JPS598478A - Exposure control device for image pickup element - Google Patents

Abstract

PURPOSE:To attain direct photometry, by using a solid-state image pickup element having an excluding function of unnecessary signal charge and an electronic shutter function for performing exposure control as specified. CONSTITUTION:The solid-state image pickup element 34 has an excluding function of the unnecessary signal charge and the photometry element 36 detects the exposure to the image pickup element 34. Further, a photometry operating circuit 39 operates a shutter time giving an adequate exposure time from an output of the photometry element 36. Moreover, a timing control circuit 315 controls the electronic shutter function of the image pickup element 34. Then, the exposure of the image pickup element 34 is started in synchronizing with a synchronizing signal used to drive it and ends with the elapse of adequate exposure time. Further, after the end of exposure, the signal charge obtained at the exposure is stored under an optically shielded transfer electrode of the image pickup element 34 and read out in synchronizing with the synchronizing signal generated succeedingly. Thus, the direct photometry is attained with the exposure control in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exposure amount device for an image sensor having a shutter function.

(2) When attempting to realize an electronic still camera using an image pickup element without using a mechanical shutter, the image pickup element itself must have a shutter function similar to that of a shutter. Here, the electronic shutter function is required to satisfy the following functions.

(1) Unnecessary charges accumulated in the light receiving section and the transfer section before the start of exposure can be eliminated at high speed.

(2) The exposure time must be the same for all pixels.

13) Exposure start and end times should not differ greatly between adjacent pixels. That is, there is no large timing difference between adjacent pixels.

(4) The signal charge after exposure can be retained during the readout period even if it is exposed to light.

An interline transfer CCI (interline transfer CCI) with an overflow drain has all these functions.
CCDs are known for surface channel frame transfer.

These image sensors with an electronic shutter function are used, for example, to obtain a single frame still image that is compatible with the video signal format of a television, or to record at a fixed period, such as in a video disc recorder. When a single-frame still image is obtained using a recording device, all imaging operations are performed in synchronization with a certain repetition period. For example, in television, one field corresponds to 1/60 second, and one i-frame per second corresponds to the repetition period. by the way,
A conventional driving method for causing an image sensor having an electronic shutter function as described above to perform a high-speed shutter operation will be described with reference to the drawings.

FIG. 1 is an explanatory diagram showing a part of an interline transfer CCI having an overflow drain and its control gate, and FIG. 2 is a timing chart of its shutter operation.

In Fig. 1, 1 is the light receiving section, 21 is the vertical transfer section which is connected to the light shielding section, and 6 is the vertical transfer section from the light receiving section to the vertical transfer section.
It is a transfer cathode for transferring electric charges. Mani,
An overflow drain 4 is installed in the light receiving section 1 to discharge unnecessary signal charges, and an overflow drain 4 is provided between the light receiving section 1 and the overflow drain 4 for the purpose of controlling the height of the potential barrier. Overflow control gate 5h''-B KEL) h-c. This overflow control gate h5< is a potential barrier that prevents pluming due to excess charge generated in the light receiving section 1 that receives intense light during normal exposure. A voltage giving a height of 4 Vc is applied, and when the CCDw shutter operation is to be performed, a voltage of 4 Vc is applied that can drain all the signal charges in the light receiving section 1 to the overflow drain 4Vc.

In Fig. 2, 1 indicates the vertical synchronization signal, and its frequency J
tJ]'J'f is 1760 seconds. (Port 1 indicates the overflow drain gate signal, when this signal is high level, that is, time '[,'o if unnecessary charge of light receiving section 1 is tiCC1') external f is drained, and when it is low level, normal overflow occurs. Acts as a drain.

Pl indicates the transfer gate' signal, and this signal h
;When the level is high, the signal lightning and load stored in the light receiving unit 1rc so far are transferred to the vertical transfer unit 2.

When using the shutter function of the conventional CCD itself, the storage retention time of signal charges in the vertical transfer section 2 is kept as short as possible to prevent deterioration due to dark current during storage storage. The exposure time Te f
It was set just before the video signal readout time TR. Setting the exposure time in this manner has the drawback that, in step 5, signal degradation due to dark current is eliminated, which is of order /l-1.

First, when photographing a subject whose brightness changes from moment to moment, Vr is required after the start of exposure (end of unnecessary charge discharge operation), when photometry is started and the appropriate exposure amount is reached.
It was not possible to transfer signal charges to the vertical transfer section. In other words, direct photometry h in silver halide still cameras
″-DekifL force) Tsutko.

If the vertical transfer section 2 is shielded from light (・ruh''-1) and holds signal charges for a long time, the light receiving section 1 will receive a strong (・light h''-1
If a little trick is taken, the vertical transfer section 2 will be affected, and the image quality will deteriorate due to the B1 current f. Therefore, according to the timing of the conventional interline CCD, the vertical synchronization signal (1
/60 seconds) to match the timing of exposure completion.
Input the subject brightness information before the exposure operation f, calculate the exposure time based on that input to find the shutter time, and then subtract the shutter time from 1/60 seconds and the time has elapsed since a certain vertical synchronization signal. Since it is necessary to start the exposure from 1 and then end the exposure at the next vertical synchronization signal, the above-mentioned 15K, so-called direct photometry, was not possible.

Second, when taking pictures by shortening the exposure time, that is, by shortening the shutter time, the vertical synchronization signal that continues to be generated at a constant timing is strictly controlled as described above when the unnecessary charge discharge operation ends. It is necessary to control the time until the transfer gate signal is generated in synchronization with the transfer gate signal, that is, the shutter time, and this requires a highly accurate measurement circuit h'', making the circuit complicated. I have one.

For example, if we consider controlling a shutter time of 1/1 [100 seconds], using the method described above, obtaining the above shutter time (Te) is (1/60 - 1 /10
00 ) seconds, that is, Teki 15A (maec') is measured.

Here, if the measurement error is Q, 1 (msec), the open side accuracy needs to be as high as ±0.64%.

The present invention solves these shortcomings, captures images using the shutter function of the image sensor itself, and outputs a stealth video signal from the image sensor in synchronization with a synchronization signal having a constant repetition period. The exposure side of the image sensor is designed to be able to respond to changes in the subject's brightness during exposure, that is, direct metering. ) equipment.

In order to achieve such an object, the present invention provides an exposure control device KA for an image sensor, a solid-state image sensor photometric element,
It is equipped with a photometric calculation circuit and a timing control circuit. Here, the solid-state image sensor (device) has a function of discharging unnecessary signal charges.The photometric element is connected to the solid-state image sensor, and the solid-state circuit calculates the shutter time, which is the appropriate exposure time, from the output of the photometric element. The control circuit controls the entire electronic shutter function of the solid-state image sensor based on the output of the photometric calculation circuit.

The frost of the solid-state image sensor and the reserved shutter function are as follows.
controlled by

Exposure of the solid-state imaging element starts in synchronization with the vertical synchronization signal used to drive the solid-state imaging element, ends when the appropriate exposure time calculated by the photometric calculation circuit has elapsed, and then the exposure ends. After that, the signal charge obtained by exposure is transferred to the light speed of the solid-state image sensor and stored under the 10 transfer electrodes.
The timing control is set to 15 which is read out in synchronization with the first vertical synchronization signal that occurs subsequently.

Hereinafter, embodiments of the present invention will be described based on all the drawings.

FIG. 6 is a block diagram of an electronic still camera according to an embodiment of the present invention. It passes through a photographing lens 32 with a built-in diaphragm 31, is further split into an optical path by a mirror, and is imaged by a CCD 34 vr. no-fu mirror 3
The other luminous flux is divided by 3, and is divided into 35
Vr is incident, and is further divided into a photometric element 36 and a viewfinder (not shown).

In this embodiment, the aperture 61 is controlled by an aperture opening/closing mechanism 67 including a morph and a magnet.
In addition, the aperture amount is detected by the aperture value detection element 38, and the information is transmitted to the photometry calculation circuit 69. (The ICD 34 is an image sensor having a shutter function, This will be explained as an element that can also be used in a video camera.

The operation timing control in the electronic still camera of this embodiment is performed by synchronizing all of the synchronization signal generation circuits 31DK that have a continuously oscillating crystal oscillator, and the output video signal of the CCD is also controlled by the f preamplifier 311 and the process circuit 312, similar to the video camera. and a recording circuit 314 which operates in synchronization with the synchronous signal generation circuit 313 and a synchronous signal addition circuit 313.
recorded in The timing control E4 for the entire camera receives the output synchronization signal from the synchronization signal generation circuit 310 and generates each required (
This is done by a camera timing control circuit 315 that generates heavy pulses. In the case of still photography, only the output video signal from the CUD 34 outside the valid period is recorded in the recording circuit 314, but the signal indicating this valid period is also transmitted from the camera timing control circuit 15 to the recording circuit 614 and recorded. used for.

The camera timing control circuit 315 outputs timing signals for opening and closing the diaphragm during photographing, controls the diaphragm drive circuit '516, and at the same time supplies necessary signals to the driving noise generating circuit '317VC of the CCI) 34. . The start of photographing is performed by the shutter trigger switch 318 KJ, which is linked to the shirt release button.

The operation of this embodiment will be explained below using the timing chart shown in FIG.

The fourth diagram J shows a vertical synchronization signal as in FIG.

Now, when the shirt release button is pressed and the shutter trigger switch 618 is closed at a timing that is completely unrelated to this vertical synchronizing signal, the fourth shutter trigger signal shown in FIG. After this shutter trigger signal is generated, the camera starts imaging fil1 at the timing of the first vertical synchronization signal.

In this case, the aperture 31, which had been open until then and provided a bright field of view fw, is stopped down to a one-stop aperture position, which is set in advance before the shutter release. At the same time, the unnecessary charge discharge signal of the CCD 34 in FIG.
′! The overflow control signal shown in is synchronized with the vertical synchronization signal after the narrowing down is completed, and the time To
becomes high level and discharges unnecessary charges from the light receiving section.

Effective exposure of the CCD starts when the overflow control signal shown in FIG. 4(c) returns to low level. Exposure is continued for a period of time Te until an exposure completion signal is obtained from the photometry calculation circuit 39 which operates at the same time.

The exposure completion signal is transmitted to the drive pulse generator 317K via the camera timing control circuit 615, and the transfer gate signal shown in FIG. 4), which was interrupted after the start of photographing, is generated at the timing shown in the same figure.

Thereafter, the signal signal transferred to the vertical transfer section of the CCD 34 is read out at a timing f in synchronization with the next vertical synchronization signal. The time Ts shown in Fig. 4) is the storage time from completion of exposure to external readout, and the maximum
Since the time is 0 seconds, the deterioration is not a problem. In this embodiment, the read video signal of one still frame is one field image of a television, and is recorded by the recording device 314Vc during time 1'R.

With the configuration of this embodiment, the photometric calculation circuit including the photometric element starts C photometry in synchronization with the vertical synchronization signal, and
I) The advantage is that an exposure completion signal is output when the appropriate exposure amount for Vt is reached (so-called direct photometry), which requires a very simple calculation operation, and a high-speed shutter time can be obtained with a circuit that is not very precise. have.

In the above explanation f, it was explained that the unnecessary charge is discharged to the overflow drain before exposure, but the present invention is not limited to this, and the unnecessary charge is discharged through the transfer gate and the vertical transfer CCI). You can also do that.

FIG. 5 shows a block diagram of an embodiment of the photometric calculation circuit of the present invention. Reference numeral 56 in FIG. 5 is the same photometric element as the photometric element 36 in FIG.

59 indicated by a broken line in the same figure is the photometry calculation circuit 69 in FIG.
It is a photometric calculation circuit with the same effect as that of , and it includes a logarithmic compression circuit 510, a sample-and-hold circuit 511, and an electronic E/H circuit.
A time converter 512 is included.

According to this configuration 9, wide-open photometry and aperture photography becomes possible.

That is, the brightness of the subject immediately before the release is pressed with the aperture open and the aperture is mechanically activated is input to the sample-and-hold circuit 511 via the photometric element inverse and logarithm compression circuit 510 and stored. Perform open metering with
, At the same time as the discharge of unnecessary charge from the CCU is completed, the voltage/time conversion circuit 512 starts calculation to convert the voltage into time,
After a predetermined period of time has elapsed, the exposure completion pulse reaches ffi to the camera timing control circuit 515 to generate a transfer gate signal and control the exposure time.

In FIG. 5f, a signal (a
l is a signal specifying the/pull state, that is, the photometry state, and the bold state, that is, the storage state.

Further, signals) and (cl) are the start and completion signals of the pressure/time conversion calculation, respectively.

FIG. 6 shows a block diagram of another embodiment of the photometric calculation circuit of the present invention, in which m, E
/The time conversion circuit is composed of a digital circuit. In the figure, 66 is a photometric element, 61o is a logarithmic network circuit, 611
It is a one-piece sample-and-hold circuit, and up to this point there is no difference from the implementation 91 in Fig. 5. 612 is a raw converter that converts the analog photometric information voltage into digital IW-conversion, and inputs this into the register 616πn1. mean. Dumble and hold circuit 611. The A7'D converter 612 and the register 616 are supplied with a photometry/memory command signal (k+) from the camera timing control circuit 614 to control these operations, and are used to adjust the A/Tll quality from photometry during shooting. Exchange and even memorization are performed.

The output of the register 616 is digital data according to photometry π, and in order to control the shutter time, in this embodiment, information on the exposure start time (timing) and shutter time, that is, appropriate exposure time information are required in this embodiment. shall be. Both of these are uniquely determined once the photometric value is determined, and instead of calculating it by calculation, it is calculated using a look up table (LOOK UP TAf3L).
E) Read-only memo IJ (II□□□I)
If you memorize K, it becomes easy 1. Here, 615 in the figure is the ROM, and the output of the register 613 is ll0M
615 address input terminal. noM615
Of the outputs, (1, denoted by at, is appropriate exposure time information, and (b1, denoted by bl) is exposure start time information.

The circuit also includes two digital comparators (coincidence detection circuits) 616 and 617 and two counters 618 and 6.
It is equipped with 19.

The operation of this embodiment will be explained below using a timing chart shown in FIG.

Immediately after the release button is pressed down and the photometric value in the open aperture state is stored, the aperture is stopped down to the mechanical π set aperture value.

Figure 7 (1) is the vertical synchronization signal and shutter trigger signal, respectively, as in Figure 4 (a) and (mouth). In synchronization with the vertical synchronization signal following the shutter trigger signal,
Figure 7 HK As shown in 1.1, the overflow control gate signal becomes high level, the discharge of unnecessary charge from C(:D starts, and the aperture is also narrowed down at the same time.The mechanical narrowing operation is completed L After T, a one-time operation is performed using the counter 619 and the digital comparator 617 to determine how much delay to start the exposure charge accumulation in the CCD with respect to the first vertical cycle signal. , the counter 619 is synchronized with the first vertical synchronization signal, stops the reset pulse (cl) which had been in the reset mode, enables counting, and counts the clock pulse fdl.
d) is horizontal synchronization signal frequency 9 = 15.75 KH3
Or, the frequency obtained by dividing this □Using the wave number is
Counter 619, digital comparators 617 and 1
This is suitable for reducing the number of bits of 10M615.

I? Output signal of OM 615 (bl is as mentioned above) K
, the signal layer to the CCD, the load accumulation start signal, and the count value te of the counter 619 in the count mode.
The digital comparator 617 outputs a signal (when l matches bl, a match signal is output) and sends this signal to the camera timing control circuit 614 to reset the counter 619 again. The overflow control signal shown in FIG. 1 is set to low level, and accumulation of signal charges is started. Therefore, the exposure start time information is shown in FIG.
Dividing the ``1 time TO'' by one cycle of the clock pulse (di) yields binary information with a value of 1.

At the same time as the charge accumulation in the CCD begins, the camera timing control circuit 614 changes the signal layer that had previously reset the counter 618 to put the counter 618 into count mode, and the counter 618 resets according to the highest shutter speed. Count clock pulses of a specified height and frequency. The count output of the counter 618 (11 is input to the digital data calculator 616, and the other input, appropriate exposure time information (when it matches al, a match signal is sent from the controller 616) b''- is obtained. At the same time, the reset pulse 1q) is activated and the reset mode is returned to. The scene is transferred and the scene is completed.

According to the configuration of this embodiment, it is only necessary to use a circuit with a small number of bits for setting the exposure start time, and seven exposure time judgments can be made accurately, and at the same time, the storage time at the vertical transfer electrode can be shortened. There are advantages.

In the above description of the embodiments, an interline transfer (II) with an overflow control gate has been described as a solid-state image sensor, but the present invention (engineering) is not limited to this. ,
(-havge PrinlingJ
), light guide rectangle, film stacked solid state image element, and various other imaging devices having a shutter function.

In addition, the aperture-priority electronic still camera described in the present invention can be
Changing the shutter time priority or program AbK can be easily done using conventional techniques.

Note that in the above embodiment, the retention time '[S is approximately 1 field (1/60 second) at maximum, but the influence of dark current over a period of this length may pose a problem with video cameras etc. that have a similar retention time. It seems that π does not have a large effect, but it is of a level that does not cause any practical problems. Further, in the above-mentioned embodiment π, an example is shown in which one frame is one field, but it is of course possible to use one frame as one field.

As is clear from the above description, according to the present invention, the VC1 is used in an exposure control device for an image sensor that reads out a video signal from a single image sensor in synchronization with a constant periodic signal and records it. In order to make the above synchronization signal f match, there is no need for step 3, so it is necessary to set the exposure start strictly at f. ] 1 is eliminated, and therefore the shutter time control circuit is simplified accordingly, which is especially effective when trying to accurately obtain a short shutter time with a high-speed shutter.

For example, as explained in the prior art, π, I A 00
Control the shutter time of 0 seconds! I] If we consider that 'J''6=1 (msec), the control Ft
Assuming that the 4 difference is ±[1,1 (mspc), the control accuracy is sufficient to be 1110%, which is 10.
The color accuracy has been significantly reduced by 64.

First, if you use the electronic shutter function of the S-image element, you can expose all the pixels at once. There will be no distortion at the first moment of curtain speed.

Furthermore, since exposure starts from the start of reading out the video signal by the shutter time,
This configuration has the advantage that it is possible to simultaneously perform photometry using the C, C (exposure to ΣD), Y:L photometry elements, and determine the point at which fogginess is completed, that is, tie-left photometry.

[Brief explanation of drawings]

Figure ii is an explanatory diagram showing a part of an interline controller/sphere CC1) having an overflow drain and its control gate, Figure 2 is an explanatory diagram of the timing of conventional shutter time control, and Figure 6 is an example of an implementation of the present invention. A block diagram of an electronic camera according to an example, FIG. 4 is a timing explanatory diagram showing its operation, FIG. 5 is a block diagram of an embodiment of the photometry calculation circuit of the present invention, and FIG. The block diagram of the embodiment, FIG. 7, is a timing explanatory diagram showing its operation. DESCRIPTION OF SYMBOLS 1... Light receiving part, 2... Vertical transfer part, 6... Transfer gate, 4... Overflow drain, 5
°' Overflow control gate, 31... Stop, 32... Photographing lens, 36... Norf mirror, 6
4... CCD, 65... Half mirror 136... Photometric element, 67... Aperture opening/closing mechanism, 38...-#! 2
Shi value detection element, 39... Photometry calculation circuit, filter 10...
Synchronous signal generation circuit, 311... preamplifier, 312...
. . . Process circuit, 613 . . . Synchronous signal addition circuit, filter 14 . . . Recording circuit, 615 .
9... Photometric calculation circuit, 510... Logarithmic compression circuit, 5
11... Sample and hold circuit, 512...
Voltage/time converter, 515...Camera timing overturning circuit. Figure 4; Figure i-5 Figure O ○ Figure Back

Claims (1)

[Scope of Claims] A solid-state imaging element having a function of discharging unnecessary signal charges, a photometric element that detects the amount of exposure to the solid-state imaging element, and a shutter time, which is an appropriate exposure time, calculated from the output of the photometric element. the solid-state image sensor; It starts in synchronization with a synchronization signal that is used for driving and has a cycle of reading out the signal charge of one frame, and ends after the appropriate exposure time calculated by the photometry calculation circuit has elapsed, and after the end of exposure, , an image sensor characterized in that signal charges obtained from exposure f are stored under a light-shielded transfer electrode of a solid-state image sensor, and are read out in synchronization with the first synchronization signal that occurs subsequently. exposure control device.