JPH05299999A - Light receiving circuit - Google Patents

Abstract

PURPOSE:To provide a light receiving circuit in which the influence of a strong disturbing light can be exactly removed, only an objective modulation signal light can be exactly detected and outputted even when a wiring shield line between a light receiving element and a signal processing part is lengthened, and an electrostatic capacity is increased, and the deterioration of a frequency responsiveness can be prevented. CONSTITUTION:This circuit is equipped with a light receiving element PD which receives the modulation signal light, and converts it into an electric signal, and an amplifier OP1 for the voltage and amplitude of the output currents of the light receiving element PD, and the virtual ground point A of the amplifier OP1 is connected with the light receiving element PD. Therefore, the load impedance of the light receiving element PD can be extremely reduced, and even when the wiring between the light receiving element PD and a signal processing part 11 is lengthened, and the electrostatic capacity of the wring is increased, only the objective modulation signal light can be exactly detected and outputted. The impedance of an impedance variable element Q3 is variably controlled so as to be decreased by the integrated value of an integration circuit 1 which integrates the output signal of the amplifier OP1, and the currents of a low frequency due to the disturbing light is by-pass processed, and removed by the impedance variable element Q3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light receiving circuit used in an object detecting photoelectric switch for controlling opening and closing of an automatic door, for example.

[0002]

2. Description of the Related Art In recent years, as an object detection device used as a starting switch for detecting an object such as a human body and controlling the operation of a crime prevention alarm device and the opening / closing of an automatic opening / closing door, a background and a moving object are detected. Non-passive infrared type that utilizes fluctuations in radiated infrared light flux due to temperature difference, one that uses the Doppler effect of microwaves, or one that detects changes in the amount of reflected light from an object by projecting infrared rays. The contact detection type is generally adopted. However, none of these non-contact detection type object detection devices has a drawback in that when an object is stationary, it cannot be detected because the infrared light flux does not change and the light amount does not change. Therefore, for example, when it is used as a start switch for opening / closing control of an automatic opening / closing door, when the human body stops near the opened automatic door and stands up, the human body may collide with the automatic door that starts the closing operation or may be caught. I have a fear of doing it. Therefore,
As a safety sensor capable of detecting a stationary object, a photoelectric switch is attached to the aforementioned object detection device.

That is, as shown in FIG. 5, for example, a passive infrared type moving object detecting device (2) is arranged at a position right above the center of an automatic door (1) of left and right sides, and the automatic door (1) is provided. (3) near the both sides of the photoelectric switch
And the light receiving section (4) are provided in a pair, and the optical signal from the light projecting section (3) to the light receiving section (4) is cut off, whereby the photoelectric switch controller (5) detects an object such as a human body. Then, a detection signal is output to the automatic door drive unit (6). Even if the detection signal from the moving object detection device (2) is lost, the automatic door drive unit (6) does not detect the automatic door (1) as long as the detection signal is input from the photoelectric switch controller (5). Control to maintain the open state.

A light receiving circuit incorporated in the photoelectric switch controller (5) has a structure as shown in FIG. 6, which will be described below. The most serious problem in the light receiving circuit for this type of photoelectric switch is disturbance due to ambient light such as sunlight or general illumination light which is stronger than the target signal light. Therefore, in general, a high frequency from the projector (3) is used. The intermittent modulated signal light is emitted to separate the ambient light from the signal light. Then, the high-frequency modulated signal light is received by the light receiving section (4).
Is converted into an electric signal by the light receiving element (PD) composed of the photodiode of the above, and is received from the power supply terminal (+ Vcc) to the light receiving element (P
Through D), an intermittent current according to the modulated signal light flows into the base of the transistor (Q1), and the current flowing through the transistor (Q1) that intermittently turns on and off is converted into a voltage by the resistor (R1). It is later output from the output terminal (Vo) via the AC coupling capacitor (C1).

On the other hand, at the connection point between the emitter of the transistor (Q1) and the resistor (R1), an integrating circuit set to perform an integrating operation only for low frequencies by the time constant of the resistor (R2) and the capacitor (C2). (I) is connected,
In this way, since the integrating circuit (I) does not perform the integrating operation on the high frequency due to the relatively long time constant, when only the modulated signal light is received, the modulated signal light is output from the output terminal (Vo). A substantially constant voltage corresponding to is output.
Then, when ambient light such as sunlight, which is substantially DC light, or low-frequency general illumination light becomes strong, the base current of the transistor (Q1) tends to increase, but this low-frequency electric signal is integrated by the integrating circuit (I). Are integrated to increase the terminal voltage of the capacitor (C2), that is, the base voltage of the transistor (Q2), the conductivity of the transistor (Q2) increases, and a part of the photocurrent from the light receiving element (PD) increases. Flows through Q2) and resistor (R3). here,
Since the conductivity of the transistor (Q2), that is, the impedance changes according to the output current of the light receiving element (PD), the low-frequency current component due to the ambient light is bypassed through the transistor (Q2), and the influence of the ambient light is generated. Can be removed to prevent malfunction from occurring.

[0006]

By the way, the light projecting portion (3) and the light receiving portion (4) of the photoelectric switch are installed in an embedded form for the sake of appearance and for the purpose of not disturbing a passerby. On the other hand, it is preferable that the photoelectric switch controller (5) and the like are also provided in the vicinity of the light receiver (4) and the like, but the space for embedding this cannot be made wide due to the structure of the building, and , Its embedding work is also difficult. Therefore, as shown in FIG. 5, the automatic door drive unit (6) and the like are arranged in the door engine case (7) in which the equipment is concentrated in the same place, thereby improving the construction efficiency. We are working to improve and maintainability.

Therefore, the light projecting section (3) and the light receiving section (4)
Since the wiring between the controller and the photoelectric switch controller (5) becomes long, the shield wire (8) is used to prevent noise and the like from entering. However, the automatic door (1)
As shown in FIG. 5, in the case of the double-pull type, especially in the case of a large size for a factory or the like, the shield wire (8) becomes very long. However, as is apparent from the light receiving circuit of FIG. 6, since the light receiving element (PD) is connected to the base of the transistor (Q1) and the load impedance of the light receiving element (PD) is high, the shield wire (8) is connected to the shield wire (8) as described above. Figure 6
Since the electrostatic capacitance (C) of the shielded wire (8) shown in (1) increases and the output current of the light receiving element (PD) bypasses to the electrostatic capacitance (C), the output from the output terminal (Vo) There is a drawback that the voltage becomes dull and it becomes impossible to distinguish the signal by the modulated signal light, in some cases the output is not output, and the frequency response is deteriorated.

Therefore, according to the present invention, even if the influence of strong ambient light is surely removed, even if the capacitance is increased by lengthening the wiring between the light receiving element and the signal processing unit, only the target modulated signal light is ensured. It is a technical object to provide a light receiving circuit which is mainly used for a photoelectric switch and which can detect and output the light and can prevent the deterioration of the frequency response.

[0009]

The present invention has a light receiving circuit configured as follows as a technical means for achieving the above-mentioned object. That is, a light receiving element for receiving the modulated signal light and converting it into an electric signal, and an amplifier for converting the output current of the light receiving element into a voltage and for amplifying the light receiving element connected to its own virtual ground point. And an impedance variable element that is connected to the output terminal of the amplifier and an impedance variable element that is connected to the virtual ground point and is variably controlled so that the impedance is reduced by the integrated value of the integration circuit. Has been done.

[0010]

When the high-frequency modulated signal light is mainly received by the light receiving element due to the weak ambient light, the output current of the light receiving element is amplified by the amplifier and converted into a voltage for output. Since this output voltage changes in accordance with the high-frequency modulated signal light, the changing time is sufficiently short compared to the time constant of the integrating circuit, and is maintained substantially constant without being integrated by the integrating circuit. .. Then, when the ambient light becomes strong, the input current to the amplifier tries to increase, but the low-frequency electric signal due to the ambient light is integrated by the integrating circuit, and the impedance of the impedance variable element is reduced according to the integrated value, A current corresponding to a low frequency component due to ambient light flows through the impedance variable element. As a result, the current due to the ambient light is excluded through the variable impedance element, and only the current due to the modulated signal light is input to the amplifier.

In this light receiving circuit, the light receiving element is connected to the virtual ground point of the amplifier, so that the load impedance of the light receiving element is extremely low. Therefore, the shield line connecting the light receiving element and the signal processing section is lengthened and shielded. Even if the capacitance of the line increases, it is possible to reliably detect and output only the target modulated signal light.

[0012]

Preferred embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows a first embodiment which is the basic configuration of the present invention. In the figure, the same or equivalent parts as in FIG. 6 are designated by the same reference numerals. The signal processing unit (11) is configured as a dual power supply system in which both power supply terminals of the operational amplifier (OP1) are connected to the positive power supply terminal (+ Vcc) and the negative power supply terminal (-Vcc), respectively. (OP1) is an inverting input terminal (-) because the non-inverting input terminal (+) is grounded.
Is also equivalent to grounding like the non-inverting input terminal (+). That is, it is virtually grounded, and the light receiving element (PD) is connected to this virtual grounding point (A). Further, the output terminal of the operational amplifier (OP1) is led to the signal output terminal (Vo) via the AC coupling capacitor (C1), and the output terminal of the operational amplifier (OP1) is integrated with the low frequency component. An integrator circuit (I) set to a time constant for operation is connected, and the connection point of the resistor (R2) and the capacitor (C2) of this integrator circuit (I) is used as a variable impedance element (Q3). Is connected to the base of the PNP transistor, and the emitter is connected to the virtual ground point (A) through the resistor (R5).

Next, the operation of the above embodiment will be described.
When the light receiving element (PD) receives only high-frequency modulated signal light due to extremely weak ambient light, the light receiving element (P
The modulated signal current photoelectrically converted by D) is a resistor (R4).
Is converted into a voltage by and output. This output voltage has a waveform corresponding to the high-frequency modulated signal light, and its changing time is extremely short compared to the time constant of the integrating circuit (I). Therefore, the integrating operation is not performed and the terminal voltage of the capacitor (C2) is not performed. Is held constant, the output voltage is maintained in a waveform obtained by photoelectrically converting the modulated signal light, and the light receiving of the modulated signal light is accurately discriminated in the subsequent circuit.

On the other hand, when strong ambient light is incident on the light receiving element (PD) and the light receiving element (PD) outputs a current in which a low frequency current including a direct current component due to the ambient light is superimposed on the modulation signal current, The output voltage converted from this current by the operational amplifier (OP1) and the resistor (R4) tends to decrease, but only the voltage corresponding to the low-frequency current component is integrated by the integrating circuit (I). That is, the capacitor (C2) of the integrating circuit (I) starts discharging, and the terminal voltage of the capacitor (C2), that is, the base voltage of the transistor as the impedance conversion element (Q3) decreases. Here, the impedance conversion element (Q3) has a high conductivity in accordance with the output voltage which is going to be lowered, that is, the impedance is lowered and a low-frequency current component which is a part of the output current of the light receiving element (PD). Flows through the resistor (R5) and the variable impedance element (Q3). In this way, since the low frequency current component is bypassed through the variable impedance element (Q3) and reliably removed, only the high frequency modulation signal current is converted to a voltage and output regardless of the presence of strong disturbance light. And good frequency response can be obtained.

Further, this light receiving circuit includes a light receiving element (P
Since the load impedance of the light receiving element (PD) is extremely low because D) is connected to the virtual ground point (A) of the operational amplifier (OP1), the light receiving element (PD) and the signal processing unit (11) are connected. Even if the shielded wire (8) is lengthened to increase the capacitance of the shielded wire (8), only the target high-frequency modulated signal light can be reliably detected and output.

FIG. 2 shows a second embodiment of the present invention which is a modification of FIG. 1, and is different from FIG. 1 in that it has a signal processing circuit (12).
Is connected to the positive power supply terminal (+ Vcc) and the ground, and the non-inverting input terminal (+) of the operational amplifier (OP1) is connected to the positive power supply terminal (+ Vcc). Voltage is two resistors (R6),
The configuration is such that only the single power source system is applied by applying the set voltage divided by (R7). As in the case of FIG.
The inverting input terminal (-) of P1) serves as a virtual ground point (A), and the same or equivalent parts as those in FIG. 1 are designated by the same reference numerals, and the operation and effect are the same as those in the case of FIG. Therefore, the description thereof will be omitted.

FIG. 3 shows a third embodiment of the present invention which is a modification of FIG. 1, and in FIG. 1, the variable impedance element (Q3) is used.
As an example, the PNP transistor is used as the element, while the variable impedance element (Q4) is replaced with the NPN transistor. With the replacement of the transistor, the signal processing unit (13) is replaced by the signal processing unit (11) shown in FIG.
In contrast, the operational amplifier (OP1) is grounded at the inverting input terminal (-) and the non-inverting input terminal (+) is used as a virtual ground point (A) for the light receiving element (P).
D). The other parts that are the same as or equivalent to those in FIG. 1 are designated by the same reference numerals, and the basic operations and effects are the same as in the case of FIG.

FIG. 4 shows a fourth embodiment of the present invention which is a modification of FIG. 1, in which the operational amplifier is a variable impedance element (OP2).
1 only in the point that the signal processing unit (14) is configured as the above, and the same or equivalent parts to those in FIG. 1 are designated by the same reference numerals, and the basic operations and effects are the same as those in FIG.
The description is omitted because it is the same as the case.

[0019]

As described above, according to the light receiving circuit of the present invention, since the light receiving element is connected to the virtual ground point of the amplifier, the load impedance of the light receiving element becomes extremely low. In addition, since the impedance of the variable impedance element is variably controlled by the integrated value of the integrating circuit having a time constant for integrating the low-frequency electric signal, the influence of strong ambient light is reduced. By bypassing the low-frequency electric signal by the variable impedance element having a low impedance, it can be reliably excluded. Therefore, even if the wiring between the light receiving element and the signal processing unit is lengthened, it is possible to reliably detect and output only the target high-frequency modulated signal light, and obtain good frequency response. it can. Moreover, since the amplifier can be configured as an inverting amplification type and a current injection type, there is an advantage that it is unlikely to be affected by electric field noise.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram of a first embodiment of the present invention.

FIG. 2 is an electric circuit of a second embodiment of the present invention.

FIG. 3 is an electric circuit diagram of a third embodiment of the present invention.

FIG. 4 is an electric circuit diagram of a fourth embodiment of the present invention.

FIG. 5 is a schematic view showing an installed state of a photoelectric switch to which the present invention is applied.

FIG. 6 is an electric circuit diagram of a conventional light receiving circuit for a photoelectric switch.

[Explanation of symbols]

 8 shielded wires 11 to 14 signal processing unit PD light receiving element OP1 operational amplifier Q3, Q4, OP2 impedance variable element I integrating circuit R2 resistor C2 capacitor Vo output terminal A virtual ground point

Claims (1)

[Claims] 1. A light-receiving element for receiving modulated signal light and converting it into an electric signal, and a virtual ground point of the signal processing unit for converting the output current of the light-receiving element into a voltage and for amplifying the voltage. An amplifier to which the light receiving element is connected, an integrator circuit connected to the output terminal of the amplifier, and an impedance variable element connected to the virtual ground point and variably controlled to reduce the impedance by the integrated value of the integrator circuit. A light receiving circuit comprising: