Light sensor

Abstract

To provide an optical sensor which can provide stable measurement regardless of brightness of surrounding environments.SOLUTION: An optical sensor includes: a light emitting element for radiating light which changes with time; a light reception element for directly or indirectly receiving light radiated from the light emitting element, the light reception element including pn junction; a measurement unit for measuring a current based on an amount of reception of light received by the light reception element; and a bias application unit for applying bias to a light reception element. The bias application unit applies the bias to the light reception element before an operation in which the light emitting element radiates light and the current based on the amount of light reception is measured so that a forward current which flows when the light reception element is turned on is flowed to the pn junction and a yield current which flows when a yield phenomenon occurs in the pn junction is flowed to the pn junction.SELECTED DRAWING: Figure 4A

Description

[Technical Field]

[0001] This invention relates to an optical sensor. [Background technology]

[0002] As an optical sensor, a proximity sensor is known that measures the distance to an object to be detected. In such a proximity sensor, light emitted from an LED is shone onto the object to be detected, and the reflected light from the object is received by a photodiode. Based on the intensity of the received light, the presence or absence of the object and the distance to the object can be measured.

[0003] Furthermore, Patent Document 1 discloses an image sensor using a photodiode as a photoelectric conversion element. In the configuration of Patent Document 1, when the amount of light incident on the photodiode decreases, the resistance of the MOS transistor that converts the sensor current flowing through the photodiode into a voltage increases. To prevent afterimages from being observed for a long period of time as a result, the charge accumulated in the junction capacitance of the photodiode is discharged. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2000-329616 [Overview of the project] [Problems that the invention aims to solve]

[0005] As described above, proximity sensors using photodiodes are known. However, it sometimes takes longer in dark environments than in bright environments for a proximity sensor to achieve stable measurement. In this regard, Patent Document 1 addresses the problem of afterimage observation time caused by the difference in the resistance value of the MOS transistor and the time constant with respect to the junction capacitance of the photodiode, depending on whether the sensor current is large or small. Therefore, applying the configuration of Patent Document 1 does not solve the above problem.

[0006] One aspect of the present invention aims to provide a light sensor capable of stable measurement regardless of the brightness of the surrounding environment. [Means for solving the problem]

[0007] An optical sensor according to one embodiment comprises a light-emitting element that emits light that changes over time, a light-receiving element including a pn junction that directly or indirectly receives light emitted from the light-emitting element, a measuring unit that measures a current generated based on the amount of light received by the light-receiving element, and a bias application unit that applies a bias to the light-receiving element. Before the operation to measure the current generated based on the amount of light received, the bias application unit applies a bias to the light-receiving element, thereby causing a forward current that flows when the light-receiving element is turned on to flow through the pn junction, or a breakdown current that flows when a breakdown phenomenon occurs in the pn junction to flow through the pn junction. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic diagram of an optical sensor according to the first embodiment of the present invention. [Figure 2] This is a circuit diagram of an optical sensor according to the first embodiment of the present invention. [Figure 3] This is a timing chart of various signals in an optical sensor according to the first embodiment of the present invention. [Figure 4A] This is a circuit diagram of the light sensor during standby operation according to the first embodiment of the present invention. [Figure 4B] This graph shows the voltage-current characteristics of the photodiode provided in the light sensor according to the first embodiment of the present invention. [Figure 5A] This is a circuit diagram of the optical sensor during proximity operation according to the first embodiment of the present invention. [Figure 5B] This graph shows the output of the integrating circuit and counter circuit during proximity operation of the optical sensor according to the first embodiment of the present invention. [Figure 6A] This graph shows the relationship between the number of measurements and the count during proximity operation of the optical sensor in the comparative example. [Figure 6B] A graph showing the relationship between the number of measurements and the count number during the proximity operation of the optical sensor according to the first embodiment of the present invention. [Figure 7] A cross-sectional view of the photodiode according to the first embodiment of the present invention. [Figure 8] A cross-sectional view of the photodiode according to the first embodiment of the present invention. [Figure 9] A cross-sectional view of the photodiode according to the first embodiment of the present invention. [Figure 10] A cross-sectional view of the photodiode according to the first embodiment of the present invention. [Figure 11] A circuit diagram of the optical sensor according to the second embodiment of the present invention. [Figure 12A] A circuit diagram of the optical sensor during the standby operation according to the second embodiment of the present invention. [Figure 12B] A circuit diagram of the optical sensor during the proximity operation according to the second embodiment of the present invention. [Figure 13] A circuit diagram of the optical sensor system according to the third embodiment of the present invention.

Mode for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same or equivalent elements are denoted by the same reference numerals, and duplicate descriptions are omitted.

[0010] <First Embodiment> The optical sensor according to the first embodiment of this invention will be described. Hereinafter, as an example of the optical sensor, a proximity sensor will be taken as an example for description.

[0011] First, the configuration of the proximity sensor according to the present embodiment will be described. FIG. 1 is a schematic diagram briefly showing the configuration of the proximity sensor according to the present embodiment, and only the main elements as the proximity sensor are shown.

[0012] As shown in the figure, the proximity sensor (light sensor) 100 comprises a substrate 110, a light-emitting diode (light-emitting element) 120, a photodiode (light-receiving element) 130, a measuring unit 140, a light-emitting lens 150, and a light-receiving lens 160. The substrate 110 is, for example, a PCB (Printed Circuit Board) substrate, and the light-emitting diode 120, photodiode 130, and measuring unit 140 are provided on the substrate 110. The light-emitting diode 120 is driven by a control unit (not shown) to output light and irradiates the object to be detected 200 with this light. In this example, the case using a light-emitting diode 120 is explained, but it is not limited to light-emitting diodes as long as it is a light-emitting element capable of emitting light, such as a laser diode. More specifically, the light output from the light-emitting diode 120 is irradiated onto the object to be detected 200 by the light-emitting lens 150 (light 170). The reflected light 180 from the object to be detected 200 is focused by the light-receiving lens 160 and incident on the photodiode 130. The photodiode 130 receives reflected light 180 from the object to be detected 200 and converts the received light into an electric current. The measurement unit 140 measures the presence and distance of the object to be detected 200 based on the current flowing through the photodiode 130. The measurement unit 140 is, for example, a Proximity Sensor (PS)-ADC (Analog-to-Digital Converter). The PS-ADC is an analog-to-digital conversion circuit that converts the analog input current from the photodiode 130 into a digital value. One example of an analog-to-digital conversion method is one that uses an integration circuit. Of course, the measurement unit 140 is not limited to a PS-ADC; it is not limited to any configuration that can measure the presence and distance of the object to be detected 200 based on the input current from the photodiode 130. In recent years, the photodiode 130 and the PS-ADC 140 are often configured on the same semiconductor chip, but they may be configured on separate semiconductor chips, and the effects described below can be obtained similarly in either configuration.

[0013] In the above configuration, when the object to be detected 200 is close to the proximity sensor 100, the intensity of the reflected light 180 received by the photodiode 130 increases, and the current flowing through the photodiode 130 increases. On the other hand, when the object to be detected 200 is far from the proximity sensor 100, the intensity of the reflected light 180 received by the photodiode 130 decreases, and the current flowing through the photodiode 130 decreases. In other words, by detecting the amount of current flowing through the photodiode 130, it is possible to determine whether the object to be detected 200 is within a certain distance from the proximity sensor 100.

[0014] Figure 2 is a more detailed circuit diagram of the proximity sensor 100 described in Figure 1. As shown in the figure, the proximity sensor 100 broadly comprises a control unit 300, a light-emitting unit 310, a photodiode 130, a measurement unit 140, a bias application unit 320, and a switch unit 330.

[0015] The light-emitting unit 310 comprises a power supply 311, a switch element 312, a current source 313, and a light-emitting diode 120 as described in Figure 1. The switch element 312 is controlled by a signal S3 provided by the control unit 300, and connects the cathode of the light-emitting diode 120 to the current source 313. The anode of the light-emitting diode 120 is also connected to the power supply 311. When the switch element 312 is turned on, for example, when the signal S3 is set to an "H" level, current is applied to the light-emitting diode 120, and the light-emitting diode 120 emits light toward the object 200 to be detected. In this way, the light-emitting diode 120 repeatedly switches between an off (off) state and an on (emitting) state due to the switch element 312. In other words, the light-emitting diode 120 emits light that changes over time. The light-emitting diode 120 may also perform intermittent operation to reduce the current consumption of the proximity sensor 100.

[0016] As explained with reference to Figure 1, the photodiode (light-receiving element) 130 generates current when reflected light 180 from the object to be detected 200 is incident on the pn junction of the photodiode 130. For example, the anode of the photodiode 130 is grounded and the cathode is connected to node N10.

[0017] The bias application unit 320 applies a bias to the photodiode 130. Specifically, before the operation in which the light-emitting diode 120 irradiates light to measure the distance to the object to be detected 200, a bias is applied to the photodiode 130 to allow the forward current that flows when the photodiode 130 is turned on to flow through the pn junction. More specifically, the bias application unit 320 comprises a negative voltage generation circuit 321 and a switch element 322. The negative voltage generation circuit 321 generates a negative voltage according to the control of the control unit 300. This negative voltage is applied to the photodiode 130 during the standby operation described later, and is the voltage that allows the forward current that flows when the photodiode is turned on to flow through the pn junction of the photodiode 130. Details of this operation will be described later. The switch element 322 is controlled by a signal S1 provided by the control unit 300 and connects the negative voltage generation circuit 321 and node N10. Then, when the signal S1 is set to, for example, a "H" level, the switch element 322 is turned on, and the negative voltage generated by the negative voltage generation circuit 321 is applied to node N10, that is, the cathode of the photodiode 130. On the other hand, when the signal S1 is set to, for example, a "L" level, and the switch element 322 is turned off, the negative voltage generation circuit 321 and node N10 are electrically disconnected.

[0018] The switch unit 330 includes a switch element 331. The switch element 331 is controlled by a signal S2 provided by the control unit 300 and connects the measurement unit 140 to node N10, i.e., the light-emitting diode 120. When the signal S2 is set to, for example, an "H" level, the switch element 331 is turned on, and the photodiode 130 and the measurement unit 140 are electrically connected. When the signal S2 is set to, for example, an "L" level, the switch element 331 is turned off, and the photodiode 130 and the measurement unit 140 are electrically disconnected.

[0019] As described above, the measurement unit 140 is, for example, a PS-ADC, and measures the distance to the object to be detected 200 based on the light received by the photodiode 130. The measurement unit 140 includes a current source 400, n-channel MOS transistors 410 and 420, an operational amplifier (amplifier) ​​430, a comparator 440, a capacitive element (capacitor) 450, and a counter circuit 460. MOS transistor 410 receives current from the current source 400 to its drain, its source is connected to node N20 (the inverting input terminal (-) of operational amplifier 430), and a voltage Vdis is applied to its gate. MOS transistor 420 has its source connected to the switch element 331, its drain connected to node N20, i.e., the inverting input terminal of operational amplifier 430, and a voltage Vch is applied to its gate. Operational amplifier 430 has its inverting input terminal (-) connected to node N20, and a reference voltage Vref is applied to its forward input terminal (+). The differential amplified signal between node N20 and the reference voltage Vref is output to node N21 as voltage Vint. One electrode of the capacitive element 450 is connected to node N20, and the other electrode is connected to node N21. The comparator 440 has its forward input terminal (+) connected to node N21, and the reference voltage Vref is applied to its inverting input terminal (-). It then outputs the comparison result between node N21 and the reference voltage Vref. The counter circuit 460 performs a count operation based on the output of the comparator 440 and outputs the count result. In this way, the measurement unit 140 is mainly composed of an operational amplifier 430 and a capacitive element 450 forming an integration circuit, and the count of the counter circuit 460 fluctuates based on the amount of charge generated by the photodiode 130.

[0020] The control unit 300 controls the operation of the entire proximity sensor 100 configured as described above. For example, it controls the operation timing of signals S1, S2, S3, voltages Vdis, Vch, and the negative voltage generation circuit 321.

[0021] Next, the operation of the proximity sensor 100 according to this embodiment will be described. Figure 3 is a timing chart of the operation phase, voltages Vch and Vdis, and signals S1, S2, and S3 of the proximity sensor 100.

[0022] As shown in the figure, the proximity sensor 100, in accordance with the command of the control unit 300, repeatedly performs a standby operation (second operation) in which it does not measure the distance to the object to be detected 200, and a proximity operation (first operation) in which it measures the distance to the object to be detected 200. The standby operation is performed before the proximity operation. First, the standby operation will be explained. The standby operation is performed by applying a bias to the photodiode 130 using the bias application unit 320 and passing current through the pn junction of the photodiode 130, thereby making the state of the lattice defects, which will be described later, approximately equal in the light environment and the dark environment, and is performed before the proximity operation. Note that in the example in Figure 3, for the sake of simplicity of explanation, the case in which the standby operation is performed after each proximity operation is shown, but the proximity operation may be performed multiple times in a row.

[0023] As shown in Figure 3, during the standby operation period (times t0-t1, t3-t4), the control unit 300 sets voltages Vch and Vdis to the "L" level, turning off MOS transistors 420 and 410, thereby putting the measurement unit 140 into a non-operating state. The control unit 300 also sets signal S1 to the "H" level and signals S2 and S3 to the "L" level, electrically connecting the bias application unit 320 and the photodiode 130, while electrically disconnecting the photodiode 130 from the measurement unit 140. Furthermore, the light emission unit 310 turns off the switch element 312, stopping the illumination of light by the light-emitting diode 120.

[0024] Figure 4A is a circuit diagram that simply shows the connection relationship between the bias application unit 320, the photodiode 130, the switch unit 330, and the measurement unit 140 during standby operation. As described above, when the switch element 322 is in the ON state and the switch element 331 is in the OFF state, the photodiode 130 is connected to the negative voltage generation circuit 321 and disconnected from the measurement unit 140. Then, based on a command from the control unit 300, the negative voltage generation circuit 321 outputs a negative voltage and applies it to the cathode of the photodiode. At this time, the negative voltage output by the negative voltage generation circuit 321 is the voltage that becomes a forward bias (for example, -0.7V) for the photodiode 130 whose anode is grounded. As a result, the photodiode 130 turns ON and an ON current I ON It plays.

[0025] Figure 4B is a graph showing the voltage-current characteristics of the photodiode 130. As shown in the figure, when a forward (positive) voltage is applied to the photodiode, a certain forward bias V ON From the moment it is applied, the on current I ON The current flows from the anode to the cathode. ON current I ON This is a forward current that increases sharply with voltage. During standby operation, the negative voltage generation circuit 321 applies a negative voltage to the cathode of the photodiode 130. As a result, since the anode of the photodiode 130 is grounded, a forward bias is applied to the pn junction of the photodiode 130. Consequently, a forward current I shown in Figure 4B is applied to the pn junction of the photodiode 130. ON Current flows through the photodiode 130 during standby operation. The reason for passing current through the photodiode 130 is to trap electrons in the lattice defects contained within the photodiode 130, thereby enabling stable proximity operation regardless of whether the environment is dark or bright. This point will be explained in detail later.

[0026] Furthermore, as a characteristic of the photodiode 130, when a reverse bias is applied, the absolute value of the reverse bias voltage remains constant (breakdown voltage V BWhen the voltage exceeds ), breakdown occurs in the pn junction, and a breakdown current Ibreak flows. The breakdown current Ibreak is a reverse current that flows from the anode to the cathode, and like the forward current, it is a current that increases sharply with the voltage. Also, the absolute value of the reverse bias voltage is the breakdown voltage V B It is less than [value], and even when the photodiode is in the off state, a small reverse leakage current Ioff flows. The current I flowing through the photodiode in the standby operation described above. ON The absolute value of is greater than the absolute value of the leakage current Ioff, and also greater than the absolute value of the dark current that flows when no light is incident on the photodiode 130.

[0027] Next, the proximity operation will be explained. As shown in Figure 3, during the proximity operation period (times t1-t3, t4-t6), the control unit 300 first turns on the MOS transistor 420 by setting the voltage Vch to a "H" level during the period t1-t2 (and t4-t5), and turns off the MOS transistor 410 by setting the voltage Vdis to a "L" level. Subsequently, the control unit 300 turns off the MOS transistor 420 by setting the voltage Vch to a "L" level during the period t2-t3 (and t5-t6), and turns on the MOS transistor 410 by setting the voltage Vdis to a "H" level. In addition, the control unit 300 sets signal S1 to a "L" level and signal S2 to a "H" level, thereby electrically disconnecting the bias application unit 320 and the measurement unit 140, and electrically connecting the photodiode 130 and the measurement unit 140 during the proximity operation period. Furthermore, the control unit 300 sets the signal S3 to an "H" level during the period of time t1 to t2 (and t4 to t5), thereby irradiating the object to be detected 200 with light from the light-emitting diode 120.

[0028] Figure 5A is a circuit diagram that simply shows the connection relationship between the bias application unit 320, the photodiode 130, the switch unit 330, and the measurement unit 140 during proximity operation. As described above, when the switch element 322 is in the off state and the switch element 331 is in the on state, the photodiode 130 is connected to the measurement unit 140 and disconnected from the negative voltage generation circuit 321. Also, at time t1 (and t4), the light-emitting diode 120 shines light onto the object to be detected 200, and the reflected light is incident on the photodiode 130, causing a current to flow through the photodiode 130. Then, during the period from time t1 to t2 (and t4 to t5), the MOS transistor 420 is turned on, and a charge corresponding to the current flowing through the photodiode 130 is charged into the capacitive element 450. Subsequently, when the light emission from the light-emitting diode 120 ends at time t2 (and time t5), the MOS transistor 410 is turned ON during the period from time t2 to t3 (and t5 to t6), causing the charge stored in the capacitive element 450 to discharge via the current source 400. In this way, the light-emitting diode 120 repeatedly switches between ON and OFF states, that is, it emits time-varying light onto the object 200 to be detected.

[0029] The operation during the proximity detection described above will be explained using Figure 5B. Figure 5B is a graph showing the output voltage Vint of the operational amplifier 430 and the count value of the counter circuit 460. As shown in the figure, the voltage Vint rises during the period (times t0 to t10) when the MOS transistor 420 is turned on and charge is stored in the capacitive element 450. Then, when the MOS transistor 420 is turned off and the MOS transistor 410 is turned on and the charge stored in the capacitive element 450 begins to discharge, the voltage Vint decreases. The voltage Vref input to the operational amplifier 430 is, for example, zero V. The counter circuit 460 then counts the period from time t10 to time t11 when the voltage Vint becomes zero V, and outputs this count value as a value corresponding to the distance to the detected object 200. In this way, the current flowing through the photodiode 130 charges the capacitive element 450, and the counter circuit 460 counts the time until this charge is discharged. The time until the charge in the capacitive element 450 is gone, that is, the count of the counter circuit 460, is output as a digital value correlated with the distance to the object to be detected 200. In this way, the measurement unit 140 measures the current generated based on the amount of light received by the photodiode 130 and determines the distance to the object to be detected 200 based on this amount of current.

[0030] As described above, the proximity sensor according to this embodiment enables stable measurement regardless of the brightness of the surrounding environment. This effect will be explained below.

[0031] The inventors of this invention discovered a problem in that when measurements are taken in both bright and dark environments, it takes time to obtain stable measurements in the dark environment. Figure 6A is a graph showing the relationship between the number of measurements and the count in a proximity sensor according to a comparative example of this embodiment. In this comparative example, the measurement results during proximity operation when the object to be detected 200 is present, without performing the standby operation described in the above embodiment. In a bright environment, detection can be confirmed from the first measurement, for example, with approximately 900 counts, and the count remains almost constant thereafter. In contrast, in a dark environment, the count in the first measurement is for example, approximately 600 counts, and the count gradually increases thereafter, becoming equivalent to the result in the bright environment after approximately 25 measurements. Thus, in a dark environment, accurate measurement results may not be obtained without waiting for multiple measurements.

[0032] Figure 6B is a graph showing the relationship between the number of measurements and the count in the proximity sensor according to this embodiment, and the results are from measurements taken under the same conditions as in Figure 6A. As shown in the figure, in this embodiment, even in a dark environment, the same count as in a bright environment was obtained in the first measurement.

[0033] The inventors of this application investigated the phenomenon in which accurate measurement results cannot be obtained in the initial measurement in a dark environment, as shown in Figure 6A, as follows. Figure 7 is a cross-sectional view of the photodiode 130. As shown, the photodiode 130 is formed, for example, by providing an n-type well 501 on a p-type silicon substrate 500. In the silicon substrate 500, carriers (electrons) are excited when light is received. These electrons move from the p-type substrate 500 to the n-type well 501, which has a lower energy level, causing a current to flow in the photodiode 130. It is also known that a certain number of lattice defects exist in the silicon substrate 500. Then, as shown in the cross-sectional view of the photodiode 130 according to the comparative example in Figure 8, some of the carriers generated by the proximity signal light (reflected light from the object to be detected 200) in a dark environment are trapped (recombined) by the lattice defects, so it is thought that not all carriers are output as signal components.

[0034] On the other hand, as shown in the cross-sectional view of the photodiode 130 in FIG. 9, in a bright environment, carriers are constantly generated and trapped in lattice defects. Therefore, it is considered that most of the carriers generated by the proximity signal light are output as signal components without being trapped in lattice defects.

[0035] Next, the mechanism by which the proximity measurement results increase when continuously performing proximity operations from a dark environment will be described. It can be considered that the state of the photodiode 130 changes to the state of a bright environment by continuously operating the proximity operation from a dark environment. FIG. 10 is a cross-sectional view of the photodiode 130 according to a comparative example and shows the state change of the photodiode 130 when continuously performing proximity operations from a dark environment. As shown in the figure, in a dark environment, the lattice defects are in the most numerous state. When performing a proximity operation in this state, many of the carriers generated by the proximity signal light are output from the photodiode as signal components, but due to the existence of lattice defects, the carriers are probabilistically trapped (recombined) in the lattice defects and are considered not to be output as signals. By repeatedly performing the proximity operation, it is considered that many of the lattice defects are recombined with the carriers and finally approach the lattice state of a bright environment.

[0036] Based on the above examination results, in the present embodiment, by making the state of lattice defects before the proximity operation the same in both the dark environment and the bright environment, this problem (it takes time for the proximity measurement results to stabilize in a dark environment) can be solved. Specifically, during the standby operation, by applying a voltage to the photodiode 130 to allow current to flow, it is possible to reduce the lattice defects in the silicon substrate 500. That is, before the operation of measuring the distance to the detection target object by irradiating light with the light-emitting element (proximity operation), the bias application unit 320 applies a bias (negative voltage in this example) to the photodiode (light-receiving element) 130. As a result, the forward current I that flows when the photodiode 130 is turned on ONA current is passed through the pn junction of the photodiode. In other words, electrons are injected into the pn junction of the photodiode 130. This traps electrons in the lattice defects within the silicon substrate 500. That is, the number of carriers trapped in the defect levels after a forward current is passed through the pn junction of the photodiode 130 is greater than the number of carriers trapped in the defect levels before the forward current is passed through the pn junction. As a result, by trapping electrons in the lattice defects of the photodiode 130 in advance before performing proximity operation, a lattice state equivalent to that in a bright environment can be obtained even in a dark environment. Therefore, even in a dark environment, almost all of the carriers generated by reflected light can be extracted as signal components from the beginning of the measurement. In this way, by applying a voltage to the photodiode 130 and passing a current before proximity operation, the distance to the object to be detected 200 can be measured under equivalent conditions in both dark and bright environments, enabling stable measurement regardless of the brightness of the surrounding environment and solving the present problem.

[0037] It is also known that diodes have the characteristic of emitting a weak amount of light when current is passed through them. It is possible that carriers are generated within the photodiode due to the weak light emitted by the photodiode itself, but even in this case, it is possible to reduce the difference in the lattice state within the silicon substrate 500 between the light environment and the dark environment by applying a bias to the photodiode 130.

[0038] <Second Embodiment> Next, a second embodiment of the optical sensor will be described. In this embodiment, the bias application unit 320 described in the first embodiment is realized by forming a bipolar transistor instead of the negative voltage generation circuit 321. Below, only the differences from the first embodiment will be described.

[0039] Figure 11 is a circuit diagram showing the bias application unit 320, photodiode 130, switch unit 330, and measurement unit 140 in the proximity sensor 100 according to this embodiment. As shown in the figure, the bias application unit 320 according to this embodiment includes a current source 323, a diode 324, and switch elements 325, 326, and 327. The current source 323 is connected to the anode of the diode 324 via the switch element 325. The switch element 325 is controlled, for example, by a signal S4 provided from the control unit 300, and turns on when the signal S4 is, for example, at the "H" level. The cathode of the diode 324 is connected to node N10, that is, the cathode of the photodiode 130. Therefore, the diode 324 and the photodiode 130 function as pnp bipolar transistors, with their respective cathodes corresponding to the base electrode. The switch element 326 connects the anode of the diode 324 to node N10. Switch element 326 is controlled, for example, by a signal S6 provided by the control unit 300, and turns on when signal S6 is set to, for example, an "H" level. Switch element 327 connects node N10, that is, the connection node between the cathode of diode 324 and the cathode of photodiode 130, to, for example, a ground node (first node). Switch element 327 is controlled, for example, by a signal S5 provided by the control unit 300, and turns on when signal S5 is set to, for example, an "H" level.

[0040] Figure 12A shows the operation of the bias application unit 320 during standby operation. As shown in the figure, during standby operation, the control unit 300 sets signals S4 and S5 to the "H" level and signal S6 to the "L" level. This turns on the switch elements 325 and 327. Then, the base potential of node N10, i.e., the bipolar transistor composed of diode 324 and photodiode 130, becomes zero V, and the bipolar transistor turns on. As a result, current flows from the current source 323 to the photodiode 130 through diode 324 and node N10. At this time, a reverse bias is applied to the pn junction in the photodiode 130, causing a breakdown phenomenon to occur in the pn junction, and the breakdown current Ibreak described in Figure 3B flows. The absolute value of the breakdown current Ibreak is the current I described in the first embodiment. ON Similarly, it is greater than the absolute value of the leakage current Ioff, and also greater than the absolute value of the dark current that flows when no light is incident on the photodiode 130. Although the above explanation was given using the example where the potential of the first node to which the base of the bipolar transistor is connected by the switch element 327 is at ground potential (zero V), it is not necessarily limited to ground potential; any potential that allows a breakdown current to flow through the photodiode 130 when the bipolar transistor is in the ON state is acceptable.

[0041] Figure 12B shows the operation of the bias application unit 320 during proximity operation. As shown in the figure, during proximity operation, the control unit 300 sets signals S4 and S5 to the "L" level and signal S6 to the "H" level. As a result, switch elements 325 and 327 are turned off, and switch element 326 is turned on. Consequently, the anode and cathode of diode 324 are at the same potential, and the cathodes of diode 324 and photodiode 130 are electrically disconnected from the first node. Therefore, the bipolar transistor composed of diode 324 and photodiode 130 is turned off, and no current flows from the current source 323 to the photodiode 130. Then, switch element 331 is turned on, and the charge based on the current flowing due to reflected light from the object to be detected 200 is charged into the capacitive element 450 of the measurement unit 140.

[0042] As described above, the bias application section 320 may be realized by configuring a bipolar transistor. In the first embodiment, the case in which a negative voltage generation circuit 321 is used as the bias application section 320 was described. However, depending on the semiconductor process used and the allowable chip size, it may be difficult to use a negative voltage circuit. In that case, the same effect as in the first embodiment can be obtained by applying a reverse bias to the photodiode 130 and allowing a breakdown current to flow. However, with a normal power supply voltage (for example, around 1.8 to 3.6V), it may not be possible to supply sufficient current. In such cases, as in this embodiment, a pnp type bipolar transistor can be formed by connecting the cathode of another diode (photodiode) to the cathode of the photodiode 130. This makes it possible to supply current to the photodiode 130 even with a normal power supply voltage.

[0043] Furthermore, according to this method, by passing a breakdown current Ibreak through the photodiode 130, carriers can be injected into the pn junction of the photodiode 130, similar to the first embodiment. As a result, even in a dark environment, a lattice state equivalent to that in a bright environment can be obtained by trapping carriers in the lattice defects of the photodiode 130 in advance before proximity operation is performed. Therefore, even in a dark environment, almost all of the carriers generated by reflected light can be extracted as signal components from the beginning of the measurement.

[0044] <Third Embodiment> Next, a light sensor according to the third embodiment will be described. In the first and second embodiments described above, the case in which the proximity sensor 100 is equipped with a light-emitting element 120 was described as an example. In contrast, this embodiment relates to a configuration in which the proximity sensor 100 does not have a light-emitting element, and the light-emitting element and the light-emitting element driving circuit are provided outside the proximity sensor 100. In the following, only the differences from the first and second embodiments will be described.

[0045] Figure 13 is a circuit diagram of the optical sensor system according to this embodiment. As shown in the figure, the optical sensor system includes a proximity sensor 100 and a light-emitting element driving circuit 1000. The configuration of the proximity sensor 100 is substantially the same as that of the first and second embodiments described above, but in the configuration of Figure 2 described in the first embodiment, the light-emitting unit 310 is eliminated and an output circuit 600 is newly provided. In Figure 13, the case in which the negative voltage generation circuit 321 described in the first embodiment is used as the bias application unit 320 is shown, but a bipolar transistor may be configured as described in Figure 11 of the second embodiment. The control unit 300 outputs a signal S3 to the output circuit 600 for driving the light-emitting element at the timing shown in Figure 3, for example, as described in the first embodiment. The output circuit 600 outputs the received signal S3 to the light-emitting element driving circuit 1000 outside the proximity sensor 100.

[0046] The light-emitting element driving circuit 1000 corresponds to the light-emitting unit 310 described in the first embodiment and has the same configuration as the light-emitting unit. As shown in the figure, the light-emitting element driving circuit 1000 includes a light-emitting diode (light-emitting element) 1120, a switch element 1312, and a current source 1313. In this example, the light-emitting diode 1120 performs the same function as the light-emitting element 120 described in Figure 1. The switch element 312 is controlled by a signal S4 provided from the output circuit 600 and connects the cathode of the light-emitting diode 1120 to the current source 1313. The anode of the light-emitting diode 1120 is also connected to the power supply. When the switch element 1312 is turned on, for example, when the signal S4, i.e., signal S3, is set to the "H" level, a current is applied to the light-emitting diode 1120, and the light-emitting diode 1120 irradiates light toward the object 200 to be detected. Furthermore, the light-emitting element driving circuit 1000 may include a driving circuit (not shown) for controlling the light-emitting diode 1120, or, although not shown, the switch element 1312 and current source 1313 may be located inside the proximity sensor 100, with only the light-emitting diode 1120 located outside the proximity sensor 100.

[0047] According to this embodiment, the proximity sensor 100 and the light-emitting element 1120 are provided independently of each other. Therefore, it is particularly useful in applications where it is desirable to increase the distance between the light-emitting element 1120 and the light-receiving element 130. <Variations, etc.> As described above, the optical sensors according to the first and second embodiments can improve the reliability of proximity operation regardless of whether the environment is dark or bright. Although various embodiments have been described above, the embodiments are not limited to those described above, and various modifications are possible.

[0048] For example, in the above embodiment, the case of a pn junction diode was described as an example for the photodiode 130, but a PIN type diode with an intrinsic semiconductor layer between the p-type layer and the n-type layer may also be used. Also, in the first embodiment, the case of using a negative voltage generation circuit 321 as the bias application unit 320 was described as an example. However, depending on the potential of the anode of the photodiode 130, a positive voltage generation circuit may also be used, as long as the configuration can apply a forward bias to the photodiode 130. This is also the case in the second embodiment, and the base potential of the virtual pnp type bipolar transistor is not limited to zero V, but is not limited to any potential at which the bipolar transistor is in the ON state. Furthermore, the period during which current is supplied to the photodiode 130 during standby operation may be controllable by, for example, the control unit 300. Alternatively, the user may set the period for supplying current to the control unit 300. An example of the period for supplying current is, for example, 100 μs, but this depends on the size of the photodiode 130 and the degree of lattice defects. Therefore, the control unit 300 may be configured to have a period set that was deemed appropriate during pre-shipment test operations, or the control unit 300 may perform a proximity operation test when power is turned on to the device equipped with the proximity sensor, and obtain an appropriate period based on the results. Examples of devices equipped with such proximity sensors include smartphones and wireless earphones. For example, when installed in a smartphone, the front of the smartphone is generally a touch panel. Therefore, when a call comes in and the user brings the smartphone close to their ear, the proximity sensor may detect this and disable the touch panel function. Also, proximity sensors are generally placed under the panel of electronic devices such as smartphones. In such cases, there is a possibility of malfunction by misidentifying reflected light from the panel of the electronic device as the object to be detected. To counter this problem, it is effective to increase the distance between the light-emitting element and the light-receiving element, and it is preferable to adopt the configuration described in the third embodiment. In the case of wireless earphones, the proximity sensor may detect when the wireless earphone comes close to the user's ear, and the wireless earphone may output sound based on this.Furthermore, the timing chart explained using Figure 3 is merely an example, and the timing of voltages Vch and Vdis, and signals S1 to S3 can be changed as appropriate, as long as standby and proximity operation are possible. Moreover, although the example of using a PS-ADC as the measurement unit 140 was explained, the configuration is not particularly limited as long as it is possible to calculate the distance to the object to be detected 200 based on the current flowing through the photodiode 130.

[0049] Although several embodiments of the present invention have been described above, the invention is not limited to the above-described forms and can be modified as appropriate. Furthermore, the above configurations can be replaced with substantially similar configurations, configurations that produce similar effects, or configurations that can achieve similar objectives.In addition, although proximity sensors have been described as examples of optical sensors in the above embodiments, the present invention is effective for all semiconductor optical sensors that receive light emitted from light-emitting elements such as photointerrupters that determine the presence or absence of a detected object, and photocouplers that determine the presence or absence of electrical signals.Furthermore, although optical sensors have been described as examples in the above embodiments, the invention is applicable to any situation in which the presence of impurities is problematic in semiconductor substrates or semiconductor layers, and in such cases, by providing the bias application unit 320, the defect rank can be reduced or completely eliminated. [Explanation of Symbols]

[0050] 100…Proximity sensor, 110…Substrate, 120, 1120…Light-emitting diode, 130…Photodiode, 140…Measurement unit, 150, 160…Lens, 170, 180…Light, 200…Detected object, 300…Control unit, 310…Light-emitting unit, 311…Power supply, 312, 322, 325, 326, 327, 331…Switching element, 313, 1313…Current source, 320…Bias application unit, 321…Negative voltage generation circuit, 323, 400…Current source, 324…Diode, 330…Switching unit, 410, 420…MOS transistor, 430…Operational amplifier, 440…Comparator, 450…Capacitor element, 460…Counter circuit, 500…p-type substrate, 501…n-type well, 600…Output circuit, 1000…Light-emitting element driving circuit

Claims

1. A light-emitting element that emits light that changes over time, or a control signal output unit for causing an external light-emitting element to emit light, A photodetector comprising a pn junction, which directly or indirectly receives light emitted from the light-emitting element, A measuring unit that measures the current generated based on the amount of light received by the light-receiving element, A bias application unit that applies a bias to the light-receiving element and It is equipped with, Prior to the operation of measuring the current generated based on the amount of light received, the bias application unit applies the bias to the light receiving element, thereby causing a forward current to flow through the pn junction when the light receiving element is turned on, or a breakdown current to flow through the pn junction when a breakdown phenomenon occurs in the pn junction, in a light sensor, The light-receiving element and the measuring unit are further provided with a switch unit that electrically connects or disconnects them. The switch unit electrically disconnects the light-receiving element and the measuring unit during the period in which the forward current or breakdown current is applied to the pn junction of the light-receiving element. A light sensor that electrically connects the light-receiving element and the measuring unit during a period of time in which the light is irradiated and a current is measured based on the amount of light received.

2. A light-emitting element that emits light that changes over time, or a control signal output unit for causing an external light-emitting element to emit light, A photodetector comprising a pn junction, which directly or indirectly receives light emitted from the light-emitting element, A measuring unit that measures the current generated based on the amount of light received by the light-receiving element, A bias application unit that applies a bias to the light-receiving element and It is equipped with, Prior to the operation of measuring the current generated based on the amount of light received, the bias application unit applies the bias to the light receiving element, thereby causing a forward current to flow through the pn junction when the light receiving element is turned on, or a breakdown current to flow through the pn junction when a breakdown phenomenon occurs in the pn junction, in a light sensor, The light-receiving element is a photodiode with its anode grounded, The bias application section includes a negative voltage generation circuit. The negative voltage generating circuit is a light sensor that applies a forward voltage to the pn junction of the photodiode by applying a negative voltage to the cathode of the photodiode, thereby causing the forward current to flow.

3. A light-emitting element that emits light that changes over time, or a control signal output unit for causing an external light-emitting element to emit light, A photodetector comprising a pn junction, which directly or indirectly receives light emitted from the light-emitting element, A measuring unit that measures the current generated based on the amount of light received by the light-receiving element, A bias application unit that applies a bias to the light-receiving element and It is equipped with, Prior to the operation of measuring the current generated based on the amount of light received, the bias application unit applies the bias to the light receiving element, thereby causing a forward current to flow through the pn junction when the light receiving element is turned on, or a breakdown current to flow through the pn junction when a breakdown phenomenon occurs in the pn junction, in a light sensor, The light-receiving element is a photodiode with its anode grounded, The bias application unit is A diode whose cathode is connected to the cathode of the aforementioned photodiode, A current source connected to the anode of the diode, The photodiode and a switch unit that connects or disconnects the cathode and first node of the diode. Furthermore, The switch unit is a light sensor that causes a breakdown current to flow through the pn junction of the photodiode by connecting the photodiode and the cathode of the diode to the first node.

4. The optical sensor according to claim 3, wherein the first node is grounded.

5. A light-emitting element that emits light that changes over time, or a control signal output unit for causing an external light-emitting element to emit light, A photodetector comprising a pn junction, which directly or indirectly receives light emitted from the light-emitting element, A measuring unit that measures the current generated based on the amount of light received by the light-receiving element, A bias application unit that applies a bias to the light-receiving element and It is equipped with, Prior to the operation of measuring the current generated based on the amount of light received, the bias application unit applies the bias to the light receiving element, thereby causing a forward current to flow through the pn junction when the light receiving element is turned on, or a breakdown current to flow through the pn junction when a breakdown phenomenon occurs in the pn junction, in a light sensor, A light sensor further comprising a control unit that controls the period during which the forward current or the breakdown current is passed through the pn junction of the light-receiving element.

6. A light-emitting element that emits light that changes over time, or a control signal output unit for causing an external light-emitting element to emit light, A photodetector comprising a pn junction, which directly or indirectly receives light emitted from the light-emitting element, A measuring unit that measures the current generated based on the amount of light received by the light-receiving element, A bias application unit that applies a bias to the light-receiving element and It is equipped with, A light sensor in which, before the operation to measure the current generated based on the amount of light received, the bias application unit applies the bias to the light receiving element, thereby causing a forward current that flows when the light receiving element is turned on to flow through the pn junction.

7. The optical sensor according to any one of claims 1 to 5, wherein the absolute values ​​of the forward current and the breakdown current flowing through the bias application unit are greater than the absolute value of the leakage current flowing when the light receiving element is in the off state.

8. The optical sensor according to any one of claims 1 to 5, wherein the absolute values ​​of the forward current and the breakdown current flowing through the bias application unit are greater than the absolute value of the dark current of the photodetector.

9. The light sensor repeatedly performs a first operation of irradiating light with the light-emitting element and measuring a current based on the amount of light received, and a second operation of not measuring a current based on the amount of light received, The optical sensor according to any one of claims 1 to 5, wherein during the second operation, the bias application unit flows the forward current or the breakdown current through the pn junction of the light-receiving element.

10. The optical sensor according to any one of claims 1 to 5, wherein the number of carriers trapped in the defect level after the forward current or the breakdown current is passed through the pn junction is greater than the number of carriers trapped in the defect level before the forward current or the breakdown current is passed through the pn junction.

11. The optical sensor according to any one of claims 1 to 6, wherein the bias application unit is configured on a semiconductor substrate containing impurities, and is a bias application circuit for passing current through the semiconductor substrate in order to reduce defect levels generated by the impurities.

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