JPH0132966B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electric shutter circuit that forms a signal for controlling shutter operation based on the optical output current of a light receiving element.

First, I will explain the program shutter used in cameras. In the early stages of development, program shutters for lens-shutter cameras used independent apertures and shutters, but recently developed shutter mechanisms have become mainstream with shutter blades and apertures. I'm getting used to it. In other words, the shutter, which also functions as an aperture, is fully closed before the release, but after the release, the aperture is opened while being controlled by the cabana.

In a camera that has both an aperture and a shutter as described above, the aperture opening area S is proportional to time t, so S
= Kt, and the exposure amount E at this time is given by E∝L·∫ ^t _O Ktdt=1/2LKt ² (1), where L is the intensity of the incident light. As is clear from equation (1) above, in order to obtain a constant exposure amount, the exposure time must be controlled in inverse proportion to the square root of the incident light intensity.

However, in conventional electric shutters for cameras, CdS was used for the light receiving element to detect incident light. By appropriately treating the CdS photodetector during the manufacturing process, it is relatively easy to obtain one with conductive properties proportional to the square root of the incident light intensity, and the exposure time can be controlled to satisfy the relationship expressed by equation (1) above. was possible. However, CdS light-receiving elements have problems such as poor response, making them unsuitable for cameras that require quick response.

In contrast, recently silicon, gallium, arsenic,
Light-receiving elements made of semiconductor materials with excellent responsiveness, such as phosphorus, have come into widespread use. However, since this type of photodetector can only obtain a current proportional to the intensity of the incident light, it has sufficient characteristics as a photodetector for a camera with a program shutter mechanism that requires the relationship described in (1) above. That said, it was difficult.

The present invention has been made in view of the above-mentioned problems of the light receiving element, and is an electric shutter circuit which generates a current proportional to the square root of the output current value of the light receiving element in a circuit manner and is easily adapted to a program shutter camera. It provides: Next, the present invention will be explained in detail with reference to Examples.

In FIG _. 1, reference numeral 1 denotes a constant current source for supplying a constant current I _r , which is supplied to a diode-connected transistor 2 and also supplied to one input terminal of a first operational amplifier 3. has been done. 1st
The output of the operational amplifier 3 is given to the other input terminal of the operational amplifier 3. The output terminal of the first operational amplifier 3 is connected to the anode side of the light receiving element 5 via a diode-connected logarithmic compression transistor 4. The light receiving element 5 is an element constructed using a semiconductor material such as CdS, Si, or GaAsP, and detects light incident on the camera and forms an electrical output corresponding to the light intensity. An input terminal of a second operational amplifier 6 is connected between the anode and cathode of the light receiving element 5. The output terminal of the second operational amplifier 6 is fed back to the connection point between the cathode of the light receiving element 5 and the operational amplifier 6, and is also connected to the base of a transistor 7 for extracting an output current. A diode-connected transistor 8 is connected to the emitter of the output transistor 7. The emitter of the transistor 8 and the emitter of the transistor 2 are connected to a reference level such as ground potential.

Next, the operation in which the output current of the above circuit is outputted as a current value proportional to the square root of the output current of the light receiving element will be explained. Note that the photovoltaic current generated in the photodetector 5 is I _L
shall be.

It is well known that a diode has the following relationship between forward voltage V _F and forward current I _F : V _F =KT/qlnI _F /I _O (2). However, q
is the amount of electron charge, K is the Boltzmann constant, T is the absolute temperature, and I _O is the reverse saturation current. First, from the relationship of the above equation (2) in the diode-connected transistor 2, the output voltage of the first operational amplifier 3 is given by V ₃ =KT/qlnI _r /I _O (3). Furthermore, from the relationship of the above equation (2) in the diode-connected transistor 4 and the above equation (3), the output voltage of the second operational amplifier 6 is V ₆ =KT/q(lnI _r /I _O +lnI _L /I _O ) (4) is given by

On the other hand, there is also the relationship between the collector current I _C and the base-emitter voltage of the output transistor 7 as V _BE =KT/qlnI _C /I _O (5), and the current flowing through the diode-connected transistor 8 is as shown above. Since it is equal to I _C of the output transistor 7, that is, the output current Iout, the relationship between the base voltage V ₇ of the transistor 7 and the output current Iout is given by V ₇ =(KT/qlnIout/I _O )×2 (6). In the above IC circuit, by designing transistors 2, 4, 7, and 8 to have the same dimensions, the reverse saturation current I _O can be made to have the same value. Therefore, from equations (4) and (5) above, KT/qlnI _r・I _L /I ² _O = KT/qlnIout ² /I ² _O , and the relationship I _r・I _L = I ² _put holds, Since I _r is a constant current value, the light receiving element outputs as the collector current of transistor 7.
An output current proportional to the square root of I _L can be derived.

In the above circuit, the areas of the transistors 7 and 8 are designed to be large, and the circuit is designed so that another voltage having a characteristic proportional to the absolute temperature can be added to the output voltage of the second operational amplifier 6. Output current can be taken out. Furthermore, information necessary for the camera, such as film sensitivity, can be added as the voltage to be added, and the accuracy of operation can be improved by increasing exposure control factors.

FIG. 2 shows another embodiment according to the invention. That is, the aperture area of the diaphragm has a limit, and the aperture area increases with time until the aperture reaches its maximum area, and an output current proportional to the square root of the incident light intensity is required as in the above embodiment. However, when obtaining the desired exposure amount, if the surrounding brightness is not sufficient and the aperture remains in that state even after it is fully opened, the exposure time and the incident light The strength is a simple proportional relationship, and the circuit shown in FIG. 1 is not necessarily sufficient. Therefore, as shown in FIG. 2, another current source 9 is connected to the collector of the transistor 8, and a current I _r2 is supplied from the current source 9 in relation to the opening time of the diaphragm, for example, in the dark, i.e.
When Iout is smaller than _Ir2 , it is also possible to output a characteristic proportional to the light receiving element output current.

As described above, according to the present invention, a current proportional to the square root of the output current of the light-receiving element can be derived with a simple circuit configuration, and the operating characteristics of the shutter mechanism and the optical output current characteristics of the light-receiving element can be compensated for in a circuit. Accordingly, an appropriate shutter control signal can be generated. Further, restrictions on elements that can be used as light receiving elements are relaxed, and a camera can be constructed using elements with excellent responsiveness.

[Brief explanation of drawings]

FIG. 1 is an electrical circuit diagram of an embodiment according to the present invention;
FIG. 2 is an electrical circuit diagram of a main part of another embodiment. 1: constant current source, 2: transistor, 3: first operational amplifier, 4...transistor for logarithmic compression, 5: light receiving element, 6: second operational amplifier, 7: output transistor, 8: transistor.

Claims (1)

[Claims] 1. A control signal for controlling the aperture operation of an aperture-shutter from closing to fully opening, based on the amount of light incident on a dedicated photometric optical system provided separately from the photographing optical system of the camera. The electric shutter circuit to be formed consists of a circuit that generates a voltage equivalent to the forward voltage when a constant current flows through the diode, and an output transistor consisting of a diode-connected transistor connected between the emitter and a reference potential. , by providing a circuit that supplies the base of the output transistor with a voltage obtained by adding a voltage obtained by logarithmically compressing the output current of the light receiving element that detects incident light to the output voltage of the voltage generating circuit. An electric shutter circuit characterized in that a current proportional to the square root of the output current is extracted from the collector of the output transistor.