JPS5922890B2 - current amplification circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a current amplification circuit for amplifying a photocurrent obtained by a photoelectric conversion element at a constant amplification factor in a photographic device such as a camera or an electronic flash device.

In general, the determining factors for exposure conditions when taking photographs include:
There are aperture value, film sensitivity, shutter speed, etc.
Exposure conditions are usually determined by calculating these determining factors based on an index value having a base of 2, such as EV value calculation using the Apex method.

Therefore, in the circuit configuration including the photoelectric conversion element used for determining the exposure conditions of photographic equipment as described above,
It goes without saying that setting the amplification factor of the photocurrent, which is proportional to the brightness of the subject by the photoelectric conversion element, to a value related to an index having a base of 2 is effective in determining the exposure conditions. Figure 1 shows an example of a conventional circuit that amplifies the photocurrent generated by the photoelectric conversion element 1 to a current that is proportionally multiplied to the base of 2. By changing the value, a current that is proportionally multiplied to the base 2 is obtained. However, with such a circuit configuration, there is a problem that the photocurrent cannot be amplified accurately due to a deviation in the set value due to an adjustment error in the resistance value of the variable resistor, and due to the accuracy of the variable resistor itself. The present invention has been made in view of these problems, and will be described in detail below with reference to the drawings.

FIG. 2 shows an embodiment of the current amplification circuit of the present invention, in which a photodiode is used as the photoelectric conversion element 1, such as a photodiode or a phototransistor.
In the figure, 2, 3, 4, 5 are diodes, 6, 7,
8, 9 are transistors, 10, 11, 12, 13, 14
is the output terminal. To explain the circuit configuration, photodiode 1 (hereinafter referred to as PD) is connected in a direction that provides a photocurrent proportional to the subject brightness, and diode 2
, 3, 4, and 5 are connected in series so that the photocurrent of PDl flows in the forward direction, and transistors 6, 7, 8, and 9 serve as forward terminals by the respective forward currents of the diodes 2, 3, 4, and 5. The voltage serves as a reference voltage between each base and emitter, and the base and emitter are connected so as to be biased in the forward direction.

The electrical characteristics of the diodes 2, 3, 4, and 5 are the same as those between the bases and emitters of the transistors 6, 7, 8, and 9 connected to both ends of the diodes. Next, in this circuit configuration, the photocurrent due to PDl is
The circuit operation in which the current is amplified to a base 2 geometrically multiplied current will be described.

Generally, in a semiconductor having a PN junction structure, the following equation holds true between forward terminal voltage and forward current.

IF=Is-Exp(q-VFA-T)...
・(1) Here, IF is the forward current, Is is a constant determined by the structure and material of the semiconductor, q is the electron charge, k is the Boltzmann constant, T is the absolute temperature, and VF is the forward terminal voltage. be.

Therefore, in the case of the present invention, diodes 2, 3, 4, 5
Since the characteristics of and the base-emitter characteristics of transistors 6, 7, 8, and 9 are set to be the same,
Diodes 2, 3, 4, 5 and transistors 6, 7, 8,
It is clear from equation (1) that if the forward terminal voltages F between the base and emitter of transistors 9 are made equal, the respective forward currents 1F (collector currents in the case of transistors) become equal.

Therefore, in such a circuit configuration, the forward current of the diode and the collector current of the transistor, which is equal to the forward current, are added and flow as the forward current of the next diode.

Now, if the photoelectric current due to PDl is IO, then the forward current 1F1 of diode 2 is 1F1=IO-1B1...
. . . {2) However, the base current IBl of the transistor 6 is extremely small compared to IO and can be ignored, so it becomes IFl'-10.

The forward terminal voltage due to the forward current 1F1 of the diode 2 is the terminal voltage between the base and emitter of the transistor 6, and therefore the collector current 1 of the transistor 6.1 is the forward current 1F1 of the diode 2 mentioned above.
is equal to

Therefore, IFl and ICl are added and output to the output terminal 11, and IFl+Icl=IO+
An output current of IO=210...{3) is obtained.

Next, considering the forward current 1F2 of the diode 3, the aforementioned output current is not only supplied to the output terminal 11 but also flows into the diode 3. This means that the output current 210 is output to .

Therefore, the forward terminal voltage due to the forward current IF2 of the diode 3 is applied between the base and emitter of the transistor 7, so that the forward terminal voltage F of the PN junction semiconductor, which satisfies the above equation (1), is equal to that of the diode. 3 is equal to transistor 7, and the forward current of diode 3 is 1
The relationship between F2 and the collector current 1C2 of the transistor 7 is IF2 - IC2. Therefore, an output current obtained by adding IF2 and IC2 described above is obtained at the output terminal 12, and its value is IF2+IC2=21F2=2(2
10)=410...-<4).

In the circuit configuration according to the present invention, since the above relationship also holds between the diodes 4 and 5 and the transistors 8 and 9, the output terminals 13 and 14 have 8 transistors, respectively.
An output current of 10,1610 is output.

}, the photocurrent 10 of PDl is output as is to the output terminal 10. Here, each output terminal 10, 11, 12,
The current output to 13 and 14 is the photocurrent 10 due to PDl.
2010, 2110, 22, respectively.
0, 2310, 2410, and each output terminal 10, 11, 12, 13, 14 has the photocurrent 10 multiplied by the base 2, that is, 2n (n=0, 1, 2, 3 ，
4) Double the amplified current is output. In this way, the current amplification circuit of the present invention can amplify the photocurrent generated by the photoelectric conversion element to the base of 2 without adjustment by applying the unique characteristics of the transistors and diodes. .

FIG. 3 is an example in which the current amplification circuit of the present invention is applied to a camera.

In the figure, 15 is the output terminal 10, 11 of the current amplification circuit of the present invention.
, 12, 13, and 14,
16 is an integrating capacitor that integrates the photocurrent amplified by 2n times flowing through the switch 15; 17 is a switch that opens in conjunction with the opening operation of the shutter and controls the integrating operation of the integrating capacitor 16; 18 is a reference voltage; A comparison circuit 19 generates an output signal when the reference voltage and the voltage of the integrating capacitor 16 become equal, and a relay switch 19 is activated by the output signal from the comparison circuit 18 to control the shutter operation of the camera.

However, as mentioned above, the output current amplified to the base of 2 is output to the output terminals 10, 11, 12, 13, and 14. Therefore, the operation of the selector switch 15 is can be made to correspond to exposure determining factors such as aperture value and film sensitivity, but here, it is made to correspond to film sensitivity,
That is, it is assumed that the changeover switch 15 is changed depending on the film sensitivity. Now, assuming that the position of the changeover switch when the film sensitivity is ASAlOO is the output terminal 10, the integrating capacitor 16 integrates a current twice the photocurrent 10 by opening the switch 17 in conjunction with the opening operation of the shutter. The integral waveform becomes, for example, as shown in FIG. 4A.

When the integrated voltage of the integrating capacitor 16 reaches the reference voltage Vs of the comparator circuit 18, the comparator circuit 18 outputs an output signal, and the shutter is closed by the operation of the relay switch 19, that is, the shutter speed is set to t in FIG. This is the time required for the integrated voltage of the integrating capacitor 16 to reach the reference voltage 8, which is represented by . Here, the film sensitivity is AS
If A4OO is used, the film sensitivity will be four times as high, so at the above-mentioned shutter speed t in the case of ASAlOO, the exposure will be completely overexposed, and some kind of correction will be required.

By the way, the output terminal 11 of the current amplification circuit according to the present invention,
12, 13, and 14 output an output current that is the output current output from the output terminal 10 multiplied by a ratio of 2 to the base. By switching from to 12, it is possible to easily correct the film sensitivity by four times as described above.

That is, the output current from the output terminal 12 is four times the output current from the output terminal 10, and the integral waveform of the integrating capacitor 16 due to this four times the output current becomes as shown in FIG. 4B, and the waveform as shown in FIG. 4A. It has a slope four times as large as that of .

Therefore, the time it takes for the comparison circuit 18 to reach the reference voltage s becomes shorter, and as shown in FIG. 4, it becomes 1/4t compared to t in the case of ASAlOO, and the sensitivity of the film becomes four times that of ASA4OO. Since the shutter speed is also reduced to 1/4, proper exposure can be obtained. Furthermore, if the reference voltage s of the comparator circuit 18 is made to vary in conjunction with the aperture value, for example, automatic exposure corresponding to any film sensitivity and aperture value becomes possible. Of course, the same effect can be obtained even if the output terminal of the current amplification circuit according to the present invention is made to correspond to the aperture value and the reference voltage Vs of the comparator circuit 18 is made to correspond to the film sensitivity. FIG. 5 shows an example in which the current amplification circuit of the present invention is used in an electronic flash device. In the figure, 21 is a thyristor connected in series with a flash discharge tube 20, 22 is a commutation capacitor, and 23 is a commutation capacitor 22. The thyristor 24 that controls the discharge timing of the flash discharge tube 20 and the thyristor 21 is a main discharge capacitor and is configured to trigger the flash discharge tube 20 and the thyristor 21 at the same time.

In FIG. 5, parts with the same numbers as those in FIGS. 2 and 3 have the same functions. As shown in the figure, it is used as the light receiving section of the light quantity control circuit of a well-known serial control type electronic flash device, and in this case as well, as in the case of the camera described above, the light is The selector switch 15 selects the output terminal corresponding to the change in the exposure determining factors such as the aperture value, and controls the integral waveform of the integrating capacitor, that is, the output signal from the comparator circuit 18.

Therefore, if the switching of the changeover switch 15 is linked to, for example, the aperture value of the camera, and the aperture value is narrowed down by one step, the output terminal is switched to the amplification factor that is one step smaller, that is, when the aperture value of the camera is F4. If the position of the changeover switch 15 is set to the output terminal 14, and if the changeover switch 15 is set to the output terminal 13 when the aperture value is changed to F5 or F6, then the aperture value is large, that is, the aperture diameter is small, and a large amount of light is required. In such a case, the integrating capacitor 16 will integrate the output current with a small amplification factor, and the output signal generation time from the comparator circuit 18 will be delayed, so that the integrated voltage will be lower than that of the comparator circuit 18.
It takes a long time to reach the reference voltage of the flash discharge tube 20, and the light emission control timing of the flash discharge tube 20 is delayed, and even if the aperture diameter is small, sufficient light quantity can be obtained.On the other hand, when the aperture value is small and the aperture diameter is large,
Since the integrating capacitor 16 integrates the output current with a large amplification factor, the output signal of the comparator circuit 18 is generated early, and the flash discharge tube 20 is controlled to emit light at an earlier timing, which prevents overexposure even if the aperture diameter becomes larger. Appropriate exposure conditions can be obtained without having to

In this case as well, if the reference voltage of the comparator circuit 18 is changed in accordance with the film sensitivity, automatic flash photography can be performed with any film sensitivity and camera aperture value, and the reference voltage can also be changed to the aperture value. Of course, the same effect can also be obtained by associating the output terminal with the film sensitivity. As explained in detail above, the current amplification circuit of the present invention is capable of amplifying the photocurrent generated by a photoelectric conversion element to a base 2 ratio without adjustment by combining a diode and a transistor. It can be applied to various exposure controls for photographic equipment.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a conventional current amplification circuit including a photoelectric conversion element, Fig. 2 is a circuit diagram showing an embodiment of the current amplification circuit of the present invention, and Figs. A circuit diagram showing an example of application of the amplifier circuit, FIG. 4 is an integral waveform diagram of the integrating capacitor shown in FIG. 3. 1...Photodiode, 2, 3, 4, 5...
...Diode, 6,7,8,9...Transistor, 15...Switch, 18...
...Comparison circuit.

Claims (1)

[Claims] 1. A photoelectric conversion element, a plurality of diodes connected in series to the photoelectric conversion element so that the photocurrent generated by the photoelectric conversion element flows in the forward direction, and a base-emitter characteristic having the same electrical characteristics as the diode. a plurality of transistors having a plurality of transistors, a plurality of output terminals respectively connected to the anodes of the plurality of diodes, and one of the outputs obtained from the plurality of output terminals to be selected and output. each of the diodes is provided between the base and emitter of each of the plurality of transistors such that an anode is connected to the base of the transistor and a cathode is connected to the emitter of the transistor; Each of the transistors is connected to the emitter of the other transistor, and the base of the first transistor among the plurality of transistors is connected to one end of the photoelectric conversion element. A current amplification circuit having a collector connected to the other end of the photoelectric conversion element.