JP2012090156A - Pulse-modulated light detection device and electronic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pulse-modulated light detection device and an electronic apparatus that eliminate a wrong operation of erroneously determining that there is an object although there is no objects to be detected.SOLUTION: A pulse-modulated light detection device 50 includes a disturbance light detection section 200 for determining whether or not an amplified pulse signal S5 synchronizes with a synchronizing timing pulse signal S2, and if determining that the amplified pulse signal S5 does not synchronize with the synchronizing timing pulse signal S2, outputting to a synchronizing timing circuit 5 a stop signal S501 to stop generating the synchronizing timing pulse signal S2.

Description

  The present invention relates to a pulse modulation type detection apparatus and an electronic device that emit light pulse-modulated from a light emitting element to detect the presence or absence of an object.

  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. 11 is a block diagram of a conventional pulse modulation type photodetection device 100. The pulse modulation type photodetector 100 includes a constant voltage circuit 101, a power supply terminal 102, a GND terminal 103, an oscillation circuit 104, a synchronization timing circuit 105, a light emitting element driving circuit 106, a light emitting element 107, a light receiving element 108, an amplifier 109, and a comparator 110. A signal processing circuit 111, an output circuit 112, an output terminal 113, and a power source 115. The load 114 has one end connected to the power supply terminal 102 and the other end connected to the output terminal 113. The operation of the pulse modulation type photo detector 100 will be described below.

  The positive terminal of the power supply 115 is connected to the input terminal of the constant voltage circuit 101 via the power supply terminal 102. The negative terminal of the power supply 115 is connected to the GND terminal of the constant voltage circuit 101 via the GND terminal 103. As a result, the constant voltage circuit 101 generates the constant voltage V using the power source 115 and supplies the constant voltage V to each circuit included in the pulse modulation type photodetection device 100.

  In the pulse modulation type photodetection device 100, the basic clock (CLK) signal S101 generated by the oscillation circuit 104 is modulated by the synchronization timing circuit 105 into the synchronization timing pulse signal S102. The light emitting element driving circuit 106 outputs the light emitting pulse signal S103 to the light emitting element 107 when the synchronization timing pulse signal S102 transmitted from the synchronization timing circuit 105 to the light emitting element driving circuit 106 is Hi. The light emitting element 107 projects pulse-modulated pulsed light L2 toward a predetermined position based on the light emission pulse signal S103 input from the light emitting element driving circuit 106.

  Consider a case where the pulse modulation type photodetecting device 100 detects the presence or absence of an object B passing in the + Y direction at the predetermined position a distance a from the light emitting element 107 and the light receiving element 108 in the + X direction. The pulsed light L2 is projected from the light emitting element 107 to the predetermined position.

  First, since the pulsed light L2 is not reflected by the object B before the object B passes the predetermined position, the reflected light of the pulsed light L2 is not incident on the light receiving element 108.

  Next, when the object B passes through the predetermined position and crosses the pulsed light L2, the pulsed light L2 is reflected by the object B, and the reflected light L3 enters the light receiving element 108.

  As described above, the pulse modulation type photodetection device 100 that detects the presence or absence of the object B passing through the predetermined position depending on whether or not the reflected light L3 from the object B is received is provided by the reflection type pulse modulation type photodetection. Referred to as a device.

  Therefore, if there is no disturbance light or the like in the surroundings, the presence or absence of the reflected light L3 incident on the light receiving element 108 is switched depending on the presence or absence of the object B crossing the pulsed light L2. The reflected light L3 incident on the light receiving element 108 is photoelectrically converted by the light receiving element 108 to obtain a light receiving pulse signal S104.

  The received light pulse signal S104 undergoes current-voltage conversion and amplification by the amplifier 109 to become an amplified pulse signal S105. The amplified pulse signal S105 input to one input terminal (for example, a positive terminal) of the comparator 110 is compared with the determination level Sth input to the other input terminal (for example, the negative terminal) of the comparator 110, and the waveform is shaped. It is output as a comparator output pulse signal S106.

  That is, the comparator 110 outputs the comparator output pulse signal S106 at a timing when the amplified pulse signal S105 generated by amplifying the received light pulse signal S104 exceeds a preset determination level Sth.

  The comparator output pulse signal S106 is compared with the synchronization timing pulse signal S102 in the signal processing circuit 111. Thus, after confirming that the reflected light L3 incident on the light receiving element 108 is synchronized with the pulsed light L2 projected from the light emitting element 107 to the predetermined position, a signal is output to the comparator output pulse signal S106. Processing is performed. The comparator output pulse signal S106 after the signal processing is output to the output circuit 112 as a signal processing circuit output signal S107.

  FIG. 12 is a timing chart showing an example of a pulse signal in the pulse modulation type photodetecting device 100 of FIG. In the basic clock signal S101 (rectangular wave pulse signal) output from the oscillation circuit 104, Hi and Low are regularly switched during one period divided into 16 segments. The number of times of switching is 16 times per cycle, and eight pulses are generated per cycle in the basic clock signal S101. When the time of one segment is 3 μsec, one period is 3 μsec × 16 = 48 μsec.

  A synchronization timing pulse signal S102 output from the synchronization timing circuit 105 indicates a segment position where the synchronization light is detected. In the example shown in FIG. 12, the synchronization timing pulse signal S102 changes from Low to Hi at the second segment position. Thereby, it is set to detect the light synchronized with the synchronization timing pulse signal S102 at the second segment position. At the same time, a light emission pulse signal S103 having a rectangular wave that changes from Low to Hi at the second segment position is output from the light emitting element driving circuit 106 to the light emitting element 107, so that the light emitting element 107 emits light.

  When there is a reflecting object (object B), the light receiving element 108 receives the reflected light L3. The light reception pulse signal S104 output from the light receiving element 108 passes through the amplifier 109 and the comparator 110. As a result, the amplified pulse signal S105 and the comparator output pulse signal S106 are output at the second segment position.

  The signal processing circuit 111 compares the synchronization timing pulse signal S102 and the comparator output pulse signal S106 at the second segment position. If the two compared signals match, it is determined that light (synchronous light) synchronized with the synchronization timing pulse signal S102 has been detected at the 16th segment position.

  In the example shown in FIG. 12, light (asynchronous light) that is not synchronized with the synchronous timing pulse signal S102 is detected between the fourth segment position and the fourteenth segment position. The determination of whether or not asynchronous light is detected is performed at the 16th segment position, similarly to the determination of whether or not synchronous light is detected.

  In the case of the conventional pulse modulation type photodetection device 100 of FIG. 11, when synchronous light is detected and asynchronous light is not detected, it is determined that the object B is present. Further, when synchronous light is detected and asynchronous light is also detected, the detection of the presence or absence of the object B is not determined (for example, the determination that there is no object B is fixed).

  In detection of asynchronous light, if a pulse signal is detected even once between the fourth segment position and the fourteenth segment position, it is determined that asynchronous light is present. Whether the asynchronous light is input once or multiple times, the same detection is performed for each asynchronous light.

  Further, for example, the following determination is performed to prevent malfunction. That is, when the same determination is continuously obtained in a plurality of cycles, the determination regarding the final presence / absence of the object is performed in the last cycle in the plurality of cycles in which the same determination is obtained. In the case of the example shown in FIG. 12, since the same determination was obtained from the first period to the third period, the final determination is performed in the last third period.

  As in the case of the conventional pulse modulation type photodetecting device 100 of FIG. 11, in Patent Document 1, when the light receiving element detects light before light projection, the light projection is interrupted. However, an object detection device is disclosed that resumes light projection when the light receiving element stops detecting light. Patent Document 2 discloses an object detection circuit that uses a pulse width detection circuit to determine whether or not the pulse width of the pulsed light detected by the light receiving element matches the pulse width emitted from the light emitting element. Yes.

Japanese Utility Model Publication No. 6-18983 (published on March 11, 1994) JP 2008-267884 A (published November 6, 2008)

  In the conventional pulse modulation type photodetecting device 100 of FIG. 11, the same comparator 110 performs the conversion of synchronous light into a digital signal and the conversion of asynchronous light into a digital signal. For this reason, the determination level Sth compared with the amplified pulse signal S105 is also the same, and is likely to cause a malfunction described below.

  As described above, even if the conventional pulse modulation type photodetecting device 100 of FIG. 11 detects the light synchronized with the synchronous timing pulse signal S102, the detection of the presence or absence of the object B is detected when the asynchronous light is detected. Do not make a decision (fix the decision result or interrupt the decision itself). This prevents malfunction due to disturbance light.

  However, in the pulse modulation type photodetecting device 100 of FIG. 11, when both minute reflected light and disturbance light from an object not to be detected exist and these lights are mixedly input to the light receiving element 108. There is a possibility of malfunction.

  The concept of the malfunction is shown in FIGS. FIG. 13 is a block diagram showing a part of an electronic device 121 in which the conventional pulse modulation type photodetecting device 100 of FIG. FIG. 14 is a waveform diagram showing respective waveforms at the time of normal operation and malfunction in the electronic apparatus 121 including the conventional pulse modulation type photodetection device 100.

  Normally, when there is no object to be detected, no light is incident on the light receiving element 108. Therefore, the amplifier 109 does not output the amplified pulse signal S105, and the comparator 110 does not output the comparator output pulse signal S106.

  Here, a minute reflected light L3 ′ from other than the object B to be detected, for example, reflected light (including stray light components) in the pulse modulation type photo detection device 100, or the pulse modulation type photo detection device 100 is installed. Consider a case where there is reflected light from the housing 120 of the electronic device 121 to be used. In this case, the reflected light L3 'that does not reach the determination level Sth is incident on the light receiving element 108 at the timing when the synchronization timing pulse signal S102 becomes Hi.

  Further, consider a case where disturbance light L <b> 3 ″, for example, light from the inverter fluorescent lamp 122 is input to the light receiving element 108. In this case, the superimposed light L3 ′ + L3 ″ in which the disturbance light L3 ″ is superimposed on the reflected light L3 ′ from the housing 120 or the like exceeds the determination level Sth at the timing when the synchronization timing pulse signal S102 becomes Hi. Therefore, the comparator 110 generates the comparator output pulse signal S106 ′ (see FIG. 14) at the timing when the synchronization timing pulse signal S102 becomes Hi, and erroneously determines that there is an object even though there is no detection target. Malfunction will occur.

  In order to prevent such a malfunction, the following three measures can be cited. As a first countermeasure, when disturbance light synchronized with the synchronization timing pulse signal S102 is detected, the determination level (threshold) for detecting the synchronization light is increased. In the second countermeasure, the level of disturbance light that is not synchronized with the synchronization timing pulse signal S102 is measured, and the determination level for detecting the synchronization light is increased according to the measured value. In the third countermeasure, when a plurality of pulses are detected during a period in which synchronous light is detected, it is determined that the malfunction is due to disturbance light.

  However, there is a limit in changing the determination level in the first countermeasure and the second countermeasure, and the circuit scale is increased by adding a circuit for changing the determination level. The first countermeasure and the second countermeasure prevent malfunction caused by superimposition of stray light synchronized with asynchronous disturbance light. Actually, when there is no synchronized stray light or extremely small Even in this case, malfunction due to asynchronous disturbance light has been confirmed. For this reason, it is necessary to prevent malfunction even when light is not superimposed.

  FIG. 15 shows a conceptual diagram of a malfunction when synchronized stray light is not superimposed. As shown in FIG. 15, the light emitting element driving circuit 106 includes a constant current circuit 201 and a switch SW202, and the switch SW202 is turned on / off by the synchronization timing pulse signal S102. As a result, the drive current flowing through the light emitting element 107 is turned on / off, and the light emitting element 107 emits / not emits light.

  As the driving current, a current of about 100 mA is necessary, and the potential on the GND side of the amplifier 109 is unsatisfactory due to the fluctuation of the current I100 due to ON / OFF of the switch SW202, particularly the inrush current I100 ′ that flows when the switch SW202 is turned ON. It becomes stable.

  Here, a noise voltage V100 is generated on the GND side of the amplifier 109 when an inrush current I100 'flows through a parasitic resistance RPA that is not intended by the designer. As a result, as a result of the GND potential of the amplifier 109 changing, a signal due to the fluctuation of the current I100 is output from the amplifier 109. The signal generated by the noise voltage V100 due to the fluctuation of the current I100 and the signal generated by the asynchronous disturbance light L3 ″ are superimposed, causing a malfunction.

  In general, suppression of fluctuations in the GND potential is performed by a bypass capacitor connected between the power supply and the GND, but there are cases where mounting and cost are difficult. Further, as a circuit configuration provided for the light receiving element 108, a method including a reference circuit having the same configuration as the amplifier 109 is used in addition to the amplifier 109. However, it is difficult to arrange the amplifier 109 and the reference circuit in exactly the same manner, and signal superposition may occur due to the difference in arrangement, which may cause malfunction.

  Therefore, reliably suppressing fluctuations in the GND potential of the amplifier 109 due to fluctuations in current when the current for driving the light emitting element is turned on is a reliable means for preventing malfunction, and it is not sufficient to change the determination level alone.

  In the object detection device of Patent Document 1, first, a light receiving element performs detection in a state where there is no light projection, and light is projected for the first time when the light receiving element stops detecting light. Therefore, when there is always light that has a certain level of brightness and should not be detected, such as a copying machine, it can hardly operate.

  Patent Document 2 proposes a method of preventing malfunction by counting the pulse width or number of pulses in the signal (G) from the comparator output and comparing it with the pulse width or number of pulses of the synchronization signal (I). Has been. However, when a signal due to disturbance light that is not synchronized with the pulsed light output from the light emitting element overlaps with a noise signal due to an inrush current generated when the light emitting element is turned on, malfunction cannot be prevented.

  As described above, when any one of the following (a) to (c) occurs, the conventional pulse modulation type photodetection device 100 has no object B (target to be detected). There is a possibility that the light receiving element 108 receives external light synchronized with the pulsed light L2 and malfunctions.

  That is, (a) a signal by reflected light L3 ′ from an object other than the object B (reflected light inside the pulse modulation type photodetection device 100 or reflected light by the casing 120 of the pulse modulation type photodetection device 100) and inverter fluorescence When a signal due to disturbance light L3 ″ such as lamp is superimposed, (b) When a noise signal due to inrush current I100 ′ generated when the light emitting element 107 is turned on and a signal due to disturbance light L3 ″ are superimposed, or (C) In a copying machine or the like using the pulse modulation type photo-detecting device 100, when there is always light that has a certain level of brightness and should not be detected, There is a possibility that the light receiving element 108 receives external light synchronized with the pulsed light L2 and malfunctions.

  The present invention has been made in view of the above-described conventional problems, and its object is to provide a pulse modulation type photodetection device that does not cause a malfunction that is erroneously determined to be present even though there is no target to be detected. And providing an electronic device.

  In order to solve the above problem, a pulse modulation type photodetection device modulates an input clock signal to generate a pulse signal composed of an active level and an inactive level, A light-emitting element that is driven so that current flows during the period and current does not flow during the inactive level period, and emits pulsed light that is synchronized with the period when the pulse signal is at the active level to a predetermined space. A light emitting element, a light receiving element arranged to receive the pulsed light reflected by the detection target passing through the predetermined space, and generating a current signal according to the received light; By performing the processing on the current signal, the voltage signal is increased by comparing the amplifier that generates the voltage signal with the voltage signal and a predetermined reference value. A comparator for generating a comparison signal composed of a first comparison signal indicating that the voltage is higher than a reference value and a second comparison signal indicating that the voltage signal is equal to or lower than the reference value; the first comparison signal; and the pulse signal; Are synchronized and if the first comparison signal is not generated during the period when the pulse signal is at the inactive level, it is determined that the detection target exists, while the second comparison signal is generated. Or a pulse modulation type photo-detecting device comprising: a determination circuit that determines that the detection target does not exist if the first comparison signal is generated during a period in which the pulse signal is at the inactive level; It is determined whether or not the voltage signal and the pulse signal are synchronized. When it is determined that the voltage signal and the pulse signal are not synchronized, a stop for stopping the generation of the pulse signal is performed. A signal characterized in that it comprises a stop circuit for outputting to said pulse signal generating circuit.

  First, when any one of the following phenomena (a) to (c) occurs, the light receiving element receives external light synchronized with the pulsed light in spite of the absence of the detection target. That is, (a) a signal by reflected light from an object other than the object to be detected (reflected light inside the pulse modulation type photodetector or reflected light from the casing of the pulse modulation type photodetector) and disturbance such as inverter fluorescent lamp light When a signal by light is superimposed, (b) When a noise signal due to an inrush current generated when the light emitting element is turned on and a signal by the disturbance light are superimposed, or (c) The pulse modulation type photodetector When there is always light that has a certain level of brightness and should not be detected in a copier or the like that uses a laser, the light receiving element is synchronized with the pulsed light even though there is no target to be detected. The outside light is received. In this case, external light that is not synchronized with the pulse light is also received.

  Thereby, although there is no target to be detected, detection of synchronized light is performed as if there is a target to be detected, while the following phenomena (1) and (2) occur. That is, (1) the voltage signal not synchronized with the pulse signal is output, and (2) the first comparison signal is generated during a period when the pulse signal is at the inactive level.

  According to the invention, (1) when the voltage signal that is not synchronized with the pulse signal is output, the stop circuit determines that the voltage signal and the pulse signal are not synchronized. Then, the generation of the pulse signal is stopped.

  Therefore, (2) when the first comparison signal is generated during a period when the pulse signal is at the inactive level, the light emitting element can be turned off.

  Since the light emitting element is turned off, the determination circuit determines that there is no detection target by outputting the comparison signal when the pulse signal is not output.

  Accordingly, it is possible to provide a pulse modulation type photodetection device that does not cause a malfunction that is erroneously determined to be an object even though there is no target to be detected.

  In the pulse modulation type photodetection device, the stop circuit may determine whether or not the voltage signal and the pulse signal are synchronized a plurality of times. Thereby, uniform asynchronous disturbance light such as inverter light can be detected.

  In the pulse modulation type photodetection device, if the stop circuit determines that the voltage signal and the pulse signal are not synchronized for a predetermined number of times in the plurality of determinations, the stop circuit generates noise light that causes a malfunction. You may determine with having detected.

  In the pulse modulation type photodetecting device, the stop circuit may determine the stop signal when the plurality of determinations determine that the voltage signal and the pulse signal are not synchronized a predetermined number of times or more. If the number of times that the voltage signal and the pulse signal are not synchronized is less than the predetermined number of times, the stop signal is not output to the pulse signal generation circuit. The normal operation may be performed.

  The disturbance light that has a high possibility of causing a malfunction is light that is uniformly generated, such as light from an inverter fluorescent lamp, and the possibility of malfunction is small in the case of only a single pulse light that is infrequent.

  Accordingly, in the plurality of determinations, the disturbance light that is uniformly generated when it is determined that the voltage signal and the pulse signal are not synchronized for a predetermined number of times or more is assumed to be asynchronous disturbance light (causing malfunction). Treated as noise light). If the number of times that the voltage signal and the pulse signal are not synchronized is less than the predetermined number, the normal operation is performed without outputting the stop signal to the pulse signal generation circuit. Thereby, the possibility of causing a malfunction can be reduced.

  In the pulse modulation type photodetection device, if the number of determinations that the voltage signal and the pulse signal are not synchronized in the plurality of determinations is less than the predetermined number, The frequency of the clock signal may be made higher.

  If the number of times that the voltage signal and the pulse signal are not synchronized is less than the predetermined number in the plurality of times of determination, the stop circuit should be detected originally such as inverter light It is determined that uniform asynchronous disturbance light cannot be detected. This is because the frequency of the uniform asynchronous disturbance light is shifted from the frequency of the clock signal used for detecting the disturbance light.

  Therefore, before judging whether or not a single disturbance light that is not uniform is detected, the disturbance light can be detected with higher accuracy by increasing the frequency of the clock signal and detecting the disturbance light again. Can be detected, and malfunction can be prevented with higher accuracy.

  In the pulse modulation type photodetector, the determination by the stop circuit is periodically performed, and after the stop circuit outputs the stop signal to the pulse signal generation circuit, the voltage signal and the pulse signal are synchronized. If it is determined that the state that has not been eliminated, the output of the stop signal may be stopped. Thereby, it becomes possible to continuously detect the detection target passing through the predetermined space.

  In order to solve the above-described problem, the pulse modulation type photodetection device modulates an input clock signal to generate a pulse signal composed of an active level and a first inactive level, and the first non-active level. A pulse signal generation circuit for generating a first signal that is a signal composed of an active level and a second inactive level, a current corresponding to the level of the pulse signal, and a current corresponding to the level of the first signal In the period when the pulse signal is at the active level, a first current is supplied as a current corresponding to the level of the pulse signal, and the first signal is supplied to the second inactive level. The light emitting element that is driven so that a second current that is smaller than the first current is supplied as a current corresponding to the level of the first signal during the period A light emitting element that emits pulsed light corresponding to the sum current to a predetermined space, and the pulsed light reflected by the detection target that passes through the predetermined space is arranged to be able to receive light; A light receiving element that generates a current signal in accordance with the current signal, an amplifier that generates a voltage signal by performing current-voltage conversion and amplification on the current signal, and compares the voltage signal with a predetermined reference value, A comparator for generating a comparison signal including a first comparison signal indicating that the voltage signal is higher than the reference value and a second comparison signal indicating that the voltage signal is equal to or less than the reference value; and the first comparison signal If the first comparison signal is not generated during a period in which the pulse signal is in the first inactive level and the pulse signal is synchronized, it is determined that there is an object to be detected. And a determination circuit that determines that the detection target does not exist if the second comparison signal is generated or the first comparison signal is generated during a period in which the pulse signal is at the inactive level. A modulation type photodetection device, wherein it is determined whether or not the voltage signal and the pulse signal are synchronized, and after determining that the voltage signal and the pulse signal are not synchronized, the pulse signal is Until the active level, the signal for causing the pulse signal generation circuit to generate the first signal in order to cause the pulse signal generation circuit to generate the first signal that is the second inactive level. And a generation circuit that outputs the generation signal to the pulse signal generation circuit.

  According to the invention, the generation circuit determines whether the voltage signal and the pulse signal are synchronized, determines that the voltage signal and the pulse signal are not synchronized, and then determines the pulse signal. In order to cause the pulse signal generation circuit to generate the first signal in order to cause the pulse signal generation circuit to generate the first signal that is the second inactive level until the signal reaches the active level. A generation circuit that outputs a generation signal that is a signal of the above to the pulse signal generation circuit.

  Accordingly, the second current corresponding to the first signal flows through the light emitting element before the first current corresponding to the pulse signal flows.

  Since the second current is smaller than the first current, fluctuations in the current flowing through the light emitting element can be made smaller than when the current flowing through the light emitting element changes from zero to the first current. By reducing the fluctuation of the current, the inrush current flowing through the GND when the current flows can be reduced. Therefore, malfunction due to the inrush current ((b) noise signal due to the inrush current generated when the light emitting element is turned on) , Malfunction when the signal due to the disturbance light is superimposed can be prevented.

  Accordingly, it is possible to provide a pulse modulation type photodetection device that does not cause a malfunction that is erroneously determined to be an object even though there is no target to be detected.

  In the pulse modulation type photodetection device, the generated signal may be a direct current signal.

  In the pulse modulation type photodetection device, the generation signal may be a signal composed of pulses.

  With these configurations, fluctuations in the current flowing through the light emitting element can be made smaller than when the current flowing through the light emitting element changes from zero to the first current. Therefore, it is possible to provide a pulse modulation type photo-detecting device that can prevent malfunction due to the inrush current and that does not cause malfunction that is erroneously determined to be an object even though there is no target to be detected.

  In the pulse modulation type photodetection device, the generation circuit may determine whether or not the voltage signal and the pulse signal are synchronized a plurality of times. Thereby, uniform asynchronous disturbance light such as inverter light can be detected.

  In the pulse modulation type photodetection device, the generation circuit generates noise light that causes a malfunction if the generation circuit determines that the voltage signal and the pulse signal are not synchronized for a predetermined number of times in the plurality of determinations. You may determine with having detected.

  In the pulse modulation type photodetection device, the generation circuit may determine the generation signal if the generation circuit determines that the voltage signal and the pulse signal are not synchronized in the plurality of determinations a predetermined number of times or more. If the number of times that the voltage signal and the pulse signal are not synchronized is less than the predetermined number of times, the generated signal is not output to the pulse signal generating circuit. The normal operation may be performed.

  The disturbance light that has a high possibility of causing a malfunction is light that is uniformly generated, such as light from an inverter fluorescent lamp, and the possibility of malfunction is small in the case of only a single pulse light that is infrequent.

  Accordingly, in the plurality of determinations, the disturbance light that is uniformly generated when it is determined that the voltage signal and the pulse signal are not synchronized for a predetermined number of times or more is assumed to be asynchronous disturbance light (causing malfunction). Treated as noise light). If the number of times that the voltage signal and the pulse signal are not synchronized is less than the predetermined number of times, the generation signal is not output to the pulse signal generation circuit and normal operation is performed. Thereby, the possibility of causing a malfunction can be reduced.

  In the pulse modulation type photodetection device, if the number of determinations that the voltage signal and the pulse signal are not synchronized is less than the predetermined number in the plurality of determinations, The frequency of the clock signal may be made higher.

  The generation circuit is configured to detect the inverter light or the like that should be detected if the number of determinations that the voltage signal and the pulse signal are not synchronized is less than the predetermined number in the plurality of determinations. It is determined that uniform asynchronous disturbance light cannot be detected. This is because the frequency of the uniform asynchronous disturbance light is shifted from the frequency of the clock signal used for detecting the disturbance light.

  Therefore, before judging whether or not a single disturbance light that is not uniform is detected, the disturbance light can be detected with higher accuracy by increasing the frequency of the clock signal and detecting the disturbance light again. Can be detected, and malfunction can be prevented with higher accuracy.

  In the pulse modulation type photodetection device, the determination by the generation circuit is periodically performed, and after the generation circuit outputs the generation signal to the pulse signal generation circuit, the voltage signal and the pulse signal are synchronized. If it is determined that the state that has not been eliminated, the output of the generation signal may be stopped. Thereby, it becomes possible to continuously detect the detection target passing through the predetermined space.

  Since the electronic apparatus according to the present invention includes any one of the above-described pulse modulation type photodetection devices, there is no malfunction that is erroneously determined as the presence of an object even though there is no target to be detected.

  As described above, the pulse modulation type photo detection device of the present invention determines whether or not the voltage signal and the pulse signal are synchronized, and when it is determined that the voltage signal and the pulse signal are not synchronized, A stop circuit that outputs a stop signal for stopping the generation of the pulse signal to the pulse signal generation circuit;

  In addition, as described above, the pulse modulation type photodetector according to the present invention determines whether or not the voltage signal and the pulse signal are synchronized, and determines that the voltage signal and the pulse signal are not synchronized. After that, until the pulse signal becomes an active level, the pulse signal generation circuit generates the first signal in order to cause the pulse signal generation circuit to generate the first signal having the second inactive level. A generation circuit that outputs a generation signal, which is a signal for the above, to the pulse signal generation circuit.

  Therefore, there is an effect of providing a pulse modulation type photodetection device and an electronic device that do not cause a malfunction that is erroneously determined as the presence of an object even though there is no target to be detected.

1 is a block diagram of a pulse modulation type photodetector according to an embodiment of the present invention. 2 is a timing chart of each pulse signal in the pulse modulation type photodetecting device of FIG. 1. It is a block diagram of another pulse modulation type photodetection device concerning an embodiment of the present invention. FIG. 4 is a circuit diagram showing a light emitting element driving circuit included in the pulse modulation type photodetecting device of FIG. 3. FIG. 4 is a timing chart of each pulse signal when a constant current source is used as a direct current source in the pulse modulation type photodetecting device of FIG. 3. FIG. 4 is a timing chart of each pulse signal when a constant current source is used as a current source for supplying a pre-current in the pulse modulation type photodetecting device of FIG. 3. It is a block diagram of another pulse modulation type photodetection device concerning an embodiment of the present invention. 8 is a timing chart of each pulse signal in the pulse modulation type photodetecting device of FIG. It is a block diagram of another pulse modulation type photodetection device concerning an embodiment of the present invention. 10 is a timing chart of each pulse signal in the pulse modulation type photodetecting device of FIG. 9. It is a block diagram of a conventional pulse modulation type photodetection device. 12 is a timing chart illustrating an example of a pulse signal in the pulse modulation type photodetection device of FIG. 11. It is a block diagram which shows a part of electronic device which accommodated the conventional pulse modulation type | mold photodetector in FIG. 11 in the housing | casing. It is a wave form diagram which shows each waveform at the time of a normal operation and a malfunctioning in an electronic device provided with the conventional pulse modulation type photodetector. It is a conceptual diagram of malfunctioning when the synchronized stray light is not superimposed.

  An embodiment of the present invention will be described below with reference to FIGS. First, a basic configuration of the pulse modulation type photodetecting device according to the present embodiment will be described with reference to FIG.

[Basic Configuration of Pulse Modulation Type Photodetector 50]
FIG. 1 is a block diagram of a pulse modulation type photodetector 50 according to the present embodiment. The pulse modulation type photodetector 50 includes a constant voltage circuit 1, a power supply terminal 2, a GND terminal 3, an oscillation circuit 4, a synchronous timing circuit 5 (pulse signal generation circuit), a light emitting element driving circuit 6, a light emitting element 7, and a light receiving element 8. , Amplifier 9, comparator 10, signal processing circuit 11 (determination circuit), output circuit 12, output terminal 13, power supply 15, and disturbance light detection unit 200. The load 14 has one end connected to the power supply terminal 2 and the other end connected to the output terminal 13. First, the operation of the portion of the pulse modulation type light detection device 50 excluding the disturbance light detection unit 200 will be described below.

  The positive terminal of the power supply 15 is connected to the input terminal of the constant voltage circuit 1 via the power supply terminal 2. The negative terminal of the power supply 15 is connected to the GND terminal of the constant voltage circuit 1 through the GND terminal 3. Thereby, the constant voltage circuit 1 generates the constant voltage V using the power supply 15 and supplies the constant voltage V to each circuit provided in the pulse modulation type photodetecting device 50.

  In the pulse modulation type photodetecting device 50, the basic clock (CLK) signal S1 generated by the oscillation circuit 4 is synchronized with the synchronous timing pulse signal S2 (pulse signal) which is composed of an active level and an inactive level in the synchronous timing circuit 5. Is modulated. The light emitting element driving circuit 6 outputs the light emitting pulse signal S3 to the light emitting element 7 when the synchronization timing pulse signal S2 transmitted from the synchronization timing circuit 5 to the light emitting element driving circuit 6 is Hi (referred to as a period stt_1). To do. The light emitting element 7 projects pulse-modulated pulsed light L2 toward a predetermined position (predetermined space) based on the light emission pulse signal S3 input from the light emitting element driving circuit 6.

  The pulsed light L2 is projected during a period when the synchronization timing pulse signal S2 is at the active level, and is not projected during a period when the synchronization timing pulse signal S2 is at the inactive level.

  Consider a case where the pulse modulation type photodetecting device 50 detects the presence or absence of an object B passing in the + Y direction at the predetermined position a distance a in the + X direction from the light emitting element 7 and the light receiving element 8. The pulsed light L2 is projected from the light emitting element 7 to the predetermined position.

  First, since the pulsed light L2 is not reflected by the object B before the object B passes the predetermined position, the reflected light of the pulsed light L2 is not incident on the light receiving element 8.

  Next, when the object B passes through the predetermined position and crosses the pulsed light L2, the pulsed light L2 is reflected by the object B. The light receiving element 8 is arranged so as to receive the reflected light L3 of the pulsed light L2, and the reflected light L3 enters the light receiving element 8. The light receiving element 8 generates a current signal corresponding to the received light.

  As described above, the pulse modulation type photodetection device 50 that detects the presence or absence of the object B passing through the predetermined position depending on whether or not the reflected light L3 from the object B is received is a reflection type pulse modulation type photodetection. Referred to as a device.

  Accordingly, if there is no disturbance light or the like in the surroundings, the presence or absence of the reflected light L3 incident on the light receiving element 8 is switched depending on the presence or absence of the object B crossing the pulsed light L2. The reflected light L3 incident on the light receiving element 8 is photoelectrically converted by the light receiving element 8 to obtain a light reception pulse signal S4 which is a current signal.

  The received light pulse signal S4 undergoes current-voltage conversion and amplification by the amplifier 9, and becomes an amplified pulse signal S5 (voltage signal) which is a voltage signal. The amplified pulse signal S5 input to one input terminal (for example, a positive terminal) of the comparator 10 is compared with a determination level Sth (predetermined reference value) input to the other input terminal (for example, the negative terminal) of the comparator 10. The waveform is shaped and output as a comparator output pulse signal S6 (comparison signal).

  That is, the comparator 10 outputs the comparator output pulse signal S6 at a timing when the amplified pulse signal S5 generated by amplifying the light reception pulse signal S4 exceeds a preset determination level Sth.

  The comparator output pulse signal S6 is compared with the synchronization timing pulse signal S2 in the signal processing circuit 11. Thereby, after confirming that the reflected light L3 incident on the light receiving element 8 is synchronized with the pulsed light L2 projected from the light emitting element 7 to the predetermined position, a signal is output to the comparator output pulse signal S6. Processing is performed. The comparator output pulse signal S6 after the signal processing is output to the output circuit 12 as a signal processing circuit output signal S7. The level of the signal processing circuit output signal S7 becomes Hi or Low depending on the presence / absence of the object B passing through the predetermined position. For example, the signal processing circuit output signal S7 becomes Hi when the object B passes the predetermined position, and becomes Low when the object B does not pass the predetermined position.

  The amplifier 9 generates an amplified pulse signal S5 by performing current-voltage conversion and amplification on the received light pulse signal S4.

  The comparator 10 generates a comparator output pulse signal S6 including a first comparison signal indicating that the amplified pulse signal S5 is higher than the determination level Sth and a second comparison signal indicating that the amplified pulse signal S5 is equal to or lower than the determination level Sth. To do.

  The signal processing circuit 11 is configured so that the first comparison signal and the synchronization timing pulse signal S2 are synchronized and the first comparison signal is not generated during a period in which the synchronization timing pulse signal S2 is at the inactive level. If the second comparison signal is generated or the first comparison signal is generated during a period when the synchronization timing pulse signal S2 is at the inactive level, the object B is determined to be present. Judge that there is no.

[Pulse signal timing chart]
FIG. 2 is a timing chart of each pulse signal in the pulse modulation type photodetector 50 of FIG. The basic clock signal S1 (rectangular wave pulse signal) output from the oscillation circuit 4 is regularly switched between Hi and Low during one period divided into 16 segments. The number of times of switching is 16 times per cycle, and eight pulses are generated per cycle in the basic clock signal S1. When the time of one segment is 3 μsec, one period is 3 μsec × 16 = 48 μsec.

  The synchronization timing pulse signal S2 output from the synchronization timing circuit 5 indicates the segment position where the synchronization light is detected. In the example shown in FIG. 2, the synchronization timing pulse signal S2 changes from Low to Hi at the second segment position. Thereby, it is set to detect the light synchronized with the synchronization timing pulse signal S2 at the second segment position. At the same time, a light emission pulse signal S3 of a rectangular wave that changes from Low to Hi at the second segment position is output from the light emitting element driving circuit 6 to the light emitting element 7, so that the light emitting element 7 emits light.

  When there is a reflector (object B), the light receiving element 8 receives the reflected light L3. The received light pulse signal S 4 output from the light receiving element 8 passes through the amplifier 9 and the comparator 10. As a result, the amplified pulse signal S5 and the comparator output pulse signal S6 are output at the second segment position.

  The signal processing circuit 11 compares the synchronization timing pulse signal S2 with the comparator output pulse signal S6 at the second segment position. If the two compared signals match, it is determined that light (synchronous light) synchronized with the synchronization timing pulse signal S2 has been detected at the 16th segment position.

  In the case of the example shown in FIG. 2, detection of light (asynchronous light) that is not synchronized with the synchronous timing pulse signal S2 is performed between the fourth segment position and the fourteenth segment position. The determination of whether or not asynchronous light is detected is performed at the 16th segment position, similarly to the determination of whether or not synchronous light is detected.

  In the case of the pulse modulation type photodetecting device 50 of FIG. 1, when synchronous light is detected and asynchronous light is not detected, it is determined that the object B is present. When synchronous light is detected and asynchronous light is also detected, the disturbance light detection unit 200 described later stops the projection of pulsed light.

  In detection of asynchronous light, if a pulse signal is detected even once between the fourth segment position and the fourteenth segment position, it is determined that asynchronous light is present. Whether the asynchronous light is input once or multiple times, the same detection is performed for each asynchronous light.

  Further, for example, the following determination is performed to prevent malfunction. That is, when the same determination is continuously obtained in a plurality of cycles, the determination regarding the final presence / absence of the object is performed in the last cycle in the plurality of cycles in which the same determination is obtained. In the case of the example shown in FIG. 2, since the same determination was obtained from the first period to the third period, the final determination is performed in the last third period.

[Disturbance light detection unit 200]
In the pulse modulation type photo detection device 50 according to the present embodiment, a disturbance light detection unit 200 (stop circuit) is added as compared with the pulse modulation type photo detection device 100 of FIG. The operation of the ambient light detection unit 200 will be described below.

  The ambient light detector 200 to which the amplified pulse signal S5 and the synchronization timing pulse signal S2 are input detects the amplified pulse signal S5 when the synchronization timing pulse signal S2 is Low (referred to as a period sect_2). When the amplified pulse signal S5 is detected in the period sect_2, it is normally at the Low level, and a high level pulse is generated in the stop signal S501 output to the synchronous timing circuit 5.

  When the stop signal S501, which is a Hi level pulse signal, is input from the ambient light detection unit 200, the synchronization timing circuit 5 turns off the synchronization timing pulse signal S2 (for example, fixes it to the Low level). As a result, the synchronization timing pulse signal S2 does not include a pulse signal (a synchronization signal P1 described later).

  In the pulse modulation type photodetecting device 50 according to the present embodiment, the synchronization signal P1 that is a high-level pulse signal is detected until asynchronous light such as disturbance light (light that is not synchronized with the synchronization timing pulse signal S2) is detected. Is output once per cycle. The synchronization signal P1 is a signal included in the amplified pulse signal S5.

  Here, consider a case where an asynchronous signal N1 generated by asynchronous light and included in the amplified pulse signal S5 is detected in the first period. In this case, a high-level pulse is generated in the stop signal S501 output from the disturbance light detection unit 200 to the synchronization timing circuit 5. When the stop signal S501, which is a Hi level pulse signal, is input to the synchronization timing circuit 5, the synchronization timing pulse signal S2 is turned OFF, and the synchronization timing pulse signal S2 after the second period includes the synchronization signal P1. Disappear.

  When the synchronization timing pulse signal S2 is turned off, the light emitting element driving circuit 6 turns off the light emitting pulse signal S3 that is a current signal for driving the light emitting element 7. As a result, the light emitting element 7 is turned off, and the light emission, that is, the projection of the pulsed light L2 is stopped.

  Here, as a method for detecting asynchronous light, there is no problem even if a method obtained by integrating asynchronous light signals and a method for detecting the peak of asynchronous light are employed. However, when the method of detecting the peak of the synchronous light is adopted, it is desirable to set the comparator threshold lower in order to detect the asynchronous light at a lower light level than the synchronous light.

  A summary of the pulse modulation type photodetecting device 50 of FIG. 1 is as follows. First, when one of the following phenomena (a) to (c) occurs, the light receiving element 8 receives external light synchronized with the pulsed light L2 even though the object B is not present. That is, (a) a signal by reflected light from an object other than the object B (reflected light inside the pulse modulation type photo-detecting device 50 or reflected light from the casing of the pulse modulation type photo-detecting device 50) and inverter fluorescent lamp light When a signal due to disturbance light is superimposed, (b) When a noise signal due to an inrush current generated when the light emitting element 7 is turned on and a signal due to the disturbance light are superimposed, or (c) a pulse modulation type photodetection device In a copying machine using 50, if there is always light that has a certain level of brightness and should not be detected, the light receiving element 8 is synchronized with the pulsed light L2 even though there is no target to be detected. The external light is received. In this case, external light that is not synchronized with the pulsed light L2 is also received.

  As a result, the detection of synchronized light as if there is a detection target despite the absence of the object B is performed, and the following phenomena (1) and (2) occur. That is, (1) an amplified pulse signal S5 that is not synchronized with the synchronization timing pulse signal S2 is output, and (2) the first comparison signal is generated during a period when the synchronization timing pulse signal S2 is at the inactive level. The

  Here, according to the above configuration, (1) when the amplified pulse signal S5 that is not synchronized with the synchronization timing pulse signal S2 is output, the disturbance light detection unit 200 determines that the amplified pulse signal S5 and the synchronization timing pulse signal S2 Are not synchronized and the generation of the synchronization timing pulse signal S2 is stopped (for example, fixed to Low). Specifically, the generation of the synchronization timing pulse signal S2 is stopped by outputting a stop signal S501 from the disturbance light detection unit 200 to the synchronization timing circuit 5.

  Therefore, (2) when the first comparison signal is generated during the period when the synchronization timing pulse signal S2 is at the inactive level, the light emitting element 7 can be turned off.

  Since the light emitting element 7 is turned off, the signal processing circuit 11 determines that there is no object B by outputting the comparator output pulse signal S6 when the synchronization timing pulse signal S2 is not output.

  Therefore, it is possible to provide the pulse modulation type photodetecting device 50 that does not cause a malfunction that is erroneously determined to be present when the object B is present even though the object B is not present.

  The pulse modulation type photo detector 50 shown in FIG. 1 turns off the synchronous light by turning off the light emitting element 7 to prevent malfunction when it detects asynchronous light. However, the current flowing through the light emitting element 7 is completely eliminated. Turn off. For this reason, there is a possibility that a delay occurs when the light emitting element 7 is turned on, making it difficult to react quickly. A pulse modulation type photodetection device 51 described below solves this problem.

[Pulse modulation type photodetection device 51]
FIG. 3 is a block diagram of the pulse modulation type photodetector 51 according to the present embodiment. The pulse modulation type photo detector 51 includes a disturbance light detection unit 201 (generation circuit) as in the case of the pulse modulation type photo detector 50 of FIG. In the pulse modulation type photodetecting device 51 of FIG. 3, a coupling capacitor C <b> 1 is provided at the output of the amplifier 9. Since the coupling capacitor C1 is provided, the amplified pulse signal S5 output to the comparator 10 and the ambient light detection unit 201 includes only an AC component.

  The disturbance light detection unit 201 to which the amplified pulse signal S5 output from the coupling capacitor C1 and the synchronization timing pulse signal S702 output from the synchronization timing circuit 705 (pulse signal generation circuit) are input includes the synchronization timing pulse signal S702. The amplified pulse signal S5 in the low period sect_2 is detected. When the amplified pulse signal S5 is detected in the period sect_2, it is normally at the low level, and a high level pulse is generated in the generation signal S701 output to the synchronous timing circuit 705.

  When the generation signal S701, which is a Hi-level pulse signal, is input from the ambient light detection unit 201, the synchronization timing circuit 705 emits a preceding signal S703 (first signal) in addition to the synchronization timing pulse signal S702. The data is output to the element driving circuit 706.

  FIG. 4 is a circuit diagram showing a light emitting element driving circuit 706 included in the pulse modulation type photodetecting device 51 of FIG. The light-emitting element driving circuit 706 in FIG. 4 is a circuit that supplies a current I1 (first current) and a current I2 (second current) for driving the light-emitting element 7 to the light-emitting element 7, and a constant current source 701 ( A first current source), a switch SW701, a constant current source 702, and a switch SW702. In the light emitting element 7, a current that is the sum of the current corresponding to the level of the synchronization timing pulse signal S702 and the current corresponding to the level of the preceding signal S703 flows.

  In FIG. 4, a constant voltage V is input to the power supply voltage input terminal of the light emitting element driving circuit 706 and the power supply voltage input terminal of the light emitting element 7. The synchronization timing pulse signal S702 is input to the control input of the switch SW701. A pre-stage signal S703 is input to the control input of the switch SW702. Before the disturbance light detection unit 201 determines that the amplified pulse signal S5 and the synchronization timing pulse signal S702 are not synchronized with each other, the preceding stage signal S703 is supplied with the current I2 until the synchronization timing pulse signal S702 becomes the active level. It is a signal for flowing through the light emitting element 7.

  The input of the constant current source 701 and the input of the constant current source 702 are connected to the input of the light emitting element 7. A light emission pulse signal S 707 that is a current signal for driving the light emitting element 7 is input to the light emitting element 7.

  The output of the constant current source 701 is connected to one end of the switch SW701. The output of the constant current source 702 is connected to one end of the switch SW702.

  The other end of the switch SW701, the other end of the switch SW702, and the other end of the light emitting element 7 are electrically grounded.

  The switch SW701 is ON / OFF controlled by a synchronization timing pulse signal S702, and the switch SW702 is ON / OFF controlled by a preceding signal S703.

  The current I1 of the constant current source 701 is a current for projecting the pulsed light L2 synchronized with the synchronization timing pulse signal S702. The current I2 of the constant current source 702 is used as a current (referred to as a pre-current) that flows through the light emitting element 7 before the current I1 of the constant current source 701 flows through the light emitting element 7. The current I2 of the constant current source 702 is smaller than the current I1 of the constant current source 701, and the pulsed light L2 is not projected from the light emitting element 7 even if the current I2 of the constant current source 702 flows to the light emitting element 7.

  The constant current source 702 can be used as a direct current source, and can also be used as a current source for flowing the pre-current. In either case, the switch SW702 is controlled to be turned on / off by the previous signal S703.

  FIG. 5 is a timing chart of each pulse signal when the constant current source 702 is used as a direct current source in the pulse modulation type photodetector 51 of FIG. In the pulse modulation type photodetecting device 51 according to the present embodiment, the synchronization signal P1 that is a high-level pulse signal is detected until asynchronous light such as disturbance light (light that is not synchronized with the synchronization timing pulse signal S702) is detected. Is output once per cycle. The synchronization signal P1 is a signal included in the amplified pulse signal S5. When the synchronization signal P1 is output, the current I1 flows through the light emitting element 7.

  Here, consider a case where an asynchronous signal N1 generated by asynchronous light and included in the amplified pulse signal S5 is detected in the first period. In this case, the synchronization timing circuit 705 outputs a DC pre-stage signal S703 from the second period based on the generation signal S701 that is a DC signal. As a result, the switch SW702 is turned on, and the constant current source 702 causes a direct current I2 to flow through the light emitting element 7.

  Before flowing the current I1 necessary for projecting the pulsed light L2 through the light emitting element 7, a direct current I2 smaller than the current I1 is passed through the light emitting element 7. Thereby, the fluctuation | variation of the electric current which flows into the light emitting element 7 can be made smaller than the case where the electric current which flows into the light emitting element 7 changes from zero to I1. By reducing the fluctuation of the current, the inrush current flowing through the GND when the current I1 flows can be reduced, so that the malfunction due to the inrush current can be prevented.

  FIG. 6 is a timing chart of each pulse signal when the constant current source 702 is used as a current source for supplying a pre-current in the pulse modulation type photodetecting device 51 of FIG. In the pulse modulation type photodetecting device 51 according to the present embodiment, the synchronization signal P1 that is a high-level pulse signal is detected until asynchronous light such as disturbance light (light that is not synchronized with the synchronization timing pulse signal S702) is detected. Is output once per cycle. The synchronization signal P1 is a signal included in the amplified pulse signal S5. When the synchronization signal P1 is output, the current I1 flows through the light emitting element 7.

  Here, consider a case where an asynchronous signal N1 generated by asynchronous light and included in the amplified pulse signal S5 is detected in the first period. In this case, the synchronization timing circuit 705 outputs a pulse-form previous-stage signal S703 (a signal made up of pulses) that is at the Hi level at the first segment position from the second cycle by the generation signal S701. As a result, a pulse-like current I2 flows at the first segment position (this current I2 is a previous current).

  Before flowing the current I1 necessary for projecting the pulsed light L2 to the light emitting element 7, a pulsed current I2 smaller than the current I1 is passed to the light emitting element 7. Thereby, the fluctuation | variation of the electric current which flows into the light emitting element 7 can be made smaller than the case where the electric current which flows into the light emitting element 7 changes from zero to I1. By reducing the fluctuation of the current, the inrush current flowing through the GND when the current I1 flows can be reduced, so that the malfunction due to the inrush current can be prevented.

  The pulse modulation type photodetecting device 51 in FIG. 3 is summarized as follows. According to the above configuration, the ambient light detector 201 determines whether or not the amplified pulse signal S5 and the synchronization timing pulse signal S702 are synchronized, and the amplified pulse signal S5 and the synchronization timing pulse signal S702 are not synchronized. Until the synchronization timing pulse signal S702 reaches the active level, the preceding signal S703 is used as the synchronization timing circuit 705 in order to cause the synchronization timing circuit 705 to generate the preceding signal S703 that is the second inactive level. A generation signal S 701 that is a signal for generating the signal to be generated is output to the synchronization timing circuit 705.

  As a result, in the light emitting element 7, the current I2 corresponding to the preceding signal S703 flows before the current I1 corresponding to the synchronization timing pulse signal S702 flows.

  Since the current I2 is smaller than the current I1, fluctuations in the current flowing through the light emitting element 7 can be made smaller than when the current flowing through the light emitting element 7 changes from zero to the current I1. By reducing the fluctuation of the current, the inrush current flowing through the GND when the current flows can be reduced. Therefore, the malfunction due to the inrush current ((b) the noise signal due to the inrush current generated when the light emitting element 7 is turned on) , Malfunction when the signal due to the disturbance light L3 '' is superimposed can be prevented.

  Accordingly, it is possible to provide the pulse modulation type photodetecting device 51 that does not cause a malfunction that is erroneously determined to be present when the object B is present even though the object B is not present.

  Next, as for the detection method of asynchronous light, disturbance light that has a high possibility of causing malfunction is uniformly generated light such as light of an inverter fluorescent lamp as shown in FIG. In the case of only pulsed light, the possibility of malfunction is small. Therefore, the possibility of causing a malfunction can be reduced by only treating the disturbance light generated uniformly as asynchronous disturbance light (noise light causing malfunction).

  As a method of detecting the asynchronous disturbance light, there is a method of integrating a signal generated by the asynchronous light. By integrating the generated signal, uniform disturbance light and infrequent pulse light can be separated. However, it is necessary to consider that an integration circuit is required and that it is difficult to set an integral value to be determined.

  In the pulse modulation type photo detectors 52 and 53 according to the present embodiment shown below, it is possible to distinguish between uniformly generated disturbance light such as inverter light and single disturbance light having a low frequency. Each pulse modulation type photodetection device will be described.

[Pulse modulation type photodetection device 52]
FIG. 7 is a block diagram of the pulse modulation type photodetector 52 according to the present embodiment. The pulse modulation type photo detector 52 of FIG. 7 is obtained by adding a register 800 to the pulse modulation type photo detector 50 of FIG. The register 800 is provided inside the ambient light detection unit 200.

  FIG. 8 is a timing chart of each pulse signal in the pulse modulation type photodetecting device 52 of FIG. In FIG. 8, S <b> 1 is a pulse signal of the oscillation circuit 4, and S <b> 2 is a synchronization timing pulse signal output from the synchronization timing circuit 5. In addition, the light emitting element 7 is driven by the light emission pulse signal S3, and the signal received by the light receiving element 8 is amplified by the amplifier 9 and output to the comparator 10 as the amplified pulse signal S5. Then, the comparator 10 outputs a comparator output pulse signal S6 to the signal processing circuit 11, and the signal processing circuit 11 compares the synchronization timing pulse signal S2 with the comparator output pulse signal S6.

  The asynchronous light detection unit included in the signal processing circuit 11 of the pulse modulation type photodetector 52 in FIG. 7 detects asynchronous light (that is, whether the amplified pulse signal S5 and the synchronous timing pulse signal S2 are synchronized) during one cycle. The determination of whether or not) is performed a plurality of times (M times). The register 800 stores the number M of asynchronous light detections. The detection number M is output from the signal processing circuit 11 to the register 800.

  As for the detection of asynchronous light in the pulse modulation type photodetection device 52, the disturbance light detection unit 200 to which the amplified pulse signal S5 and the synchronization timing pulse signal S2 are input is the amplified pulse in the period sect_2 in which the synchronization timing pulse signal S2 is Low. The signal S5 (that is, asynchronous light) is detected M times. If the amplified pulse signal S5 (that is, asynchronous light) is detected a predetermined number of times or more in the period sect_2, it is determined that uniform asynchronous disturbance light is detected (that is, it is determined that noise light that causes a malfunction is detected).

  The disturbance light detection unit 200 outputs a stop signal S501 corresponding to the detection result of uniform asynchronous disturbance light to the synchronous timing circuit 5. The synchronization timing circuit 5 stops the synchronization timing pulse signal S2 if the stop signal S501 indicates that asynchronous light has been detected a predetermined number of times or more. On the other hand, if the stop signal S501 indicates that the number of asynchronous light detections is less than the predetermined number, the possibility of malfunction is low. Therefore, the synchronization timing circuit 5 maintains a normal detection state.

  The pulse modulation type photo detector 52 of FIG. 7 will be summarized. As described above, disturbance light that has a high possibility of causing malfunction is light that is uniformly generated, such as light from an inverter fluorescent lamp. For example, in the case of only single-shot pulse light with a low frequency, the possibility of malfunction is small. .

  Therefore, in the pulse modulation type photodetecting device 52 of FIG. 7, it is uniform when it is determined that the amplification pulse signal S5 and the synchronization timing pulse signal S2 are not synchronized more than a predetermined number of times in the plurality of determinations. Disturbance light generated in is treated as asynchronous disturbance light (noise light that causes malfunction). If the number of times that the amplified pulse signal S5 and the synchronization timing pulse signal S2 are not synchronized is less than the predetermined number of times, a stop signal S501 for stopping the generation of the synchronization timing pulse signal S2 is set to the synchronization timing. Normal operation is performed without outputting to the circuit 5. Thereby, the possibility of causing a malfunction can be reduced.

  Note that, when trying to detect uniform asynchronous disturbance light such as inverter light, the disturbance light detection unit 200 causes malfunction when the amplified pulse signal S5 (that is, asynchronous light) is detected M times in the period sect_2. It is desirable to determine that noise light has been detected.

  7 includes the register 800 in the disturbance light detector 200 of the pulse modulation photodetector 50 of FIG. 1, the disturbance of the pulse modulation photodetector 51 of FIG. A register 800 may be included in the light detection unit 201. This makes it possible to determine whether or not the amplified pulse signal S5 and the synchronization timing pulse signal S702 are synchronized a plurality of times (M times), so that uniform asynchronous disturbance light such as inverter light is detected. be able to.

[Pulse Modulation Photodetector 53]
FIG. 9 is a block diagram of the pulse modulation type photodetector 53 according to the present embodiment. FIG. 10 is a timing chart of each pulse signal in the pulse modulation type photodetector 53 of FIG. In the pulse modulation type photo detector 53 of FIG. 9, until the asynchronous light such as disturbance light is detected, the sync light 1 is detected by the sync timing pulse signal S2 as in the case of the pulse modulation type photo detector 50 of FIG. One light is emitted per cycle.

  Here, as shown in FIG. 10, a case is considered in which the number of times the asynchronous signal N1 is input during the first period is equal to or less than a predetermined number. In this case, the disturbance light detection unit 200 determines that uniform asynchronous disturbance light such as inverter light that should be detected is not detected, and outputs the frequency change signal S901 to the oscillation circuit 4. The oscillation circuit 4 changes the frequency of the basic clock signal S1 based on the frequency change signal S901. In FIG. 14, as the frequency of the basic clock signal S1 is changed from the third period, the third period is changed to 36 μsec with respect to 48 μsec of the first and second periods.

  As described above, when uniform asynchronous disturbance light that should be detected a predetermined number of times in one cycle is not detected a predetermined number of times, it is used for detecting the frequency of the uniform asynchronous disturbance light and the disturbance light. The frequency of the basic clock signal S1 is shifted.

  Therefore, before determining whether or not a single disturbance light that is not uniform is detected, the frequency (detection frequency) of the basic clock signal S1 is increased, and the disturbance light is detected again. It becomes possible to detect ambient light with high accuracy and prevent malfunctions with higher accuracy.

[Continue detection of object B]
In the pulse modulation type photo detectors 50, 52 and 53 according to the present embodiment, the determination by the disturbance light detection unit 200 is periodically performed, and a stop signal S501 is output to the synchronization timing circuit 5 to generate the synchronization timing pulse signal S2. If the asynchronous light is not detected after the stop (that is, if the disturbance light detection unit 200 determines that the state where the amplified pulse signal S5 and the synchronization timing pulse signal S2 are out of synchronization has been eliminated), the stop is performed. The output of the signal S501 may be stopped and the output of the synchronization timing pulse signal S2 may be restarted. Similarly, in the pulse modulation type photodetector 51 according to the present embodiment, the determination by the disturbance light detection unit 201 is periodically performed, and after the generation signal S701 is output to the synchronous timing circuit 5, the asynchronous light is not detected. If this is the case (that is, if the disturbance light detection unit 201 determines that the state where the amplified pulse signal S5 and the synchronization timing pulse signal S2 are out of synchronization has been eliminated), the output of the generation signal S701 may be stopped. Thereby, it becomes possible to detect the object B continuously.

〔Electronics〕
Since the electronic apparatus according to the present invention includes any one of the pulse modulation type photodetecting devices 50 to 53, the malfunction that is erroneously determined that the object B is present does not occur even though the object B is not present. .

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  The pulse modulation type photodetection device of the present invention can prevent malfunction due to inrush current (mutation current) generated when the light emitting element is turned on, so that FA and OA equipment such as copying machines and printers, and game machines, etc. It can be suitably used for electronic devices such as amusement devices.

50 to 53 Pulse modulation type photodetector 1 Constant voltage circuit 2 Power supply terminal 3 GND terminal 4 Oscillation circuit 5,705 Synchronization timing circuit (pulse signal generation circuit)
6 Light-Emitting Element Drive Circuit 7 Light-Emitting Element 8 Light-Receiving Element 9 Amplifier 10 Comparator 11 Signal Processing Circuit (Determination Circuit)
12 Output circuit 13 Output terminal 14 Load 15 Power supply 200 Ambient light detector (stop circuit)
201 Ambient light detector (generation circuit)
701 Constant current source 702 Constant current source 706 Light emitting element driving circuit 800 Register B Object C1 Coupling capacitance I1 Current (first current)
I2 current (second current)
L2 Pulse light L3 Reflected light M Number of detections N1 Asynchronous signal P1 Synchronization signal S1 Basic clock signal S2, S702 Synchronization timing pulse signal (pulse signal)
S3 Light emission pulse signal S4 Light reception pulse signal S5 Amplification pulse signal (voltage signal)
S6 Comparator output pulse signal (comparison signal)
S7 Signal processing circuit output signal S501 Stop signal S701 Generation signal S703 Previous stage signal (first signal)
S707 Light emission pulse signal S901 Frequency change signal SW701 switch SW702 switch Sth determination level (predetermined reference value)
V constant voltage sect_1 period sect_2 period

Claims (15)

A pulse signal generation circuit that modulates an input clock signal to generate a pulse signal composed of an active level and an inactive level;
A light-emitting element that is driven so that current flows during the active level period and current does not flow during the inactive level period, and pulse light synchronized with the period when the pulse signal is at the active level is predetermined. A light-emitting element that emits light in the space,
A light receiving element arranged to receive the pulsed light reflected by the detection target passing through the predetermined space and generating a current signal according to the received light;
An amplifier for generating a voltage signal by performing current-voltage conversion and amplification on the current signal;
Comparing the voltage signal with a predetermined reference value, from a first comparison signal indicating that the voltage signal is higher than the reference value and a second comparison signal indicating that the voltage signal is less than or equal to the reference value A comparator that generates a comparison signal
If the first comparison signal and the pulse signal are synchronized and the first comparison signal is not generated during a period when the pulse signal is at the inactive level, it is determined that the detection target exists, On the other hand, a determination circuit is provided that determines that the detection target does not exist if the second comparison signal is generated or the first comparison signal is generated during a period when the pulse signal is at the inactive level. A pulse modulation type photodetection device,
It is determined whether or not the voltage signal and the pulse signal are synchronized, and when it is determined that the voltage signal and the pulse signal are not synchronized, a stop signal for stopping the generation of the pulse signal is used as the pulse signal. A pulse modulation type photodetecting device comprising a stop circuit for outputting to a generating circuit.   2. The pulse modulation type photodetector according to claim 1, wherein the stop circuit determines whether or not the voltage signal and the pulse signal are synchronized with each other a plurality of times.   The stop circuit determines that noise light causing malfunction is detected if it is determined a predetermined number of times that the voltage signal and the pulse signal are not synchronized in the plurality of determinations. The pulse modulation type photodetecting device according to claim 2. The stop circuit, in the plurality of determinations,
If it is determined a predetermined number of times that the voltage signal and the pulse signal are not synchronized, the stop signal is output to the pulse signal generation circuit,
If the number of times that the voltage signal and the pulse signal are not synchronized is less than the predetermined number, the normal operation is performed without outputting the stop signal to the pulse signal generation circuit. The pulse modulation type photo detection device according to claim 2 or 3.   The stop circuit increases the frequency of the clock signal if the number of determinations that the voltage signal and the pulse signal are not synchronized is less than the predetermined number in the plurality of determinations. The pulse modulation type photo detection device according to claim 3 or 4.   The determination by the stop circuit is periodically performed, and it is determined that the state in which the voltage signal and the pulse signal are not synchronized is eliminated after the stop circuit outputs the stop signal to the pulse signal generation circuit. Then, the output of the stop signal is stopped. The pulse modulation type photo detection device according to claim 1, wherein The input clock signal is modulated to generate a pulse signal composed of an active level and a first inactive level, and a first signal composed of the first inactive level and the second inactive level. A pulse signal generation circuit for generating a signal of 1;
The sum of the current corresponding to the level of the pulse signal and the current corresponding to the level of the first signal flows, and during the period in which the pulse signal is at the active level, the current corresponding to the level of the pulse signal In a period in which the first current is supplied as the current and the first signal is at the second inactive level, the current corresponding to the level of the first signal is a current smaller than the first current. A light-emitting element that is driven so that two currents are supplied, the light-emitting element emitting a pulsed light corresponding to the sum of currents to a predetermined space;
A light receiving element arranged to receive the pulsed light reflected by the detection target passing through the predetermined space and generating a current signal according to the received light;
An amplifier for generating a voltage signal by performing current-voltage conversion and amplification on the current signal;
Comparing the voltage signal with a predetermined reference value, from a first comparison signal indicating that the voltage signal is higher than the reference value and a second comparison signal indicating that the voltage signal is less than or equal to the reference value A comparator that generates a comparison signal
If the first comparison signal and the pulse signal are synchronized and the first comparison signal is not generated during a period in which the pulse signal is at the first inactive level, there is an object to be detected. On the other hand, if the second comparison signal is generated or the first comparison signal is generated during a period when the pulse signal is at the inactive level, a determination circuit that determines that there is no detection target. A pulse modulation type photodetecting device comprising:
After determining whether or not the voltage signal and the pulse signal are synchronized, and after determining that the voltage signal and the pulse signal are not synchronized, until the pulse signal becomes the active level, In order to cause the pulse signal generation circuit to generate the first signal having an inactive level of 2, the generation signal, which is a signal for causing the pulse signal generation circuit to generate the first signal, A pulse modulation type photodetection device comprising a generation circuit for outputting to a generation circuit.   8. The pulse modulation type photo detector according to claim 7, wherein the generated signal is a DC signal.   8. The pulse modulation type photo detector according to claim 7, wherein the generated signal is a pulse signal.   10. The pulse modulation type photo detection device according to claim 7, wherein the generation circuit determines whether or not the voltage signal and the pulse signal are synchronized with each other a plurality of times.   The generation circuit determines that noise light causing a malfunction is detected if it is determined that the voltage signal and the pulse signal are not synchronized for a predetermined number of times in the plurality of determinations. The pulse modulation type photo detection device according to claim 10. The generation circuit, in the plurality of determinations,
If it is determined that the voltage signal and the pulse signal are not synchronized more than a predetermined number of times, the generation signal is output to the pulse signal generation circuit,
If the number of times that the voltage signal and the pulse signal are not synchronized is less than the predetermined number, the normal operation is performed without outputting the generation signal to the pulse signal generation circuit. The pulse modulation type photo detection device according to claim 10 or 11.   The generation circuit may increase the frequency of the clock signal if the number of determinations that the voltage signal and the pulse signal are not synchronized is less than the predetermined number in the plurality of determinations. The pulse modulation type photo detection device according to claim 11 or 12.   The determination by the generation circuit is periodically performed, and it is determined that the state in which the voltage signal and the pulse signal are not synchronized is eliminated after the generation circuit outputs the generation signal to the pulse signal generation circuit. Then, the output of the generation signal is stopped. The pulse modulation type photo detection device according to claim 7, wherein the generation signal is stopped.   An electronic apparatus comprising the pulse modulation type photodetection device according to claim 1.

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