JPH0513428B2 - - Google Patents

Description

[Detailed description of the invention] (Technical field) The present invention relates to an imaging device.

(Prior Art) When using a solid-state image sensor, such as a CCD (charge coupled device), for example, in a television camera,
By changing the driving method of the solid-state image sensor,
It has been proposed in the past that the storage time of an image sensor can be made shorter than the field (or frame) time of a television signal.

For example, in a solid-state image sensor called a frame transfer type, the charge in the light receiving part that performs photoelectric conversion and charge accumulation is forcibly removed by vertical transfer once in the middle of the vertical period, and then the charge is removed for the remaining period of the vertical period. For example, Japanese Patent Application No. 55-61098 proposes a driving method in which the storage time is set as a substantial storage time.

According to the above method, for example, in an NTSC TV camera, the storage time is usually 1/60 second, but this can be changed to 1/120 second, 1/500 second, etc. There is no need to make a small aperture even when a large amount of light is incident. Therefore, a blurring effect can be obtained.
In addition, effects such as an image of a high-speed moving object being prevented from blurring are produced. However, when performing the above operation, the actual accumulation time is shortened, especially when the charge accumulated in the middle of the vertical period is eliminated inside the image sensor without being extracted as a signal as described above. In this case, the amount of charge to be removed becomes extremely large. For example, if the effective accumulation time t ₁ is 1/500 seconds, the difference between the accumulation time t ₂ of the charge to be removed and t ₁ is t ₂ /t ₁ = (1/60-1/500)/ 1/500≒7.3 This is about 7.3 times, and if the charge accumulated at t ₁ is at the standard level, at t ₂ it will be at the standard level.
7.3 times more charge is accumulated. When such a large amount of charge is accumulated, it is extremely difficult to eliminate it all within the image sensor so that it does not affect the substantial accumulation time. In particular, the amount of charge generated in so-called highlight areas on the screen is extremely large, and when vertical transfer is performed to discharge charge in the middle of the vertical period, a large amount of charge remains and is output to the screen. There will be a negative impact on.

(Objective) It is an object of the present invention to eliminate the drawbacks of the above-mentioned conventional example, and at the same time to propose an imaging device in which no adverse effect appears on the screen even if the actual storage time is set short.

(Example) Examples of the present invention will be described below with reference to the drawings.

An embodiment of the present invention will be described using a frame transfer type CCD as an example of imaging means.

To explain with reference to FIG. 1, the figure shows an example of a frame transfer type CCD. In the figure, 1 indicates a frame transfer type CCD, and 2 indicates an electrical signal in response to incident light , an imaging unit that generates and stores charges; 3 a storage unit that takes in the charges generated and accumulated in the imaging unit 2 and temporarily stores them; 4 a storage unit 3; 5 is an output amplifier section provided on the output side of the horizontal register section 4 for converting the charges into a voltage.

As is well known, the imaging unit 2 has a two-dimensional array of imaging cells arranged in a predetermined number of rows, and
The storage unit 3 has an equal number of two-dimensional arrays of storage cells along the same rows and columns, and
The horizontal register section 4 has a one-dimensional array along the rows of charge transfer cells, the number of which is at least equal to the number of memory cell arrays in the memory section 3, except for a predetermined area of the imaging section 2. It is shaded.

When such a frame transfer type CCD 1 is driven at the television cycle, charges generated and accumulated in the imaging section 2 are vertically transferred from the imaging section 2 to the storage section 3 during the vertical blanking period of the television. Further, the charges stored in the storage section 3 are step-transferred to the horizontal register section 4 one line at a time during the horizontal blanking period.

Further, the charges in the horizontal register section 4 are horizontally transferred to the output amplifier section 5 within the period of one horizontal line.

A single-phase drive anti-blooming gate type CCD will be described below.

FIG. 2 is a diagram showing the configuration of main electrodes near the boundary between the imaging section 2 and the storage section 3.

10CS is a channel stop that separates horizontal pixels, φI is a drive electrode for the light receiving section, φABG is an anti-blooming gate electrode, φS is a storage section drive electrode,
CB is the drive barrier area, CW is the drive well area,
VB is a virtual barrier area, and VW is a virtual well area.

FIG. 3 is a cross-sectional view taken along line A-A' in FIG.
A virtual phase potential is formed at VB and VW by the injection of P ions, and from the viewpoint of electrons, CB > CW, VB
＞VW n so as to form a potential distribution
Ions are implanted. 21 indicates the transfer direction of this CCD. FIG. 4 is a potential distribution diagram of this CCD, in which VB and VW are fixed to virtual phases, and the potentials of the CB, CW, and ABG sections change as shown in FIG. 4 depending on the driving voltage. FIG. 5 shows the drive voltage waveform of this CCD, where IV indicates the vertical period.

A transfer pulse is added to φI at the beginning of the vertical period, and it takes an intermediate value IM during other charge accumulation periods. At this time, the potentials of CW and VW are almost the same, so charges are accumulated in both CW and VW. or,
The charges accumulated in CW and VW during transfer are automatically added, and by shifting the added charges for each field in this embodiment, the position of the center of gravity of sensitivity is shifted to perform an interlace operation.

A transfer pulse is applied to the electrode φS at the same time as the transfer pulse of φI, and the charge is transferred from the light receiving part to the storage part. After that, a shift pulse of 1 pulse per horizontal period 1H is used to transfer the charge from the storage part to the horizontal register. .

During vertical transfer, φABG is fixed at a predetermined intermediate potential ABM between the virtual potentials of regions VB and VW to prevent vertical transfer from being interrupted, and at the same time, continuous pulses of about 500 KHz to 2 MHz are applied during other periods.
Unnecessary charges above a predetermined level are removed by charge recombination.

A method for removing unnecessary charges by charge recombination is disclosed in Tokuhan Sho.
58-75838, etc., by driving φABG, a part of the accumulated charge is pushed up to the potential of the recombination center, and by recombining with holes, unnecessary charges are periodically removed. It is something.

FIG. 6 shows a driving voltage waveform for a so-called electronic shutter operation in which vertical charge transfer is performed during storage to substantially reduce the storage time.

In φI, compared with FIG. 5, a vertical transfer pulse is added in the middle of the vertical period. Therefore, the charges accumulated during the _T1 period are removed by this vertical transfer pulse, resulting in a substantial accumulation time.

In addition, φI is at the V level of TL in the figure in the T ₁ period, and T ₂
The period will be at the level of IM. The potential distribution during light reception is made different between T ₁ and T ₂ .

Figure 7a shows when φI is at the IM level, and Figure 7b shows when φI is at the IM level.
In figure a, which shows the potential distribution of the light receiving part at the IL level, the maximum amount of charge is the sum of the electricity Q ₁ accumulated in CW and the charge Q ₂ accumulated in VW after excess charge is removed. In Figure b, only _Q3 is accumulated after excess charge is removed. Therefore, the amount of charge to be removed later is reduced, so that overflow of charges that occurs during vertical transfer can be reduced.

FIG. 8 is a diagram showing an embodiment of the configuration of an imaging device according to the present invention. 101 is a reference oscillator, 102 is a frequency divider, 103 and 104 are first and second drive pulse generation circuits, 105 is a drive circuit, 106 is a power source that generates various drive voltages, 1 is a CCD that is an image sensor, 108 is a time setting circuit, 109 is a setting switch, 110 is a control signal generation circuit, 111 is a smoothing circuit that smoothes the output of the sensor 1, and 112 is an exposure control member that controls the exposure force of the sensor.

The oscillation output of the reference oscillator 101 is frequency-divided into necessary signals by a frequency divider 102, pulses necessary for driving the CCD are generated by drive pulse generation circuits 103 and 104, and the level is set by 105 to the voltage supplied from a power supply 106. shifted and power amplified,
Drives CCD1. On the other hand, the vertical retrace pulse VD is input to the time setting circuit 108, and a vertical transfer trigger pulse PT is generated. Furthermore, φ1 due to PT and VD
A control signal C _I is generated to control the level during accumulation, and PT and C _I are connected to the drive pulse generation circuit 10.
4 to control φI.

Further, the output of the sensor 1 is smoothed, and the exposure control member servo-controls the amount of incident light in accordance with this smoothed output. Note that 101 to 106 and 108 to 110 constitute control means.

FIG. 9 is a timing chart of the image pickup device shown in FIG.

T is one vertical period. When setting the accumulation time to _T1 , the time setting circuit 108 sets _T2 =(T- _T2 ). C _I becomes "H" during the T ₁ period and "L" during the T ₂ period, and correspondingly, _φI becomes the I _L level during the T ₁ period and the I _M level during the T ₂ period.

In the above embodiments, a single-phase drive type frame transfer type CCD having an excess charge discharge structure by recombination has been described, but the present invention can also be applied to other types when the potential distribution changes depending on the driving conditions. It can be implemented.

Furthermore, in this embodiment, anti-blooming gate electrodes are provided in the virtual regions VB and VW by charge recombination, so during the period _T1 , the potential levels seen from the electrons in the drive regions CB and CW are set to VB and VW. However, if the anti-blooming gate electrode ABG is provided on the drive region side, the potential level seen from electrons in the drive regions CB and VW regions is lowered relative to VB and VW.

Further, according to the embodiment of the present invention, the charge accumulation state during the T ₁ period is changed from the charge accumulation state during the T ₂ period, and the charge accumulation state during the T _{1 period} is changed.
Since the amount of charge saturation during the period is smaller than the amount of saturated charge accumulated during the _T2 period, blooming is less likely to occur, and blooming can be prevented without substantially changing the power consumption of the image sensor.

(Effects) As described above, according to the present invention, a good image can be obtained even when the storage time of the solid-state image sensor is made shorter than the vertical period.

In addition, blooming can be effectively prevented without significantly increasing power consumption.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a frame transfer type CCD according to the present invention, FIG. 2 is a diagram showing an example of the main electrode configuration of the configuration shown in FIG. 1, FIG. 3 is a schematic cross-sectional view of the configuration shown in FIG. FIG. 5 is a timing chart in a movie imaging mode having an accumulation time of one field; FIG. 6 is a timing chart in an imaging mode having an accumulation time of one field or less;
7a and 7b are diagrams showing potential distribution examples in the T ₂ period and T ₁ period of FIG. 6, respectively, FIG. 8 is a diagram showing a configuration example of the imaging device of the present invention, and FIG. This is a timing chart of the configuration. 1... Frame transfer type CCD, 2... Light receiving section,
108...Time setting circuit, 110...Control signal generation circuit.

Claims (1)

[Claims] 1. An imaging means having a plurality of pixels and a charge recombination electrode for recombining charges in each pixel, and reading accumulated charges from a light receiving section of the imaging means at a predetermined period. At the same time, the charge is substantially accumulated in the second period after eliminating the charge accumulated in the first period within the predetermined period, and each pixel in the first period is By making the number of charge storage potential wells in the pixel smaller than the number of charge storage potential wells in each pixel in the second period, the amount of charge that can be recombined by the charge recombination electrode during the first period is reduced. An imaging device comprising: a control means for increasing the amount during the second period.