JPS6250678A - Optical modulation type detecting device - Google Patents

Abstract

PURPOSE:To prevent a light emission signal from being decided erroneously, to cut the DC component of a photodetection signal due to disturbing light, to increase the response speed, and to perform IC-implementation by providing a switch means on the input side of an amplifier for the photodetection signal. CONSTITUTION:A light emitting element is driven with a pulse signal from an oscillation circuit 12 to project the light emission signal (a) on a body A, and its reflected light is guided in a photodetecting element 14. The photodetection output is supplied to the amplifier 15, whose output is detected 17 synchronously through a decision circuit 16, further decided 19, and outputted 20. In this case, the switch means 25 consisting of bipolar transistors (TR) which are turned ON and OFF with the output of the circuit 12 is provided on the input side of the amplifier 15. Then, the input to the amplifier 15 is fixed at a reference voltage V1 with the output of the means 25 at timing except in the light emission of the element 11 and the fixed state of the input to the amplifier 15 is released in the light emission of the element 11 to amplify and transmit the photodetection output to a next stage.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention emits pulse-modulated light from a light emitting element,
The present invention relates to a light modulation type detection device that uses a light receiving element to detect the reflection or transmission of this light by an object, and determines the presence or absence of an object from the received light signal.

Background Art The configuration of a conventional example of this type of light modulation type detection device is shown in Fig. 3.
Further, its operation timing chart is shown in FIG.

In FIG. 3, the light emitting element 1 is pulse-driven through the light emitting element drive circuit 3 by a pulse signal from the oscillation circuit 2, and as a result, the light emitting element 1 outputs a pulse-modulated fourth signal.
A light emitting signal shown in the figure (A') is projected.

The light thus projected is reflected by or transmitted through the object A and enters the light receiving element 4. As a result, the pulsed light incident on the light receiving element 4 detects the presence or absence of the object A (here, #4
It is turned on and off depending on whether the object A is present (as shown in Figure (b)) as a high level, and when it is absent as a low level.

The output of the light-receiving element 4 is amplified by an AC7 amplifier 5, and the received light signal d is input to the next-stage determination circuit 6, where it is compared with a predetermined determination level. The output e of the -determination circuit 6 is input to a synchronization detection circuit 7, where synchronization with the light emission timing of the light emitting element 1 is detected. The synchronization detection signal f is input to the next-stage integration circuit 8, and its integral output g is compared with a predetermined judgment level in the judgment circuit 9, and the judgment result is outputted from the output circuit 10 as a judgment signal.

In the above operation, when the pulsed light from the light emitting element 1 and the disturbance light C shown in FIG. 4(c) are incident on the light receiving element 4, the light receiving signal d amplified by the AC amplifier 5 is The waveform becomes as shown by the reference mark d1 in the figure (d). This waveform d1 is determined by the determination circuit 6 as shown in FIG.
The waveform is shaped as shown by the reference numeral e1 in e), and further converted into a waveform as shown by the reference numeral f1 in FIG. 4(f) in the synchronization detection circuit 7. Output f of synchronization detection circuit 7
is shaped into an integral waveform by the integrating circuit 8 in the next stage, so the part of the integral waveform corresponding to f1 is suppressed to be lower than the determination level of the next determining circuit 9, and malfunctions caused by the upward disturbance light C are suppressed. Avoided.

Problems to be Solved by the Invention In the configuration of the conventional example described above, an integrating circuit 8 with a long time constant is required to prevent malfunctions due to disturbance light C, which not only slows down the response of the circuit but also requires a large capacity. Since this method requires the use of capacitors, it is difficult to miniaturize the circuit configuration and integrate it into an IC.

An object of the present invention is to solve the above-mentioned technical problems and provide an optical modulation type detection device that has a fast response speed and is suitable for miniaturization and IC implementation.

Means for Solving the Problems The present invention uses a light receiving element to detect when pulse-modulated light emitted from a light emitting element is reflected by or passes through an object, and determines the presence or absence of an object from the received light signal. The light modulation type detection device includes: an amplifier that amplifies the received light signal; a determination circuit that is AC coupled to the amplifier and determines the amplified output from the amplifier; and a control signal synchronized with the light emitting element drive signal to determine the reference level. A standard that consists of bipolar transistors connected in antiparallel to turn on and off between the voltage source and the input terminal of the amplifier, and maintains the input terminal of the judgment circuit at the reference level at timings other than the timing when the light emitting element is emitting light. This is a light modulation type detection device characterized by including a level holding means.

According to the present invention, the DC signal portion corresponding to the disturbance light in the received light signal is cut by the AC coupling between the amplifier and the determination circuit, and the determination of the received light signal at a timing that does not correspond to the light emission of the received light signal is performed. This can be avoided by using a reference level holding means.

Therefore, it is possible to eliminate the use of an integrating circuit that requires a large capacity capacitor to prevent malfunctions due to ambient light, thereby improving response speed and making it possible to adapt to miniaturization and IC implementation.

The light-emitting element 11 of the embodiment is pulse-driven through the light-emitting element drive circuit 13 by a pulse signal from the oscillation circuit 12, and as a result, the light-emitting element 11 emits a pulse-modulated signal as shown in FIG.
) is emitted.

In this way, the projected light is reflected by or transmitted through the object A and enters the light receiving element 14.

As a result, the pulsed light incident on the light receiving element 14 is turned on and off depending on the presence or absence of the object A.

Here, as shown in FIG. 2(b), when the object A is present, the level is set to high, and when there is no object, the level is set to low.

The output from the light receiving element 14 is applied to the input terminal of the AC amplifier 15 via a coupling capacitor C1 and a line 1. A switching means 25 is interposed between the connecting point 30 on the radio 1 and the oscillation circuit 12. The switching hand Fi25 is composed of bipolar transistors Tri and Tr2 connected in antiparallel and controlled to be turned on and off by a control pulse signal from the oscillation circuit 12. Trunk star Tr1. The base of Tr2 is commonly connected to the oscillation circuit 1.
The emitter of the transistor Tri and the collector of the transistor Tr2 are connected to the reference voltage ■
Connected to 1. The collector of the transistor Tri and the emitter of the transistor Tr2 are connected to a common connection point 3.
Connected to 0. Oscillation circuit 12 line! Pulse signal and line derived through 2! The pulse signal derived through line No. 3 is derived from the zero oscillation circuit 12 through line No. 3, which has the same phase but whose high level period and low level period are in opposite states. When the pulse signal of the transistor Tr1. Tr2 becomes ON state. As a result, the input terminal of the AC amplifier 15 is fixed at the reference voltage (1), thereby interfering with the signal applied via the line (1). On the other hand, when the pulse signal derived from the oscillation circuit 12 via the line 3 is at a low level, that is, while the light emitting element 11 is emitting light, the transistor Tri
, Tr2 is turned off. As a result, AC amplifier 1
The input terminal 5 is released from the fixed state by the reference voltage 1 and becomes free, so that the signal applied via the line 1 is input to the AC amplifier 15. As a result, only the change in the amount of light emitted by the light receiving element 14 detected during this period is amplified and output.

Therefore, only signals that are not affected by the disturbance light C can be obtained, and malfunctions can be prevented.

The output from AC amplifier 15 is applied to one input terminal of determination circuit 16 via coupling capacitor C2. The DC component is removed by this coupling capacitor C2. The determination circuit 16 compares it with a predetermined determination level, and provides a determination signal e, which is the determination result, to the synchronization detection circuit 17. The synchronization detection circuit 17 receives the pulse signal from the oscillation circuit 12, and detects synchronization with the light emission timing of the light emitting element 11. The synchronization detection signal f from the synchronization detection circuit 17 is given to the determination circuit 19 and compared with a predetermined determination level, and the determination result is sent from the output circuit 20 to the determination signal g.
is output as

In the above configuration, when there is an outer 8L light C, the received light signal d amplified by the AC amplifier 15 has a waveform in which the portion corresponding to the outer 8L light C has the waveform shown by reference marks di and d2 in FIG. 2(d). . As mentioned above, the amplifier 15
1 is fixed at the reference voltage v1 during the period when the light emitting element 11 is not emitting light, and therefore, only during the period when the light emitting element 11 is emitting light, the signal based on the amount of light from the light receiving element 14 is sent to the determination circuit via the amplifier 15. Giving to 16 is cheating. This can prevent malfunctions caused by the disturbance light C during the period when the light emitting element 11 is not emitting light.

On the other hand, during the period when the light emitting element 11 emits light, the amplifier 1
5 becomes 7 Lee, and as a result, only the change in the amount of light detected by the light receiving element 14 during this period is given to the judgment circuit 16 as a light reception signal d and compared, and the output e is shown in FIG. 2(e). The output of the synchronization detection circuit 17 has the waveform shown in FIG. 2(f) of MS2. Moreover, the waveform d1 of the light reception signal d corresponding to the disturbance light C. In the portion d2, the DC component is effectively cut by the capacitors cl and c2, so that it does not affect the output of the determination circuit 16, and malfunctions caused by the disturbance light C can be prevented as a whole.

In this way, it is possible to eliminate the effects of ambient light without adding an integrating circuit, improving responsiveness compared to the prior art, and eliminating the need for large capacitors, allowing for smaller devices and IC can be realized.

Furthermore, since the switching means 25 is provided on the input side of the amplifier 15, for example, when the switching means is provided on the output side of the amplifier 15, the amplifier 15
When disturbance light c strong enough to saturate is incident, the time constant of the AC amplifier 15 causes the AC amplifier output level to reach the next sampling time before a sufficient period has elapsed within the sampling period, and the determination circuit input is switched. Noise may occur if the switch is turned off. However, in the present invention, since the switching means 20 is provided on the input side of the amplifier 15, it is possible to accurately detect the light reception signal while preventing noise.

Effects As described above, according to the present invention, the operation of determining a light emission signal at a timing that does not correspond to the light emission of the light emitting element is avoided, and the DC signal portion of the received light signal that corresponds to disturbance light is effectively affected by AC coupling. There is no need to add an integrating circuit that requires a large capacity capacitor to prevent malfunctions due to ambient light (this improves response speed and allows for miniaturization and IC implementation.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is an operation timing chart thereof, FIG. 83 is a block diagram of a conventional detection device, and FIG. 4 is a block diagram of the prior art detection device shown in FIG. It is an operation timing chart. 11... Light emitting element, 12... Transmission circuit, 13...
Light emitting element drive circuit, 14... Light receiving element, 15...A
C amplifier, 16.19... Judgment circuit, 17... Synchronization detection circuit, 20... Output circuit, 25... Switching means, Trl, Tr2... Transistor, C1, C
2...Coupling capacitor

Claims (1)

[Claims] A light modulation system in which a light receiving element detects when pulse-modulated light emitted from a light emitting element is reflected by or passes through an object, and the presence or absence of an object is determined from the received light signal. The shape detection device includes: an amplifier that amplifies the received light signal; a determination circuit that is AC-coupled with the amplifier and determines the amplified output from the amplifier; and a reference level voltage source and the input of the amplifier by a control signal synchronized with the light emitting element drive signal. It is composed of bipolar transistors connected in antiparallel to turn on and off between the terminal and the reference level holding means that holds the input terminal of the determination circuit at the reference level at a timing other than the timing when the light emitting element is emitting light. A light modulation type detection device characterized by the following.