Photoelectric conversion device

Abstract

To reduce leakage current caused by a switch that adjusts the gain of an amplifier in a photoelectric conversion device.SOLUTION: A photoelectric conversion device (photoelectric conversion device 100) has a control mechanism in which, when the gain of an amplifier (amplifier 7) is set to a first gain, a first switch (first switch 1) and a third switch (third switch 3) are set to a non-conducting state, and, a second switch (second switch 2) is set to a conducting state, so that, at the first switch (first switch 1), the potential of one end (one end 11) is made the same as the potential of the other end (the other end 12).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a photoelectric conversion device. [Background technology]

[0002] In a photoelectric conversion device, a light detection element such as a photodiode converts a current output in response to received light into a voltage and outputs the voltage.

[0003] Some of such photoelectric conversion devices are provided with a configuration for switching the gain of an amplifier included in the photoelectric conversion device in order to widen the range of light levels to be detected (Patent Document 1). The photoelectric conversion circuit described in Patent Document 1 is provided with a first resistor for setting a gain for detecting low-level light and a second resistor for setting a gain for detecting high-level light, as resistors for setting the gain of the amplifier.

[0004] Patent Document 1 describes a photoelectric conversion circuit having the following configuration. A first switch is connected to a first resistor, and a second switch is connected to a second resistor. When the first switch is in an on state and the second switch is in an off state, the gain of the amplifier is set by the first resistor. When the second switch is in an on state and the first switch is in a non-conducting state, the gain of the amplifier is set by the second resistor. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Actual total number 1-132113 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the photoelectric conversion circuit described in Patent Document 1, when the first switch and the second switch are configured as semiconductor switches, the following problem may occur: When the first switch or the second switch is made non-conductive, if the potentials at both ends of the non-conductive switch are different, leakage current may occur in the switch due to the structure of the semiconductor switch.

[0007] When such leakage current occurs, the photoelectric conversion circuit outputs a voltage that is lower than the voltage level that should be output, and is unable to output a voltage at an accurate level corresponding to the received light.

[0008] The present invention has been made to solve such problems, and its object is to suppress the generation of leakage current due to a switch that switches the gain of an amplifier in a photoelectric conversion device. [Means for solving the problem]

[0009] A photoelectric conversion device according to one aspect of the present invention includes an amplifier having an inverting input terminal, a non-inverting input terminal, and an output terminal; a photodetector connected between the non-inverting input terminal and the inverting input terminal of the amplifier; a first resistor provided between the inverting input terminal and the output terminal of the amplifier and setting a gain of the amplifier to a first gain; a second resistor provided between the inverting input terminal and the output terminal of the amplifier and setting the gain of the amplifier to a second gain; a first switch consisting of a semiconductor switch having one end connected to the second resistor and the other end connectable to the output terminal of the amplifier; a second switch connected to the non-inverting input terminal of the amplifier and having a first terminal receiving a reference potential, a second terminal receiving a reference potential, a third switch connectable between the other end of the first switch and the second terminal; and a control device controlling the first switch, the second switch, and the third switch. When the control device sets the gain of the amplifier to a second gain, it controls the first switch and the third switch to a conductive state and the second switch to a non-conductive state, and when the control device sets the gain of the amplifier to a first gain, it controls the first switch and the third switch to a non-conductive state and the second switch to a conductive state, thereby making the potential of one end and the potential of the other end of the first switch the same potential. Effect of the Invention

[0010] When the gain of the amplifier is set to the first gain, the control device sets the first switch and the third switch to a non-conductive state and sets the second switch to a conductive state, thereby controlling the first switch to have the same potential at one end and the same potential at the other end, thereby suppressing the generation of leakage current by the first switch, which is a semiconductor switch that switches the gain of the amplifier. [Brief description of the drawings]

[0011] [Figure 1] 1 is a circuit diagram showing a configuration of a photoelectric conversion device 100 according to a first embodiment. [Diagram 2] 2 is a circuit diagram showing an example of a semiconductor switch used as a first switch 1. FIG. [Diagram 3] 4 is a flowchart showing an example of control of a first switch 1, a second switch 2, and a second switch 3 in the photoelectric conversion device 100. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings. In the following, the same or corresponding parts in the drawings will be given the same reference numerals, and in principle, the description thereof will not be repeated. Although several embodiments will be described below, it is intended from the beginning of the application that the configurations described in each embodiment will be appropriately combined. First Embodiment [Configuration of photoelectric conversion device 100] 1 is a circuit diagram showing a configuration of a photoelectric conversion device 100 according to a first embodiment. The photoelectric conversion device 100 includes a first switch 1, a second switch 2, a third switch 3, a first resistor 4, a second resistor 5, a photodetector element 6, an amplifier 7, a first terminal 8, and a second terminal 9. The photoelectric conversion device 100 can be applied to various devices including a light receiving element, such as a liquid chromatograph device and a photometer device.

[0013] The light detection element 6 is composed of a photodiode that outputs a detection signal according to the received light. The amplifier 7 is composed of an operational amplifier having an inverting input terminal 71, a non-inverting input terminal 72, and an output terminal 73. The amplifier 7 is supplied with, for example, +5 V as a positive power supply and with, for example, −5 V as a negative power supply.

[0014] The first terminal 8 receives the ground potential GND as a reference potential. The light detecting element 6 is connected between the first terminal 8 and an inverting input terminal 71 of the amplifier 7. The non-inverting input terminal 72 of the amplifier 7 is connected to the first terminal 8.

[0015] A first resistor 4 is connected between the output terminal 73 and the inverting input terminal 71 of the amplifier 7. A third switch 3, a first switch 1, and a second resistor 5 are further connected in series between the output terminal 73 and the inverting input terminal 71 of the amplifier 7. The third switch 3, the first switch 1, and the second resistor 5 are connected in parallel with the first resistor 4 between the output terminal 73 and the inverting input terminal 71 of the amplifier 7.

[0016] When the first switch 1 and the third switch 3 are both conductive, the second resistor 5 connects between the output terminal 73 and the inverting input terminal 71 of the amplifier 7. By providing the first resistor 4 and the second resistor 5 between the output terminal 73 and the inverting input terminal 71 of the amplifier 7, the amplifier 7 functions as an inverting amplifier.

[0017] The first resistor 4 is used to set the gain of the amplifier 7 to a first gain. The second resistor 5 is used to set the gain of the amplifier 7 to a second gain. The first resistor 4 has a larger resistance value than the second resistor 5.

[0018] For example, the relationship between the resistance value of the first resistor 4 and the resistance value of the second resistor 5 is as follows. When the first resistor 4 and the second resistor 5 are connected in parallel between the output terminal 73 and the inverting input terminal 71 of the amplifier 7, the resistance value of the first resistor 4 is set to be larger than the resistance value of the second resistor 5 so that the current flowing through the first resistor 4 can be ignored. Therefore, the first gain set using the first resistor 4 has a larger gain value than the second gain set using the second resistor 5.

[0019] The second terminal 9 receives the ground potential GND as a reference potential, similar to the first terminal 8. The second switch 2 is provided between the second terminal 9 and the first switch 1. It can also be said that the second switch 2 is provided between the second terminal 9 and the third switch 3.

[0020] The first switch 1 is, for example, a semiconductor switch. The second switch 2 is, for example, an analog switch or a mechanical switch. The third switch 3 is, for example, an analog switch or a mechanical switch.

[0021] Specifically, the first switch 1 has one end 11 connected to the second resistor 5, and the other end 12 connected to one end 21 of the second switch 2 and one end 31 of the third switch 3. The second switch 2 has one end 21 connected to the other end 12 of the first switch 1 and one end 31 of the third switch 3. The third switch 3 has one end 31 connected to the other end 12 of the first switch 1 and one end 21 of the second switch 2, and the other end 32 connected to the output terminal 73 of the amplifier 7.

[0022] The first switch 1 and the third switch 3 are used to switch the resistor that sets the gain between the first resistor 4 and the second resistor 5. The second switch 2 is used to suppress leakage current from occurring in the first switch 1 when the second resistor 5 is not used as the resistor that sets the gain.

[0023] For example, in a semiconductor switch such as the first switch 1, due to its structure made of semiconductors, if the potential difference between the potential of one end and the potential of the other end becomes large, leakage current may occur. In a semiconductor switch such as the first switch 1, if the potential of one end and the potential of the other end are made the same potential, the potential difference between the potential of the one end and the potential of the other end disappears, so it is possible to suppress the occurrence of leakage current caused by the structure of the semiconductor switch as described above. The second switch 2 is used to suppress the occurrence of leakage current by making the potential of one end 11 of the first switch 1 the same potential as the potential of the other end 12 of the first switch 1 when the second resistor 5 is not used as a resistor for setting the gain.

[0024] The third switch 3 is used for switching the resistor that sets the gain between the first resistor 4 and the second resistor 5, and also for the following purpose. When the second switch 2 is in a conductive state to suppress leakage current of the first switch 1 as described above, if the output terminal 73 of the amplifier 7 is connected to the second terminal 9, a current may flow from the output terminal 73 to the second terminal 9, causing a drop in the output voltage Vout of the photoelectric conversion device 100. In order to prevent such a drop in the output voltage Vout of the photoelectric conversion device 100, the third switch 3 is controlled to a non-conductive state when the second switch 2 is in a conductive state.

[0025] The control device 40 controls the photoelectric conversion device 100. The control device 40 can individually control the first switch 1, the second switch 2, and the third switch 3 by sending control signals to the first switch 1, the second switch 2, and the third switch 3, for example, as indicated by dashed lines in the figure.

[0026] For example, when setting the gain of the amplifier 7 to a first gain (high gain), the control device 40 controls the first switch 1, the second switch 2, and the third switch 3, and sets the gain of the amplifier 7 by the first resistor 4. On the other hand, when setting the gain of the amplifier 7 to a second gain (low gain), the control device 40 controls the first switch 1, the second switch 2, and the third switch 3, and sets the gain of the amplifier 7 by the second resistor 5. In this way, the control device 40 can execute control to switch the gain of the amplifier 7 between the first gain (high gain) and the second gain (low gain).

[0027] The control device 40 determines whether to switch the gain of amplifier 7 to a first gain (high gain) state or a second gain (low gain) state based on data input from an input device (not shown) connected to the control device 40 or on control data stored in the control device 40.

[0028] The control device 40 is composed of a computer including a CPU (Central Processing Unit) 41, memory 42 (various storage devices including ROM (Read Only Memory), RAM (Random Access Memory), and non-volatile memory such as flash memory), and an input / output buffer (not shown) for inputting and outputting various signals.

[0029] The ROM stores various software programs that indicate processing procedures related to the controls executed by the control device 40. The CPU 41 loads the software programs stored in the ROM into the RAM or the like and executes them. By executing such software programs, various controls such as the controls of the first switch 1, the second switch 2, and the third switch 3 in the photoelectric conversion device 100 are executed.

[0030] [Example of the first switch 1] Fig. 2 is a circuit diagram showing an example of a semiconductor switch used as the switch 1. Fig. 2 shows a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) relay 80 as an example of the semiconductor switch. In the following, an example in which a semiconductor switch constituting a MOSFET is used as the first switch 1 will be described.

[0031] The MOSFET relay 80 includes a first terminal 81 , a second terminal 82 , a third terminal 83 , a fourth terminal 84 , a light emitting element 20 , a light receiving element 30 , a first MOSFET 50 , and a second MOSFET 60 .

[0032] The first MOSFET 50 is a transistor having a gate 51, a drain 52, and a source 53. The second MOSFET 60 is a transistor having a gate 61, a drain 62, and a source 63. The source 53 of the first MOSFET 50 and the source 63 of the second MOSFET 60 are connected.

[0033] For example, when the MOSFET relay 80 is turned on, the light-emitting element 20 is caused to emit light by causing a current to flow between the first terminal 81 and the second terminal 82 by the control device 40 as shown in Fig. 1. The light-emitting element 20 is, for example, a light-emitting diode.

[0034] The light emitted by the light-emitting element 20 is received by the light-receiving element 30. The light-receiving element 30 generates a voltage according to the light received from the light-emitting element 20. The voltage generated by the light-receiving element 30 is applied between the gate 51 and source 53 of the first MOSFET 50 and between the gate 61 and source 63 of the second MOSFET 60. This causes the first MOSFET 50 and the second MOSFET 60 to operate, and the third terminal 83 and the fourth terminal 84 are connected in a conductive state.

[0035] On the other hand, when the light emitting element 20 is not emitting light, the first MOSFET 50 and the second MOSFET 60 do not operate, and the third terminal 83 and the fourth terminal 84 are not electrically connected to each other.

[0036] The first terminal 81 and the second terminal 82 are called primary side terminals because they are the terminals to which a current for operating the MOSFET relay 80 is input. The third terminal 83 and the fourth terminal 84 are called secondary side terminals because they are the terminals that become conductive in response to a current input to the first terminal 81 and the second terminal 82, which are the primary side terminals.

[0037] When such a MOSFET relay 80 is used as the first switch 1 in Fig. 1, for example, the third terminal 83 is connected to the second resistor 5 in Fig. 1, and the fourth terminal 84 is connected to the second switch 2 and the third switch 3. A control signal from the control device 40 in Fig. 1 is input to the first terminal 81 or the second terminal 82.

[0038] When MOSFET relay 80 is used as first switch 1 in FIG. 1, if the potential of third terminal 83 at one end and the potential of fourth terminal 84 at the other end are made the same by the function of second switch 2 when MOSFET relay 80 is in a non-conducting state, leakage current can be suppressed in the structure of MOSFET relay 80 as shown in FIG. 2.

[0039] 1, when the MOSFET relay 80 is in a conductive state, a current flows through the light-emitting element 20, causing a potential difference between the first terminal 81 and the second terminal 82 on the primary side. In such a conductive state, a potential difference occurs between the first terminal 81 and the second terminal 82 on the primary side and the third terminal 83 and the fourth terminal 84 on the secondary side due to the potential difference caused by the current flowing through the light-emitting element 20, and there is a risk of a leakage current occurring between the primary side and the secondary side.

[0040] However, when the first switch 1 is in a conductive state, negative feedback works by the current passing through the second resistor 5. In that case, negative feedback works in the amplifier 7 by the current including the leakage current between the primary side and secondary side of the first switch 1, so that it is possible to prevent the leakage current between the primary side and secondary side of the first switch 1 from affecting the output voltage Vout of the photoelectric conversion device 100.

[0041] As described below, the first switch 1 may be a semiconductor switch other than the MOSFET relay 80 shown in FIG.

[0042] A semiconductor switch constituting a junction field effect transistor may be used as the first switch 1. The junction field effect transistor is abbreviated as JFET (Junction Field Effect Transistor). The JFET is a semiconductor switch having a gate terminal, a source terminal, and a drain terminal. When the JFET is used as the first switch 1, for example, the source terminal of an n-channel JFET having an n-type semiconductor embedded in the gate portion is connected to the second resistor 5 in FIG. 1, and the drain terminal is connected to the second switch 2 and the third switch 3. Then, the first switch 1 is controlled to either a conductive state or a non-conductive state by a control signal given to the JFET from the control device 40 in FIG. 1.

[0043] For example, when no voltage is applied between the gate terminal and the source terminal of the n-channel JFET by a control signal from the control device 40, the first switch 1 is in a conductive state. On the other hand, when a sufficiently large negative voltage is applied between the gate terminal and the source terminal, the first switch 1 is in a non-conductive state.

[0044] Even when such a semiconductor switch as a JFET is used as the first switch 1, it is possible to suppress leakage current caused by the structure of the semiconductor switch by setting both ends of the first switch 1 to the same potential when the first switch 1 is in a non-conducting state. In this case, the second switch 2 and the third switch 3 may be semiconductor switches constituting a MOSFET relay 80.

[0045] Also, a semiconductor switch constituting a bipolar transistor may be used as the first switch 1. A bipolar transistor is a semiconductor switch having a base terminal, an emitter terminal, and a collector terminal. When a bipolar transistor is used as the first switch 1, for example, an npn transistor using n-type semiconductors for the emitter and collector and a p-type semiconductor for the base has an emitter terminal connected to the second resistor 5 in FIG. 1, and a collector terminal connected to the second switch 2 and the third switch 3. Then, the first switch 1 is controlled to either a conductive state or a non-conductive state by a control signal given to the bipolar transistor from the control device 40 in FIG. 1.

[0046] For example, when a voltage is applied between the base terminal and the emitter terminal by a control signal from the control device 40, the first switch 1 is in a conductive state. On the other hand, when no voltage is applied between the base terminal and the emitter terminal, the first switch 1 is in a non-conductive state.

[0047] Even when a semiconductor switch such as a bipolar transistor is used as the first switch 1, it is possible to suppress leakage current caused by the structure of the semiconductor switch by setting both ends of the first switch 1 to the same potential when the first switch 1 is in a non-conducting state. In this case, the second switch 2 and the third switch 3 may be semiconductor switches constituting a MOSFET relay 80.

[0048] Also, a semiconductor switch constituting a switching diode may be used as the first switch 1. A diode is a semiconductor switch having a cathode terminal and an anode terminal. When a diode is used as the first switch 1, for example, the cathode terminal is connected to the second resistor 5 in FIG. 1, and the anode terminal is connected to the second switch 2 and the third switch 3. Depending on whether a positive voltage is applied between the anode terminal and the cathode terminal, the first switch 1 is in either a conductive state or a non-conductive state.

[0049] In this way, when a semiconductor switch such as a diode is used as the first switch 1, by making both ends of the first switch 1 the same potential when the first switch 1 is in a non-conducting state, a positive voltage is applied between the anode terminal and the cathode terminal, thereby making it possible to suppress the current flowing through the first switch 1. In this case, the second switch 2 and the third switch 3 may be semiconductor switches that constitute the MOSFET relay 80.

[0050] [Example of control of photoelectric conversion device 100] Fig. 3 is a flowchart showing an example of control of the first switch 1, the second switch 2, and the third switch 3 in the photoelectric conversion device 100. The control shown in Fig. 3 is executed by the control device 40. The flowchart in Fig. 3 will be described below with reference to the configuration in Fig. 1.

[0051] In step S1, it is determined whether or not the current state is one in which the gain of the amplifier 7 is to be set to a first gain (high gain). If it is determined in step S1 that the gain of the amplifier 7 is to be set to the first gain (high gain), then in step S2, control is executed to bring the first switch 1 and the third switch 3 into a non-conducting state and bring the second switch 2 into a conducting state.

[0052] In this state, most of the current corresponding to the amount of light detected by the photodetector element 6 flows through the first resistor 4, and the current flowing through the second resistor 5 is negligibly small. This is because the first switch 1 and the third switch 3 are brought into a non-conductive state, so that the second resistor 5 is not connected between the output terminal 73 and the inverting input terminal 71 of the amplifier 7.

[0053] As a result, the gain of the amplifier 7 is set to the first gain (high gain) by using the first resistor 4. In this case, the current voltage according to the amount of light detected by the light detection element 6 is converted to a voltage by the amplifier 7 and the first resistor 4 at an amplification factor corresponding to the first gain (high gain), and the output voltage Vout thus amplified is output from the photoelectric conversion device 100.

[0054] In this way, when the gain of the amplifier 7 is set to the first gain using the first resistor 4, negative feedback is performed in the amplifier 7 with most of the current passing only through the first resistor 4, so that the potential of one end 11 of the first switch 1 becomes the ground potential GND. This is because, when such negative feedback is performed, the potential Vin- of the inverting input terminal 71 of the amplifier 7 becomes the same potential as the potential Vin+ of the non-inverting input terminal 72 of the amplifier 7 due to the structure of the operational amplifier that constitutes the amplifier 7.

[0055] In this manner, when the first switch 1 is in a non-conductive state, if the potential V1 at one end 11 and the potential V2 at the other end 12 of the first switch 1 are different, there is a risk of leakage current occurring as described above. However, in the photoelectric conversion device 100, when the gain of the amplifier 7 is set to the first gain (high gain) using the first resistor 4, the second switch 2 is brought into a conductive state, and therefore the potential V2 at the other end 12 of the first switch 1 becomes the ground potential GND received by the second terminal 9 to which the second switch 2 is connected.

[0056] Therefore, when the first switch 1 is in a non-conductive state, the second switch 2 operates to make the potential V1 at one end 11 and the potential V2 at the other end 12 of the first switch 1 the same potential (ground potential GND). As a result, when the first switch 1 is in a non-conductive state, the second switch 2 operates to suppress the occurrence of leakage current. In that case, since the third switch 3 is in a non-conductive state, the output voltage Vout is not affected by the ground potential GND via the second switch 2.

[0057] On the other hand, if it is determined in the above-mentioned step S1 that the gain of the amplifier 7 is not in a state to be set to the first gain (high gain), the gain of the amplifier 7 is in a state to be set to the second gain (low gain). If it is determined in step S1 that the gain of the amplifier 7 is not in a state to be set to the first gain (high gain), control is executed in step S3 to bring the first switch 1 and the third switch 3 into a conductive state and bring the second switch 2 into a non-conductive state.

[0058] In this state, most of the current corresponding to the amount of light detected by the light detection element 6 flows through the second resistor 5, and the current flowing through the first resistor 4 is negligible. This is because the first switch 1 and the third switch 3 are brought into a conductive state, so that the second resistor 5 is connected between the output terminal 73 and the inverting input terminal 71 of the amplifier 7, and the resistance value of the first resistor 4 is significantly greater than that of the second resistor 5. As described above, the relationship between the resistance values ​​of the first resistor 4 and the second resistor 5 is such that the resistance value of the first resistor 4 is greater than that of the second resistor 5, so that when the first resistor 4 and the second resistor 5 are connected in parallel between the output terminal 73 and the inverting input terminal 71 of the amplifier 7, the current flowing through the first resistor 4 is negligible.

[0059] As a result, the gain of the amplifier 7 is set to the second gain using the second resistor 5. In this case, a current corresponding to the amount of light detected by the light detection element 6 is converted to a voltage by the amplifier 7 and the second resistor 5, amplified by an amplification factor corresponding to the second gain, and the amplified output voltage Vout is output from the photoelectric conversion device 100. In this case, since the second switch 2 is in a non-conductive state, the output voltage Vout is not affected by the ground potential GND via the second switch 2.

[0060] [Effects obtained in the first embodiment] The effects obtained in the first embodiment are listed below.

[0061] As described in Figures 1 and 3, when the gain of amplifier 7 is set to the first gain, control device 40 sets first switch 1 and third switch 3 to a non-conductive state and second switch 2 to a conductive state, thereby controlling first switch 1 to make potential V1 at one end 11 and potential V2 at the other end 12 the same potential, thereby suppressing the generation of leakage current by first switch 1, which is a semiconductor switch for switching the gain of amplifier 7.

[0062] As explained in Figures 1 and 3, when the gain of amplifier 7 is set to the first gain, control device 40 controls first switch 1 to make potential V1 at one end 11 and potential V2 at the other end 12 the same potential corresponding to ground potential GND, thereby suppressing the generation of leakage current by first switch 1.

[0063] 1 and 3, since the second resistor 5 has a smaller resistance value than the first resistor 4, when the first switch 1 and the third switch 3 are in a conductive state, the current flowing through the first resistor 4 can be made negligibly small, and most of the current can be made to flow through the second resistor 5. As a result, when the first switch 1 and the third switch 3 are in a conductive state, the gain of the amplifier 7 can be set to the second gain using the second resistor 5 without providing a special switch in the first resistor 4.

[0064] As described in Figures 1 and 3, since the first gain has a larger gain value than the second gain, leakage current can be suppressed in amplification at high gain, where leakage current has a significant effect on the output voltage Vout of the photoelectric conversion device 100 when leakage current occurs.

[0065] As described in FIG. 2, since the semiconductor switch is constituted by the MOSFET relay 80, in such a configuration, it is possible to suppress the occurrence of leakage current when the gain of the amplifier 7 is switched.

[0066] As described with reference to FIGS. 1 and 3, since the light detection element 6 is made of a photodiode, it is possible to suppress the occurrence of leakage current with respect to the detection output of the light detection element 6 when the gain of the amplifier 7 is switched. <Second embodiment> In the second embodiment, an example will be described in which the reference potential in the photoelectric conversion device 100 shown in FIG. 1 is a potential other than the ground potential GND.

[0067] In the second embodiment, the potential of the first terminal 8 and the potential of the second terminal 9 shown in Fig. 1 are the potential GND+α as shown within the dashed line in Fig. 1. In this case, when the first switch 1 and the third switch 3 are put into a non-conductive state and the second switch 2 is put into a conductive state in step S2 shown in Fig. 3, the potential V1 of one end 11 and the potential V2 of the other end 12 of the first switch 1 become the same potential GND+α.

[0068] With such a configuration, in the second embodiment, it is possible to obtain the same effects as those obtained in the first embodiment for a configuration similar to that of the first embodiment, and further, it is possible to obtain the following configuration for a configuration different from that of the first embodiment.

[0069] As described in Figures 1 and 3, when the gain of amplifier 7 is set to the first gain, the control device 40 controls the first switch 1 to make the potential V1 at one end 11 and the potential V2 at the other end 12 the same potential corresponding to a predetermined potential GND+α that is different from the ground potential GND, thereby suppressing the generation of leakage current by the first switch 1.

[0070] [Modification of the embodiment] (1) In the above-described embodiment, two resistors, the first resistor 4 and the second resistor 5, are used as resistors for setting the gain of the amplifier 7, and the magnitude of the gain of the amplifier 7 is changed by selectively switching between these resistors. However, this is not limiting, and three or more resistors may be used as resistors for setting the gain of the amplifier 7. In that case, for each additional resistor among the three or more resistors, a switch having a configuration similar to that of the first switch 1 and a switch having a configuration similar to that of the second switch 2 shown in FIG. 1 may be provided.

[0071] (2) In the second embodiment described above, an example has been described in which a potential GND+α is used as a reference potential different from the ground potential GND. However, the present invention is not limited to this example, and a potential GND-α may be used as a reference potential different from the ground potential GND.

[0072] (3) In the above-described embodiment, an example in which a photodiode is used as the light detection element 6 has been shown. However, the present invention is not limited to this, and the light detection element 6 may be any element that outputs a detection signal in response to the detected light, and other light detection elements such as a phototube and a phototransistor may be used instead of the photodiode.

[0073] [Appendix] As described above, the present embodiment includes the following disclosures. [Configuration 1] An amplifier (amplifier 7) having an inverting input terminal (inverting input terminal 71), a non-inverting input terminal (non-inverting input terminal 72), and an output terminal (output terminal 73), A light detection element (light detection element 6) connected between the non-inverting input terminal (non-inverting input terminal 72) and the inverting input terminal (inverting input terminal 71) of the amplifier (amplifier 7), A first resistor (first resistor 4) provided between the inverting input terminal (inverting input terminal 71) and the output terminal (output terminal 73) of the amplifier (amplifier 7) and setting the gain of the amplifier (amplifier 7) to a first gain, A second resistor (second resistor 5) provided between the inverting input terminal (inverting input terminal 71) and the output terminal (output terminal 73) of the amplifier (amplifier 7) and setting the gain of the amplifier (amplifier 7) to a second gain, A first switch (first switch 1) composed of a semiconductor switch having one end (one end 11) connected to the second resistor (second resistor 5) and the other end (the other end 12) connectable to the output terminal (output terminal 73) of the amplifier (amplifier 7), A first terminal (first terminal 8) connected to the non-inverting input terminal (non-inverting input terminal 72) of the amplifier (amplifier 7) and receiving a reference potential, A second terminal (second terminal 9) receiving the reference potential, A second switch (second switch 2) connectable between the other end (the other end 12) of the first switch (first switch 1) and the second terminal (second terminal 9), a third switch (third switch 3) capable of connecting the other end (other end 12) of the first switch (first switch 1) and the output terminal (output terminal 73) of the amplifier (amplifier 7); a control device (control device 40) that controls the first switch (first switch 1), the second switch (second switch 2), and the third switch (third switch 3), The control device (control device 40) When the gain of the amplifier (amplifier 7) is set to the second gain, the first switch (first switch 1) and the third switch (third switch 3) are brought into a conductive state, and the second switch (second switch 2) is brought into a non-conductive state (step S2); When the gain of the amplifier (amplifier 7) is set to the first gain, the first switch (first switch 1) and the third switch (third switch 3) are brought into a non-conductive state, and the second switch (second switch 2) is brought into a conductive state, thereby controlling the first switch (first switch 1) to make the potential (V1) of the one end (one end 11) and the potential (V2) of the other end (other end 12) the same potential (step S1), in the photoelectric conversion device (photoelectric conversion device 100).

[0074] According to this configuration, when the gain of the amplifier is set to the first gain, the control device sets the first switch and the third switch to a non-conductive state and sets the second switch to a conductive state, thereby controlling the first switch to have the same potential at one end and the same potential at the other end, thereby suppressing the generation of leakage current by the first switch, which is a semiconductor switch for switching the gain of the amplifier. [Configuration 2] The photoelectric conversion device (photoelectric conversion device 100) according to configuration 1, wherein the reference potential is a ground potential (ground potential GND).

[0075] According to this configuration, when the gain of the amplifier is set to the first gain, the control device controls the first switch to set the potential at one end and the potential at the other end to the same potential corresponding to the ground potential, thereby suppressing the generation of leakage current by the first switch. [Configuration 3] The photoelectric conversion device (photoelectric conversion device 100) according to configuration 1, wherein the reference potential is a predetermined potential (GND+α) different from a ground potential (ground potential GND).

[0076] According to this configuration, when the gain of the amplifier is set to the first gain, the control device controls the first switch to set the potential at one end and the potential at the other end to the same potential that corresponds to a predetermined potential different from the ground potential, thereby suppressing the generation of leakage current by the first switch. [Configuration 4] The photoelectric conversion device (photoelectric conversion device 100) according to any one of configurations 1 to 3, wherein the second resistor (second resistor 5) has a smaller resistance value than the first resistor (first resistor 4).

[0077] According to this configuration, since the second resistor has a smaller resistance value than the first resistor, when the first switch and the third switch are in a conductive state, the current flowing through the first resistor is negligibly small, and most of the current flows through the second resistor. As a result, when the first switch and the third switch are in a conductive state, the gain of the amplifier can be set to the second gain using the second resistor without providing a special switch for the first resistor. [Configuration 5] The photoelectric conversion device (photoelectric conversion device 100) according to any one of configurations 1 to 4, wherein the first gain has a larger gain value than the second gain.

[0078] According to this configuration, since the first gain has a larger gain value than the second gain, leakage current can be suppressed in high gain amplification where leakage current has a significant effect on the output of the photoelectric conversion device. [Configuration 6] The photoelectric conversion device (photoelectric conversion device 100) according to any one of configurations 1 to 5, wherein the first switch is a semiconductor switch constituting a MOSFET relay (MOSFET relay 80).

[0079] According to this configuration, in the case where the first switch is a semiconductor switch constituting a MOSFET relay, it is possible to suppress the occurrence of leakage current when switching the gain of the amplifier. [Configuration 7] The photoelectric conversion device (photoelectric conversion device 100) according to any one of configurations 1 to 5, wherein the first switch (first switch 1) is made of a semiconductor switch constituting a junction field effect transistor.

[0080] According to this configuration, when the first switch is a semiconductor switch that constitutes a junction field effect transistor, it is possible to suppress the occurrence of leakage current when switching the gain of the amplifier. [Configuration 8] The photoelectric conversion device (photoelectric conversion device 100) according to any one of configurations 1 to 5, wherein the first switch (first switch 1) is made of a semiconductor switch forming a bipolar transistor.

[0081] According to this configuration, when the first switch is a semiconductor switch that constitutes a bipolar transistor, it is possible to suppress the occurrence of leakage current when switching the gain of the amplifier. [Configuration 9] The photoelectric conversion device (photoelectric conversion device 100) according to any one of configurations 1 to 5, wherein the first switch (first switch 1) is a semiconductor switch forming a diode.

[0082] According to this configuration, when the first switch is a semiconductor switch that constitutes a bipolar transistor, it is possible to suppress the occurrence of leakage current when switching the gain of the amplifier. [Configuration 10] The photoelectric conversion device (photoelectric conversion device 100) according to any one of configurations 1 to 9, wherein the photodetection element (photodetection element 6) is made of a photodiode.

[0083] With this configuration, it is possible to suppress the occurrence of leakage current when the gain of the amplifier is switched with respect to the detection output of the light detection element made of a photodiode.

[0084] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0085] 71 inverting input terminal, 72 non-inverting input terminal, 73 output terminal, 7 amplifier, 6 photodetector element, 4 first resistor, 5 second resistor, 11 one end, 12 other end, 1 first switch, 8 first terminal, 9 second terminal, 3 third switch, 40 control device, 100 photoelectric conversion device, 80 MOSFET relay.

Claims

1. an amplifier having an inverting input terminal, a non-inverting input terminal, and an output terminal; a photodetector element connected between the non-inverting input terminal and the inverting input terminal of the amplifier; a first resistor provided between the inverting input terminal and the output terminal of the amplifier, the first resistor setting a gain of the amplifier to a first gain; a second resistor provided between the inverting input terminal and the output terminal of the amplifier, the second resistor setting the gain of the amplifier to a second gain; a first switch including a semiconductor switch having one end connected to the second resistor and the other end connectable to the output terminal of the amplifier; a first terminal connected to the non-inverting input terminal of the amplifier and receiving a reference potential; a second terminal for receiving the reference potential; a second switch capable of connecting between the other end of the first switch and the second terminal; a third switch capable of connecting the other end of the first switch and the output terminal of the amplifier; a control device that controls the first switch, the second switch, and the third switch; The control device includes: when a gain of the amplifier is set to the second gain, the first switch and the third switch are controlled to be in a conductive state and the second switch is controlled to be in a non-conductive state; A photoelectric conversion device in which, when the gain of the amplifier is set to the first gain, the first switch and the third switch are made non-conductive and the second switch is made conductive, thereby controlling the first switch to make the potential of the one end and the potential of the other end the same.

2. The photoelectric conversion device according to claim 1 , wherein the reference potential is a ground potential.

3. The photoelectric conversion device according to claim 1 , wherein the reference potential is a predetermined potential different from a ground potential.

4. 4. The photoelectric conversion device according to claim 1, wherein the second resistor has a smaller resistance value than the first resistor.

5. 4. The photoelectric conversion device according to claim 1, wherein the first gain has a larger gain value than the second gain.

6. 4. The photoelectric conversion device according to claim 1, wherein the first switch is a semiconductor switch constituting a MOSFET relay.

7. 4. The photoelectric conversion device according to claim 1, wherein the first switch is a semiconductor switch that constitutes a junction field effect transistor.

8. 4. The photoelectric conversion device according to claim 1, wherein the first switch is a semiconductor switch that constitutes a bipolar transistor.

9. 4. The photoelectric conversion device according to claim 1, wherein the first switch is a semiconductor switch that constitutes a diode.

10. 4. The photoelectric conversion device according to claim 1, wherein the light detection element is a photodiode.

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