JPS6230363B2 - - Google Patents

Description

Detailed Description of the Invention The present invention separates instantaneous pulsed light such as flash light, which exists superimposed on light whose brightness is constant over time, into an electrical signal corresponding to the brightness of this pulsed light. This invention relates to a detection circuit for detecting instantaneous light.

Conventionally, a circuit that separates and detects alternating current components such as instantaneous pulsed light that exists superimposed on light whose brightness is constant over time, that is, stationary light, converts incident light into a photocurrent according to its brightness. A commonly used circuit is one in which a load is connected in series with a photoelectric element, a capacitor is connected to the load, and only the voltage fluctuation component appearing at the load is extracted through the capacitor.

However, in the circuit using a resistor as the load described above, in order to generate a voltage between the terminals of the resistive load without saturating in response to wide changes in the brightness of stationary light, a power source that supplies a relatively large voltage is required. Requires. Therefore, it is possible to use a logarithmic compression element such as a diode instead of a resistive load, but in this case, the intensity of the signal corresponding to the pulsed light detected via the capacitor will depend on the intensity of the stationary light. Especially when the brightness of the steady light is high, the voltage change in response to the pulsed light appearing on the load becomes even smaller, and sometimes it becomes difficult to even detect the change itself.

The present invention provides an instantaneous light detection circuit that can operate with a low voltage source and is capable of detecting a signal according to the intensity of pulsed light that is superimposed on the steady light without being affected by the steady light. It is something.

Hereinafter, an embodiment of an instantaneous light detection circuit applied to a distance measuring device for an automatic focusing camera shown in the drawings will be described in detail.

FIGS. 1 and 2 show the basic configuration of a light beam projection type distance measuring device that applies the principle of triangulation and is suitable for a conventionally known automatic focusing device for a camera. In FIG. 1, light emitted from a light source 1 is focused into a beam by a condenser lens 2,
The light is irradiated toward an object on the optical axis 3. An imaging lens 4 is arranged at a position separated from the condensing lens 2 by a baseline length d with respect to its optical axis 3, and a plurality of photoelectric elements 9, 10, 11, and 12 are arranged on its imaging surface. ing. Now, in the drawing, each point 5, 6, 7 and 8 on the optical axis 3 corresponds to a photoelectric element 9, 10, 11
If the configuration is such that the images are formed on each of the light receiving surfaces of 5 and 12, for example, points 5, 6, 7, 8
If there is an object at the position of The incident light is called signal light to distinguish it from steady light such as sunlight). Therefore, by detecting which photoelectric element 9, 10, 11, 12 the signal light is incident on, the distance to the object can be determined. FIG. 2 shows a circuit that handles the output signals of the photoelectric elements, and each photoelectric element is connected to photoelectric conversion circuits 13, 14, 15, and 16 that convert the photocurrents generated by these elements into voltage signals. The output of each photoelectric conversion circuit is voltage comparison circuit 1
7, 18, 19 and 20, respectively. The other input of each voltage comparator circuit is connected to a constant reference voltage source 25 to provide a reference voltage for comparison. The output of each voltage comparison circuit is in registers 21, 22, 23 and 24.
is connected to the input. The clock inputs of these registers are also connected to the output of one shot 27. 28 is a light source driving circuit which drives the light source 1 to turn on for a certain period of time in response to the output pulse of the one shot 27. Here, when the switch 26 of the one shot 27 is closed based on the distance measurement command, a "high" level pulse is output from the one shot 27 for a certain period of time, and in response, a light beam is projected onto the object to be ranged. be done. In this way, a voltage signal corresponding to the intensity of the signal light is output from the photoelectric conversion circuit connected to the photoelectric element to which the signal light has arrived due to the reflection, and the level of this signal is determined by the voltage source 2.
When the voltage exceeds the voltage level No. 5, a "high" level voltage signal is output from the voltage comparator circuit under the signal series, and this is stored in the register. As seen above, this type of optical beam projection type distance measuring device has a simple structure in principle and operates in a simple manner, but to date it has not yet been put into practical use as a product built into a camera. It has not yet become a reality. One of the reasons that prevents this from being put into practical use is that the intensity of the signal light incident on each photoelectric element must be weak, and in addition, steady light such as sunlight is incident on the photoelectric element at the same time. This is probably because it is not easy to effectively separate and detect the components of the signal light.

The present invention solves the problem of effectively separating and detecting weak signal light components mixed with stationary light, which was considered difficult in the past, by introducing new circuit technology, and enables the above-mentioned type of measurement. The goal is to bring distance devices to practical use. That is, when putting this type of distance measuring device into practical use, the following must be taken into consideration. A light beam projection type distance measuring device must have a small size and power consumption, and furthermore, must have a low manufacturing cost. Attempts to satisfy such demands will result in many contradictory problems. For example, in order to facilitate the detection of signal light, the light emission intensity of the light source may be increased, but this increases the power consumption of the device and also increases its size. On the other hand, if the base line length d is also shortened in order to make the shape smaller, the precision of the optical system must be made higher, leading to an increase in the manufacturing cost.

On the other hand, there are constraints necessarily imposed by the geometrical and optical aspects of this type of device. As is clear from simple calculations, for example, in the configuration shown in Figure 1, the distances from lens 2 to points 5 and 8 are 1 m and 5 m, respectively, the baseline length d is 25 mm, and the focal length of lens 4 is 20 mm. Then, photoelectric elements 9 and 12
The distance is 400μ. Therefore, the arrangement pitch of each photoelectric element is approximately 130 if they are arranged at equal intervals.
becomes μ. By the way, an image having a size of 130 μ on the imaging plane of the lens 4 corresponds to a light source having a size of about 7 mm at the position of the point 5 at a distance of 1 m, for example. This means that the width of the cross section of the light beam projected towards the object must be less than 7 mm at point 5. If the cross-sectional width of the light beam is larger than this, the signal light will also enter the adjacent photoelectric element even though it is unnecessary. For this reason, in this ranging system,
It is required to form an extremely narrow light beam.

Assume now that a light beam is formed by focusing an image of a light source 1 having a fixed light emitting surface at a finite distance using a condensing lens 2, as shown in FIG. If the distance between the light source 1 and the lens 2 is 20 mm, and the distance from the lens 2 to the imaging point is 2 m, the image for the light source 1 at this point will be magnified 100 times. The cross-sectional width of the light beam at this point is 10
In order to make the width less than mm, the width of the light emitting surface of the light source 1 must be less than 100μ.

Furthermore, as can be seen from FIG. 3, the light beam spreads out after passing the imaging point 10 of the lens 2, and its cross-sectional area gradually increases. Therefore, when forming a narrow light beam using the condensing lens 2, the light emitting area of the light source 1 must be made small enough to approach a point light source. Light emitting diodes are usually the most likely candidate for a light source that meets the constraint of having a light source with an extremely small light emitting area. However, when a light emitting diode is used as the light source 1, it is impossible to make the light emission intensity that much higher than that of steady light due to the structure of the light emitting diode, and therefore, bright signal light cannot be expected.

The present invention provides a method for detecting signal light whose intensity is extremely small compared to steady light, such as when a light emitting diode is used as the light source 1, in which temporal changes are relatively small in a photoelectric conversion circuit including a photoelectric element. A current control circuit that allows only the photocurrent corresponding to slow steady light to pass through, and a current control circuit that accepts the increased photocurrent when the photocurrent increases with a fairly steep temporal change, is installed to control the influence on the intensity of the steady light. The first feature is that an instantaneous light detection circuit is provided that extracts a signal according to the brightness of signal light without receiving it.

One embodiment of the present invention includes a photoelectric element, a current control element connected in series with the photoelectric element, an input connected to a connection point between the photoelectric element and the current control element, and an output of the current control element. a buffer circuit connected to the control electrode; a first capacitor connected to the buffer circuit so as to maintain a control voltage applied to the control electrode of the current control element; and a base connected to the connection point; It is characterized by including an input transistor in which a photocurrent generated in response to instantaneous pulsed light incident in addition to steady light is applied to the photoelectric element, and a current corresponding to the photocurrent is output from the collector. The present invention provides an instantaneous light intensity detection circuit.

The present invention will now be described in detail with reference to FIGS. 4 to 13. Note that in the drawings, the same numbers indicate similar parts.

FIG. 4 is a diagram showing the basic configuration of a photoelectric conversion circuit according to the present invention. In FIG. 4, the first current circuit has a transistor 31 whose collector is connected to the anode of the photoelectric element 30, an input is connected to a connection point 32 between these two elements, and an output is connected to the base of the transistor 31. It is composed of a buffer circuit 33 and a delay capacitor connected between the base and emitter of the transistor 31. The transistor 31 is controlled so that a photocurrent corresponding to light that is regularly incident on the photoelectric element 30 flows as a collector current. From the connection point 32 to the transistor 3 constituting the second current circuit
The circuit via the base emitter 5 receives a photocurrent corresponding to the light incident on the photoelectric element 30 in an impulse manner in addition to the constant light. The constant current source 36 is
This is provided to maintain the collector current of the transistor 35 at the constant current value when only steady light is incident on the photoelectric element 30, regardless of the magnitude of the photocurrent due to the steady light. A capacitor 37 connected in parallel with the constant current source 36 is a transistor 3.
5. Suppresses rapid fluctuations in emitter potential. Transistors 38 and 39 form a current mirror circuit, and a current similar to the collector current of transistor 35 is output from the collector of transistor 39. A load 40 for extracting a photoelectrically converted signal is connected to the collector of the transistor 39. A constant current source 41 connected to the base of the transistor 35 supplies a dummy current that plays the role of a photocurrent in response to constant light of a specific intensity when no light is incident on the photoelectric element 30. In other words, the constant current source 41 is not directly involved in the signal light detection operation, but rather assists the circuit operation to maintain the transistors 31 and 35 in a steady state even in the absence of steady light. be.

In the circuit configured as above, first,
The operation of the first current circuit including the transistor 31 is controlled between the collector of the transistor 31 and the transistor 35.
Consider separating the base from the constant current source 41 and excluding the constant current source 41. It is now assumed that only light with a constant intensity that does not vary over time is incident on the photoelectric element 30. A photocurrent corresponding to the incident light at this time flows as a collector current of the transistor 31. This is because the collector of the transistor 31 is in a state where negative feedback is applied via the buffer circuit 33, and this negative feedback operation causes the base of the transistor 31 to change to the voltage necessary to convert the photocurrent into the collector current. This is because it becomes biased.
On the other hand, when only stationary light is incident on the photoelectric element 30, the capacitor 34 is merely charged to the above bias voltage and does not participate in the circuit operation. Here, a case will be considered in which impulse light is incident on the photoelectric element 30 in addition to steady light. The rise of this impulse light is caused by the output resistance of the buffer circuit 33 and the capacitor 34 where the signal delay function is utilized.
It is assumed that the time constant is sufficiently fast compared to the time constant of the time constant circuit consisting of. When such impulse light is incident, the base of the transistor 31 is maintained at a bias voltage corresponding to the photocurrent due to the steady light before the impulse light is incident, in a time region shorter than the time constant. Therefore, during this period, the transistor 31 is still in a state where only the photocurrent due to the steady light can flow.
Due to its collector characteristics, the transistor 31 exhibits extremely high resistance to the photocurrent that increases due to the incidence of impulse light. The behavior of the first current circuit including such a transistor 31 occurs in a wide range of intensity of stationary light.

Next, to explain the photocurrent detection operation according to the impulse light using the circuit shown in FIG. 4, the photoelectric element 3
In a steady state where only steady light is incident on the transistors 35 and 38, the constant current source 3
A constant current of 6 is applied. Naturally, the transistor 35 requires a base current, and this base current is filled with a portion of the photocurrent. Even if there is no steady light and no photocurrent is generated, the constant current source 4
The base current of the transistor 35 is guaranteed by the dummy current of 1. In steady state,
Regardless of the intensity of the stationary light, the transistor 35 flows a constant current determined by the constant current source 36. Next, when impulse light is incident on the photoelectric element 30 and a photocurrent corresponding to the impulse light is generated, as described above, the transistor 31 exhibits an extremely high resistance to this increased current, and prevents it from passing through. Thus, the potential at the collector of transistor 31 increases, and the increased photocurrent flows into the base of transistor 35. The base current corresponding to this increase is amplified by the transistor 35 and appears as its collector current. As described above, the photocurrent corresponding to the impulse light is generated by the transistor 35, which in a steady state flows a constant collector current regardless of the intensity of the steady light.
It is taken out as an amplified collector current at . In addition, in the above operation, the capacitor 37, like the capacitor 34, acts to keep the inter-terminal voltage constant. Due to this effect,
The increased photocurrent is allowed to flow into the base of transistor 35 as base current. Now,
The amplified photocurrent can be converted into a voltage signal by connecting a load to the collector of transistor 35. Note that the same effect can be obtained even if the transistor 31 as the current control element is replaced with a field effect transistor. Further, the constant current source 36 can also be omitted.

Next, a specific embodiment of the voltage signal conversion circuit will be described with reference to FIG.

FIG. 5 shows a configuration of the photoelectric conversion circuit shown in FIG. 4 into a circuit suitable for a semiconductor integrated circuit. In FIG. 5, the buffer circuit 33 in FIG.
The transistor 35 and the capacitor 37 that constitute the second current circuit also serve as the capacitor 34, respectively. That is, transistor 35
The base of the transistor 31 is in a state where negative feedback is applied through the transistor 31, and due to the operation of this negative feedback, the base of the transistor 31 is biased with the voltage necessary to convert the photocurrent into the collector current. Become. The cathode of the photoelectric element 30 is connected to the transistor 4, which is the output of a constant voltage circuit composed of a constant current source 42, transistors 43, 44, and 45.
It is connected to the base of 4. transistor 44
A voltage that is the sum of the base-emitter voltages of the two transistors 44 and 45 is output as a constant voltage from between the base and ground. On the other hand, between the anode of the photoelectric element 30 and the ground, the sum voltage between the bases and emitters of the two transistors 31 and 35 appears. These two voltages are approximately equal, so even if there is a potential difference between both terminals of the photoelectric element 30, the value is small, so it can be considered that a short circuit current is output from the photoelectric element 30. . The base and collector of transistor 38 are connected through the emitter and base of transistor 46. The collector of the transistor 39 is loaded with a transistor 47 as a first load, and a series circuit as a second load consisting of three transistors 48, 49 and 50 diode-connected to form a logarithmic compression circuit. It is connected.

Further, the collector of the transistor 39 serving as a signal output terminal is connected to the inverting input terminal 56 of the operational amplifier 55. The other input terminal 57 of this operational amplifier 55 is connected to a constant current source 5 serving as a reference voltage source.
2 and the collector of the transistor 53. A constant current source 52 and two diode-connected transistors 53 and 54 are connected to the connection point.
The base-emitter voltage V of the transistor is
A constant voltage of 2V _BE is created for two _BEs . The output 58 of the operational amplifier 55 is connected to the base of a transistor 59, and a diode-connected transistor 60 is connected between the collector of the transistor 59 and ground. In addition, the transistor 60
A capacitor 61 is connected in parallel with. The base of the transistor 60 is the transistor 4.
It is connected to the base of 7. Thus, the signal output terminal 51 is connected to the operational amplifier 55 and the transistor 5.
Negative feedback is applied via 9, 60 and 47.

In the circuit of FIG. 5 configured as above,
First, a case where only steady light is incident on the photoelectric element 30 will be considered. In this case, the photoelectric element 30
The photocurrent generated by the current source 41 and the dummy current from the current source 41 flow through the transistor 31 as its collector current, except for the portion that becomes the base current of the transistor 35. A constant current from a current source 36 is passed through the collector of the transistor 35. The capacitor 37 is charged to a base-emitter voltage corresponding to the collector current of the transistor 31.
In such a steady state, the collector current of transistor 39 is constant, and transistors 38 and 39
If the shapes and characteristics of the transistors 35 and 35 are the same,
If the emitter areas of both transistors are made different, the current will be proportional to the area ratio. When the collector current of the transistor 39 is constant, the voltage between the signal output terminal 51 and the ground becomes the voltage between the non-inverting input terminal 57 and the ground due to the negative feedback effect of the operational amplifier 55, that is, the voltage between the two transistors 53 and the ground connected in series. The base-emitter voltage 2V _BE of the two bases due to 54 is equal to the reference voltage. In this case, transistor 39
Most of the constant collector current from the transistor 47 flows as the collector current of the transistor 47 for the following reason. Now, between the output terminal 51 and the ground is 2
The voltage is maintained at V _BE . Therefore, this voltage of 2V _BE is applied to the series circuit made up of the three transistors 48, 49, and 50. That is, the base of each transistor
A voltage of 2/3V _BE is applied between the emitters. For example, if V _BE =540 mV, the voltage applied to each of transistors 48, 49, and 50 is 360 mV, which is 180 mV smaller than V _BE . Due to its logarithmic characteristics, the collector current of a transistor changes by about 1000 for a 180mV change in base-emitter voltage. Therefore, in a steady state, only about 1/1000th of the current flowing through the series circuit of transistors 53 and 54 flows through the series circuit of transistors 48, 49, and 50, which is the second load. For example, the series circuit 53,5
If the current flowing through transistor 4 and the collector current of transistor 47 are both 4 μA, the current flowing through transistors 48, 49, and 50, which are the second loads, will be about 4 nA.

Next, the operation when signal light is incident on the photoelectric element 30 in addition to the steady light will be described. The base of the transistor 31 is biased so that only a constant collector current for ambient light flows.
Therefore, the increase in photocurrent with respect to the incidence of signal light on the photoelectric element 30 flows into the base of the transistor 35 as in the case of FIG. The photocurrent corresponding to the signal light flowing into the base is amplified by the transistor 35 and converted into a collector current of the transistor 39. Similar to the case of the transistor 31, the transistor 47 exhibits extremely high resistance against a sudden increase in the collector current of the transistor 39. This is due to the delay effect of the capacitor 61 on the base and emitter of the transistor 47. Therefore, the increased collector current flows into the series circuit of transistors 48, 49, and 50, which is the second load. Since this second load is a diode load, it is proportional to the logarithm of the supplied current. In other words, a logarithmically compressed voltage is generated across the terminals of the load. Let us now quantitatively consider how much voltage signal is generated by the second load in response to the incidence of signal light. Now, assume that the current value of the constant current source 36 is 0.4 μA, and the current amplification factor h _FE of the transistor 35 is 100. It is assumed that the emitter area of transistor 39 is ten times larger than that of transistor 38. If this is the case, in the steady state, the collector current of transistor 39 is
The collector current (0.4 μA) of No. 8 is 4 μA, which is 10 times the collector current (0.4 μA). Also, the base current of the transistor 38 is
It becomes 4nA. Note that the current value of the constant current source 41 may be set to be larger than 4 nA. On the other hand, the transistors 48, 49, and 50 forming the second load and the transistors 53 and 54 forming the constant voltage source each have the same shape and characteristics, and a voltage of 540 mV is generated from the constant voltage source. shall be. In this case, as mentioned above, the second load
A current of 4nA will flow. Now, assume that a signal light is incident on the photoelectric element 30, and a photocurrent of 100 PA is generated in response. As mentioned above, this photocurrent flows into the base of the transistor 35,
It is multiplied by 100 by transistor 35 and further multiplied by 10 by transistor 39, amplified to 100 nA, and appears at the collector of transistor 39. this
A collector current of 100 nA is passed to the second load. In the state before the signal light is incident, a current of 4 nA was flowing through the second load, so the current increase in the second load is 25 times. In general, for a doubling of the collector current of a transistor, the base
Since the emitter voltage increases by 18 mV (at an ambient temperature of 25°C), for a 25 times increase in collector current, approximately
Increase by 83mV. Therefore, for the entire second load
Increases by about 250mV. Thus, the signal light corresponding to a photocurrent of 100 PA was converted to a voltage of 250 mV. Next, the photocurrent due to the signal light is 100nA (in the above case
1000 times), the current flowing into the second load is 100 μA, which corresponds to an increase of 2500 times. Therefore, from the second load
A voltage signal increased by about 610mV is output.

The above is the operation of converting the signal light into a voltage signal according to its intensity. Note that it is clear that the voltage signal output from the terminal 51 has an impulse-like waveform even if the signal light has a step-like shape. Therefore, in order to save energy of the light source, the signal light may be an impulse-like single light emission.

As described in detail above, by using the photoelectric conversion circuit shown in FIG. 5, it is possible to separate and detect the signal light from the stationary light in a wide brightness region of the stationary light. Note that in the embodiment of FIG. 5, the function of the second load by the transistors 48, 49, and 50 is replaced by
This can be done by connecting a diode 48' between the collectors of transistors 39 and 53 as shown in the figure. However, in this case, the constant current value of the constant current source 52 is set to be sufficiently larger than the current value corresponding to the signal light output from the transistor 39 so that the collector potential of the transistor 53 is kept constant. . Further, a circuit configuration is provided in which the collector of the NPN transistor 47, which is one of the loads, is connected to the collector of the PNP transistor 39.
This portion can also be constructed into a circuit as shown in FIG. 11 by adding two transistors 39' and 47'. In either case, the collector characteristics of the transistor serving as the first load are utilized.

Now, if the photoelectric conversion circuit of FIG. 5 is applied to blocks 13, 14, 15, and 16 in FIG.
In principle, it is possible to perform distance detection, but there are still problems that need to be resolved for practical use. Now, suppose that the emitted light beam is sufficiently narrow and ideal, and the image of the "bright area" on the object irradiated by this beam is as shown in Figure 6. Even if the light components are connected on a specific photoelectric element according to the distance from It is. This is because the signal light incident on a specific photoelectric element to form an image is reflected on the light receiving surface of that photoelectric element, and the reflected light is further reflected on the imaging lens surface. This is because internal reflections occur within the provided housing. Furthermore, the actual light beam is
As shown in Figure 3, the cross-sectional area changes depending on the distance, the distribution of light also changes, and with the addition of components due to the aberration of the light projecting lens 2, the result is considerably far from ideal. I end up. Moreover, the imaging lens 4 forms a sharp image only of powder at a specific distance. As described above, the signal light is incident not only on a specific photoelectric element depending on the distance to the object, but also on other photoelectric elements. For example, as shown in Figure 6, the intensity distribution of the incident light on the array surface of the photoelectric elements shows that the signal light is incident toward photoelectric element _P3 , but it is also incident on the remaining three photoelectric elements. .
Therefore, it can be seen that distance cannot be detected only by detecting whether or not signal light is incident on each photoelectric element. Therefore, in order to detect that the signal light is incident on the photoelectric element P ₃ in FIG. 6, the output signal of the photoelectric conversion circuit including the photoelectric element P ₃ and the output signal of the other photoelectric conversion circuit In order to determine this, for example, it is sufficient to determine the level of the reference voltage source 25 for voltage comparison in FIG. 2. However, since the intensity of the signal light varies depending on the distance to the object and its reflectance, appropriate discrimination cannot be performed by fixing the level of the reference voltage source 25. Therefore, it is conceivable to change the reference voltage level according to the intensity of the signal light in order to detect the target distance signal.

Hereinafter, a reference voltage changing circuit that changes the reference voltage level according to the intensity of signal light and a distance measuring device to which this circuit is applied will be described.

First, to explain the relationship between the output signal of the photoelectric conversion circuit and _the reference voltage using _FIG . One of the output signals of the photoelectric conversion circuit is shown. The voltage level S ₁ corresponds to the collector potential of the transistor 53 in the circuit of FIG. 5, and also corresponds to the output level of each photoelectric conversion circuit in a steady state. The voltage level S ₂ is a constant reference level that is set higher than the voltage level S ₁ plus the amplitude of noise included in the output of each photoelectric conversion circuit in a steady state. The voltage signal _S3 is a reference voltage that is changed depending on the signal light targeted here. This reference voltage _S3 is
As described below, it is produced using the output signal A ₁ that reaches the voltage level S ₂ first among the outputs of each photoelectric conversion circuit.

Hereinafter, the structure and operation of an embodiment of the reference voltage changing circuit that generates the reference voltage _S3 will be explained with reference to the circuit shown in FIG. 8, which shows the overall structure of an automatic focusing device. In FIG. 8, a circuit portion surrounded by a dotted line 70 constitutes the above-mentioned reference voltage changing circuit. In this reference voltage change circuit, each non-inverting input of operational amplifiers 71, 72, 73, and 74 is connected to the output of photoelectric conversion circuits 13, 14, 15, and 16, respectively. Note that the circuit shown in FIG. 5 is used for these photoelectric conversion circuits. The outputs of operational amplifiers 71, 72, 73, 74 are connected to transistors 75, 7 whose collectors are connected to the positive terminal of the power supply.
6, 77, and 78 bases, respectively. The emitters of these transistors are connected to the inverting inputs of the operational amplifiers 71, 72, 73, and 74, respectively, and one end 85 of the resistor 79
are commonly connected. The other end of the resistor 79 is connected to a node 86 between the emitter of the transistor 82 and the resistor 83, and the node 86 is connected to each inverting input of the voltage comparison circuits 17, 18, 19, and 20. The other end of the resistor 83 is connected to a constant current source 84 and to the inverting input of the operational amplifier 81 . The non-inverting input of this operational amplifier 81 is connected to the constant voltage source 80, and the output is connected to the transistor 82.
connected to the base of Here, constant voltage source 8
0, the constant voltage source constituted by the constant current source 52 and transistors 53 and 54 in the photoelectric conversion circuit of FIG. 5 is also used. Therefore,
The voltage level that constant voltage source 80 provides to the non-inverting input of operational amplifier 81 is equal to level S ₁ in the graph of FIG. Note that the resistor 79 is divided into voltage comparison circuits 17, 18, 1 as shown in FIG.
It may be connected to the inverting inputs 9 and 20 to change their respective levels.

As for the operation of the reference voltage changing circuit having the above configuration, in the circuit shown in FIG.
7, 18, 19, and 20 were given a constant voltage by a constant voltage source 25. In the circuit shown in FIG. A voltage that changes over time is applied according to the output signal of the photoelectric conversion circuit.

Now, in FIG. 8, let's first consider the case where only stationary light is incident. In this case, the photoelectric conversion circuit is at level S ₁ in the graph of FIG.
It outputs a voltage of . On the other hand, since the voltage at level S ₁ is also input to the non-inverting input of operational amplifier 81, the level of the inverting input of operational amplifier 81 is also maintained at level S ₁ by the action of negative feedback via transistor 82 and resistor 83. It's dripping. Therefore, connection point 8
6, a voltage of level S ₂ higher than level S ₁ by the voltage drop across resistor 83 due to the current of constant current source 84 appears, and this voltage of level S ₂ is applied to operational amplifier 7.
1, 72, 73, 74 and voltage comparison circuit 17,
It is applied to each inverting input of 18, 19, and 20. Therefore, the respective outputs of the operational amplifier and the voltage comparison circuit all output "low" level voltages, and the transistors 75, 76, 77, and 78 are in a cut-off state. Therefore, no current flows through the resistor 79, and the connection points 85 and 8
6 is at the same potential _S2 .

Next, a description will be given of the operation when a voltage signal corresponding to signal light is output from the photoelectric conversion circuit. For example, assume that the photoelectric conversion circuit 14 outputs a voltage signal that first reaches level _S2 , such as waveform _A1 in the graph of FIG. This waveform A ₁ is initially at level S ₁ and rises as the signal light is incident. Now, when this waveform _A1 reaches the level _S2 , the output of the arithmetic circuit 72, which has been at the "low" level, starts to turn to the "high" level, and the transistor 76 has its base forward biased. become. In this way, the operational amplifier 72 becomes capable of negative feedback operation via the transistor 76, and the voltage level of its inverting input changes to equally follow the non-inverting input, that is, the output voltage _A1 of the photoelectric conversion circuit 14. Arithmetic amplifiers 71, 72, 73, 7
Since the inverting inputs of transistors 4 and 4 are at a common potential, in the current state, except for the operational amplifier 72, the voltage level of the inverting input is still higher than that of the non-inverting input, and the transistors 75, 77, 78 is placed in a blocked state. Thus, connection point 85
The voltage level moves to follow the output voltage waveform _A1 from _t1 to _t2 while the output voltage of the photoelectric conversion circuit 14 is higher than the level _S2 . When the waveform _A1 exceeds the level _S2 , the emitter current of the forward biased transistor 76 flows through the resistors 79 and 83.
The current flows into the constant current source 84 via. Then, the inverting input of the operational amplifier 81 is pulled up to a voltage level higher than the level _S1 , and the operational amplifier 81 outputs a "low" level voltage. Thus, the transistor 82 is placed in a cut-off state, and a voltage from the connection point 86 is lower than the voltage level at the connection point 85 by a constant voltage υc corresponding to the product of the resistance value of the resistor 79 and the constant current value of the constant current source 84. A signal _S3 is output. This voltage signal _S3 is used as a comparison reference voltage in voltage comparison circuits 17, 18, 19, 20.
The magnitude of each output signal of the photoelectric conversion circuit is compared and detected based on this voltage.

In this way, between t ₁ and t ₂ , in the above example, the voltage comparison circuit 18 outputs a "high" level ("1") voltage. Photoelectric conversion circuit 1
If the output signal from the source other than 4 is as shown by waveform _A2 in FIG.
From 0, a "low" level ("0") voltage is output. The above has been about the operation when the output of the photoelectric conversion circuit 14 is relatively large compared to others, but the same operation applies to the output of any photoelectric conversion circuit. In addition, if the main part of the signal light is incident toward the middle part of two adjacent photoelectric conversion elements, the outputs of the photoelectric conversion circuits corresponding to these photoelectric elements will both be at the screening voltage at the same time.
It will be higher than the level of S ₃ . Furthermore, depending on the state of the intensity distribution of the signal light on the array surface of the photoelectric elements, a case may occur in which three outputs of the photoelectric conversion circuit exceed the discrimination level at the same time. The above is the operation of the reference voltage changing circuit.

Here, the overall operation of the circuit device shown in FIG. 8 will be described. Assume that the circuit device is now ready for operation and power is being supplied to each part of the circuit. A capacitor 108 that stores the light emission energy of the light emitting diode 1 is charged with a power supply voltage via a resistor. The optical axis of the light projecting lens 2 is directed toward the object to be photographed, and the switch 26 is closed. In response, one shot circuit 27
A “high” level (“1”) voltage signal is emitted for a certain period of time. This voltage signal makes transistors 105 and 106 conductive, and the charges in capacitor 108 are discharged at once through transistor 106 and light emitting diode 1. In this way, an impulse-like light beam is emitted toward the subject.
At the same time, the "1" signal from the one shot circuit 27 is input to the registers 21, 22, 23, 24, 87.
cp and input D of register 87.
Note that 88 is a reset pulse generation circuit that generates a reset pulse for resetting these registers when a power switch (not shown) is turned on. When the register is reset, the output becomes "0". A beam of light is emitted, as described above,
“1” from any one or two or three adjacent voltage comparator circuits 17, 18, 19, and 20
signal is output. However, depending on the subject, a signal of "1" may not be output at all. For registers 21, 22, 23, 24, and 87, when "1" is input to the two inputs D and cp at the same time, the output is set to "1", and even if the input becomes "0" afterwards, the output is not reset. The output "1" state is maintained until the output is turned off or the power is turned off. Incidentally, each register is constructed using an AND gate and an R-S flip-flop as shown in FIG. Now, when a signal of "1" is output from the voltage comparator circuit 18, "1" is output from the one shot circuit 27 along with this signal.
The output of the register 22 is set to the "1" state by the signal. At this time, register 8
7 is also set to "1" to record that the light beam was emitted. Signals from the register group are converted by a decoder 89 into output signals corresponding to short distance and long distance as shown in FIG. 9, for example. After the distance information is collected in the register group, the photographing lens 100 is retracted from the closest position to an infinite position by an appropriate driving means, and in conjunction with this operation, the brush 99 is retracted from, for example, eight contact points. Single terminal 90
- slid over 97 and 98. Connect the brush 99 to the contact terminal, for example 92, which outputs “1”.
When the base current flows through the brush 99 and the contact piece 98, the transistor 101 becomes conductive. Due to this conduction, the transistor 102
is cut off, the excitation of the electromagnet 103 is cut off, and the locking lever 104 is operated to lock the retracting operation of the lens 100. The distance of the photographing lens is automatically adjusted to a position according to the distance information detected in this manner. As described in detail above, the introduction of the reference voltage changing circuit makes it possible to put a light beam projection type distance measuring device into practical use, and its effects are extremely large.

As described above, the present invention includes a photoelectric element, a first current circuit having a current control terminal to which the photocurrent of the photoelectric element is input, and a first current circuit that responds to the photocurrent of the photoelectric element and increases when the photocurrent increases. a control circuit that controls the voltage level of the current control terminal so that the current flowing through the first current circuit also increases;
a voltage maintenance circuit that is connected to the current control terminal of the current circuit and maintains the voltage level of the current control terminal at the level before the sudden change in response to a sudden change in the photocurrent, and an input of the first current circuit; connected to
Instantaneous light detection characterized by having a second current circuit that branches the difference between the current of the first current circuit and the photocurrent, and detecting instantaneous light from the current branched to the second current circuit. This is a newly created circuit and has great practical value as it can reliably detect instantaneous light with a simple circuit configuration.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the principle of triangulation, Fig. 2 is a circuit diagram for processing the output signal of the conventionally used photoelectric element shown in Fig. 1, and Fig. 3 is an explanatory diagram of the condensing lens. Figure 4 is a circuit diagram of photoelectric conversion according to the present invention,
Figure 5 is a circuit diagram showing another embodiment of Figure 4;
The figure is an intensity distribution diagram of the incident light of the photoelectric element, Figure 7 is a relationship diagram between the output signal of the photoelectric conversion circuit and the reference voltage, Figure 8 is a circuit diagram in which the photoelectric conversion circuit is incorporated into an automatic focus adjustment device, and Figure 9 is a diagram of the relationship between the output signal of the photoelectric conversion circuit and the reference voltage. The figure is an explanatory diagram of the output signal of the decoder of FIG. 8, FIGS. 10 and 11 are circuit diagrams each showing a partial modification of FIG. 5, and FIGS. FIG. 7 is a circuit diagram showing a modification of the section. 30... Photoelectric element, 31, 35... Transistor, 33... Buffer circuit, 34, 37... Capacitor, 36, 41... Constant current source.

Claims (1)

[Claims] 1. A photoelectric element, to which a photocurrent of the photoelectric element is input,
a first current circuit having a current control terminal; and controlling the voltage level of the current control terminal in response to the photocurrent of the photoelectric element such that as the photocurrent increases, the current flowing through the first current circuit also increases. a voltage maintenance circuit that is connected to the current control terminal of the first current circuit and maintains the voltage level of the current control terminal at the level before the sudden change in response to a sudden change in the photocurrent; a second current circuit that is connected to the input of the first current circuit and branches the difference between the current of the first current circuit and the photocurrent; An instantaneous light detection circuit characterized by detecting light. 2. In the circuit described in claim 1 above, the photoelectric element is a photodiode;
and the first current circuit includes a first transistor having a collector connected to the anode of the photodiode, and the second current circuit further includes a second transistor having a base connected to the anode of the photodiode. What to do. 3. In the circuit according to claim 2, the emitter of the second transistor is connected to the base of the first transistor, and further a constant current circuit is connected between the base and emitter of the first transistor. A capacitor is connected in parallel, and the collector of the first transistor is subjected to negative feedback via the base and emitter of the second transistor. 4. The circuit described in claim 2 above is characterized in that a buffer circuit is provided between the collector and base of the first transistor, and negative feedback is applied via the buffer circuit. thing. 5. The circuit according to claim 4, characterized in that the delay characteristic is imparted by a capacitor connected to the output section of the buffer circuit.