JPH0677099B2 - Photoelectric conversion device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a charge storage type photoelectric conversion device used for a focus detection device and the like, and particularly to control of a charge storage time of the photoelectric conversion device.

(Prior Art) When a charge storage type solid-state image sensor such as a CCD or MOS image sensor which is widely used at present is used for a focus detection device such as a single-lens reflex camera, when the subject is dark, the integration time becomes longer. It becomes longer, the time required for one focus determination becomes longer, the dark current component in the output signal becomes larger, the dynamic range is reduced, and the influence of variations in dark current between cells becomes remarkable. Therefore, high-precision focus detection is difficult. Further, as the dynamic range decreases, the focus display width also becomes wider in the case of focus aid.

Here, a conventional focus detection device using a CCD image pickup device will be described with reference to FIG. 9. In order to detect a lateral shift of an image, the CCD image sensor 1 arranged on the image forming surface of the photographing lens is a photodiode array. 2, a transfer gate 3, a CCD shift register 4, and an exposure control photometric device (hereinafter abbreviated as monitor) 5. Transfer gate 3
Is a transfer gate for transferring the charges of the photodiode array 2 to the CCD shift register 4. The monitor 5 is a photometric element for controlling the charge storage time of the photodiode array 2. As described above, the focus detection device using the CCD image line sensor 1 operates as shown in the timing chart of FIG. First, when a monitor reset pulse MR from a control circuit (hereinafter abbreviated as CPU) 7 is supplied to the monitor 5, the monitor 5 is reset to a predetermined level, and the potential changes with an inclination according to the brightness of the subject. Change. When the monitor 5 reaches the reference potential V _ref , the output of the comparator 6 is inverted. The time from the supply of the monitor reset pulse MR until the output of the comparator 6 is inverted (hereinafter referred to as photometric information) is T _M. The CPU 7 counts this photometric information T _M , supplies the transfer gate pulse φ _T to the transfer gate 3, and transfers the charges integrated to the photodiode array 2 during the integration time T _int = T _M to the CCD shift register 4. . The photodiode array 2 has masked photodiodes (mask dummies) at both ends thereof and holds only dark output. The dark output is compensated by taking the difference between the output voltage of the mask dummy and the output of the unmasked photodiode. After subtracting the dark output by the dark output compensating circuit 9, the signal is output by the amplifier 10. Is amplified and sent to the arithmetic circuit 8 to perform focus detection calculation and input to the CPU 7. The result is displayed on a display device (not shown) or the photographing lens is driven.

In a photoelectric conversion device such as a conventional focus detection device using a charge storage type photoelectric conversion element array that operates in this way, the integration time becomes long when the subject is dark, and it is necessary for one focus determination. As the time becomes longer, the dark current component in the output signal becomes larger as shown in FIGS. 7A and 7B, the dynamic range is reduced, and the effect of the dark current variation among cells becomes remarkable. However, high precision focus detection has been difficult. Further, as shown in the right side of FIG. 7C, the focus display width also becomes wide in the case of the focus aid as the dynamic range decreases.

Furthermore, the control of the charge storage time of the conventional photoelectric conversion device is performed when the monitor 5 reaches the reference potential V _ref as described above.
Since the charge accumulation is completed, it is necessary to provide a complicated circuit for real-time processing.

(Purpose) In view of the above points, an object of the present invention is to obtain an electric charge accumulation time in advance by calculation using the output of a photoelectric conversion element for monitoring before the amount of received light of a photoelectric conversion element array reaches an appropriate amount. Every other time, it is to provide a photoelectric conversion device having a simple configuration that does not require a complicated circuit for terminating the charge accumulation in real time by terminating the charge accumulation when this time has elapsed.

(Outline) In order to achieve the above object, the present invention provides a charge storage type photoelectric conversion element array for receiving subject light, and a brightness of the subject light for controlling the charge storage time of the photoelectric conversion element array. After the start of charge accumulation in the photoelectric conversion device for monitoring and the photoelectric conversion device for monitoring that outputs side light information according to the above, the charge accumulation time of the photoelectric conversion device array is calculated based on the output of the photoelectric conversion device for monitoring. The calculation means and the control means for ending the charge accumulation in the photoelectric conversion element array when the charge accumulation time calculated by the calculation means elapses after the charge accumulation is started.

(Example) Before describing an example of the present invention, the outline of the present invention will be described. An exposure control element (hereinafter referred to as a monitor) adjacent to a photodiode array that receives a subject image.
When the integration time of the photodiode array is determined based on the output information of T, and the time when the output information of the monitor is obtained is T _M and the integration time of the photodiode array is T _int , T _int = n · T _M (n> Set to the relationship of 1). Since the output of the photodiode array has an appropriate output level V _op at the integration time T _int , the charge corresponding to V _op / n is accumulated in the photodiode at the integration time T _M. Here, to set the maximum integration time T _{int · MAX} allowable, even if the conventional T _int of the integration time _{(T int> T int · MAX} ) is required, abort the integration at T _{int · MAX.} At this time,
As a means for making the focused display width substantially equal to the focused focused display width when it is bright (in the case of focus aid). That is, the gain G when amplifying the photodiode output to a predetermined level V _op is Therefore, the gain of the amplifier for optimizing the photodiode output is obtained from the monitor output information T _M (in the case of focus aid and auto focus), and this is set in the variable gain amplifier. Alternatively, the amplifier is not used, or the gain is kept constant, and the threshold value for the evaluation value for focusing display is controlled by the monitor output information T _M (in the case of focus aid). Even in this case, it is possible to obtain substantially the same effect as when the variable gain amplifier described above is used.

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

FIG. 1 is a block diagram showing a configuration of the present invention, and reference numerals 2 to 5 are CCD image line sensors 1. The charges of the photodiode array 2 are transferred to the CCD shift register 4 by the transfer gate 3. The monitor 5 is a photometric element for controlling the charge storage time of the photodiode array 2, and an exposure control photometric element 11 that shields the same photometric element as the monitor 5 is provided near the monitor.

Next, the operation of the focus detection apparatus using the CCD image line sensor 1 configured as described above will be described with reference to the timing chart of FIG. 2. First, the monitor reset pulse MR is sent from the CPU 7 which is the control circuit. It is supplied to the monitor 5 and the exposure control photometric element 11. Then, the monitor 5 is reset to a predetermined level, and the potential changes with an inclination according to the brightness of the subject. Photometer for exposure control
In 11, the dark current component accumulates with time, and the differential amplifier 12
When the output of the comparator reaches the reference potential V _ref , the output of the comparator 6 is inverted. The time from the supply of the monitor reset pulse MR from the CPU 7 to the monitor 5 until the output of the comparator 6 is inverted (photometric information) is T _M. The counter 13 measures this T _M and sends the result to the CPU 7. This CPU 7 supplies the transfer gate pulse φ _T to the transfer gate 3 after nT _M (n> 1) has elapsed since sending the monitor reset pulse MR.
The charges integrated in the photodiode array 2 during the integration time T _int = n · T _M are transferred to the CCD shift register 4, the dark output is subtracted by the dark output compensating circuit 9, and then amplified by the variable gain amplifier 10. The signal is sent to the arithmetic circuit 8 to perform the focus detection calculation (the focus detection calculation may be analog or digital), and the result is displayed on the display device (not shown) via the CPU 7 or the photographing lens is driven. To do.

It should be noted that some other drive clock pulses are required to drive the CCD image line sensor 1, but they are omitted here. Further, this embodiment is premised on a CCD image line sensor having a structure in which the charges of the photodiode are cleared before the operation of integrating the charges is started.
Further, as the monitor 5, it is not necessary to provide an element adjacent to the photodiode array 2 as shown in FIG.
A method in which a floating gate is provided on the photodiode and the charge of the photodiode is read out nondestructively, or another method may be used.

In FIG. 1, a light-shielding (for exposure control) element 11 is provided, and the difference between this output and the output of the monitor 5 is taken into consideration.
This is because the monitor 5 also produces a dark output proportional to the integration time, and the intended purpose cannot be achieved unless the dark output is canceled.

Next, the time until the output of the comparator 6 is inverted (photometric information) T _M , the integration time T _int of the photodiode array 2 and the gain setting of the variable gain amplifier 10 will be described.

FIG. 3 shows an example thereof. In this example, the maximum integration time T _{int · MAX is set} to 300 [ms], and T _int = 3T _M is set within the range of T _M 100 [ms]. In addition, amplifier 1 within the range of T _M 100 [ms]
The gain of 0 is G _O.

In the range of T _M > 100 [ms], the integration time T _int is 300 [ms] and the gain G of the amplifier 10 is Automatically set to.

With such a configuration, even when the maximum integration time is required when the subject is dark, the integration time is less than or equal to the arbitrarily set maximum integration time, and the reduction of the dynamic range due to the dark current component is avoided. To be The configuration of the variable gain amplifier 10 in this case is shown in FIG. (For details of the configuration and operation of the variable gain amplifier 10, refer to Television Engineering Handbook, Vol. 6, Television Electronic Circuit P6-71.) That is, the output from the dark output compensating circuit 9 is applied to the RF input terminal, and the output from the CPU 7 is sent. The input is applied to the AGC input terminal, and the output terminal is connected to the input terminal of the arithmetic circuit 8. The AGC input and RF input can be exchanged.

The gain setting of the variable gain amplifier 10 is not limited to that shown in FIG. 3, and may be stepwise as shown in FIG. A configuration example of the variable gain amplifier 10 in this case is shown in FIG. The output of the dark output compensation circuit 9 is connected to Vin which is the non-inverting input terminal of the operational amplifier, the output from the CPU 7 is connected to DATA BUS and CONTROL LINES,
The output terminal Vout of the operational amplifier is connected to the input terminal of the arithmetic circuit 8.

As another embodiment, the gain value G obtained from the CPU 7 is set to D / A.
Alternatively, the value may be converted and the output of the differential amplifier 12 may be analog-multiplied.

The above is an example in which the output of the CCD image line sensor 1 is controlled by the gain of the variable gain amplifier 10 by the monitor output to recover the decrease in the dynamic range when the subject is dark. This case is shown on the right side of FIG. 7, but in this case, both focus aid and autofocus can be supported.

In the case of only the focus aid, the gain of the amplifier is not controlled by the monitor output, but the threshold for focus display is controlled so that the focus display width is the same as when the subject is bright.

When the evaluation value is S and the threshold value for focus display is S _O , the focus display width is displayed when | S | <S _O. This threshold value S _O is controlled by the monitor output. That is, when the evaluation value is dark, the inclination with respect to the defocus becomes small as shown on the right side of FIG. 7, but the focus display threshold may be made smaller accordingly. An example at this time is shown in FIG. Similar to that shown in FIG. 3, it shows the case where T _int = 3 T _M and T _{int · MAX} = 300 [ms]. The threshold when the subject is bright
_SOO . Clearly G / G _O = (S _O / S _OO ) ^-1 .

(Effect of the Invention) According to the present invention, the charge storage time is calculated in advance before the amount of light received by the photoelectric conversion element array reaches an appropriate amount by using the output of the photoelectric conversion element for monitoring, and this time is calculated. Since the charge accumulation is terminated when the time elapses, it is possible to provide a simple configuration that does not require a complicated circuit for terminating the charge accumulation in real time.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a focus detection apparatus according to an embodiment of the present invention, FIG. 2 is an operation timing chart of the focus detection apparatus shown in FIG. 1, and FIG. A diagram showing the relationship with the photometric information T _M and the gain of the variable gain amplifier, FIG. 4 is a circuit diagram showing an example of the configuration of the variable gain amplifier, and FIG. 5 shows a configuration different from that of FIG. The relationship between the maximum integration time and the photometric information T _M when a variable gain amplifier is used, and a diagram showing the gain of the variable gain amplifier. FIG. 6 is a circuit diagram showing another example of the configuration of the variable gain amplifier. 7A, 7B and 7C are diagrams showing the CCD output, the output after dark output compensation and the evaluation value, respectively, when the subject is bright and dark, and FIG. 8 is the above-mentioned diagram used for the focus aid. 3 figures,
Similar to FIG. 5, a diagram showing the relationship between the maximum integration time and the photometric information T _M , and the threshold value of the evaluation value. FIG. 9 is a block diagram showing the configuration of a conventional focus detection device, FIG. FIG. 9 is an operation timing chart of the focus detection device of FIG. 9 described above. 1 ... CCD image line sensor (imaging element for focus detection) 2 ... photodiode array 5 ... exposure control element (monitor) 9 ... dark output compensation circuit 10 ... gain variable amplifier

Claims (4)

[Claims] 1. A charge storage type photoelectric conversion element array for receiving subject light, and a monitor photoelectric output device for outputting photometric information according to the brightness of the subject light in order to control a charge storage time of the photoelectric conversion element array. And a calculating means for calculating in advance the charge accumulation time until the charge accumulation of the photoelectric conversion element array is completed based on the output of the converting means and the monitor photoelectric conversion means; and the calculating means after the charge accumulation is started. Control means for performing a time counting operation based on the charge accumulation time calculated by the above, and for ending the charge accumulation of the photoelectric conversion element array when the above-mentioned calculated charge accumulation time has elapsed. Photoelectric conversion device. 2. The calculating means outputs information on the maximum storage time T _intMAX to the control means when the calculated charge storage time T _int is _longer than the maximum storage time T _intMAX. The photoelectric conversion device according to claim 1, wherein: 3. The amplifying means for amplifying a photoelectric conversion signal output from the photoelectric conversion element array when the calculated charge accumulation time T _int is _longer than the maximum accumulation time T _intMAX. The photoelectric conversion device according to claim 2, further comprising: Wherein said calculating means, when the photometric information output by the monitoring photoelectric converter and T _M, the charge storage time T _int, calculated from T _int = n · T _M, the photometric information When T _M is larger than T _M = T _intMAX / n, the gain of the amplifier for amplifying the output of the photoelectric conversion element array is controlled by the photometric information T _M. The photoelectric conversion device according to the item.