JPH0629232U - Photoelectric detector - Google Patents

Abstract

(57) [Summary] [Object] The present invention aims to make the amplitude of the final output voltage almost constant regardless of the influence of ambient light. [Configuration] A second detection circuit 22 is provided in parallel with the first detection circuit 21, and an operating threshold value of the second detection circuit 22 is set higher than that of the first detection circuit 21 by a threshold circuit 36. The output voltage of both the detection circuits 21 and 22 is added and the addition circuit 23 outputs the added voltage. [Effect] Therefore, it is possible to detect all the changes in the current flowing through the phototransistor 25 and reflect them in the output voltage of the adder circuit 23, and when the light emission output of the LED 24 is modulated at a predetermined frequency, the influence of ambient light can be reduced. The amplitude of the output voltage of the adder circuit 23 can be made substantially constant regardless of the relationship.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a photoelectric detection device used for optical multiplex communication of an automobile and applied to an optical switch or the like which is turned on or off by blocking an optical path.

[0002]

[Prior art]

 Conventionally, a photoelectric detection device applied to an optical switch or the like which is turned on by blocking an optical path is configured as shown in FIG. 3, for example.

That is, the inverting input terminal of the operational amplifier 4 of the detection circuit 3 is connected to the collector of the phototransistor 2 that receives light from the light emitting diode (hereinafter referred to as LED) 1 through the gain setting resistor 5, The reference power source 6 is connected to the non-inverting input terminal of 4 and the ground, and the feedback resistor 7 is connected to the output terminal of the operational amplifier 4 and the inverting input terminal. A detection circuit 3 is constituted by 7, and when the phototransistor 2 receives light, a photocurrent flows through the resistors 7 and 5 to the collector and emitter of the phototransistor 2.

Further, the inverting input terminal of the comparator 8 is connected to the collector of the phototransistor 2, and the reference potential of the reference power supply 9 connected to the non-inverting input terminal of the comparator 8 is compared with the collector potential of the phototransistor 2. , When the former reference potential is higher than the latter collector potential, the output voltage of the comparator 8 becomes the power supply voltage V _CC , and the current resulting from this output passes through the current limiting resistor 10 and the reverse current blocking diode 11 to the collector of the phototransistor 2. It flows as a photocurrent to the emitter.

By the way, when the light emission output of the LED 1 is modulated at a predetermined frequency, and as shown in FIG. Voltage is V₁, V₂, The resistance value of each resistor 5, 7, 10 is R₁, R₂, R₃, The current flowing in the collector of the phototransistor 2 via the resistors 7 and 5 is I₁, The resistance flowing through the resistor 10 and the diode 11 to the collector of the phototransistor 2 is I₂, The potential of the collector of the phototransistor 2 is V _a , The output voltage of the operational amplifier 4 is V₀Then, the influence of ambient light is small and V_a> V ₂ Current I₂= 0, and the photocurrent I of the phototransistor 2 is_LIs the current I₁And as a result, the light emission output of LED1 modulated as shown in FIG.₀Is V as shown in FIG.₁And (V₁＋ I₁・ R₂).

On the other hand, when the influence of ambient light is great and the apparent base current of the phototransistor 2 increases and V _a <V ₂ , the output voltage of the comparator 8 becomes V _CC and the phototransistor 2 outputs Saturation is prevented and h _fe of the phototransistor 2 is prevented from lowering. In this state, if the light emission output of the LED 1 is modulated at the predetermined frequency as described above, the phototransistor 2 via the resistors 7 and 5 is used. The current flowing in the collector is (I ₁ + ΔI ₁ ) in consideration of the increase in ambient light, where I ₁ is the current when the influence of ambient light is small, and when the ambient light is large. The change ΔI _L in the photocurrent of the phototransistor ₂ is the sum of the current increase ΔI ₁ and the current ΔI ₂ flowing through the phototransistor 2 via the resistor 10 and the diode 11.

Since the output voltage of the comparator 8 fluctuates with the amplitude of ΔI ₁ · R ₂ , the output voltage of the comparator 8 changes while the LED 1 repeats light emission and extinction even if the influence of ambient light is large. Operates normally as an optical switch.

[0008]

[Problems to be solved by the device]

However, as described above, when the emission output of the LED 1 is extremely small for some reason while the influence of ambient light is large, or when h _{fe of the} phototransistor 2 is small, or dust on the light receiving surface of the phototransistor 2 is reduced. When the change ΔI _{L in the} photocurrent of the phototransistor 2 becomes very small due to the effect of adhesion of the light, the change ΔI ₁ in the current flowing through the detection circuit 3 becomes even smaller, compared to the case where the influence of ambient light is small. As a result, the change in the output voltage of the comparator 8 of the detection circuit 3, that is, the amplitude becomes extremely small, the change in the output voltage cannot be detected accurately, and the detection accuracy of the optical signal by the LED 1 deteriorates.

Further, if the ratio of the resistors 5 and 7 (= R ₂ / R ₁ ) is increased in order to increase the gain of the operational amplifier 4, the operational amplifier 4 is saturated immediately, so that the resistance ratio (R ₂ / R ₁ ) is adjusted. Therefore, the detection accuracy of the detection circuit 3 may be deteriorated.

On the other hand, it may be considered that an amplifier is provided in the subsequent stage of the detection circuit 3 and the output voltage of the detection circuit 3 is amplified, but it is difficult to set the gain of the amplifier and there is a possibility that waveform distortion and noise resistance may be reduced.

Therefore, the present invention has been made in order to solve the above problems, and an object thereof is to make it possible to make the amplitude of the final output voltage substantially constant regardless of the influence of ambient light. And

[0012]

[Means for Solving the Problems]

 A photoelectric detection device according to the present invention generates a voltage corresponding to a photocurrent of a photodetector connected to the photodetector circuit and a photodetector, in which a photocurrent flows by receiving light from the photodetector. A first detection circuit, a second detection circuit which is connected in parallel to the first detection circuit to the light receiving circuit, and which generates an output voltage according to the photocurrent of the light receiving element, and the second detection circuit And a threshold circuit for setting the operating threshold value of the second detection circuit higher than that of the first detection circuit, and an adder circuit for adding the output voltages of the both detection circuits and outputting an added voltage. It is characterized by having.

[0013]

[Action]

 In this invention, a second detection circuit is provided in parallel with the first detection circuit, and an operating threshold value of the second detection circuit is set higher than that of the first detection circuit by a threshold circuit. Since the output voltage is added and the added voltage is output by the adder circuit, all the changes in the current flowing through the light receiving element are detected and reflected in the output voltage of the adder circuit. When the modulation is performed at a predetermined frequency, the amplitude of the output voltage of the adding circuit becomes almost constant regardless of the influence of the ambient light.

[0014]

【Example】

 1 is a detailed connection diagram of an embodiment of the photoelectric detection device of the present invention, and FIG. 2 is a block diagram.

Explaining the outline of the overall configuration, as shown in FIG. 2, first and second detection circuits 21 and 22 are provided in parallel, and both detection circuits 21 and 22 are connected to a light receiving element. The output voltages of the detection circuits 21 and 22 are added by the adder circuit 23.

More specifically, as shown in FIG. 1, a phototransistor 25, which is a light-receiving element that receives light from the LED 24, which is a light-emitting element, and an NPN whose emitter is grounded and to which a collector is connected. Type switching transistor 26, a base resistor 27 connected to the base of the transistor 26 for applying a switching control signal to the base, and a bias resistor 28 provided between the base and the emitter of the transistor 26. The phototransistor 25 receives the light from the LED 24 when the transistor 26 is turned on, and a photocurrent flows through the phototransistor 25.

Then, the inverting input terminal of the operational amplifier 31 is connected to the collector of the phototransistor 25 via the gain setting resistor 30, and the feedback resistor 32 is connected between the output terminal and the inverting input terminal of the operational amplifier 31. At the same time, the non-inverting input terminal of the operational amplifier 31 is connected to the connection point of the two voltage dividing resistors 33 and 34 provided between the power source of the voltage V _D and the ground, and these resistors 30, 32 to 34 and The first detection circuit 21 is configured by the operational amplifier 31, and when the phototransistor 25 receives light having a certain intensity or more, a current I ₁ flows through the resistors 32 and 30 to the collector of the phototransistor 25.

Note that V _E represents the voltage of the negative power supply.

The inverting input terminal of the operational amplifier 37 is connected to the collector of the phototransistor 25 via the gain setting resistor 35 and the threshold circuit 36, and feedback is provided between the output terminal and the inverting input terminal of the operational amplifier 37. Resistor 38 is connected, and the non-inverting input terminal of the operational amplifier 37 is connected to the connection point of the two voltage dividing resistors 39 and 40 provided between the power source V _D and the ground. The second detection circuit 22 is constituted by 38 to 40 and the operational amplifier 37, and when the phototransistor 25 receives light of higher intensity, the phototransistor 25 is connected to the collector of the phototransistor 25 via the resistors 38 and 35 and the threshold circuit 36. When the current I ₂ flows and the intensity of light received by the phototransistor 25 is low, the current I ₂ becomes zero.

At this time, the threshold circuit 36 includes a diode 36a and a Zener diode 36b, the anodes of which are connected to each other, the cathode of the diode 36a is connected to the collector of the phototransistor 25, and the cathode of the Zener diode 36b is connected. The intensity of light received by the phototransistor 25 is high, and the difference between the power source of the voltage V _D and the collector voltage V _a of the phototransistor 25 is connected to the resistor 35, and the difference between the forward voltage drop V _F of the diode 36 a and the zener of the zener diode 36 b. If it is larger than the sum of the voltage V _ZD , the current I ₂ flows as described above.

Furthermore, the output terminals of the operational amplifiers 31 and 37 of both detection circuits 21 and 22 are connected to the inverting input terminals of the operational amplifier 45 via the DC cut capacitors 41 and 42 and the gain setting resistors 43 and 44, respectively. A feedback resistor 46 is connected between the output terminal of the operational amplifier 45 and the inverting input terminal, and the non-inverting input terminal of the operational amplifier 45 is connected to the power source V. _D Is connected to the connection point of two voltage dividing resistors 47 and 48 provided between the ground and the ground, and the adder circuit 23 is configured by the resistors 43, 44, 46 to 48 and the operational amplifier 45. The output voltages of 21 and 22 are added and output.

Next, the operation will be described.

Now, when the influence of the ambient light is small, that is, when the relationship of V _a > (V _D −V _F −V _ZD ) is established, as described above, the resistance 38, since the current I ₂ is 0 which flows through the 35 and Shi heard circuit 36, the photocurrent I _L of the phototransistor 25 is equal to the current I ₁ flowing through the resistor 32, 30 of the first detection circuit 21, The output voltages V ₁ and V ₂ of both detection circuits 21 and 22 are expressed as follows. However, V _b and V _c are the potentials of the non-inverting input terminals of the operational amplifiers 31 and 37, respectively, and R ₃₂ is the resistance value of the resistor 32.

V ₁ = V _b + I ₁ · R ₃₂ (I) V ₂ = V _c (II) Then, the photocurrent of the phototransistor 25 changes to I ₀ and I _{L due} to the modulation of the light emission output of the LED 24. Change between the detection voltages 21 and 22 due to the change in the photocurrent, ΔV ₁ and ΔV _{2 become} ΔV ₁ = (I _L −I ₀ ) · R ₃₂ and ΔV ₂ = 0. For example, when the resistance values of the resistors 44 and 46 are made equal, the output voltage V ₀ of the adder circuit 2 3 is expressed as follows. However, V _d is the potential of the non-inverting input terminal of the operational amplifier 45.

V ₀ = V _d − (I _L −I ₀ ) · R ₃₂ (III) Therefore, from the formula (III), the change amount of the output voltage of the adder circuit 23, that is, the amplitude is (I _L −I ₀ ) .R _32. At this time, as I ₂ = 0 and I _L = I ₁ as described above, the amplitude of the photocurrent (I _L −I ₀ ) is the change amount of the current I ₁ . It becomes equal to ΔI ₁ , and the amplitude of the output voltage of the adder circuit 23 becomes ΔI ₁ · R ₃₂ .

Next, when the influence of ambient light increases, the relationship of V _a <(V _D −V _F −V _ZD ) is established, and the operational amplifiers 31 and 37 are not saturated yet, the second detection is performed. Since the current I ₂ flows through the resistors 38 and 35 of the circuit 22 and the threshold circuit 36, the photocurrent I _L of the phototransistor 25 becomes I _L = I ₁ + I _{2 and} the outputs of both detection circuits 21 and 22. The voltages V ₁ and V ₂ are expressed as follows, respectively. However, R ₃₈ is the resistance value of the resistor 38.

V₁= V_b＋ I₁・ R₃₂ … (IV) V₂= V_c＋ I₂・ R₃₈ (V) Then, the photocurrent of the phototransistor 25 is I due to the modulation of the light emission output of the LED 24.₀, I_LBetween the two detection circuits 21, 22 due to the change in the photocurrent, the change ΔV₁, ΔV₂Is ΔV₁= ΔI₁・ R₃₂, ΔV₂= ΔI ₂ ・ R₃₈And the output voltage V of the adding circuit 23 becomes₀Is represented as follows.

V ₀ = V _d − {ΔI ₁ · R ₃₂ + ΔI ₂ · R ₃₈ } (VI) Therefore, the amplitude of the output voltage of the adder circuit 23 is the variation ΔV of the output voltage of both detection circuits 21 and 22. ₁ becomes equal to the added value of ΔV ₂ , and the output voltage of the adding circuit 23 increases by the change ΔV _{2 of the} second detection circuit 22 compared to the conventional case, so that the influence of ambient light is small. However, the amplitude of the final output voltage does not decrease.

Furthermore, when the influence of the ambient light becomes large and the operational amplifier 37 of the second detection circuit 23 is saturated, the output voltage V of the second detection circuit 23 is increased.₂Is a constant limit value V_2GTherefore, the photocurrent of the phototransistor 25 becomes I due to the modulation of the light emission output of the LED 24.₀, I_LOutput voltage V corresponding to the direct current component due to the capacitor 41 _2G Is cut, the output voltage V of the adder circuit 23 is V₀Is V₀= (V_d-ΔI ₁ ・ R₃₂), The output voltage V₀Is the variation ΔV of the output voltage of the first detection circuit 21.₁(= ΔI₁・ R₃₂).

At this time, the resistance value of each resistor is normally set so that the operational amplifier 37 does not saturate in this way, so that the output voltage of the adder circuit 23 is used in the state represented by the above formula (VI). However, even when the operational amplifier 37 is saturated, ΔV remains the same as before. ₁ Output voltage V equal to the amplitude of₀The amplitude of is obtained.

By the way, when the amplitude of the final output voltage is measured depending on the presence or absence of ambient light with the conventional configuration shown in FIG. 3 and the configuration of the present invention shown in FIG. 1, the output when the ambient light is present is shown in FIG. The amplitude of the voltage is 15% when there is no ambient light, whereas in FIG. 1, the amplitude of the output voltage is the same when there is no ambient light and when there is no ambient light.

Incidentally, when there is no ambient light, the photocurrent of the phototransistor by the LED is 10 μA, and when there is ambient light, the photocurrent component of the phototransistor by the ambient light is 2 mA and the photocurrent component by the LED is 10 μA. The measurement conditions were set so that

Therefore, the change amount of the output voltage of the first detection circuit 21 and the change amount of the output voltage of the second detection circuit 22 having an operation threshold value higher than that of the first detection circuit 21 are sent to the adder circuit 23. Since the addition is performed more, all the change in the current flowing through the phototransistor 25 can be reflected in the output voltage of the adder circuit 23, and when the light emission output of the LED 24 is lowered for some reason or when the h _{fe of the} phototransistor 25 is small. In this case, the amplitude of the output voltage of the adder circuit can be made almost constant even when the amount of change in the photocurrent of the phototransistor 25 is very small, and it is possible to prevent the detection accuracy of the optical signal from the LED 24 from decreasing. Problems such as waveform distortion due to the latter-stage amplifier circuit can be solved.

Needless to say, the configurations of the two detection circuits 21, 22 and the light receiving circuit 29 are not limited to those described above.

[0035]

[Effect of device]

 As described above, according to the photoelectric detection device of the present invention, the second detection circuit is provided in parallel with the first detection circuit, and the operating threshold of the second detection circuit is detected by the threshold circuit. Since the output voltage of both detection circuits is added and the added voltage is output by the adder circuit when the light output of the light emitting element is modulated at a specified frequency, the influence of ambient light is small. Regardless of the above, the amplitude of the output voltage of the adder circuit can be made substantially constant, and it becomes possible to prevent the detection accuracy of the optical signal from being reduced by the light emitting element, which is suitable for optical switches and the like.

[Brief description of drawings]

FIG. 1 is a connection diagram of an embodiment of a photoelectric detection device of the present invention.

FIG. 2 is a block diagram of the present invention.

FIG. 3 is a connection diagram of a conventional photoelectric detection device.

FIG. 4 is an operation explanatory diagram of FIG. 3;

[Explanation of symbols]

 21, 22 First and second detection circuit 23 Adder circuit 24 LED (light emitting element) 25 Phototransistor (light receiving element) 29 Light receiving circuit

Claims (1)

[Scope of utility model registration request] 1. A light receiving circuit comprising a light receiving element through which a photocurrent flows by receiving light from a light emitting element, and a first detection circuit connected to the light receiving circuit for generating an output voltage according to the photocurrent of the light receiving element. A second detection circuit which is connected to the light receiving circuit in parallel with the first detection circuit and generates an output voltage according to the photocurrent of the light receiving element; and the second detection circuit which is provided in the second detection circuit. And a threshold circuit for setting the operation threshold of the detection circuit higher than that of the first detection circuit, and an adder circuit for adding the output voltages of the both detection circuits and outputting the added voltage. And photoelectric detector.