JPH0697800A - Photodetector - Google Patents

Abstract

PURPOSE:To share an oscillator section so as to integrate the reflection type and transparent type photodetectors by using a turning ON notification signal showing that a light emitting element is turned on and synchronizing the light emitting element with the driving oscillator for a logic circuit. CONSTITUTION:In the case of the reflection type, the bases of transistors(Tr) 29 and 30 to which comparison signals are to be applied are grounded in advance to prevent the operation. Trs 25 and 28 are controlled based on the comparison of reference voltages V1 and V2 by charge voltage Vc of a capacitor 13 and resistors 14-16 by applying the power source Vcc. A light emitting diode and a logic circuit are driven by periodically outputting the high-level output voltage Vo of the Tr 25. In the case of the transparent type, comparison signals are applied to the bases of Trs 29 and 30. In this case, Trs 19 and 20 are forcedly turned off when the comparison signal is 'H' and the charge of the voltage Vc is not performed until the comparison signal becomes 'L'. Then, when the comparison signal becomes 'L', Tr 25, 28-30 are turned off and the charge of the voltage Vc is restarted. As the result, the Vo synthesized with the comparison signal can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photodetector suitable for both reflection type and transmission type optical paths formed by a light emitting element and a light receiving element.

[0002]

2. Description of the Related Art Generally, a photodetector is used for detecting passage of an object. The photodetector detects whether or not an object blocks an optical path formed between the light emitting element and the light receiving element, and controls the operation of a predetermined load based on the detection result. There are roughly two types of photodetectors. One is a reflection type in which a light receiving element receives an optical signal emitted from a light emitting element through a reflecting plate, and the other is a light receiving element directly receiving an optical signal emitted from the light emitting element. It is a transparent type. In the former case, the light emitting element and the light receiving element can be arranged close to each other. Therefore, when integrating the photodetector, an oscillator for blinking the light emitting element and an oscillator for operating the logic circuit described later are operated on a single chip. The light emitting device and the logic circuit can be easily synchronized with each other. However, in the latter case, a distance according to the size of the passing object is required between the light emitting element and the light receiving element. Therefore, when integrating the photodetector, the above oscillator should be shared on a single chip. Is impossible. Therefore, when the transmissive photodetector is integrated, it is necessary to have a two-chip configuration in which the driving portion of the light emitting element and the driving portion of the logic circuit are arranged on different chips. That is, to operate the transmissive photodetector,
A means for synchronizing the oscillators between the chips is required. Hereinafter, the reflection type photodetector shown in FIG. 4 and the transmission type photodetector shown in FIG. 5 will be described. The same parts in FIGS. 4 and 5 are designated by the same reference numerals.

In FIG. 4, (1) is an oscillator having a specific oscillating frequency, and supplies an oscillating clock divided by a predetermined frequency to each section. (2) is a drive circuit, for example, 20
It operates by applying the oscillation clock divided to 0 KHz (5 μsec cycle). Specifically, the drive circuit (2) generates a drive pulse that becomes a high level for 5 μsec in the 120 μsec cycle. (3) is a light emitting diode (light emitting element), and a drive pulse is generated for 5 μsec.
Only emits a light signal. Reference numeral (4) is a light receiving diode (light receiving element), which operates by receiving an optical signal reflected via the reflection plate (5). (6) is an amplifier,
The voltage generated by the conduction of the light receiving diode (4) is amplified. Reference numeral (7) is a comparator, which compares the output voltage of the amplifier (6) with the reference voltage and generates a high-level comparison signal (lighting notification signal) for 5 μsec in which the light emitting diode (3) emits light. That is, the high level output of the comparator (7) is synchronized with the oscillation frequency of the oscillator (1). (8) is a logic circuit, for example, 5
An oscillation clock divided by 0 KHz (20 μsec cycle) is applied to operate. Specifically, the logic circuit (8) uses the high level period (1
Logic processing is performed so that the high level output of the comparator (7) can be passed in 0 μsec. That is, since the oscillator (1) is shared by the drive circuit (2) and the logic circuit (8), the operations of the drive circuit (2) and the logic circuit (8) are synchronized. Then, the output of the logic circuit (8) is subjected to signal processing to control the operation of the load (not shown) in the subsequent stage. For example, when the load is a relay, the relay is turned off when an object blocks the optical path.

In FIG. 5, (9) is an oscillator (1).
Is an oscillator provided independently of, for example, 50 KH
The oscillation clock divided by z is supplied to the logic circuit (8). (10) is a synchronization control circuit, which synchronizes the oscillating operations of the oscillators (1) and (9) in order to synchronize the operations of the drive circuit (2) and the logic circuit (8). And, like the reflection type photodetector described above,
The operation of the load is controlled according to the state of the optical path.

[0005]

As described above, when integrating the reflection type and transmission type photodetectors, the logic circuit (8) is included in the reflection type photodetector of one chip configuration. There is a problem that the oscillator part to be operated cannot be shared with the oscillator part to operate the logic circuit (8) in the transmissive photodetector having a two-chip structure.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a photodetector which can share an oscillator portion in integrating reflective and transmissive photodetectors.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and is characterized in that it drives a light emitting element to blink in synchronization with a first oscillation clock. A circuit, a light receiving element that receives an optical signal emitted from the light emitting element, and a lighting notification that generates a lighting notification signal indicating that the light emitting element is turned on by using a voltage that is proportional to a current flowing through the light receiving element. A circuit, and a logic circuit that logically processes the output of the lighting notification circuit using a second oscillation clock that is synchronized with the first oscillation clock, and an optical path formed by the light emitting element and the light receiving element is a predetermined object. In the photodetector that controls the state of the load in the subsequent stage by the output of the logic circuit depending on whether or not the power supply voltage is cut off, a charging circuit that charges the power supply voltage with a predetermined time constant, and the power supply voltage is divided. A reference voltage generating circuit for generating a first reference voltage and a second reference voltage higher than the first reference voltage; a first comparator for comparing the charging voltage of the charging circuit with the first reference voltage; and the charging circuit. Set by the output of the second comparator that is reset when the power is turned on and the charging voltage of the charging circuit becomes greater than the second reference voltage, and a second comparator that compares the charging voltage of And an RS flip-flop that is reset by the output of the first comparator when the charging voltage of the charging circuit becomes lower than the first reference voltage,
A first discharging circuit that discharges the charging voltage based on the set output of the RS flip-flop, and the charging voltage is forcibly discharged in synchronization with the lighting notification signal regardless of the charging state of the charging circuit. An oscillator including a second discharge circuit and a set circuit for forcibly setting the RS flip-flop in synchronization with the lighting notification signal regardless of the state of charge of the charge circuit is provided, and an oscillator output of the oscillator is provided. Based on this, the operations of the drive circuit and the logic circuit are synchronized.

[0008]

According to the present invention, when the photodetector is used as a transmissive type, the light emitting element driving oscillator and the logic circuit driving oscillator are activated by using the lighting notification signal indicating that the light emitting element is turned on. They can be synchronized, and the oscillator for driving the logic circuit can be shared by the reflection type and transmission type photodetectors.

[0009]

The details of the present invention will be described in detail with reference to the drawings. 1 is a circuit diagram showing an oscillator portion of the present invention used in a photodetector, FIG. 2 is a waveform diagram when the circuit of FIG. 1 is used in a reflection type photodetector, and FIG. 3 is a transmission type of FIG. FIG. 7 is a waveform diagram when used in the photodetector of FIG.

In FIG. 1, (11), (12) and (1
3) is a resistor and a capacitor (charging circuit) connected in series between the power source Vcc and the ground, and the resistors (11) (12)
Is charged with a time constant determined by the resistance value of the capacitor and the capacity of the capacitor (13), and the charging voltage V is applied across the capacitor (13).
generate c. (14) (15) (16) are resistors (reference voltage generating circuit) connected in series between the power supply Vcc and ground
That is, the reference voltage V1 and the reference voltage V2 are generated.
The resistance values of the resistors (14), (15) and (16) are set to be equal, and V1 = Vcc / 3 and V2 = 2Vcc / 3. (1
Reference numeral 7) is a first comparator which compares the charging voltage Vc with the reference voltage V1 and outputs a high-level comparison signal when the charging voltage Vc is smaller than the reference voltage V1. (18) is a second comparator, which has a charging voltage Vc and a reference voltage V2.
When the charging voltage Vc becomes higher than the reference voltage V2, a high-level comparison signal is output. The transistors (19) (20) and the resistor (21) form an RS flip-flop, and by inserting the resistor (21) between the base of the transistor (19) and the collector of the transistor (20), The RS flip-flop is forcibly reset when the power supply Vcc is turned on. In this embodiment, it is assumed that the base of the transistor (19) is a set terminal, the base of the transistor (20) is a reset terminal, and the collector of the transistor (20) is an output terminal. (22) and (23) are constant current sources, which supply a constant current to the collectors of the transistors (19) and (20) that form the RS flip-flop. (2
Reference numeral 4) is a control transistor which performs an on / off operation with the output of the first comparator (17), which is turned on when the charging voltage Vc is lower than the reference voltage V1 and forcibly pulls the base of the transistor (19) to a low level. In (25), the collector is connected to the power supply Vcc through the resistor (26),
The emitter is grounded through the resistor (27), and is a transistor that performs on / off operation with the collector output of the transistor (20). When the transistor (25) is off, the output voltage Vo becomes low level and the transistor (2
When 5) is on, the output voltage Vo becomes high level.
(28) is a transistor as the first discharge circuit,
It turns on when the output voltage Vo is at high level, and the charging voltage Vc
Discharge. Reference numeral (29) denotes a transistor (set circuit) to which the comparison signal of the comparator (7) shown in FIGS. 4 and 5 is applied, which is turned on when the high level comparison signal is applied, and is turned on by the transistor (20). Forcibly lowers the bass to low level. Reference numeral (30) is a transistor that is turned on at the same time as the transistor (29) when a high-level comparison signal is applied, and functions as a second discharging circuit for forcibly discharging the charging voltage Vc regardless of the level of the charging voltage Vc. .

The operation when the circuit of FIG. 1 is used for a reflection type photodetector will be described below with reference to the waveform diagram of FIG. When integrating a reflection type photodetector, since only one oscillator is used, the bases of the transistors (29) and (30) to which the comparison signal of the comparator (7) is applied are connected to the ground in advance, and the transistor ( 29) (30)
Will not work.

First, when the power supply Vcc is turned on, the voltage dividing operation of the reference voltage generating circuit is performed and the reference voltages V1 and V2 are generated. At the same time, in the RS flip-flop, the transistor (20) is turned on earlier than the transistor (19) (because the RS flip-flop is reset).
The transistor (25) is turned off, and the transistor (28) is turned off in accordance with the low level of the output voltage Vo. Therefore, the charging voltage Vc starts to gradually increase from 0V according to the time constant determined by the resistors (11) and (12) and the capacitor (13).

When the charging voltage Vc is lower than the reference voltage V1, the control transistor (24) turns on the first comparator (1).
Although it is turned on by the high level comparison signal output from 7), there is no change in the state of the RS flip-flop. That is,
The transistor (28) remains off. Charging voltage V
When c further rises to a level between the reference voltages V1 and V2, the comparison output of the first comparator (17) becomes low level and the control transistor (24) turns off.
Since the comparison output of the second comparator (18) is also at the low level, the state of the RS flip-flop does not change and the transistor (28) remains off. After that, when the charging voltage Vc exceeds the reference voltage V2, the comparison output of the second comparator (18) becomes high level, so that the transistor (19) is turned on (RS flip-flop is set) and the transistor (25) is turned on. When turned on, the output voltage Vo becomes high level, and the transistor (28) is turned on. That is, the discharging operation of the charging voltage Vc is started. Then, the charging voltage Vc starts to drop and reaches a level between the reference voltages V1 and V2 again. At this time, since the comparison output of the second comparator (18) becomes low level, the output terminal of the second comparator (18) becomes high impedance,
The constant current of the constant current source (22) flows into the base of the transistor (19) through the resistor (21), and the transistor (19) continues the ON operation. Now, considering the base voltage at which the transistors (19) (25) can operate, a resistor (2
The base voltage for operating the transistor (25) must be set high because the transistor 7) is connected. Therefore, a resistor (21) is connected to the base of the transistor (19). That is, the transistor (2
The base of 5) is supplied with more base current than the base of the transistor (19), and the transistor (25)
Keeps on. That is, when the charging voltage Vc is falling between the reference voltages V1 and V2, the output voltage Vo remains at the high level and the discharging operation is continued.
After that, when the charging voltage Vc becomes lower than the reference voltage V1, the control transistor (24) is turned on by the high level comparison output, and the base of the transistor (19) is grounded (RS flip-flop is reset). Therefore, as the transistor (25) turns off, the transistor (28) also turns off, and the charging of the charging voltage Vc is started again. Hereinafter, this operation will be repeated. Thus, a so-called oscillator operation in which the high-level output voltage Vo is periodically output as shown in FIG. 2 is performed. By dividing the output voltage Vo by a predetermined frequency, for example, a waveform having a high level for 5 μsec in a 120 μsec cycle is created. This waveform is used for driving the blinking of the light emitting diode (3) through the driving circuit (2) of FIG. 4 and also for driving the logic circuit (8).
That is, the operations of the drive circuit (2) and the logic circuit (8) are synchronized.

Next, the operation when the circuit of FIG. 1 is used in a transmission type photodetector will be described with reference to FIG. In this case, the comparison signal of the comparator (7) of FIG. 5 is applied to the bases of the transistors (29) and (30). Time t0
Previously, the oscillation of the circuit of FIG. 1 was in the free-run state, as described above. Then, based on the oscillation of an independent oscillator for the drive circuit (2) of FIG.
Is driven to blink, and the charging voltage Vc is the reference voltages V1 and V2.
If a high-level comparison signal of 5 μsec is output from the comparator (7) at time t0 while the voltage rises during the period, the charging voltage Vc is below the reference voltage V2 when the transistor (30) is turned on. Instantly from 0V
When the transistor (29) is turned on, the output voltage Vo becomes high level and the transistor (28) is also turned on. Even if the charging voltage Vc becomes lower than the reference voltage V1 and the transistor (19) is forcibly turned off during the high level period of the comparison signal, the transistor (20) is also forcibly turned off. The charging with the charging voltage Vc is not performed until the voltage goes low. After that, when the comparison signal goes low,
The transistors (25) (28) (29) (30) are turned off and the charging of the charging voltage Vc is restarted. Then, when a high-level comparison signal is generated, the above operation is repeated. As a result, the output voltage Vo synchronized with the comparison signal as shown in FIG. 5 is obtained, that is, the circuit of FIG. 1 performs the oscillation operation synchronized with the oscillator for driving the drive circuit (2).

From the above, when the circuit of FIG. 1 is used in a reflection type photodetector, the comparison signal is prevented from being applied to the transistors (29) and (30), and conversely the circuit of FIG. When using a transistor (29) (3
It is only necessary to use different ones like applying the comparison signal to 0),
The circuit of FIG. 1 can be shared by both photodetectors.

[0016]

According to the present invention, when the photodetector is used as a transmissive type, a light emitting notification signal indicating that the light emitting element is turned on is used to generate an oscillator for driving the light emitting element and an oscillator for driving the logic circuit. Can be synchronized with each other, and the advantage that the oscillator for driving the logic circuit can be shared by the reflection type and transmission type photodetectors is obtained. In other words, it is not necessary to separately develop the oscillator part when developing the reflection type and transmission type photodetectors, and it is possible to obtain the effects of reducing the development cost and further shortening the development time.

[Brief description of drawings]

FIG. 1 is a diagram showing a circuit of the present invention.

FIG. 2 is a waveform diagram when the circuit of the present invention is used in a reflection type photodetector.

FIG. 3 is a waveform diagram when the circuit of the present invention is used in a transmissive photodetector.

FIG. 4 is a diagram showing a reflection type photodetector.

FIG. 5 is a diagram showing a transmissive photodetector.

[Explanation of symbols]

(11) (12) (14) (15) (16) (21)
Resistor (13) Capacitor (17) First Comparator (18) Second Comparator (19) (20) (28) (29) (30) Transistor

Claims (2)

[Claims] 1. A drive circuit for driving a light emitting element to blink in synchronization with a first oscillation clock, a light receiving element for receiving an optical signal emitted from the light emitting element, and a voltage proportional to a current flowing through the light receiving element. Using a lighting notification circuit that generates a lighting notification signal indicating that the light emitting element has been lit, and a logic circuit that logically processes the output of the lighting notification circuit using a second oscillation clock that is synchronized with the first oscillation clock. A photodetector for controlling a load state in a subsequent stage by an output of the logic circuit according to whether or not a predetermined object blocks an optical path formed by the light emitting element and the light receiving element, A charging circuit for charging a voltage with a predetermined time constant; a reference voltage generating circuit for dividing the power supply voltage to generate a first reference voltage and a second reference voltage higher than the first reference voltage; A first comparator for comparing a charging voltage of an electric circuit with the first reference voltage; a second comparator for comparing a charging voltage of the charging circuit with the second reference voltage; Is set by the output of the second comparator when the charging voltage of is higher than the second reference voltage, and the output of the first comparator when the charging voltage of the charging circuit is lower than the first reference voltage. An RS flip-flop that is reset, a first discharge circuit that discharges the charging voltage based on a set output of the RS flip-flop, and the synchronization notification signal, regardless of the charging state of the charging circuit. A second discharging circuit for forcibly discharging the charging voltage, and the RS flip-flop synchronized with the lighting notification signal regardless of the charging state of the charging circuit. Includes a set circuit for forcibly set up, an oscillator consisting of an optical detector, characterized in that synchronizing the operation of said drive circuit and said logic circuit based on the oscillation output of the oscillator. 2. The oscillator is for operating the logic circuit, and when the drive circuit and the logic circuit are operated by using different oscillators, the lighting notification signal is used to synchronize both oscillators. The photodetector according to claim 1, characterized in that: