period that is arbitrarily set, and during this time, one of the transfer electrodes 18 and 19 (electrode 18 in this embodiment) shown in FIG. , The third electrode 20 is provided at the "H" level to which a voltage is applied, and charges are accumulated. And during this time
Clock signal φp for charge transfer, both .phi.V ₁ and .phi.V ₂ is stopped and maintaining the respective states of each of the electrodes, does not perform the field shift and vertical electrical transmission charges.

The other electrode (the electrode 19 in this embodiment) provided at the “L” level at the time of this charge accumulation acts as a potential barrier between the transfer cells in the vertical direction.

When exposure is performed for a predetermined period and the shutter is closed, the mode shifts to the read mode and the signal charges generated under the filter corresponding to each color are read in a frame sequential manner.

FIG. 4 shows the read timing in the read mode.

First, the signal charge of the color R accumulated under the transfer electrode 18 (φV ₁ ) in the photosensitive transfer area 15 is read. At that time, as shown in FIG. 5, the electrode 20 (φp) is maintained at the “H” level, and the G and B signal charges generated under the photosensitive region are directly stored. The signal charge of color R accumulated in the transfer cell under the transfer voltage 18 is transferred row by row by driving the transfer electrodes 18 and 19 alternately (φV _{1 to} φV ₂ ), and is sent to the horizontal CCD. To be

The horizontal CCD is two-phase driven (φH _{1 to} φH ₂ ) to transfer charges at high speed in the horizontal direction, and supplies the charges to the output amplifier 12. Output amplifier
12 sequentially reads out the signal charges for one row in accordance with the read timing (φs). Then, the signal charges of the color R generated in each transfer cell of the photosensitive transfer area 15 are all read out in 1/60 seconds by repeating the above operation and recorded in a storage means such as a frame memory.

Next, the signal charges of the light receiving cells corresponding to the color G of the photosensitive area 14 are read out. That is, as shown in FIG.
When 20 (φp) is provided at the “L” level and the transmission electrode 18 (φV ₁ ) corresponding to this light receiving cell is provided at the “H” level, the signal charge of the color G is transferred from the photosensitive area 14 to the photosensitive transfer area. Field-shifted to 15. The field-shifted color G signal charge is transferred to the transfer electrode 1 as in the case of the R signal.
Vertically transferred by 8,19 and output amplifier 1 via horizontal CCD
2 is supplied and read. Then, in 1/60 seconds, the signal charges of all colors G for one screen are read and similarly recorded in the storage means.

When the reading of the signal charge of the color G is completed, the signal charge of the light receiving cell corresponding to the color B of the photosensitive area is finally read. That is, in FIG. 5, the electrode 20 (φp) is "L".
The signal charge of color B is field-shifted by providing the transfer electrode 19 (φV ₂ ) on the light receiving cell corresponding to the filter of color B at the “H” level while being provided at the level. The field-shifted signal charge of the color B is vertically transferred by the transfer electrodes 18 and 19 like the signal charges of the previous colors R and G, and further, an image for one screen is displayed in 1/60 seconds via the horizontal CCD. Are all read as.

As described above, the signal charges of the colors R, G and B, which are read out in the field sequential manner and are recorded in the storage means, constitute one screen when the signal charges for three fields are taken out from the storage means. Is output as a composite.

Incidentally, FIG. 5 already referred to shows the operation of the electrode φp and the operation timings of the vertical and horizontal transfer electrodes in each mode of FIG.

Incidentally, in the above embodiment, the photocapacitor type CCD
However, the present invention can also be applied to a CCD having a light receiving cell using a PN junction.

(Effects of the Invention) As described above, according to the method for driving a solid-state image sensor of the present invention, when the subject image is captured by being applied to an electronic still camera, it is not driven during non-shooting before operating the shutter button. Since it is provided in the state, power consumption can be reduced.

Further, by applying the present invention to a solid-state image pickup device capable of obtaining a frame-sequential output, and using this device in an electronic still camera, both improvement in resolution and sensitivity can be obtained.

In addition, by using such a solid-state image sensor with frame sequential output, the sweeping of the dark charges of R, G, and B in the entire light receiving area can be completed in one field period (1/60 seconds) using the shutter operation as a trigger signal. it can.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a configuration of a solid-state image pickup device according to one embodiment of the present invention, FIG. 2 is a main part surface view showing the structure of the light receiving part of FIG. 1 from the surface, and FIGS. FIG. 6 is a timing diagram for explaining the driving method of the present invention, and FIG. 6 is a diagram for explaining the signal reading sequence of the device. 10: Light receiving part, 11: Horizontal charge transfer part 12: Output amplifier, 14: Photosensitive area 15: Photosensitive transfer area 18, 19: Transfer electrode, 20: Third electrode R: Red filter, G: Green filter B: Blue filter

Claims (1)

(57) [Claims] 1. A photosensitive area comprising at least a plurality of light receiving elements, a vertical charge transfer section attached to each vertical column of the light receiving elements, and a horizontal charge transfer section, wherein the vertical charge transfer section is provided. Not only can the charge formed by the light receiving element be transferred, but also photoelectric conversion can be performed by itself, and a signal of one of the three primary colors or complementary colors can be formed in the vertical charge transfer section, and the remaining light can be formed in the light receiving element. Drive of the solid-state image sensor in which the color filters that form signals of the two colors are arranged, and the photosensitive region and the vertical charge transfer unit are exposed by the shutter operation for a predetermined period to output the signal charges of the respective colors in a frame-sequential manner. In the method, the element is driven only when the standby mode before the shutter operation is performed and the trigger signal generated by the shutter operation is started. And a sweep mode in which all the charges formed in the vertical charge transfer section are swept simultaneously, and an exposure in which the shutter is opened and the charge transfer clock signal is stopped in synchronization with the completion of the sweep of the charges / Accumulation mode and after closing the shutter, first read out the signal charge of the vertical charge transfer unit to the outside via the horizontal charge transfer unit,
Thereafter, a read mode is sequentially executed in which signals for one screen corresponding to one color of the light receiving element and signals for one screen corresponding to another color are sequentially read out in a frame-sequential manner. Driving method of solid-state imaging device.