JP5043052B2 - PULSE MODULATION TYPE PHOTODETECTION DEVICE AND ELECTRONIC DEVICE HAVING THE SAME - Google Patents

Description

  The present invention relates to a pulse modulation type photodetector. In particular, an interface circuit that changes the emission pulse waveform of a pulse modulation type photodetection device that detects the presence or absence of an object by projecting pulse-modulated light from a light emitting element according to the presence or absence of an object, In a two-line pulse modulation type photodetection device that detects a change as a signal, saves a signal line for transmitting the presence or absence of an object, and enables signal transmission between the pulse modulation type photodetection device and an interface circuit. The present invention relates to prevention of false detection when an abnormal state of wiring occurs, and then the abnormal state is recovered and the photodetector is automatically restored.

  In electronic devices such as copying machines and printers such as FA and OA devices, and amusement devices such as game machines, it may be necessary to detect the presence or absence of objects such as recording paper, coins and balls in a predetermined path. For the detection of the presence / absence of such an object, a light detection device that detects the presence / absence of an object using light is preferably used because it is a non-contact type with respect to the object.

  FIG. 5 is a block diagram showing a schematic configuration of a conventional pulse modulation type photodetecting device 101 corresponding to a three-wire system. The pulse modulation type photo-detecting device 101 operates with three terminals of a power supply terminal 102, a GND terminal 103 and an output terminal 104. The power supply terminal 102 is connected to the output of the power supply 106, and the GND of the power supply 106 is electrically grounded.

  The light emitting element 107 and the pulse modulation type photo detector 101 are biased by the power supply terminal 102 and operate. Depending on the presence / absence of the object 108, processing is performed to convert an optical signal indicating whether or not the pulsed light from the light emitting element 107 is incident on the light receiving element 109 into an electrical signal, and information on the presence / absence of the object is output from the output terminal 104. Yes.

  Since the output circuit 110 connected to the output terminal 104 is an open collector output, an output as a voltage signal can be obtained by inserting the output load 105 between the output terminal 104 and the power supply terminal 102. Three terminals of the power supply terminal 102, the GND terminal 103, and the output terminal 104 are connected to the interface circuit, and supply of power supply voltage and a signal indicating the presence or absence of an object are transmitted.

  The conventional pulse modulation type photodetector has three terminals as shown in FIG. 5, and outputs a detection signal of the presence / absence of an object to the interface circuit as a voltage. Therefore, when the voltage at the output terminal 104 becomes abnormal, the abnormal voltage is detected, the voltage abnormality is determined in the interface circuit, the error signal is output and the determination of the presence / absence of the object is interrupted. It prevented false detection.

  On the other hand, when a plurality of the above-mentioned pulse modulation type photo detection devices are used in one device, there is a strong demand for wire saving for the pulse modulation type photo detection device, and the output terminal is omitted and it is configured with two terminals. A two-wire pulse modulation type photodetection device has been proposed.

  6 is different from the pulse modulation type photodetector 101 of FIG. 5 in that there is no output terminal and an output load 115 is provided between the power source terminal 112 and the power source 116. It is that. The GND of the power supply 116 is connected to the GND terminal 113 and is electrically grounded. As a method for detecting the presence or absence of an object in this configuration, a voltage value that varies depending on the output load 115 by changing the current consumption flowing from the power supply terminal 112 by changing the pulse waveform of the light emitting element 117 when the object 118 is present or absent. Is used to determine the presence or absence of an object. The light receiving element 119 receives the pulsed light from the light emitting element 117.

  The current flowing through the power supply terminal 112 is added to the drive current when the drive transistor 114 is turned on with respect to the level of the power supply bias current normally flowing through the two-wire pulse modulation type photodetection device 111. The current waveform fluctuates in a pulse manner in accordance with ON / OFF of the drive transistor 114. By extracting the change in the power supply bias current, a pulse modulation type photodetection device can be realized even in a configuration without an output terminal. For example, a change in the voltage fluctuation cycle of the power supply terminal 112 is detected by changing the pulse cycle depending on the presence or absence of an object, such as increasing the pulse cycle when there is an object with respect to the pulse cycle when there is no object, The presence or absence of an object can be detected.

  However, in the case of the two-wire pulse modulation type photodetection device 111 proposed in FIG. 6, when the resistance value of the output load 115 is increased, the potential of the power supply voltage circuit 120 is lowered. When a wiring for supplying a bias current is short-circuited to GND or the like, there is a problem that a large current flows.

  Therefore, the pulse modulation that eliminates the influence of the output load 115 in the proposed two-wire pulse modulation type photo-detecting device 111 and solves the problem related to the current when the potential of the wiring is abnormal, such as a short circuit between the power supply terminal 112 and the GND terminal 113. Type photodetection devices have been proposed.

  In this pulse modulation type photodetection device, the interface circuit and the pulse modulation type photodetection circuit include a power supply line that supplies a bias current of the interface circuit via the light emitting element, and a ground line that is electrically grounded. Connected with only two lines. The interface circuit supplies a bias current to the pulse modulation photodetection circuit, detects a pulse component in the bias current, and outputs an object detection state, and outputs the bias current when the bias current supply line is short-circuited. And a function for automatically restoring the bias current when the short circuit is recovered.

  In the pulse modulation type photodetector, when the bias current supply line is short-circuited, unlike the overcurrent prevention method by the output load, by shutting down the supply of the bias current to the pulse modulation detection circuit, Prevents overcurrent at short-circuit, and automatically recovers when the abnormal state due to short-circuit is resolved. This automatic return function is a function particularly required for amusement detection devices such as pachinko ball detection.

  Regarding the above-described automatically returning pulse modulation type photodetector, another conventional two-line pulse modulation type photodetector will be described with reference to FIGS. 7 and 8. FIG.

  FIG. 7 is a block diagram showing a schematic configuration of another conventional two-wire type pulse modulation type photodetection device 131. The two-wire pulse modulation type photo detector 131 includes a pulse modulation type photo detection device (sensor circuit) 132 and an interface circuit 133.

  The pulse modulation type photodetection device 132 includes a bias current terminal 134, a light emitting element 135, a light receiving element 136, a dummy PD 137, an amplifier 138, a dummy amplifier 139, a resistor 140, a resistor 141, a capacitor 142, a capacitor 143, a comparator circuit 144, a constant voltage. The circuit 145 includes a clock generation circuit 146, a signal processing circuit (pulse signal generation circuit) 147, a current source circuit (current generation circuit) 148, and a GND terminal 149.

  The interface circuit 133 includes a bias current supply terminal 150, a GND terminal 151, a power supply terminal 152, and a signal output terminal 153, and has a function of shutting down the bias current supply terminal 150 when an overcurrent flows through the bias current supply terminal 150. Prepare.

  In the pulse modulation type photodetection device 132, the bias current terminal 134 is connected to the bias current supply terminal 150 of the interface circuit 133. The anode of the light emitting element 135 is connected to the bias current terminal 134, and the cathode of the light emitting element 135 is connected to the input of the constant voltage circuit 145 and the current source circuit 148.

  The cathode of the light receiving element 136 is connected to the input of the amplifier 138 and one end of the resistor 140. The output of the amplifier 138 and the other end of the resistor 140 are connected to one end of the capacitor 142. The other end of the capacitor 142 is connected to the first input of the comparator circuit 144.

  The cathode of the dummy PD 137 is connected to the input of the dummy amplifier 139 and one end of the resistor 141. The output of the dummy amplifier 139 and the other end of the resistor 141 are connected to one end of the capacitor 143. The other end of the capacitor 143 is connected to the second input of the comparator circuit 144.

  The output of the comparator circuit 144 and the output of the clock generation circuit 146 are connected to the signal processing circuit 147, respectively. The output of the signal processing circuit 147 is connected to the current source circuit 148.

  A constant voltage is applied from the constant voltage circuit 145 to the amplifier 138, the dummy amplifier 139, the comparator circuit 144, the clock generation circuit 146, and the signal processing circuit 147.

  Anode of light receiving element 136, anode of dummy PD 137, GND terminal of amplifier 138, GND terminal of dummy amplifier 139, GND terminal of comparator circuit 144, GND terminal of constant voltage circuit 145, GND terminal of clock generation circuit 146, signal processing circuit The GND terminal 147 and the GND terminal and GND terminal 149 of the current source circuit 148 are electrically grounded.

  In the interface circuit 133, the power supply terminal 152 is connected to the output of the external power supply 154 and supplied with power. The GND of the external power supply 154 is electrically grounded.

  The pulse modulation type photodetection device 132 is configured to operate upon receiving a bias from a bias current circuit provided in the interface circuit 133. The interface circuit 133 converts the pulse component in the bias current flowing from the bias current supply terminal 150 into a voltage, and detects the voltage-converted pulse component as a signal. Thereafter, the object detection state of the pulse modulation type photodetection device 132 is determined by the signal processing circuit of the interface circuit 133, and the presence / absence state of the object is output to the signal output terminal 153. When the bias current supply terminal 150 is in contact with another potential and an overcurrent flows, the terminal is shut down.

  FIG. 8 is an example of a waveform diagram of a light emission pulse signal in the presence or absence of object detection in another conventional two-line pulse modulation type photodetection device. FIG. 8A is a waveform diagram of a light emission pulse signal with an object (without light), and FIG. 8B is a waveform diagram of a light emission pulse signal with no object (with light). FIG. 8C is a waveform diagram of the basic clock signal.

  Each light emission pulse signal in FIGS. 8A and 8B is generated by a signal processing circuit 147 in the pulse modulation type photodetection device 132. The waveform of the light emission pulse signal is composed of three pulses and one cycle of a header pulse signal 165, a reference pulse signal 166, and a status pulse signal 167.

  In order to generate each light emission pulse signal, a reference clock signal shown in FIG. 8C is required. The basic clock signal is generated by the clock generation circuit 146 in FIG. The clock signal shown in FIG. 8C is a clock signal generated by the clock generation circuit 146.

  In the two-wire type pulse modulation type photo detector 131, when the power is turned on or when returning from the shutdown, the pulse modulation type photo detection device 132 immediately detects the presence or absence of an object when outputting a light emission pulse signal in the absence of an object. start.

  In other words, if the pulse light (pulse signal light) in the absence of an object is not detected a predetermined number of times (predetermined number of cycles) after turning on the power or returning from shutdown, the object is detected as being present (if it is blocked by the object). The light emission pulse signal in the absence of the object changes to the light emission pulse signal in the presence of the object.

  In the normal operation state, the state indicating the presence / absence of an object is changed by detecting / not detecting a predetermined number of light emission pulses.

  As a pulse modulation type photodetection device other than the above, as a device for detecting the presence / absence of an object using light, in Patent Document 1, the output voltage at the time of ON is reduced and the light beam is blocked or switched at the time of incidence. A photoelectric switch that adds hysteresis to the characteristics is disclosed. Patent Document 2 discloses a pulse modulation type photodetection device with reduced current consumption. Patent Document 3 discloses a pulse modulation type photodetection device, a pulse modulation type photodetection method, and an electronic apparatus using the same, which can suppress erroneous detection due to disturbance light.

  As an error detection method, Patent Document 4 discloses a method of detecting an abnormal state by an interface circuit and maintaining an immediately previous state or outputting an error signal.

JP-A-6-132801 (published on May 13, 1994) JP 2007-129364 A (published on May 13, 2007) JP 2006-145483 A (published June 8, 2006) JP 2008-104064 A (published May 1, 2008)

  In the two-wire pulse modulation type photo-detecting device 131 in which the load resistance problem of FIG. 7 is improved, the power supply line for supplying the bias current is shorted to GND or other external potential, and the function of shutting down the supply of the bias current works. The pulse modulation type photodetection device 132 is completely shut down.

  However, when the above-described operation is performed in the two-line pulse modulation type photodetection device 131, if the state after the automatic recovery after the shutdown is different from the actual detection state of the object, After the presence / absence detection state becomes an unknown state and is restored by the automatic restoration function, there is a possibility of causing a false detection.

  Further, by repeating the shutdown and the automatic return, there is a possibility that an erroneous detection in which the state with the object and the state without the object are alternately repeated although the state of the presence / absence of the object has not changed may occur. Therefore, when the pulse modulation type photodetection circuit shuts down and automatically recovers, a function for preventing the erroneous detection is required.

  For example, as in the conventional example shown in FIGS. 7 and 8, when the signal output when the automatic recovery is performed after the shutdown is an object-less state pulse signal, the state where the light is blocked (the object-present state) is simultaneously performed. When generated, the output signal is switched to an object presence state pulse signal. When the shutdown state occurs again in a state where the light is blocked, the light emission pulse signal that is output when the automatic recovery is performed after the shutdown becomes the no-object state pulse signal.

  In other words, in this case, when shutdown and return are repeated, the object-free state pulse signal and the object-present state pulse signal are repeated even though the object presence / absence state does not change from the light-shielding state (the object present state). It is transmitted to the interface circuit.

  The present invention has been made in view of the above-described conventional problems, and the object thereof is to alternately repeat the state with an object and the state without an object even though the state of the presence or absence of the object has not changed. An object of the present invention is to provide a pulse modulation type photo-detecting device and an electronic device including the same, which can reduce the line without causing erroneous detection.

  In order to solve the above problems, a pulse modulation type photodetecting device of the present invention includes a first oscillation circuit that generates a basic clock signal, a pulse signal generation circuit that generates a synchronous timing pulse signal based on the basic clock signal, and A pulse modulated light detection circuit having a light receiving element for receiving the reflected light of the pulse light synchronized with the synchronization timing pulse signal by the object to be detected or the pulse light not blocked by the object, and projecting the pulse light A pulse modulation type photo-detecting device having a light-emitting element, and an interface circuit for supplying a bias current to the light-emitting element and the pulse-modulation photo-detection circuit, the clock signal having the same cycle as the basic clock signal The second oscillation circuit to be generated, the pulse component in the bias current is converted into a voltage signal Output bias current detection circuit, integration circuit for integrating the voltage signal, header detection circuit for detecting the header pulse signal of the voltage signal included in the signal output from the integration circuit by a comparator circuit for header detection, the voltage Based on a differentiation circuit for differentiating a signal, a signal detection circuit for detecting a differentiated voltage signal output from the differentiation circuit by a signal detection comparator circuit, a header detection circuit, and a signal output from the signal detection circuit A signal processing circuit for determining an object detection state of the pulse modulation type photodetection device; an output circuit for outputting the result of the determination as a voltage signal or a current signal; and an output terminal; Comparing the voltage with a first reference voltage in the interface circuit, and An interface circuit having a short detection circuit for detecting that a current supply line is short-circuited, and a shutdown circuit for shutting down the supply of the bias current when the short circuit is short-circuited, wherein the interface circuit and the pulse modulation type photo detection circuit include: In the pulse modulation type photodetecting device connected to the interface circuit by only two lines of a power supply line for supplying a bias current of the interface circuit via the light emitting element and a ground line electrically grounded, When the short circuit is recovered and the bias current is restored, the pulse modulation type photodetection circuit always outputs the same state pulse signal indicating the presence or absence of an object as an initial pulse signal, and the pulse received by the light receiving element. By detecting changes in the presence or absence of light, It has a determination start pulse light detection means for starting determination of the presence or absence of a body.

  According to the invention, when the short circuit is recovered and the bias current is restored by the determination start pulse light detecting means, the same state signal indicating the presence or absence of the object is always output as the initial pulse signal. Thereby, the determination of the presence / absence of the object is not started immediately, and the state indicating the presence / absence of the object does not change.

  Next, when the presence or absence of the pulsed light received by the light receiving element changes, the output of the initial pulse signal is stopped, and a normal state for determining the presence or absence of an object is entered.

  Therefore, even if the shutdown and the return are repeated, the erroneous state in which the object presence state and the object absence state are alternately repeated although the state of the presence / absence of the object does not change does not occur. Therefore, it is possible to provide a pulse modulation type photo-detecting device having good object detection characteristics.

  In the pulse modulation type photodetection device, the initial pulse signal is an object-less state pulse signal indicating that there is no object, and the presence or absence of the object is determined by detecting the pulsed light synchronized with the light receiving element. May start.

  Let us consider a case where the signal output when the interface circuit of the pulse modulation type photodetection device automatically recovers after the shutdown is the no object state pulse signal.

  In this case, the light reception signal / voltage detection circuit 40 detects the voltage of the constant voltage circuit 15 after the automatic recovery, generates a voltage recovery signal, and transmits it to the signal processing circuit 17. The current source circuit 18 outputs an object-free state pulse signal, which is a current signal, in response to a signal output from the signal processing circuit 17 to which the voltage return signal is input.

  In the conventional two-wire type pulse modulation type photodetection device, when the automatic recovery is performed after the shutdown, the determination of the presence / absence of the object is started immediately, and it is determined that there is an object when the light is not detected a predetermined number of times, A state (pulse signal output from the current source circuit 18) indicating the presence or absence of an object changes.

  However, in the pulse modulation type photodetection device, the change in the state indicating the presence or absence of the object is always canceled by the determination start pulse light detecting means. Therefore, the presence / absence of the object is not detected immediately, and the presence / absence of the object is detected even when the light emitted from the light emitting element and incident on the light receiving element is not detected by the object a predetermined number of times. The state indicating “” does not change without the object.

  Next, when there is actually no object, when the pulsed light is emitted from the light emitting element and incident on the light receiving element, the output of the initial pulse signal is stopped and the normal state for determining the presence or absence of the object Migrate to That is, the determination of the presence / absence of the object is not started until light is detected by the light receiving element.

  Therefore, even if the state where the shutdown, the return and the return are repeated in the light shielding state (the state with the object) occurs, the state is always fixed in the state without the object, the false detection is suppressed, and a good object detection characteristic can be obtained. .

  In the pulse modulation type photodetection device, the initial pulse signal is an object presence state pulse signal indicating that an object is present, and the presence or absence of the object is determined by the light receiving element not detecting the synchronized pulsed light. May start.

  When the signal that is output when the automatic recovery is performed after the shutdown is performed is the object presence state pulse signal, in the conventional two-line pulse modulation type photodetection device, in a state where the pulse light is irradiated, When the pulsed light is detected a predetermined number of times, the state is switched to the no-object state, and when a state in which the shutdown and the automatic return are repeated occurs, the state with the object and the state without the object are alternately repeated, resulting in erroneous detection.

  In the pulse modulation type photodetection device, the change in the state indicating the presence or absence of the object is always canceled by the determination start pulse light detection means. Accordingly, even when the light emitted from the light emitting element and incident on the light receiving element is detected a predetermined number of times without immediately starting the determination of the presence or absence of the object, the state indicating the presence or absence of the object is The object remains unchanged.

  Next, when the object is actually present and the pulsed light emitted from the light emitting element is blocked and is not incident on the light receiving element, the output of the initial pulse signal is stopped, and the normal presence / absence judgment for the presence of the object is performed. Transition to the state. That is, the determination of the presence / absence of the object is not started until the light receiving element is in a state where no light is detected.

  Accordingly, even if a state in which the shutdown and the return are repeated in the transmission state (no object state) occurs, the state is always fixed in the object presence state, erroneous detection is suppressed, and good object detection characteristics can be obtained.

  In any one of the pulse modulation type photodetection devices, the pulse modulation type photodetection circuit includes a constant voltage circuit, and the determination start pulse light detection unit includes a latch circuit and a shift register circuit. When the output is connected to the reset input of the shift register circuit, and the pulse modulation type photodetection circuit recovers the short circuit and the bias current is restored, the voltage is applied from the constant voltage circuit to the set input of the latch circuit. The shift register circuit is reset when the latch circuit is set, whereby the initial pulse signal is output, and the reset of the shift register circuit is performed by the light receiving element. Is canceled when the presence or absence of the pulse light received is changed, thereby stopping the output of the initial pulse signal. Is, determination of the presence or absence of the object may be initiated.

  Accordingly, when the short circuit is recovered and the bias current is restored, the initial pulse signal is output, and the state indicating the presence / absence of the object is changed without immediately starting the determination of the presence / absence of the object. There is nothing.

  The reset of the shift register circuit is canceled when the presence or absence of the pulsed light received by the light receiving element is changed, the output of the initial pulse signal is stopped, and the normal state for determining the presence or absence of an object is entered. Transition.

  Therefore, even if the shutdown and the return are repeated, the erroneous state in which the object presence state and the object absence state are alternately repeated although the state of the presence / absence of the object does not change does not occur. Therefore, it is possible to provide a pulse modulation type photo-detecting device having good object detection characteristics.

  In the pulse modulation type photodetection device, the determination start pulse light detection means has a function of interrupting the determination of the presence / absence of the object when the light receiving element detects pulse light that is not synchronized with the synchronization timing pulse signal. And when the short circuit is recovered and the bias current is restored, determination of the presence / absence of the object may be started after confirming that the non-synchronized pulsed light is not detected.

  Accordingly, when detecting the non-synchronized pulsed light even after returning from the shutdown, the determination of the presence / absence of the object is not started, so that it is possible to prevent erroneous detection of the presence / absence of the object. I can do it.

  Since the electronic apparatus according to the present invention includes any one of the above-described pulse modulation type photodetection devices, the object presence state and the object absence state are alternately repeated even though the object presence / absence state has not changed. False positives will not occur.

  As described above, according to the present invention, when the short circuit is recovered and the bias current is restored, the pulse modulation type photodetector circuit always outputs the same state pulse signal indicating the presence or absence of an object as an initial pulse signal. It has a determination start pulse light detecting means for starting the determination of the presence / absence of the object by detecting a change in the presence / absence of the pulsed light received by the element.

  Therefore, pulse-modulated photodetection that enables line-saving without false detection that occurs alternately in the presence of an object and in the absence of an object, despite the fact that the presence or absence of the object has not changed. There exists an effect of providing an apparatus and an electronic device provided with the same.

1 is a block diagram showing a schematic configuration of a two-wire pulse modulation type photodetection device according to an embodiment of the present invention. It is a block diagram which shows the interface circuit which concerns on embodiment of this invention. (A) And (b) is a block diagram which shows schematic structure of a received light signal / voltage detection circuit and a part of signal processing circuit based on Embodiment of this invention. It is a block diagram which shows schematic structure of the other 2 wire | line type pulse modulation type | mold photodetection apparatus which concerns on embodiment of this invention. It is a block diagram which shows schematic structure of the conventional 3 line type | formula pulsed light modulation type | mold optical detection apparatus. It is a block diagram which shows schematic structure of the conventional 2 line type | formula pulsed light modulation type | mold photodetection apparatus. It is a block diagram which shows schematic structure of the other conventional 2 wire | line type pulse modulation type | mold photodetector. (A) is a waveform diagram of a light emission pulse signal with an object (no light), (b) is a waveform diagram of a light emission pulse signal with no object (with light), and (c) is a basic clock signal. It is a waveform diagram.

  One embodiment of the present invention will be described below with reference to FIGS.

  FIG. 1 is a block diagram showing a schematic configuration of a two-wire pulse modulation type photodetector 1 according to an embodiment of the present invention. The two-wire pulse modulation type photodetection device 1 includes a pulse modulation type photodetection device (sensor circuit) 2 and an interface circuit 3 as in the conventional two-line type pulse modulation type photodetection device.

  The pulse modulation type photodetection device 2 includes a bias current terminal 4, a light emitting element 5, a light receiving element 6, a dummy PD (photodiode) 7, an amplifier 8, as in the conventional two-wire type pulse modulation type photodetection device. A dummy amplifier 9, a resistor 10, a resistor 11, a capacitor 12, a capacitor 13, a comparator circuit 14, a constant voltage circuit 15, a clock generation circuit 16, a signal processing circuit (pulse signal generation circuit) 17, a current source circuit 18 and a GND terminal 19 In addition, a light reception signal / voltage detection circuit 40 is provided.

  The input of the light reception signal / voltage detection circuit 40 is connected to the output of the comparator circuit 14 and the output of the constant voltage circuit 15. Thus, it has a function of detecting both the light reception signal output from the comparator circuit 14 and the voltage output from the constant voltage circuit 15.

  The interface circuit 3 includes a bias current supply terminal 20, a GND terminal 21, a power supply terminal 32, a signal output terminal 33, an abnormal signal output terminal 51, a logic inversion terminal 52, and an output enable terminal 53. Details will be described in [Interface circuit 3] with reference to FIG.

  In the pulse modulation type photodetecting device 2, the bias current terminal 4 is connected to the bias current supply terminal 20 of the interface circuit 3. The anode of the light emitting element 5 is connected to the bias current terminal 4, and the cathode of the light emitting element 5 is connected to the input of the constant voltage circuit 15 and the current source circuit 18.

  The cathode of the light receiving element 6 is connected to the input of the amplifier 8 and one end of the resistor 10. The output of the amplifier 8 and the other end of the resistor 10 are connected to one end of the capacitor 12. The other end of the capacitor 12 is connected to the first input of the comparator circuit 14.

  The cathode of the dummy PD 7 is connected to the input of the dummy amplifier 9 and one end of the resistor 11. The output of the dummy amplifier 9 and the other end of the resistor 11 are connected to one end of the capacitor 13. The other end of the capacitor 13 is connected to the second input of the comparator circuit 14.

  The output of the light reception signal / voltage detection circuit 40 is connected to the signal processing circuit 17. The output of the clock generation circuit 16 is connected to the signal processing circuit 17. The output of the signal processing circuit 17 is connected to the current source circuit 18.

  A constant voltage is applied to the amplifier 8, the dummy amplifier 9, the comparator circuit 14, the clock generation circuit 16, and the signal processing circuit 17 from the constant voltage circuit 15.

  The anode of the light receiving element 6, the anode of the dummy PD 7, the GND terminal of the amplifier 8, the GND terminal of the dummy amplifier 9, the GND terminal of the comparator circuit 14, the GND terminal of the constant voltage circuit 15, the GND terminal of the clock generation circuit 16, and a signal processing circuit The GND terminal 17 and the GND terminal 19 and the GND terminal 19 of the current source circuit 18 are electrically grounded.

  The operation of the two-wire pulse modulation photodetection device 1 will be described as follows. Consider a case where the signal output when the interface circuit 3 is automatically restored after being shut down is an object-less state pulse signal.

  In this case, the light reception signal / voltage detection circuit 40 detects the voltage of the constant voltage circuit 15 after the automatic recovery, generates a voltage recovery signal, and transmits it to the signal processing circuit 17. The current source circuit 18 outputs an object-free state pulse signal, which is a current signal, in response to a signal output from the signal processing circuit 17 to which the voltage return signal is input.

  In the conventional two-wire type pulse modulation type photodetection device, when the automatic recovery is performed after the shutdown, the determination of the presence / absence of the object is started immediately, and it is determined that there is an object when the light is not detected a predetermined number of times, A state (pulse signal output from the current source circuit 18) indicating the presence or absence of an object changes.

  However, in the two-wire pulse modulation photodetection device 1, the voltage return signal is input to the signal processing circuit 17 after the automatic return. As a result, the no-object-state pulse signal is continuously output from the current source circuit 18, so that the change in the state indicating the presence / absence of the object is always canceled. Therefore, even if the light emitted from the light emitting element 5 and incident on the light receiving element 6 is not detected by the light blocking object (object) a predetermined number of times without immediately starting the determination of the presence or absence of the object, The state indicating presence / absence does not change in the state of no object.

  Next, when there is actually no object, and pulsed light is emitted from the light emitting element 5 and incident on the light receiving element 6, the light receiving signal / voltage detection circuit 40 detects the signal from the comparator circuit 14 at least once. To do. As a result, the voltage return signal is canceled, and the two-wire pulse modulation type photodetector 1 shifts to the normal determination state similar to the conventional example. That is, until the light receiving element 6 detects light, the determination of the presence / absence of an object is not started.

  By having the above configuration, even if the state where the shutdown and return are repeated in the above-described light shielding state (the state with an object) occurs, the state is always fixed without the object, the false detection is suppressed, and a good object detection characteristic is obtained. I can do it.

  When the signal output upon automatic recovery after shutdown is an object presence state pulse signal, in the conventional two-wire pulse modulation type photodetection device, the pulse light is irradiated with the pulse light. When a state is detected a predetermined number of times, the state is switched to an object-free state, and when a state in which a shutdown and an automatic return are repeated occurs, the object-present state and the object-free state are alternately repeated, resulting in erroneous detection.

  Also in this case, the light reception signal / voltage detection circuit 40 detects the voltage of the constant voltage circuit 15 after automatic recovery, generates a voltage recovery signal, and transmits it to the signal processing circuit 17. The current source circuit 18 outputs an object presence state pulse signal that is a current signal in response to a signal output from the signal processing circuit 17 to which the voltage return signal is input.

  In the two-wire pulse modulation type photodetector 1, the voltage return signal is input to the signal processing circuit 17 after the automatic return. As a result, the object presence state pulse signal continues to be output from the current source circuit 18, so that the state change indicating the presence or absence of the object is always canceled. Therefore, even when the light emitted from the light emitting element 5 and incident on the light receiving element 6 is detected a predetermined number of times without immediately starting the determination of the presence or absence of the object, the state indicating the presence or absence of the object is It does not change as it is.

  Next, when the object is actually present and the pulsed light emitted from the light emitting element 5 is blocked and does not enter the light receiving element 6, the light reception signal / voltage detection circuit 40 receives the pulsed light from the comparator circuit 14 at least once. In the case of non-detection as described above, the voltage return signal is canceled, and the two-wire pulse modulation type photodetector 1 shifts to the normal determination state. That is, the determination of the presence / absence of an object is not started until the light receiving element 6 does not detect light.

  By having the above configuration, even if a state where the shutdown and return are repeated in the transmission state (no object state) is always fixed in the object presence state, false detection is suppressed, and good object detection characteristics can be obtained. I can do it.

  The signal processing circuit 17 in FIG. 1 operates in the same manner as the signal processing circuit 147 in FIG. 7, and generates the respective light emission pulse signals in FIGS. 8A and 8B.

  FIG. 3A is a block diagram showing a schematic configuration of the light reception signal / voltage detection circuit 40 and a part of the signal processing circuit 17 according to the embodiment of the present invention. The output of the constant voltage circuit 15 is connected to a set of latch circuits 68. The output of the comparator circuit 14 is connected to the first input of the NAND circuit 71. The output of the NAND circuit 71 is connected to the input of the inverter 101 and one input of the NAND circuit 72. The output of the inverter circuit 101 is connected to the reset of the latch circuit 68. The output bar Q of the latch circuit 68 is connected to the other input of the NAND circuit 72.

  The output of the NAND circuit 72 is connected to the reset of the state determination shift register circuit 69 included in the signal processing circuit 17. The output Q of the state determination shift register circuit 69 is connected to the current source circuit 18 and the input of the inverter 73. The output of the inverter 73 is connected to the input D of the state determination shift register circuit 69, the second input of the AND circuit 71, and the input of the inverter 74. The output of the inverter 74 is connected to the second input of the AND circuit 75.

  The output of the comparator circuit 14 via the inverter 76 is connected to the first input of the AND circuit 75. The output of the AND circuit 75 is connected to a set of state determination shift register circuits 69.

  A third input of the AND circuit 71 receives an object-free state pulse signal generated by the pulse signal generation circuit 17 based on the basic clock of the clock generation circuit 16 of FIG. An object presence state pulse signal generated by the pulse signal generation circuit 17 is input to the third input of the AND circuit 75. A determination clock signal is input to the input CLK of the state determination shift register circuit 69. The state determination shift register circuit 69 is in the reset state in the initial state immediately after the power is turned on.

  The voltage return signal output from the constant voltage circuit 15 is an initial signal that becomes a high voltage only at the time of rising, and the output of the comparator circuit 14 is set to a high voltage when there is an input signal (no object), and a state determination shift. The register circuit 69 has a predetermined number of stages.

  Here, as described above, when the pulse modulation type photodetection device 2 is in the shutdown state, and then the wiring abnormality is improved and the circuit automatically recovers, the voltage of the constant voltage circuit 15 recovers (becomes a high voltage), and the latch circuit 68. Is set. Since the output bar Q of the latch circuit 68 becomes a low voltage and a low voltage is input to the input of the NAND circuit 72, the state determination shift register circuit 69 is always fixed in the reset state. For this reason, the transition of the state indicating the presence or absence of an object does not occur.

  Next, let us consider a case where the state when the interface circuit 3 in FIG. 1 is automatically restored after being shut down is the no object state pulse signal state. In this case, when the actual state of no object occurs, the no object state pulse signal input to the third input of the NAND circuit 71 becomes a high voltage. 1 receives the synchronized pulsed light, and the first input of the NAND circuit 71 detects an output signal that is a high voltage from the comparator circuit 14. Furthermore, since the output Q of the state determination shift register circuit 69 is a low voltage, the output of the inverter 73 is also a high voltage, and the high voltage is input to the second input of the NAND circuit 71.

  Therefore, the output of the NAND circuit 71 becomes a low voltage, and the output of the inverter 101 becomes a high voltage. As a result, a high voltage is input to reset the latch circuit 68, and the latch circuit 68 is reset. Accordingly, the state determination shift register circuit 69 is released from the reset state and starts an operation of determining the presence or absence of an object.

  Similarly, let us consider a case where the state when the interface circuit 3 in FIG. 1 is automatically returned after being shut down is an object presence state pulse signal state.

  FIG. 3B is a block diagram showing a schematic configuration of the light reception signal / voltage detection circuit 40 and a part of the signal processing circuit 17 according to the embodiment of the present invention. The output of the constant voltage circuit 15 is connected to a set of latch circuits 68. The output of the comparator circuit 14 via the inverter 77 is connected to the first input of the NAND circuit 78. The output Q of the state determination shift register circuit 69 is connected to the inputs of the current source circuit 18 and the inverter 79. The output of the inverter 79 is connected to the input D of the state determination shift register circuit 69, the input of the inverter 80, and the second input of the AND circuit 81. The output of the inverter 80 is connected to the second input of the NAND circuit 78.

  The output of the NAND circuit 78 is connected to one input of the NAND circuit 82 and the input of the inverter 102. The output of the inverter 102 is connected to the reset of the latch circuit 68. The output bar Q of the latch circuit 68 is connected to the other input of the NAND circuit 82, and the output of the NAND circuit 82 is connected to a set of state determination shift register circuits 69 included in the signal processing circuit 17.

  The output of the comparator circuit 14 is connected to the first input of the AND circuit 81. The output of the AND circuit 81 is connected to the reset of the state determination shift register circuit 69.

  A third input of the AND circuit 81 receives an object-free state pulse signal generated by the pulse signal generation circuit 17 based on the basic clock of the clock generation circuit 16 of FIG. An object presence state pulse signal generated by the pulse signal generation circuit 17 is input to the third input of the NAND circuit 78. A determination clock signal is input to the input CLK of the state determination shift register circuit 69. The state determination shift register circuit 69 is set in the initial state immediately after the power is turned on.

  Consider a case where the wiring abnormality is improved in this configuration and the object is automatically returned to the presence state. The voltage of the constant voltage circuit 15 recovers (becomes a high voltage), and the latch circuit 68 is set. Further, since the output bar Q of the latch circuit 68 becomes a low voltage and the low voltage is inputted to the input of the NAND circuit 82, the state determination shift register circuit 69 is always fixed in the set state. For this reason, the transition of the state indicating the presence or absence of an object does not occur.

  When the object present state is actually reached, the object present state pulse signal input to the third input of the NAND circuit 78 becomes a high voltage. 1 does not receive the pulsed light, and the output of the inverter 77 becomes a high voltage due to the low output signal from the comparator circuit 14, and the high voltage is input to the first input of the AND circuit 75. Is done. Further, since the output Q of the state determination shift register circuit 69 is a high voltage, the output of the inverter 80 is also a high voltage, and the high voltage is input to the second input of the NAND circuit 78.

  Accordingly, all the inputs of the NAND circuit 78 become a high voltage, the output voltage of the NAND circuit 78 becomes a low voltage, and the output of the inverter 102 becomes a high voltage. Then, the latch circuit 68 is reset. Accordingly, the state determination shift register circuit 69 is released from the set state and starts an operation of determining the presence or absence of an object.

  FIG. 4 is a block diagram showing a schematic configuration of another two-wire pulse modulation type photodetector (two-wire pulse light modulation type object detection device) 70 according to the embodiment of the present invention. FIG. 4 shows a configuration in which the light reception signal / voltage detection circuit 40 is changed to a noise light signal / voltage detection circuit 41 in the two-wire pulse modulation type photodetection device 1 shown in FIG.

  Here, the noise light signal is light received by the light receiving element 6 at a timing different from the pulse light signal synchronized with the clock signal output from the clock generation circuit 16 of FIG. 1, and means an asynchronous signal.

  Similar to the two-line pulse modulation photodetector 1, the two-wire pulse modulation photodetector 70 automatically shuts down after the pulse modulation photodetector 2 is shut down, and then the wiring abnormality is improved and then automatically returns. The determination of the presence / absence of an object is canceled by the signal from the constant voltage circuit 15.

  Here, in the two-wire pulse modulation photodetector 70, when the noise light signal / voltage detection circuit 41 detects the asynchronous noise light signal from the comparator circuit 14, the state determination shift register circuit 69 is reset. The determination of the presence / absence of an object is started only after a state in which no noise light signal is detected is confirmed.

  That is, when detecting light other than the synchronized pulsed light even after returning from the shutdown state, the determination of the presence / absence of the object is not started, and thus it is possible to prevent erroneous detection of the presence / absence of the object.

  The noise light signal / voltage detection circuit 41 can also operate the light reception signal / voltage detection circuit 40 in addition to the above-described operation. The above-described operation can be realized by a logic circuit, for example.

[Interface circuit 3]
FIG. 2 is a block diagram of the interface circuit 3 according to the embodiment of the present invention. The interface circuit 3 includes a bias current supply terminal 20, a GND terminal 21, a bias current detection circuit 22, a reference voltage generation circuit 23, a constant voltage circuit 24, a header detection comparator circuit 25, a signal detection comparator circuit 26, an integration circuit 27, It has a differentiation circuit 28, a clock generation circuit 29, a signal processing circuit 30, an output circuit 31, a power supply terminal 32 and a signal output terminal 33.

  The interface circuit 3 includes an open detection comparator circuit 44, a short detection comparator circuit 45, a power supply voltage drop detection comparator circuit 46, a logic inversion comparator circuit 47, an output enable comparator circuit 48, an abnormal signal processing circuit (abnormal 49), an abnormal signal output circuit 50, an abnormal signal output terminal 51, a logic inversion terminal 52, an output enable terminal 53, and resistors 54 to 59.

  In the interface circuit 3, the bias current supply terminal 20 is connected to the current output terminal of the bias current detection circuit 22. The power supply terminal 32 is connected to the output of the external power supply 34, the input of the constant voltage circuit, and the input of the bias current detection circuit 22.

  The voltage output of the bias current detection circuit 22 is connected to the input of the integration circuit 27 and the input of the differentiation circuit 28. The output of the reference voltage generation circuit 23 is connected to the first input of the header detection comparator circuit 25 and the first input of the signal detection comparator circuit 26. The output of the integration circuit 27 is connected to the second input of the header detection comparator circuit 25. The output of the differentiation circuit 28 is connected to the second input of the signal detection comparator circuit 26.

  The output of the header detection comparator circuit 25, the output of the signal detection comparator circuit 26, and the output of the clock generation circuit 29 are connected to a signal processing circuit 30. The output of the signal processing circuit 30 is connected to the input of the output circuit 31, and the output of the output circuit 31 is connected to the signal output terminal 33.

  A constant voltage is applied from the constant voltage circuit 24 to the reference voltage generation circuit 23, the header detection comparator circuit 25, the signal detection comparator circuit 26, the clock generation circuit 29, and the signal processing circuit 30.

  The GND terminal of the bias current detection circuit 22, the GND terminal of the reference voltage generation circuit 23, the GND terminal of the constant voltage circuit 24, the GND terminal of the header detection comparator circuit 25, the GND terminal of the signal detection comparator circuit 26, and the clock generation circuit 29 , The GND terminal of the signal processing circuit 30, the GND terminal of the output circuit 31, the GND terminal 21, and the input of the external power source 34 are electrically grounded.

  In the interface circuit 3, the first input of the open detection comparator circuit 44 and the second input of the short detection comparator circuit 45 are connected to the voltage output of the bias current detection circuit 22.

  Second input of open detection comparator circuit 44, first input of short circuit detection comparator circuit 45, second input of power supply voltage drop detection comparator circuit 46, first input of logic inversion comparator circuit 47, and output enable A reference voltage output from the reference voltage generation circuit 23 is applied to the first input of the comparator circuit 48. The first input of the power supply voltage drop detection comparator circuit 46 is a voltage obtained by dividing the voltage output from the power supply terminal 32 by the resistor 54 and the resistor 55.

  The output of the open detection comparator circuit 44, the output of the short detection comparator circuit 45, and the output of the power supply voltage drop detection comparator circuit 46 are connected to the signal processing circuit 30. The outputs of the logic inversion comparator circuit 47 and the output enable comparator circuit 48 are connected to the signal processing circuit 30 and the abnormal signal processing circuit 49.

  The logic inversion terminal 52 is connected to one end of the resistor 56, and the other end of the resistor 56 is connected to one end of the resistor 57 and the second input of the logic inversion comparator circuit 47. The output enable terminal 53 is connected to one end of the resistor 58, and the other end of the resistor 58 is connected to one end of the resistor 59 and the second input of the output enable comparator circuit 48.

  The abnormal signal processing circuit 49 is connected to the signal processing circuit 30 and the abnormal signal output circuit 50, and the abnormal signal output circuit 50 is connected to the abnormal signal output terminal 51.

  The open detection comparator circuit 44, the short detection comparator circuit 45, the power supply voltage drop detection comparator circuit 46, the logic inversion comparator circuit 47, the output enable comparator circuit 48, and the abnormal signal processing circuit 49 are fixed from the constant voltage circuit 24. A voltage is applied.

  GND terminal of the open detection comparator circuit 44, GND terminal of the short circuit detection comparator circuit 45, GND terminal of the power supply voltage drop detection comparator circuit 46, GND terminal of the logic inversion comparator circuit 47, GND of the output enable comparator circuit 48 The GND terminal of the abnormal signal processing circuit 49, the GND terminal of the abnormal signal processing circuit 49, the GND terminal of the abnormal signal output circuit 50, one end of the resistor 55, the other end of the resistor 57, and the other end of the resistor 59 are electrically connected. Is grounded. In FIG. 2, a portion surrounded by a one-dot chain line constitutes a channel unit block 60.

  The pulse modulation type photodetection device 2 is configured to operate upon receiving a bias from a bias current detection circuit 22 provided in the interface circuit 3. In the interface circuit 3, the voltage output from the external power supply 34 connected between the power supply terminal 32 and the GND terminal 21 is input to the bias current detection circuit 22, and the pulse modulation type light detection is performed from the bias current supply terminal 20. A bias current I is supplied to the device 2.

  The pulse component in the bias current I flowing from the bias current supply terminal 20 is voltage-converted, and the voltage-converted pulse component is detected as a signal in the header detection comparator circuit 25 or the signal detection comparator circuit 26. Thereafter, the object detection state of the pulse modulation type photodetection device 2 is determined by the signal processing circuit 30, and the presence / absence state of light is output from the output circuit 31 to the signal output terminal 33 by a voltage signal or a current signal.

  In the interface circuit 3, the abnormal signal output terminal 51 is connected to the supply voltage of the interface circuit 3 when the supply line of the bias current I to the pulse modulation type photodetecting device 2 is disconnected or shorted to the GND line. An abnormal signal is generated when the voltage drops.

  If the signal output from the abnormal signal output terminal 51 in the normal state is High, the signal output from the abnormal signal output terminal 51 when the abnormality occurs is Low.

  Since the signal output terminal 33 needs to be output along with the output logic at the time of abnormality when the abnormality occurs, the output of the abnormality detection comparator circuit is input to the signal processing circuit 30 and output from the signal output terminal 33 at the time of abnormality. A signal is output.

  The abnormal signal processed by the signal processing circuit 30 is input to the abnormal signal processing circuit 49 and output from the abnormal signal output circuit 50. The interface circuit 3 includes a plurality of bias current supply terminals 20, signal output terminals 33, and channel unit blocks 60 corresponding to the number of sensor devices to be provided so that a plurality of sensor devices represented by the pulse modulation type photodetection device 2 can be connected. It can be created by providing.

  In this case, the abnormality signal is output by inputting signals from the signal processing circuits 30 of all the channels to the abnormality signal processing circuit 49 so that an abnormality signal is output when an abnormality is detected in one of the channels. After that, an abnormal signal is output from the abnormal signal output terminal 51.

  When the supply line of the bias current I is open (open), the bias current I stops flowing, and the output of the bias current detection circuit 22 becomes low, so that it becomes lower than the open reference voltage output from the reference voltage generation circuit 23. Then, the open state is detected by the open detection comparator circuit 44.

  When the power supply voltage of the interface circuit 3 decreases, when the power supply voltage decrease reference voltage output from the reference voltage generation circuit 23 becomes lower, the power supply voltage decrease detection comparator circuit 46 detects the power supply voltage decrease state.

  When a certain voltage or more is input to the logic inversion terminal 52, the logic inversion comparator circuit 47 operates and processes so as to invert the output of each signal processing circuit.

  When a voltage equal to or higher than a certain voltage is input to the output enable terminal 53, the output enable comparator circuit 48 operates to process the output of each signal processing circuit so as to be fixed regardless of the input state.

  The pulse modulation type photo-detecting device of the present invention reduces the number of lines without causing erroneous detection in which the presence / absence of an object is repeated alternately even though the state of the presence / absence of the object has not changed. Therefore, it can be suitably used for electronic devices such as a detecting device such as coins and balls in an FA device and OA device such as a copying machine and a printer, or an amusement device.

DESCRIPTION OF SYMBOLS 1,70 Two-line-type pulse modulation type photodetector 2 Pulse modulation type photodetector 3 Interface circuit 4 Bias current terminal 5 Light emitting element 6 Light receiving element 7 Dummy PD
8 amplifier 9 dummy amplifier 10, 11, 54 to 59 resistor 12, 13 capacitor 14 comparator circuit 15 constant voltage circuit (constant voltage circuit)
16 Clock generation circuit (first oscillation circuit)
17 Signal processing circuit (pulse signal generation circuit, determination start pulse light detection means)
18 Current source circuit (determination start pulse light detection means)
19, 21 GND terminal 20 Bias current supply terminal 22 Bias current detection circuit 23 Reference voltage generation circuit 24 Constant voltage circuit 25 Header detection comparator circuit 26 Signal detection comparator circuit 27 Integration circuit 28 Differentiation circuit 29 Clock generation circuit (second oscillation) circuit)
30 Signal processing circuit 31 Output circuit 32 Power supply terminal 33 Signal output terminal 34 External power supply 40 Light reception signal / voltage detection circuit (determination start pulse light detection means)
41 Noise light signal / voltage detection circuit (determination start pulse light detection means)
44 Open detection comparator circuit 45 Short detection comparator circuit 46 Power supply voltage drop detection comparator circuit 47 Logic inversion comparator circuit 48 Output enable comparator circuit 49 Abnormal signal processing circuit 50 Abnormal signal output circuit 51 Abnormal signal output terminal 52 Logic Inversion terminal 53 Output enable terminal 68 Latch circuit 69 Shift register circuit for state determination (shift register circuit)
71, 72, 78, 82 NAND circuit 75, 81 AND circuit 73, 74, 76, 77, 79, 80, 101, 102 Inverter I Bias current

Claims (6)

A first oscillation circuit that generates a basic clock signal, a pulse signal generation circuit that generates a synchronous timing pulse signal based on the basic clock signal, and reflected light of pulsed light synchronized with the synchronous timing pulse signal by an object to be detected; Or a pulse modulation type photodetection circuit having a light receiving element that receives the pulsed light not blocked by an object, and a pulse modulation type photodetection device having a light emitting element that projects the pulsed light, and
An interface circuit for supplying a bias current to the light emitting element and the pulse modulation type photodetection circuit, a second oscillation circuit for generating a clock signal having the same cycle as the basic clock signal, and a pulse component in the bias current A bias current detection circuit that converts the voltage and outputs it as a voltage signal, an integration circuit that integrates the voltage signal, and a header pulse signal of the voltage signal included in the signal output from the integration circuit by a header detection comparator circuit Header detection circuit for detecting, differentiation circuit for differentiating the voltage signal, signal detection circuit for detecting the differentiated voltage signal output from the differentiation circuit by a signal detection comparator circuit, the header detection circuit, and the signal detection Based on the signal output from the circuit, the pulse modulation type photodetection device Of determining the signal processing circuit object detection state, and the result of the determination, and outputs as a voltage signal or a current signal, an output circuit and an output terminal,
A short detection circuit that compares the voltage of the supply line of the bias current with a first reference voltage in the interface circuit and detects that the bias current supply line is short-circuited; and supply of the bias current at the time of the short circuit An interface circuit having a shutdown circuit for shutting down
The interface circuit and the pulse modulation type photodetection circuit include the interface circuit and only the two lines of a power supply line for supplying a bias current of the interface circuit via the light emitting element and an electrically grounded ground line. In the connected pulse modulation type photodetection device,
When the short circuit is recovered and the bias current is restored, the pulse modulation type photodetection circuit always outputs the same state pulse signal indicating the presence or absence of an object as an initial pulse signal, and the light receiving element receives the light. A pulse modulation type photo-detecting device comprising: a determination start pulse light detecting means for starting the determination of the presence / absence of the object by detecting a change in presence / absence of pulsed light.   The initial pulse signal is an object-free state pulse signal indicating that there is no object, and the detection of the presence or absence of the object is started by detecting the pulsed light synchronized with the light receiving element. Item 2. The pulse modulation type photodetection device according to Item 1.   The initial pulse signal is an object presence state pulse signal indicating that an object is present, and the determination of the presence / absence of the object is started when the light receiving element does not detect the synchronized pulsed light. Item 2. The pulse modulation type photodetection device according to Item 1. The pulse modulation type photodetection circuit has a constant voltage circuit,
The determination start pulse light detection means includes a latch circuit and a shift register circuit,
The output of the latch circuit is connected to the reset input of the shift register circuit,
The pulse modulation type photodetector circuit sets the latch circuit by inputting a voltage from the constant voltage circuit to the set input of the latch circuit when the short circuit is recovered and the bias current is restored.
The shift register circuit is reset by setting the latch circuit, whereby the initial pulse signal is output,
The reset of the shift register circuit is canceled when the presence or absence of the pulsed light received by the light receiving element changes, whereby the output of the initial pulse signal is stopped and the determination of the presence or absence of the object is started. The pulse modulation type photodetection device according to any one of claims 1 to 3.   The determination start pulse light detection means has a function of interrupting the determination of the presence or absence of the object when the light receiving element detects pulse light that is not synchronized with the synchronization timing pulse signal, the short circuit is recovered, 2. The pulse modulation type according to claim 1, wherein when the bias current is restored, determination of the presence / absence of the object is started after a state in which the non-synchronized pulsed light is not detected is confirmed. Photodetector.   An electronic apparatus comprising the pulse modulation type photodetection device according to claim 1.

Images