JPH0440762A - Electronic still camera - Google Patents

Abstract

PURPOSE:To prevent a tail leaving phenomenon due4 to a smear by eliminating an undesired charge out of a charge store part and a charge transfer part before the exposure applied to a photoelectric transducer and discontinuing the transfer of charge until the shielding of light is over to an image pickup element including the photoelectric transducer after the high speed transfer of charge. CONSTITUTION:A system control circuit 17 revolves an aperture blade 2 via a stepping motor drive circuit 5. Then the drive of the blade 2 is stopped, a CCD 3 stops the discharge of the charge to a base board part and the storage of the signal charge is started in response to a subject image obtained by the photoelectric conversion. Then the circuit 17 revolves the blade 2 via the circuit 5 in order to shield the light to the CCD 3. When the light is shielded to the CCD 3 by the blade 2, a CCD drive circuit 6 actuates a vertical transfer register 6 and transfers the signal charge successively and vertically to output them via a horizontal transfer register. The read signals are processed by a signal processing circuit 7 and a recording circuit 8 and then recorded to a video floppy 9 via a magnetic head 10.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an electronic still camera that uses an image sensor to capture and record instantaneous images of a subject using an electronic shutter.

2. Description of the Related Art Electronic still cameras have been put into practical use that capture and record instantaneous images of objects by combining an imaging device such as a CCD and a recording device that records on a floppy disk. Unlike conventional film cameras, electronic still cameras of this type have the advantage of not requiring any processing such as developing or printing, and that the images taken can be instantly checked on a monitor, such as a television. There is.

By the way, this type of electronic still camera, like an optical film camera, requires so-called exposure control, which controls the amount of exposure on the image plane during shooting, and uses the aperture and shutter to control the amount of exposure to the image sensor. There is. As methods for controlling the opening/closing time (shutter speed) of the shutter, two methods are widely used: (1) a method using a mechanical shutter, and (2) a method using an electronic shutter.

This method using a mechanical shutter is a method such as a well-known lens shutter or a four-force shutter, in which a shutter curtain is mechanically opened for a predetermined period of time to perform exposure.

On the other hand, in the method using an electronic shutter, the charges accumulated in the light receiving part (photodiode, etc.) of the image sensor immediately before exposure are swept out, and after a predetermined period of time (equivalent to the shutter speed) has elapsed, the accumulated charges are transferred. I'm trying to read it out. Since this electronic shutter does not use mechanical elements, it has the advantage that it can be made smaller in size than the above-mentioned mechanical shutter, and the accuracy of the shutter speed can be significantly increased.

Problems to be Solved by the Invention However, in the method using the mechanical shutter described above, in the case of a lens shutter, the shutter blades suddenly try to close in the middle of the opening operation of the shutter blades, so the influence of inertia and friction of the shutter blades However, since it is not possible to improve the accuracy of the shutter speed, and the change over time is large, the ±0.3 (EV) required for electronic still cameras is required when controlling exposure.
It was difficult to ensure exposure accuracy within In the case of a focal frame shutter, the accuracy of the shutter speed is better than that of a lens shutter, but since there are mechanical elements, it is difficult to achieve the above calculation accuracy at high speeds, and there is also the problem of changes over time. However, when considered as an exposure mechanism, since there is also an aperture mechanism, there is also the problem that the size becomes large and the cost also increases.

Next is the method using a conventional electronic shutter, but since there are no mechanical elements in the shutter mechanism, the shutter accuracy is sufficiently high compared to a mechanical shutter, and it is possible to achieve the above exposure accuracy, but it is possible to achieve the above exposure accuracy. There are problems.

Conventionally, electronic shutters using interline transfer type image sensors sweep out the charge accumulated in the light receiving part (photodiode, etc.) of the image sensor just before exposure.
Immediately after this sweep operation, the accumulated charge is transferred to the vertical transfer register and read out immediately after a predetermined period of time (corresponding to the shutter time, and the end point of the shirt time is approximately aligned with the vertical synchronization signal) has elapsed. . In such a configuration, if light continues to be irradiated onto the image sensor during charge transfer in the vertical transfer register, the vertical transfer register will not be completely shielded from light (it is extremely difficult with current technology to completely shield the vertical transfer register). smear charges occur, especially when there are high-brightness areas on the subject (for example, sunlight filtering through trees, reflections of sunlight, spotlights, etc.). There was a problem in that a white tail appeared due to the addition of smear charge to the signal charge and transfer toward the bottom of the screen. One possible solution to this problem is to block the light to the image sensor immediately after transferring the vertical transfer register signal charge, but generally it takes some time to completely block the light, and the above-mentioned operation is required for that time. appears, so it is not a perfect solution.

The present invention takes the above-mentioned problems into consideration, eliminates the mechanical shutter mechanism, performs high-precision exposure control using an electronic shutter mechanism of a solid-state image sensor, and provides an electronic still image without the trailing phenomenon caused by the smear that occurs during charge transfer. The purpose is to provide cameras.

Means for Solving the Problems In order to achieve the second object, the present invention removes unnecessary charges from the stain accumulation area by a charge discharge means before exposing the photoelectric conversion element, and removes unnecessary charges from the charge transfer part by a high-speed transfer means. This is an electronic still camera in which, after the high-speed transfer by the high-speed transfer means, the charge transfer section stops transferring charges until the light-shielding means completes light-shielding of the image sensor including the photoelectric conversion element.

As a configuration, exposure to an image sensor including a photoelectric conversion element,
A means for blocking incident light during periods other than the exposure time, a charge storage section that stores charges generated by photoelectric conversion due to exposure to the photoelectric conversion element, a charge transfer section that transfers the charges accumulated in the charge storage section, and a charge transfer section that transfers the charges accumulated in the charge storage section. A transfer means for controlling the transfer of the charges accumulated in the charge accumulation section to the charge transfer section, and a transfer means for discharging unnecessary charges accumulated in the charge accumulation section to the substrate section before exposure to the photoelectric conversion element, and for transferring the unnecessary charges accumulated in the charge accumulation section to the photoelectric conversion element. A charge discharging means that stops this discharging operation during the exposure time to the conversion element, a high-speed transfer means that transfers unnecessary charges accumulated in the charge transfer section at high speed using a transfer clock with a frequency higher than the normal frequency, and this high-speed transfer means After high-speed transfer by the transfer means, a charge transfer stop means is provided to stop the charge transfer by the charge transfer unit, and the charge transfer stop means is provided to stop the charge transfer by the charge transfer unit during the period until the light shielding means securely blocks the image sensor from light. , unnecessary charges are removed from the charge storage section by the charge discharge means, unnecessary charges are removed from the charge transfer section by the high-speed transfer means during exposure, and charge transfer by the charge transfer section is reliably carried out by shielding the image sensor from light by the light shielding means. This is an electronic still camera that is stopped by a charge stopping means.

Operation The electronic still camera of the present invention having the above configuration sequentially discharges unnecessary charges accumulated in the charge accumulation section to the substrate section by the charge discharging means until immediately before shooting, and after setting the aperture to a predetermined aperture at the time of shooting. The discharge by the charge discharging means to the substrate section is stopped and accumulation of signal charges (predetermined exposure) is started, and the signal charges are accumulated in the charge transfer section at an arbitrary timing within the predetermined time required for the exposure (corresponding to the shutter time). The unnecessary charge is discharged by the high-speed transfer means using high-speed transfer, and the charge transfer stop means stops the tt charge transfer section from the end of the high-speed transfer until at least the light incident on the image sensor is blocked by the post-exposure light-shielding means. The charge transfer is stopped, and the signal charges accumulated in the charge storage section are transferred to the charge transfer section immediately after exposure. After the light is shielded, the transfer function is operated again at a predetermined timing to read out the signal charge.

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

FIG. 1 is a block diagram showing the configuration of an electronic still camera according to an embodiment of the present invention. As components, 1 is a photographing lens, and 2 is an aperture blade (three in this example) provided with a plurality of holes of different diameters, which will be described later! This constitutes a light shielding means. 3 is an interline transfer type COD (hereinafter simply referred to as COD) which is an image sensor; 4 is a stepping motor for rotating the aperture blades 2 to select a desired aperture; and 6 is a motor for driving the stepping motor 4. A well-known stepping motor drive circuit mainly composed of switching transistors, 6 is a C
A COD drive circuit that generates various pulses and clocks for charge transfer to drive the CD3, 7 a signal processing circuit that processes the signals obtained from the COD and obtains a luminance signal and a color difference line sequential signal, 8 a signal processing circuit The signal obtained by the circuit 7 is frequency modulated and sent to the video floppy 9 via the magnetic head 1o.
A recording circuit that amplifies the signal to a sufficient level for recording.
11 is a motor for rotationally driving the video floppy disk 9;
Reference numeral 12 denotes a motor drive control circuit comprising a well-known speed control and phase control circuit for driving and controlling the motor 11 to rotate at a constant rotation speed and a constant rotational phase, and a motor drive circuit; 13 is a motor drive control circuit provided in the center core of the video floppy e; A PG pin 14 indicates the rotation phase of the PG pin 13, and a PG sensor 15 is arranged in the center core of the video floppy e and is configured in a coil shape for detecting the rotation phase.
1 is an amplifier circuit that amplifies the signal obtained from the PG sensor 14 and shapes the waveform into a rectangular wave; 16 is a phase shifter that delays the signal output from the amplifier circuit 16 by a predetermined value; and 17 is a microcontroller that controls these systems. A system control circuit consisting of a computer and its peripheral circuits; 18 is a release SW that provides a trigger for photographing;

FIG. 2 is a timing chart showing the timing from photographing to recording in the same embodiment. (a) shows the phase shifter 16
The PG double signal (b), which is the output of
) and the VD signal (b) are adjusted by the phase shifter 16 so that the PG signal (a) precedes by approximately 4H period. (C) is a timing chart showing the operating time of the diaphragm 9 blades 2 constituting the light shielding means, where the sloping part indicates that the diaphragm 9 blades 2 are in operation, and the flat part indicates that the diaphragm 9 blades 2 are in operation, and the flat part indicates that the diaphragm 9 blades 2 are in operation, and the flat part indicates that the diaphragm 9 blades 2 are in operation. It shows that (d) is a vertical transfer 5TOP signal by the charge transfer stop means that gives a command to stop the vertical transfer clock after high-speed transfer (described later); (e) is the shutter pulse that determines the exposure time (shatter time) by the light shielding means; (f) ) is the vertical transfer clock used to transfer the signal charge of the vertical transfer register 303 that constitutes the charge transfer section shown in FIG. The clock cycle indicated by the mark is shorter than the normal transfer cycle (that is, has a higher frequency), that is, it is a part where high-speed transfer (driving) is performed by the high-speed transfer means. Further, when this clock is adjusted to the correct size, the transfer of signal charges is stopped. (q) is a photodiode 301.30 which is a photoelectric conversion element shown in FIG.
This signal is a φSUB clock signal for discharging (sweeping out) unnecessary charges accumulated in the CCD 3 by the charge discharging means of the substrate portion (substrate) of the CCD 3. When charges are accumulated, υ is stopped. (h) is photodiode 301, 302 of CCD3
A transfer gate pulse is a transfer means for transferring signal charges accumulated in the vertical transfer register 303, and (i) is a recording gate for recording an instantaneous image of the subject obtained by photographing on the video floppy disk 9.

FIG. 3 is an operational diagram for explaining the structure and operation of the aperture blade 3 constituting the light shielding means.
indicates a part of the lens barrel (not shown), and light passes through this hole to the CC
The light incident on the CCD 3 is naturally blocked by blocking this hole. 20, 21.
Reference numeral 22 denotes a fixed diaphragm in the shape of a round hole, which is provided in each of the 9 diaphragm blades 3 with a diameter that provides a predetermined aperture value. The aperture blades 2 are rotated by a stepping motor 4 in the directions of arrows A) and A).

FIG. 4 shows the configuration of an interline transfer type CCD 3 which is an image sensor used in the electronic still camera of this embodiment. Reference numerals 301 and 302 are photoelectric conversion elements for accumulating charges (lead lines). 303 is a part of the charge transfer unit; a vertical transfer register vertically transfers the signal charges accumulated in the photodiodes 301 and 302; 304 is a photodiode that performs horizontal transfer of the charge transfer unit; Horizontal transfer register, 305°30
Reference numeral 6 denotes a transfer gate (including 2 of the same shape without a leader line), which is a transfer means for controlling transfer. In addition, unnecessary charges accumulated in the photodiodes 301 and 302 are transferred to 9C by charge discharge means without going through the vertical transfer register 303.
It is structured so that it can be directly discharged to the substrate section (not shown, located on the back side of FIG. 4) of the CD3.

When the transfer gates 305 and 306 are opened by the transfer gate pulse (h), the signal charges accumulated in the photodiodes 301 and 302 are transferred to the vertical transfer register 303. The signal charges transferred to the vertical transfer register 303 are normally transferred vertically to the horizontal transfer register 304 by one horizontal gap every 1H by a vertical transfer clock synchronized with the horizontal synchronization code, −
Charges for the horizontal line are transferred to the output terminal of the CCD 3.

The signal charges accumulated in the photodiodes 3C1 and 302 in this way are sequentially read out as described above.

Incidentally, the present CCD 3 has a structure in which unnecessary charges accumulated in the vertical transfer register 303, which is a part of the charge transfer section, can be discharged at high speed using a vertical transfer clock having a higher frequency than the normal transfer frequency. This frequency is determined from the transfer efficiency of the CCD 3, and in this example is approximately 800 KHz.
It is set nearby.

The operation of the electronic still camera of this embodiment configured as described above will be described below.

When power is supplied to each circuit, each circuit receives the φSUB clock (q) under the control of the system control circuit 17, the charge discharging means composed of the COD drive circuit 6, and the high-speed transfer means.
, a vertical transfer clock (f), and a horizontal transfer clock (not shown), and output the photodiode 301 of the CCD 3,
The dark charges, which are unnecessary charges generated in the vertical transfer registers 303 . The dark charges generated in the horizontal transfer register 304 are sequentially discharged to the outside of the CCD 3 by each transfer operation (normal drive) by a high-speed transfer means. In addition, the system control circuit 17 calculates and determines the aperture value and shutter speed (shutter speed) at the time of shooting to obtain appropriate exposure according to the output of a photometric sensor (not shown) (which measures the brightness of the subject). . The following explanation will be given assuming that as a result of the calculation, the aperture value I)21 and the shutter speed Tel are determined.

When the release 5W18 is pressed after power is turned on, the system control circuit 17 turns on the motor drive control circuit 12 to rotate the video floppy 9 through the motor 11.

Once the rotation of the video floppy 9 has stabilized at the specified rotation speed,
Next, the system control circuit 17 drives the stepping motor 4 via the Nutesoping motor drive circuit 6 to drive the aperture blades 2.
Rotate the aperture blade 2 from the initial position (FIG. 3 GA) in the direction of the arrow ('7). When the aperture blades 2 rotate to a predetermined position and stop as shown in FIG. 3(B), the system control circuit 17 sends the COD drive circuit 6 to the shutter speed Ts, which is shorter by the time T82 required for high-speed transfer, which will be described later. time T
The shutter pulse (,) with a pulse width corresponding to 81 is fully output.

The COD drive circuit 6 stops the φSUB clock (q) at the timing of the rising edge of this shutter pulse (e). Therefore, in the CCD 3, the charge discharging means stops discharging charges to the substrate, and accumulation of signal charges corresponding to the subject image by photoelectric conversion is started. At this timing, the vertical transfer clock (f) does not stop, and unnecessary charges in the vertical transfer register 303 are discharged to the outside of the CCD 3 using the normal vertical transfer clock (f) until the shutter pulse (e) falls. .

Next, when the time T81 has elapsed, the system control circuit 17 lowers the shutter pulse (,) and simultaneously performs vertical transfer 5TO.
Output (raise) P signal (d).

The high-speed transfer means of the COD drive circuit 6 detects the fall of this shutter pulse (e) (vertical transfer S TOP signal (
d) rises), the vertical transfer clock (
After increasing the frequency of f) and switching from normal driving to high-speed driving and draining unnecessary charges from the vertical transfer register 303 at high speed, the vertical transfer clock (f) is stopped to stop the transfer of charges.

By the way, as described above, immediately after the φSUB clock (q) stops in the photodiodes 301 and 302 of the CCD 3, accumulation of signal charges corresponding to the subject image by photoelectric conversion is started. Then, when a transfer gate pulse (h) is output from the COD drive circuit 6, the transfer gate serving as transfer means operates, and the signal charges accumulated up to that point are transferred to the vertical transfer register 303. That is, this transfer gate pulse (h) causes the time Ts (=Ts1
+Ts2), the photodiode 301
, 302 are transferred to the vertical transfer register 30.
It will be transferred to 3.

In the above operation, while the aperture blades 2 are rotating, the CCD 3 is irradiated with incident light until the regular aperture value is reached and in the groove where the light is completely blocked, but this light accumulates in the photodiode 301. The unnecessary charge 302 is discharged to the substrate section by the φSUB clock (cr) by the charge discharge means until before the shutter pulse (fil) is passed;
After the elapse of time Ts1, unnecessary charges are discharged by high-speed driving by the high-speed transfer means as described above from the fall of the shutter pulse (e). By being transferred, the sum of the parnu width TS1 of this shutter pulse (e) and the high speed drive time T82 actually corresponds to a predetermined shutter time (exposure time) Ts.

Then, the system control circuit 17 outputs the shutter pulse (e).
When the stepping motor 4 is turned down, the stepping motor 4 is driven through the stepping motor drive circuit 6 to block the incident light to the CCD 3.
The aperture blades 2 are rotated six times in the direction of the arrow (A) from the state shown in FIG. 3(B) to the state q. Figure 3 (q
1 shows a state in which incident light to the CCD 3 is blocked by a portion between the aperture hole 2Q and the aperture hole 21 constituting the light blocking means.

When the light to the CCD 3 is blocked by the aperture blades 2 to an extent that there is no problem, the system control circuit 17 sets the vertical transfer 5TOP signal (d) to the "L" level (in this embodiment, this level is 1L).
(Although the timing to set the level is explained as a state in which the light is completely blocked, this is not necessarily necessary, and there is no problem as long as the amount of incident light begins to be blocked to a range that does not affect the image.) Vertical transfer 5TOP signal (d) is “
When the level becomes L'', the COD drive circuit 6 generates a normal period vertical transfer clock (f) in synchronization with the next VD signal (b) as shown in FIG.
03 to sequentially vertically transfer the signal charges and output them via the horizontal transfer register 304. At this time, this VD
At the rising edge of the PG multiplied signal a) immediately before the signal (b), the system control circuit 17 activates the bidet processing circuit 7. The data is processed by a recording circuit 8 and recorded on a video floppy 9 via a magnetic head 10. In this case, since the aperture blades 2 have returned to their initial positions, the series of photographing sequences ends with the above recording.

As described above, according to this embodiment, the unnecessary charges accumulated in the photodiodes 301 and 302 immediately before the photographing are discharged to the substrate section by the φSUB clock (cr) by the charge discharging means, and when the photographing (N light) ends. The dark charge and smear charge accumulated in the vertical transfer register 303 up to the last moment are discharged by normal driving of the vertical transfer clock (f) and high-speed driving by the high-speed transfer means, and further, the vertical transfer of the post-exposure signal charge by the vertical transfer register 303 is performed. During operation, CCD
3 is a state where the charge transfer section is shielded from light by the aperture blades 2 constituting the light shielding means, and when light is incident on the CCD 3, the vertical transfer V-signuter 303 is stopped, so the transfer is performed as in the conventional case. It is possible to record a signal without causing a trailing phenomenon due to smear charges caused by light continuing to enter the vertical transfer register 303.

Furthermore, as in this embodiment, the aperture blades 2 constituting the light shielding means
By having an aperture υ function and a light shielding function, the configuration of the optical section can be made very simple.

However, the diaphragm and light shielding means use a conventional diaphragm/shape range shutter configuration in which the aperture diameter is changed using multiple aperture blades (however, it only has the diaphragm and light shielding functions and does not have the original shutter function). It goes without saying that the object of the present invention can also be achieved.

In addition, in this embodiment, the timing of the end of light shielding by the aperture 9 blades 2 after exposure is determined by the vertical transfer clock (f) as shown in the figure.
) is brought close to substantially coincide with the rise of the VD signal (b) that causes the VD signal (b) to operate again. This makes it possible to significantly shorten the period T1 during which the vertical transfer register 303 is stopped, thereby reducing the amount of dark charges generated in the vertical transfer register 303, which has advantages and disadvantages in terms of S/H.

However, in COD where the generation of dark charges in the vertical transfer register 303 is not a problem, it is not necessary to take such an operation timing.

Furthermore, in this embodiment, regarding the drive of the CCD 3, the VD signal is used as the reference for the V rate of the COD drive circuit 6. However, even if this is vsYNc (vertical synchronization signal), the VD signal simply replaces vsYNc. There is no problem to answer with this invention.

In this embodiment, the initial position of the aperture blades 2 is set to a light-shielding state, but the unnecessary charges accumulated in the photodiodes 301 and 302 immediately after the start of exposure (shaft time) are discharged to the substrate section by the φSUB clock (q). In addition, the unnecessary charge accumulated in the vertical transfer register 303 immediately before the end of exposure, that is, immediately before the signal charge is transferred, is discharged by normal and high-speed driving.
There is no problem with the answer even if you set it in a position where the light is irradiated.

Incidentally, in this embodiment, the end of the high-speed discharge of unnecessary charges is synchronized with the end of the shutter time T5, but this high-speed discharge is performed at the timing between the rise of the shutter pulse (e) and the transfer gate pulse (11). It goes without saying that the object of the present invention can be achieved wherever there is, but this cannot be avoided.

As is clear from the detailed description of the invention, according to the present invention, unnecessary charges accumulated in the photoelectric conversion element, which is a charge accumulation section, immediately before photographing are discharged to the substrate section by the charge discharge means, and immediately before the end of exposure. Unnecessary charges such as dark charges and smear charges accumulated in the charge transfer section until then are discharged by normal transfer and high-speed driving by the high-speed transfer means. Since the exposure is controlled by an electronic shutter rather than by an electronic shutter, it is not affected by the accuracy of the shutter mechanism, allowing for highly accurate exposure control, and eliminating the trailing phenomenon caused by smear even if there are high-brightness areas in the subject. It is possible to provide an electronic still camera that can record instantaneous images without causing any blemishes, and its effects are significant.

[Brief explanation of drawings]

FIG. 1 is a timing chart showing the operation timing of an electronic still camera according to an embodiment of the present invention, FIG. 3 is a plan view illustrating the operation of the aperture blades in the same embodiment, and FIG. 4 is an interline transfer type camera. It is a schematic diagram of COD. 2...9 aperture blades (shading means), 3...
Interline transfer type CCD (imaging device), 4
. . . Stepping motor, 5 . . . Stepping motor drive circuit, 6 . . . CCD drive circuit, 17 . Name of agent: Patent attorney Shigetaka Awano and one other person

Claims (1)

[Scope of Claims] (1) Exposure to an image sensor including a photoelectric conversion element, a light shielding means for blocking incident light except during the exposure time, and accumulation of charges generated by photoelectric conversion due to exposure to the photoelectric conversion element. a charge storage section that transfers the charges accumulated in the charge accumulation section; a transfer means that controls the transfer of the charges accumulated in the charge accumulation section to the charge transfer section; and a charge storage section that transfers the charges accumulated in the charge accumulation section. charge discharging means for discharging unnecessary charges accumulated in the substrate section to the substrate section before exposing the photoelectric conversion element to the substrate section, and stopping the discharging operation during the exposure time for the photoelectric conversion element; a high-speed transfer means for transferring unnecessary charges accumulated in a transfer section at high speed using a transfer clock having a frequency higher than a normal frequency; The period includes a charge transfer stopping means for stopping charge transfer by the charge transfer section, and before exposing the photoelectric conversion element, unnecessary charges are removed by the charge discharging means and high-speed transfer means, and the charge transfer is stopped. The electronic still camera is configured to stop the charge transfer by the charge transfer stop means until the image sensor is blocked from light by the light shield means. (2) The electronic still camera according to claim 1, wherein the light shielding means has a diaphragm configuration for the incident light when exposing the photoelectric conversion element. (2) The diaphragm configuration includes a first light-shielding plate having an aperture hole, and a second light-shielding plate having an exposure hole on a plate surface that overlaps the first light-shielding plate and moves relatively parallel to the first light-shielding plate. 3. The electronic still camera according to claim 2, comprising two light shielding plates. (4) The electronic still camera according to claim 1, wherein the light blocking of the image sensor by the light blocking means is performed immediately before the rise of the vertical synchronization signal.