JPH0795827B2 - Camera drive - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a camera drive device using a solid-state image sensor.

(Background of the Invention) Conventionally, a video camera having a high shutter speed has advantages such as an improved dynamic resolution during normal operation, and a clear and blur-free image obtained in slow motion reproduction or still reproduction. However, the device that realizes this has a drawback that the whole device becomes large and heavy because it is necessary to provide a mechanical rotary shutter on the front surface of the image pickup device, and the handling becomes inconvenient.

(Object of the Invention) An object of the present invention is to solve these drawbacks and to provide a camera driving device having a high-speed shutter function using a solid-state imaging device.

(Summary of the Invention) In order to achieve this object, the present invention sets an effective exposure period in a vertical blanking period of a camera or a period including the vertical blanking, and further, in the period, vertical transfer of a solid-state image sensor is performed. The technical point is that the sharpness of the image is improved by performing high-speed charge transfer of the image portion and discharging the unnecessary charge of the light receiving portion.

(Embodiment) An embodiment in which an interline transfer CCD (IT-CCD) having a MOS diode structure is used for the light receiving portion will be described below.

FIG. 1 is a schematic explanatory view of an IT-CCD applied to this embodiment. In FIG. 1, reference numeral 1 is a light receiving portion, and this light receiving portion 1
Has a structure for storing signal charges photoelectrically converted using a MOS diode instead of a pn junction photodiode. A vertical transfer unit 2 transfers the signal charges of the light receiving unit 1 to the horizontal transfer unit 3. The horizontal transfer unit 3 transfers the signal charges of one horizontal line transferred from the vertical transfer unit 2 to the floating diffusion amplifier 4. The floating diffusion amplifier 4 converts the signal charge sent from the horizontal transfer unit 3 into a signal voltage and outputs it.

On the other hand, 5 are OFD and OFCG, which serve to discharge excess charges when signal charges larger than the charges that can be transferred by the vertical transfer unit 2 are generated in the light receiving unit 1.

FIG. 2 shows a II-II sectional structure including the light receiving portion 1 and the vertical transfer portion 2 shown in FIG. 1 and its potential structure.

First, in the sectional structure of FIG. 2A, the aluminum 7 shields the vertical transfer portion 2 from light, and a transparent polysilicon electrode forming a sensor gate (hereinafter referred to as “SG”) under the aluminum 7. 8a is provided. Further, the polysilicon electrode 8b surrounded by the silicon oxide (SiO ₂ ) 9 becomes the electrode of the vertical transfer portion 2.

In such a cross-sectional structure, the polysilicon gate 8b of the vertical transfer part 2 also serves as a transfer gate, and the electrode voltage of the polysilicon electrode 8b is operated at three levels, and the transfer gate functions at the highest voltage. To fulfill. OFCG5a is a polysilicon electrode 8a.
It is common with the SG formed in, and therefore OFCG5a cannot be controlled independently.

Further, looking at the structure of the light receiving portion 1, SG composed of the polysilicon electrode 8a, silicon oxide (SiO ₂ ) 9 and P-type silicon substrate 10
In this case, a MOS structure photodiode is formed instead of the pn junction photodiode.
A transparent protective film 11 is formed on the surface.

Here, the charge distribution due to the gate voltage in the MOS structure of the P-type silicon substrate 10 which becomes the light receiving portion 1 is shown in FIG.

FIG. 3A shows a potential state and a charge distribution state when a voltage of + Vg is applied to the SG electrode, and electrons are stored at the interface between the P-type silicon 10 and the silicon oxide (SiO ₂ ) 9.
However, the potential of the P-type silicon substrate 10 is 0V.

The signal charge accumulation state shown in FIG. 3A is called an inversion type.

On the other hand, the polysilicon electrode that constitutes the sensor gate
The potential state and charge distribution state when a voltage of -Vg is applied to 8a are shown in Fig. 3 (b).

Electrons are driven from the interface between the P-type silicon substrate 10 and silicon oxide (SiO ₂ ) 9 to the inside of the P-type silicon substrate 10 (on the right side of the paper), and instead, holes are stored in the interface portion. This state is called storage type. In this way, by applying the sensor gate voltage −Vg to the storage type, all the electrons of the signal charge can be discharged to the substrate side (right side of the paper) without discharging to the OFD, and the signal is received at the light receiving part. A state where there is no charge can be realized by controlling the sensor gate voltage to -Vg.

By the way, in the actual CCD driving, as is apparent from the sectional structure of FIG. 2A, the SG potential given by the polysilicon electrode 8a of the light receiving portion 1 is the potential of the surrounding vertical transfer portion 2 and the like. SG because it is closely related to the state
It is necessary to control not only the voltage but also the vertical transfer gate voltage provided by the polysilicon electrode 8a.

The potential state of each portion by the control of the vertical transfer gate voltage corresponding to the control of the SG voltage will be described with reference to the potential state diagrams of FIGS. 2B to 2D.

First, during normal video operation, since the electrode voltage + Vg is constantly applied to the SG of the light receiving unit 1, the potential of TG6 is higher than the potentials of the light receiving unit 1 and OFCG5a, as shown in FIG. 2 (b). is there.

However, if only the SG voltage of the light receiving part 1 is changed to -Vg, the second
As shown in FIG. 6C, only the potential of the light receiving portion 1 changes to the state shown by the broken line, and the potential of TG6 becomes lower than the potentials of the light receiving portion 1 and OFCG5a, and the light receiving portion 1
The charge leaks from the vertical transfer unit 2 to the vertical transfer unit 2. Therefore, the potential of TG6 needs to be higher than the potential of the light receiving portion 1, and the voltage applied to the vertical transfer portion 2 also needs to be lower than the SG voltage to raise the potential. Thus, the potential state when a negative voltage is applied to the vertical transfer unit 2 is shown by a broken line in FIG. If the potential state shown by this broken line is obtained,
Since the potential of the light receiving portion 1 is always lower than the potential of the surroundings and the potential inside the substrate is lower than that, the signal charge of the light receiving portion 1 must be surely discharged into the substrate of the light receiving portion 1. Is possible.

However, FIGS. 2B to 2D show only the potential state in the interface region, and the potential state inside the substrate is not considered. Actually, in the case shown in FIG. 2D, a part of the charge discharged into the substrate wraps around to the vertical transfer portion side, but in the present invention, this charge is transferred at high speed and discharged to the outside of the sensor. ing.

A method of driving the video camera using the IT-CCD described above will be described with reference to FIG.

The figure shows a video operation with a shutter speed of 1/2000 seconds, FLD is a frame signal, and the H state indicates an odd field and the L state indicates an even field.

BLK is a blanking signal, HD is a horizontal sync signal, SG
Indicates a sensor gate signal voltage, and V1, V2, V3, and V4 indicate vertical transfer electrodes, respectively.

The vertical blanking period starts from the time point T1 and ends at the time point T7, and within this period, the video signal projected on the television does not appear.

At time T2, the sensor gate voltage SG of the light receiving portion is set to a negative voltage, and as shown in FIG. 3 (b), the signal charges accumulated in the period of about 1 field are discharged into the substrate (right side of the drawing), Remove charge from the light receiving part.

Here, as described above, since some of the charges sneak into the vertical transfer unit side, high-speed charge transfer is performed from time T2 in order to eliminate this charge, and the charges sneak into the vertical transfer unit side are transferred to the outside of the sensor. Exhale to. Although the charge discharged here is unnecessary, there is no problem because it is within the vertical blanking period.

The sensor gate voltage SG is made to be a positive voltage again at the time point T3, and the accumulation of optical signal charges is newly started. The high-speed charge transfer of the vertical transfer unit performed from the time T2 is performed until time T4, and within this period, at least 263 stages of vertical transfer corresponding to one scan of the field signal are performed. The unnecessary electric charges of are completely abolished.

Next, in the period from time T5 to T6, the voltage of the vertical transfer electrode
V1 is set to the highest possible voltage in three levels, and the signal charges accumulated in the light receiving section are transferred to the vertical transfer section. That is,
This period T3 to T6 is the exposure period, and the signal charge obtained during this period becomes a signal equivalent to a high-speed shutter (1/2000 second).

Next, from time T6 to time T8, which is the same as the normal video operation, the image displayed by the high-speed shutter is displayed on the television.

In the even field, the CCD is the same as in the odd field.
Since it drives, it is possible to obtain an image taken with a high-speed shutter. Further, in this embodiment, the case where the shutter speed is set to about 1/2000 seconds has been described, but at a shutter speed higher than this, it can be realized by performing the same timing control as in this embodiment at time points T3 and T10.

Next, a driving method of the video camera in which the shutter speed is 1/1000 second will be described with reference to FIG.

The vertical blanking period is about 1.3 mS, and about 1 mS of this is required to be allocated to the exposure period, so the driving method is slightly different from the case of the shutter speed of 1/2000 seconds.

In FIG. 5, at time T2, the sensor voltage SG of the light receiving portion is set to a negative voltage, and as shown in FIG. 3 (b), the signal charge accumulated in the period of about 1 field is discharged into the substrate and the light receiving portion is discharged. The electric charge is removed from the sensor, and at this time, high-speed charge transfer is performed from the simultaneous point T2 in order to eliminate the electric charge that has spilled to the vertical transfer unit side, and the charge is discharged to the outside of the sensor.

At time T3, the sensor gate voltage SG is set to a positive voltage again, and the accumulation of photo signal charges is newly started.

The high-speed charge transfer of the vertical transfer section performed from time T2
By performing the transfer up to T4, the unnecessary charges in the vertical transfer section are completely eliminated by the transfer within this period.

The exposure time is the time after the unnecessary charges are discharged from the light receiving unit.
In the period from T3 to T6, the signal charge accumulated in the light receiving unit during this period T3 to T6 is transferred to the vertical transfer unit in the period from time T5 to T6.

Here, in normal video operation, if expressed at the timing shown at HD, the signal charge of the light receiving part is transferred to the transfer part at the time of 8.5H, but a video camera with a shutter speed of 1/1000 seconds In the case of driving, it is transferred at the time of 16.5H, so if it is left as it is, it will be displayed 8 hours downward on the television screen.

In order to solve this problem, the vertical transfer section is shifted by 8 stages in the period from time T7 to time T8 to eliminate the influence on the television screen between time T8 and T9, and the shutter speed is 1/1000 seconds. The image of can be displayed. still,
Since the even field is driven in the same way as the odd field, images can be displayed without any problem.

Next, a method of driving the video camera when the shutter speed is 1/500 seconds will be described with reference to FIG.

In this case, the shutter speed is 1/1000 second, except that the positions of time points T1, T2, and T3 are brought before the vertical blanking period than when the shutter speed is 1/1000 second. The same drive as in the case is performed.

This reduces the effective video signal period and reduces the effective screen of the television by about 5%. However, since it is overscanned by a normal monitor, it can be put to practical use.

In the embodiment, an interline transfer CCD having a MOS diode structure in the light receiving portion is used as the image pickup means, but the invention is not limited to this, and various solid-state image pickup elements can be used.

(Effects of the Invention) As described above, according to the present invention, a high-speed shutter video operation can be realized only by driving a solid-state image sensor without using an external shutter device or the like, so that the optical system can be simplified. It is possible to reduce the size and weight of the apparatus, and since the shutter is electrically driven, it is possible to realize a highly accurate shutter time.

Further, normally, when the shutter time is 1/30 seconds, it is too bright and causes image deterioration due to diffraction development of the diaphragm. However, the video operation of the high-speed shutter according to the present invention makes the diaphragm brighter by 4 to 5 steps. Therefore, it is extremely effective in eliminating such image deterioration.

Further, in this driving, since the entire image pickup surface is exposed at the same timing, the shutter efficiency becomes 100%, and an excellent high-speed shutter without image distortion can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view of an IT-CCD to which the present invention is applied, FIG. 2 is a sectional view taken along the line II-II of FIG. 1 and a potential state, and FIG. 3 is FIG. Fig. 4 is a charge distribution diagram showing the operating principle of signal charge accumulation and discharge in the light receiving part of Fig. 4, Fig. 4 is a timing chart of the video operation when the shutter speed is 1/2000 seconds, and Fig. 5 is the shutter speed of 1/2000. FIG. 6 is a timing chart of the video operation when the shutter speed is 1000 seconds, and FIG. 6 is a timing chart of the video operation when the shutter speed is 1/500 seconds. 1: Light receiving part 2: Vertical transfer part 3: Horizontal transfer part 4: Floating diffusion amplifier 5: OFCG and OFD 5a: Overflow control gate (OFCG) 5b: Overflow drain (OCG) 6: Transfer gate (TG) 7: Aluminum 8a: Sensor gate 8b: Vertical transfer gate 9: Silicon oxide 10: P-type silicon substrate

Claims (1)

[Claims] 1. A camera including a solid-state imaging device having a light-receiving MOS diode structure for accumulating optical signal charges, wherein a sensor for setting an effective exposure time within a period including vertical blanking and controlling the state of the light-receiving unit. A camera driving device, comprising: a control unit for discharging unnecessary charges in a light receiving unit before exposure is started by controlling a gate voltage to a storage type and performing high-speed charge transfer in a vertical transfer unit of a solid-state image sensor.