LIGHT DETECTION CIRCUIT

Abstract

This photodetection circuit comprises: a photodetection element that outputs a signal current; a current-to-voltage converter section that converts the signal current into a first signal voltage; a first current removal section that removes a first current from the signal current; and a second current removal section that removes a second current from the signal current. The first current removal section determines the level of the first current based on the level of a low-frequency component at a predetermined time and maintains the level of the first current. The second current removal section includes a feedback circuit, a smoothing capacitor, and a second transistor. The feedback circuit outputs a second signal voltage with a level corresponding to the first signal voltage. The smoothing capacitor smooths the second signal voltage.The second transistor removes a second current from the signal current, with a level corresponding to the second signal voltage smoothed by the smoothing capacitor.

Description

Technical field

[0001] The present disclosure relates to a light detection circuit. State of the art

[0002] Patent literature 1 discloses a light detection circuit. The light detection circuit comprises a position sensing device (PSD), a current-to-voltage converter circuit, and a distance circuit. The current-to-voltage converter circuit converts the signal current output by the position sensing device into a signal voltage. The distance circuit removes a stationary component contained in the signal current based on a stationary component contained in the signal voltage. State of the art patent literature Patent literature 1: Japanese unexamined Patent publication no. JP H4-142416 A Summary of the invention Problems to be solved by the invention

[0003] For example, when light is detected with a photodetection element such as a photodiode, a low-frequency component contained in a signal current and output by the photodetection element can be removed from the signal current. This low-frequency component could be, for example, a current component due to background light and / or a dark current component. Fig. Figure 21 is a diagram showing a reference example of a photodetection circuit with a function for removing a low-frequency component from a signal stream. A photodetection circuit 100 shown in the figure comprises a photodetection element 101, a current-to-voltage converter circuit 102 connected to the photodetection element 101, an amplifier 103 for feedback, a smoothing capacitor 104, and a transistor 105. The current-to-voltage converter circuit 102 is a charge amplifier with an amplifier 106 and a capacitor 107 and converts a signal stream output by the photodetection element 101 into a signal voltage. The amplifier 103 amplifies the difference between a voltage on the input side and a voltage on the output side of the current-to-voltage converter circuit 102 and outputs the amplified difference. The smoothing capacitor 104 smooths the output voltage of the amplifier 103.The smoothed output voltage is fed into the gate of transistor 105. Transistor 105 extracts a low-frequency component contained in the signal current from the signal current output by the photodetection element 101 in response to a voltage applied to its gate.

[0004] The in Fig. However, the circuit 100 shown in Figure 21 exhibits the following problems. The larger the low-frequency component to be removed, the greater the transconductance of transistor 105, which leads to an increase in the loop gain. Consequently, the frequency band of the low-frequency component extracted from the signal current expands. Therefore, there is a risk that a signal component will also be extracted that should not be extracted. To avoid such a problem, the capacitance of the smoothing capacitor 104 can be increased, but this would increase the time required for charge accumulation in the smoothing capacitor 104. Therefore, if the photodetection circuit 100 operates intermittently, a long settling time for the feedback process is required each time the photodetection circuit 100 transitions from a non-operating state to an operating state.There is therefore a compromise between maintaining a small frequency band of the low-frequency component extracted from the signal stream and shortening the settling time of the feedback process.

[0005] The purpose of the present disclosure is to provide a photodetection circuit that can shorten the settling time of the feedback process while keeping the frequency band of the low-frequency component extracted from the signal stream small. Means to solve the problem [1] A photodetection circuit according to one aspect of the present disclosure comprises a photodetection element, a current-to-voltage converter unit, a first current removal unit, and a second current removal unit. The photodetection element is configured to output a signal current in response to the incident signal light. The current-to-voltage converter unit has a signal input terminal and a signal output terminal and is configured to convert the signal current input to the signal input terminal into a first signal voltage and output the first signal voltage from the signal output terminal, the signal input terminal being connected to the photodetection element. The first current removal unit is connected to the photodetection element and is configured to extract a first current from the signal current.The second current removal unit is connected to the photodetection element and configured to extract a second current from the signal current. The signal current comprises a signal component and a low-frequency component, which has a lower frequency than the signal component or a constant magnitude. The first current removal unit is configured to determine the magnitude of the first current based on the magnitude of the low-frequency component at a predetermined time and maintains this magnitude. The second current removal unit includes a feedback circuit section, a smoothing capacitor, and a second transistor. The feedback circuit section is connected to the signal output terminal of the current-to-voltage conversion unit and configured to output a second signal voltage with a magnitude equal to the first signal voltage.The smoothing capacitor is configured to smooth the second signal voltage. The second transistor is configured to extract a second current from the signal current, with a magnitude corresponding to the second signal voltage smoothed by the smoothing capacitor.

[0006] According to the photodetection circuit shown in [1] above, a certain portion (first current) of the low-frequency component contained in the signal current is extracted from the signal current by the first current removal unit. The remaining portion (second current) of the low-frequency component contained in the signal current is extracted from the signal current by the second current removal unit. This remaining portion is a fluctuation of the low-frequency component after a predetermined time. With this configuration, the low-frequency component to be removed by the second current removal unit, which performs a feedback operation on the low-frequency component, is reduced, thus reducing the transconductance of the second transistor and the loop gain. As a result, the frequency band of the low-frequency component extracted from the signal current in the second current removal unit, i.e., the frequency band of the second current, becomes narrower.Since the charge to be accumulated in the smoothing capacitor is reduced, the time required for charge accumulation in the smoothing capacitor is shortened. Therefore, the settling time of the feedback process can be shortened. Thus, according to the photodetection circuit described in [1] above, it is possible to shorten the settling time of the feedback process while simultaneously keeping the frequency band of the low-frequency component extracted from the signal current small.

[0007] [2] In the photodetection circuit according to [1] above, the first current removal unit can comprise a voltage-holding capacitor, a first switching element, and a first transistor. The voltage-holding capacitor is configured to be charged by a current from the photodetection element. The first switching element is configured to switch a current flow from the photodetection element to the voltage-holding capacitor on and off. The first transistor has a control terminal, a first current terminal, and a second current terminal. A voltage based on a voltage across the voltage-holding capacitor is applied to the control terminal of the first transistor. The first current terminal is connected to the photodetection element. The second current terminal is connected to a constant-potential line.

[0008] The photodetection circuit according to [2] above operates, for example, as follows. Initially, during a period when the first signal voltage output by the photodetection circuit is not used outside the photodetection circuit, the first switching element allows the signal current to flow from the photodetection element to the voltage-holding capacitor. This causes the charge to accumulate in the voltage-holding capacitor, increasing the voltage across it. Since the voltage-holding capacitor allows a high-frequency signal component contained in the signal current to pass through at this time, the voltage across the voltage-holding capacitor depends mainly on the magnitude of the low-frequency component contained in the signal current.After the predetermined time described above, at which the voltage across the voltage-holding capacitor no longer changes, the first signal voltage output by the photodetection circuit is used outside the photodetection circuit. The first switching element switches at the predetermined time, so that no current flows from the photodetection element to the voltage-holding capacitor. This allows the voltage across the voltage-holding capacitor to be determined based on the magnitude of the low-frequency component at the predetermined time and maintained at a constant value even after the predetermined time. The voltage across the voltage-holding capacitor is applied to the control terminal of the first transistor, and the first transistor extracts an initial current from the signal current with a magnitude corresponding to the voltage across the voltage-holding capacitor.Thus, according to the photodetection circuit according to [2] above, the magnitude of the first current can be determined based on the magnitude of the low-frequency component at a predetermined time.

[0009] [3] In the photodetection circuit according to [2] above, the first switching element can be an amplifier with a control terminal for selecting whether or not an output should be made. In this case, the time required to accumulate the charge can be reduced, since the charge caused by the signal current can be accumulated more quickly in the voltage-holding capacitor. The time required for charge accumulation in the voltage-holding capacitor is the time during which the first signal voltage, corresponding to the light intensity of the signal light, cannot be output, i.e., the dead time. According to the photodetection circuit according to [3] above, it is possible to reduce the dead time. Furthermore, by equipping the amplifier with a function for switching the current flow from the photodetection element to the voltage-holding capacitor on and off, the number of components can be further reduced.

[0010] [4] In the photodetection circuit according to [1] above, the first current removal unit can comprise a voltage-holding capacitor, a first resistor, and a first transistor. The voltage-holding capacitor is configured to be charged by a current from the photodetection element. The first resistor is provided in a current path flowing from the photodetection element to the voltage-holding capacitor. The first transistor has a control terminal, a first current terminal, and a second current terminal. A voltage based on the voltage across the voltage-holding capacitor is applied to the control terminal. The first current terminal is connected to the photodetection element. The second current terminal is connected to a constant-potential line.

[0011] The photodetection circuit according to [4] above operates, for example, as follows. Initially, during a period when the first signal voltage output by the photodetection circuit is not used outside the photodetection circuit, a portion of the signal current flows from the photodetection element through the first resistive element to the voltage-holding capacitor. This stores charge in the voltage-holding capacitor to increase the voltage across it. Since the voltage-holding capacitor allows a high-frequency signal component contained in the signal current to pass through at this time, the voltage across the voltage-holding capacitor depends mainly on the magnitude of the low-frequency component contained in the signal current.After the predetermined time at which the voltage across the voltage-holding capacitor ceases to change, the first signal voltage output by the photodetection circuit is used outside the photodetection circuit. If the period is sufficiently short, the voltage across the voltage-holding capacitor is determined based on the magnitude of the low-frequency component at the predetermined time and maintained at an approximately constant value during this period. The voltage across the voltage-holding capacitor is applied to the control terminal of the first transistor, and the first transistor extracts a first current from the signal current with a magnitude corresponding to the voltage across the voltage-holding capacitor. Thus, according to the photodetection circuit described in [4] above, the magnitude of the first current can be determined based on the magnitude of the low-frequency component at a predetermined time.

[0012] [5] In the photodetection circuit according to [2] or [4], the first current removal unit can further include a first amplifier configured to amplify a current flowing from the photodetection element to the voltage-holding capacitor or a voltage applied from the photodetection element to the voltage-holding capacitor. In this case, the charge caused by the signal current can accumulate more quickly in the voltage-holding capacitor, thus reducing the time required for charge accumulation. The time required for charge accumulation in the voltage-holding capacitor is the time during which the first signal voltage, corresponding to the light intensity of the signal light, cannot be output, i.e., the dead time. According to the photodetection circuit according to [5] above, it is possible to reduce the dead time.

[0013] [6] In the photodetection circuit according to one of the above [2] to [4], the first current removal unit may further comprise a transistor. The transistor is connected in series with the first transistor between the photodetection element and a constant potential line. A voltage based on the voltage across the voltage-holding capacitor is applied to a control terminal of the transistor. In this case, it is possible to adjust the magnitude of the gate voltage required to turn on the first transistor.

[0014] [7] In the photodetection circuit according to one of the above [2] to [4], the first current removal unit may further comprise a first short-circuit switch connected in parallel to the voltage-holding capacitor. If the first current removal unit is not used, one electrode pair of the voltage-holding capacitor may be short-circuited via the first short-circuit switch to prevent malfunction of the first transistor due to unnecessary charge accumulation in the voltage-holding capacitor.

[0015] [8] In the photodetection circuit according to one of the above [1] to [7], the second current removal unit may further include a second switching element. The second switching element is connected in series between the light detector element and the smoothing capacitor and is configured to switch a current flow from the light detector element to the smoothing capacitor on and off. The photodetection circuit operates, for example, as follows. First, during a period when the first signal voltage output by the photodetection circuit is not used outside the photodetection circuit, the second switching element allows the signal current to flow from the photodetection element to the smoothing capacitor. This causes the charge to accumulate in the smoothing capacitor to increase the voltage across the smoothing capacitor. Then, the first signal voltage output by the photodetection circuit is used outside the photodetection circuit.At this point, the second switching element is switched so that no current flows from the photodetection element to the smoothing capacitor. The smoothing capacitor then smooths the second signal voltage. According to the photodetection circuit of [8], the charge can thus be stored in the smoothing capacitor in advance before the first signal voltage is used outside the photodetection circuit, thereby further reducing the settling time of the feedback process in the second current removal unit.

[0016] [9] In the photodetection circuit according to [8] above, the feedback circuit section can include a second amplifier. The second amplifier has an input terminal and an output terminal. The input terminal of the second amplifier is connected to the signal output terminal of the current-to-voltage conversion unit. The output terminal of the second amplifier is connected to the smoothing capacitor. The second amplifier can further include a control terminal for selecting whether or not to produce an output. According to the photodetection circuit according to [9], the second amplifier is controlled so that it does not produce an output if the charge in the smoothing capacitor has accumulated in advance. This prevents some of the current from flowing from the photodetection element into the second amplifier, and the charge can be efficiently accumulated in the smoothing capacitor.

[0017]

[10] In the photodetection circuit according to [8] above, the feedback circuit section may include a second amplifier. The second amplifier has an input terminal and an output terminal. The input terminal of the second amplifier is connected to the signal output terminal of the current-to-voltage converter unit. The output terminal of the second amplifier is connected to the smoothing capacitor. The second current removal unit may further include a third switching element. The third switching element is connected in series between the second amplifier and the smoothing capacitor. The third switching element toggles the relationship between the second amplifier and the smoothing capacitor between a connected state and a disconnected state.According to the light detection circuit of

[10] , during the prior accumulation of charge in the smoothing capacitor, the relationship between the second amplifier and the smoothing capacitor is put into a disconnected state by the third switching element. This prevents part of the current from flowing from the light detection element to the second amplifier, and the charge can be efficiently accumulated in the smoothing capacitor.

[0018]

[11] In the photodetection circuit according to [8] above, the feedback circuit section may include a second resistive element. The second resistive element comprises one end and another end. One end of the second resistive element is connected to the signal output terminal of the current-to-voltage converter unit. The other end of the second resistive element is connected to the smoothing capacitor. The second current removal unit may further include a third switching element. The third switching element is connected in series with the second resistive element between the signal output terminal of the current-to-voltage converter unit and the smoothing capacitor. The third switching element toggles the relationship between the signal output terminal and the smoothing capacitor between a connected state and a disconnected state.According to the photodetection circuit

[11] , during the prior accumulation of charge in the smoothing capacitor, the relationship between the signal output terminal and the smoothing capacitor is switched to a disconnected state by the third switching element. This prevents part of the current from the light detection element from flowing through the second resistive element, and the charge can be efficiently accumulated in the smoothing capacitor.

[0019]

[12] In the photodetection circuit according to [8] above, the second current removal unit can further comprise a third amplifier configured to amplify a current flowing from the photodetection element to the smoothing capacitor or a voltage applied from the photodetection element to the smoothing capacitor. In this case, the settling time of the feedback process in the second current removal unit can be further reduced because the accumulation of charge in the smoothing capacitor is accelerated.

[0020]

[13] In the photodetection circuit according to [8] above, the second switching element can be an amplifier with a control terminal for selecting whether or not an output should be made. In this case, the time required to accumulate the charge in the smoothing capacitor can be reduced. The time required to accumulate the charge in the smoothing capacitor is the time during which the first signal voltage, corresponding to the light intensity of the signal light, cannot be output, i.e., the dead time. According to the photodetection circuit according to

[13] above, it is possible to reduce the dead time. Furthermore, by equipping the amplifier with a function for switching the current flow from the photodetection circuit to the smoothing capacitor on and off, the number of components can be further reduced.

[0021]

[14] In the photodetection circuit according to [8], the current-to-voltage converter unit can be configured to switch the input of the signal current to the signal input terminal on and off. According to the photodetection circuit according to

[14] , during the prior accumulation of charge in the smoothing capacitor, the current-to-voltage converter unit is controlled so that no signal current is injected into the signal input terminal. This prevents any current from flowing from the photodetection element to the current-to-voltage converter unit, and the charge can be efficiently accumulated in the smoothing capacitor.

[0022]

[15] In the light detector circuit according to [2] or [3] above, the second current removal unit may further comprise a second switching element connected in series between a node between the first switching element and the voltage holding capacitor and the smoothing capacitor, and configured to switch on and off a current flow from the light detection element to the smoothing capacitor together with the first switching element.

[0023]

[16] In the photodetection circuit according to [2] or [3] above, the second current removal unit may further comprise a second switching element connected in series between the photodetection element and the smoothing capacitor and configured to switch on and off a current flow from the photodetection element to the smoothing capacitor. The first switching element may be connected in series between a junction between the second switching element and the smoothing capacitor and the voltage-holding capacitor and configured to switch on and off a current flow from the photodetection element to the voltage-holding capacitor together with the second switching element.

[0024]

[17] In the light detection circuit according to any of the above points [1] to

[16] , the second current removal unit may further comprise a second short-circuit switch connected in parallel to the smoothing capacitor. If the second current removal unit is not used, one electrode pair of the smoothing capacitor may be short-circuited via the second short-circuit switch to prevent malfunction of the second transistor. Advantageous effects of the invention

[0025] According to the present disclosure, it is possible to provide a photodetection circuit that can shorten the settling time of a feedback circuit while suppressing the expansion of the frequency band of components extracted from a signal stream. Brief description of the drawings Fig. Figure 1 is a circuit diagram showing the configuration of a photodetection circuit according to one embodiment. Fig. Figure 2 is a diagram showing the operation of a photodetection circuit. Fig. Figure 3 is a circuit diagram showing the configuration of a first current removal unit according to a modification. Fig. Figure 4 is a circuit diagram showing the configuration of a first current removal unit according to a modification. Fig. Figure 5 is a circuit diagram showing the configuration of a first current removal unit according to a modification. Fig. Figure 6 is a circuit diagram showing the configuration of a first current removal unit according to a modification. Fig. Figure 7 is a circuit diagram showing the configuration of a second current removal unit according to a modification. Fig. Figure 8 is a circuit diagram showing the configuration of a second current removal unit according to a modification. Fig. Figure 9 is a circuit diagram showing the configuration of a second current removal unit according to a modification. Fig. Figure 10 is a circuit diagram showing the configuration of a current-to-voltage converter unit according to a modification. Fig. Figure 11 is a circuit diagram showing the configuration of a current-to-voltage conversion unit according to a modification. Fig. Figure 12 is a circuit diagram showing the configuration of a photodetection circuit according to a modification. Fig. Figure 13 is a circuit diagram showing the configuration of a second current removal unit according to a modification. Fig. Figure 14 is a circuit diagram showing the configuration of a photodetection circuit according to a modification. Fig. Figure 15 is a circuit diagram showing the configuration of a photodetection circuit according to a modification. Fig. Figure 16 is a circuit diagram showing the configuration of a photodetection circuit according to a modification. Fig. Figure 17 is a circuit diagram showing the configuration of a photodetection circuit according to a modification. Fig. Figure 18 is a circuit diagram showing the configuration of a light detector circuit according to a modification. Fig. Figure 19 is a circuit diagram showing the configuration of a photodetection circuit according to a modification. Fig. Figure 20 is a circuit diagram showing the configuration of a light detection circuit according to a modification. Fig. Figure 21 is a diagram showing a reference example of a photodetection circuit with a function for removing a low-frequency component from a signal stream. Description of the embodiments

[0026] In the following, embodiments of a photodetection circuit according to the present disclosure are described in detail with reference to the accompanying diagrams. In the description of the diagrams, identical elements are designated with the same reference numerals, and their repeated description is omitted.

[0027] Fig. Figure 1 is a circuit diagram showing the configuration of a photodetection circuit 1A according to an embodiment of the present disclosure. The photodetection circuit 1A receives signal light L from an external source and outputs a first signal voltage V1 corresponding to the light intensity of the signal light L. As shown in Figure 1, the photodetection circuit 1A receives signal light L from an external source and outputs a first signal voltage V1 corresponding to the light intensity of the signal light L. Fig. As shown in Figure 1, the photodetection circuit 1A according to the present embodiment comprises a photodetection element 10, a current-to-voltage converter unit 20, a first current removal unit 30, a second current removal unit 40 and a control unit 50.

[0028] The photodetection element 10 is, for example, a photodiode or a position sensing device (PSD). The photodetection element 10 can be one of several photodetection elements included in a photodetection element assembly. In this case, a photodetection circuit 1A is provided for each photodetection element. The signal light L falls on the photodetection element 10. The photodetection element 10 outputs a signal current J corresponding to the light intensity of the signal light L. If the photodetection element 10 is a photodiode, the cathode of the photodiode is connected to a bias line 61. The bias line 61 is a first constant-potential line with a higher potential than a reference potential line 62. The reference potential line 62 is a second constant-potential line with a lower potential than the bias line 61. The signal current J contains a signal component and a low-frequency component.The low-frequency component is a component with a lower frequency than the signal component or with a predetermined magnitude. For example, the low-frequency component includes one or both of the following currents: a current due to background light contained in the signal light L, and a dark current generated in the photodetection element 10.

[0029] The current-to-voltage converter unit 20 has a signal input terminal 21 and a signal output terminal 22. The signal input terminal 21 is connected to the photodetection element 10 via a wire 63. If the photodetection element 10 is a photodiode, the signal input terminal 21 is connected to the anode of the photodiode. The current-to-voltage converter unit 20 converts the signal current J input to the signal input terminal 21—more precisely, a current obtained from the signal current J by subtracting a first current J1 and a second current J2, which will be described later—into the first signal voltage V1. The current-to-voltage converter unit 20 outputs the first signal voltage V1 via the signal output terminal 22. In one example, the current-to-voltage converter unit 20 is a charge amplifier. The charge amplifier has an amplifier 23 and a capacitor 24.One end of capacitor 24 is connected to the input terminal of amplifier 23, and the other end of capacitor 24 is connected to the output terminal of amplifier 23. Alternatively, the current-to-voltage converter unit 20 can be a transimpedance amplifier. The transimpedance amplifier has an amplifier and a resistor. One end of the resistor is connected to the input terminal of the amplifier, and the other end of the resistor is connected to the output terminal of the amplifier. The circuit configuration of the current-to-voltage converter unit 20 is not limited to the charge amplifier and the transimpedance amplifier, but can be any of the various circuit configurations capable of converting a current into a voltage.

[0030] The first current removal unit 30 is connected to the photodetection element 10 and removes the first current J1 from the signal current J. In one example, the first current removal unit 30 is connected to a node N1 on the wiring 63 between the photodetection element 10 and the current-to-voltage conversion unit 20. The first current removal unit 30 is configured to determine the magnitude of the first current J1 based on the magnitude of the low-frequency component of the signal current J at a predetermined time and to maintain the magnitude of the first current J1.

[0031] The first current removal unit 30 in the present embodiment comprises a voltage-holding capacitor 31, a first switching element 32, and a first transistor 33. The voltage-holding capacitor 31 is configured to be charged by the current from the photodetection element 10. In particular, one electrode of the voltage-holding capacitor 31 is connected to the photodetection element 10 via the first switching element 32 and node N1. The other electrode of the voltage-holding capacitor 31 is connected to the reference potential line 62. The capacitance of the voltage-holding capacitor 31 is, for example, 100 fF or more and 1 pF or less. The voltage-holding capacitor 31 is, for example, a MOS capacitor. The first switching element 32 is connected in series between node N1 and the voltage-holding capacitor 31.The first switching element 32 switches the current flow from the photodetection element 10 to the voltage-holding capacitor 31 on or off. In other words, the first switching element 32 toggles the connection between the photodetection element 10 and the voltage-holding capacitor 31 between a connected state and a disconnected state. In the present embodiment, the first switching element 32 comprises a switch 32a. The switch 32a can be a mechanical switch or a semiconductor switch such as a transistor.

[0032] The first transistor 33 is configured to extract the first current J1 from the signal current J, the magnitude of which corresponds to the voltage across the voltage-holding capacitor 31. The first transistor 33 has a control terminal 33a (gate), a first current terminal 33b (drain), and a second current terminal 33c (source). In this embodiment, the first transistor 33 is an N-channel MOSFET (metal-oxide-semiconductor field-effect transistor). The control terminal 33a is connected to a node N2 between an electrode of the voltage-holding capacitor 31 and the first switching element 32. A voltage based on the voltage across the voltage-holding capacitor 31, for example, the voltage across the voltage-holding capacitor 31 itself, is applied to the control terminal 33a.The first power connection 33b is connected to a junction N3 between the first switching element 32 and junction N1, and via junctions N3 and N1 to the photodetection element 10. The second power connection 33c is connected to the reference potential line 62.

[0033] A resistive element 311 can be provided in series with the voltage-holding capacitor 31 between node N2 and the reference potential line 62, or the resistive element 311 can be omitted. The resistive element 311 can be provided in a similar manner in each of the modifications described below. In the example shown, the resistive element 311 is connected between the voltage-holding capacitor 31 and the reference potential line 62, but the resistive element 311 can also be connected between node N2 and the voltage-holding capacitor 31.

[0034] The second current removal unit 40 is connected to the photodetection element 10 and removes the second current J2 from the signal current J. In one example, the second current removal unit 40 is connected to a node N4 between the photodetection element 10 and the current-to-voltage conversion unit 20. Node N4 can be located between node N1 and the current-to-voltage conversion unit 20, node N1 can be located between node N4 and the current-to-voltage conversion unit 20, or node N4 can be shared with node N1. The second current removal unit 40 determines the magnitude of the second current J2 by ​​feedback of the first signal voltage V1.

[0035] The second current removal unit 40 in the present embodiment comprises a feedback circuit section 41, a smoothing capacitor 42, a second transistor 43, and a second switching element 45. The feedback circuit section 41 is connected to the signal output terminal 22 of the current-to-voltage converter unit 20 and outputs a second signal voltage V2, the magnitude of which corresponds to the first signal voltage V1. The feedback circuit section 41 in the present embodiment includes a second amplifier 44. The second amplifier 44 comprises a first input terminal 44a, a second input terminal 44b, and an output terminal 44c. The first input terminal 44a is a non-inverting input terminal and is connected to a node N5 between the signal input terminal 21 of the current-to-voltage converter unit 20 and the photodetection element 10.The second input terminal 44b is an inverting input terminal and is connected to the signal output terminal 22 of the current-to-voltage converter unit 20. The output terminal 44c is connected to an electrode of the smoothing capacitor 42. The second amplifier 44 outputs the second signal voltage V2 via the output terminal 44c. The second signal voltage V2 is a voltage whose magnitude is proportional to the difference between a voltage applied to the first input terminal 44a and a voltage applied to the second input terminal 44b, i.e., the first signal voltage V1.

[0036] The smoothing capacitor 42 smooths the second signal voltage V2. In the present embodiment, the other electrode of the smoothing capacitor 42 is connected to the reference potential line 62. The capacitance of the smoothing capacitor 42 is, for example, 100 fF or more and 1 pF or less. The smoothing capacitor 42 is, for example, a MOS capacitor.

[0037] The second transistor 43 is configured to extract the second current J2 from the signal current J. The magnitude of this second current corresponds to the second signal voltage V2, which has been smoothed by the smoothing capacitor 42. The second transistor 43 has a control terminal 43a, a first current terminal 43b, and a second current terminal 43c. The control terminal 43a is connected to a node N6 between an electrode of the smoothing capacitor 42 and the feedback circuit section 41. The second signal voltage V2, smoothed by the smoothing capacitor 42, is applied to the control terminal 43a. The first current terminal 43b is connected to node N4 and, via node N4, to the photodetection element 10. The second current terminal 43c is connected to the reference potential line 62.The gain of the second transistor 43 is smaller than the gain of the first transistor 33, for example 1 / 10 or less of the gain of the first transistor 33.

[0038] A resistive element 421 can be provided in series with the smoothing capacitor 42 between node N6 and the reference potential line 62, or the resistive element 421 can be omitted. In each modification described later, the resistive element 421 can be provided in a similar manner. In the example shown, the resistive element 421 is connected between the smoothing capacitor 42 and the reference potential line 62, but the resistive element 421 can also be connected between node N6 and the smoothing capacitor 42.

[0039] The second switching element 45 is connected in series between the photodetection element 10 and the smoothing capacitor 42. The second switching element 45 is configured to switch the current flow from the photodetection element 10 to the smoothing capacitor 42 on and off. In other words, the second switching element 45 toggles the relationship between the photodetection element 10 and the smoothing capacitor 42 between a connected state and a disconnected state. In the present embodiment, one end of the second switching element 45 is connected to a node N7 located between node N4 and the second transistor 43. The other end of the second switching element 45 in the present embodiment is connected to node N6. The second switching element 45 in the present embodiment includes a switch 45a. The switch 45a can be a mechanical switch or a semiconductor switch, such as a transistor.Alternatively, the second switching element 45 can be an amplifier with a control terminal for switching between performing an output and omitting an output. In this case, the amplifier can switch between a first state and a second state. The first state is a state in which a current (or voltage) applied to the input terminal is amplified, and the amplified current (or voltage) is output from the output terminal. The second state is a state in which the output terminal is in a high-impedance state, and a signal at the input terminal is not passed to the output terminal.

[0040] The control unit 50 is connected to each control terminal of the first switching element 32 and the second switching element 45. The control unit 50 controls the switching operations of the first switching element 32 and the second switching element 45 individually. Specifically, the control unit 50 controls the on / off switching of switch 32a and switch 45a individually. Alternatively, the control unit 50 can control the switching operations of the first switching element 32 and the second switching element 45, i.e., the on and off switching of switch 32a and switch 45a, together. In this case, the control terminals of the first switching element 32 and the second switching element 45 can be connected to the control unit 50 via common wiring.The control unit 50, for example, is a timing circuit arranged on a chip that also houses the photodetection element 10, the current-to-voltage converter unit 20, the first current distance unit 30, and the second current distance unit 40. Alternatively, the control unit 50 could be, for example, a personal computer, a smart device such as a smartphone or tablet terminal, or a computer such as a cloud server. A computer acting as the control unit 50 includes a hard disk drive (HDD), a storage device such as flash memory or RAM (random access memory), and a processor (CPU: central processing unit). The control unit 50 could be a microcomputer or an FPGA (field-programmable gate array).

[0041] The photodetection circuit 1A according to the present embodiment with the configuration described above operates as follows. First, during a period in which the first signal voltage V1 output by the photodetection circuit 1A is not used outside the photodetection circuit 1A, the control unit 50 controls the first switching element 32 so that current flows from the photodetection element 10 to the voltage-holding capacitor 31. As described in Fig. As shown in Figure 2, the first switching element 32 allows a portion of the signal current J to flow from the photodetection element 10 to the voltage-holding capacitor 31. As a result, charge accumulates in the voltage-holding capacitor 31, increasing the voltage across it. At this point, the voltage-holding capacitor 31 allows a high-frequency signal component contained in the signal current J to pass through. Therefore, the voltage across the voltage-holding capacitor 31 depends primarily on the magnitude of the low-frequency component contained in the signal current J.

[0042] During the aforementioned period, the control unit 50 controls the second switching element 45 so that the current flows from the photodetection element 10 to the smoothing capacitor 42. As in Fig. As shown in Figure 2, the second switching element 45 allows the remainder of the signal current J to flow from the photodetection element 10 to the smoothing capacitor 42. As a result, charge accumulates in the smoothing capacitor 42, and the voltage across the smoothing capacitor 42 increases. At this point, the smoothing capacitor 42 allows the high-frequency signal component contained in the signal current J to pass through. Therefore, the voltage across the smoothing capacitor 42 depends primarily on the magnitude of the low-frequency component contained in the signal current J.

[0043] The period during which the signal current J flows from the photodetection element 10 to the voltage-holding capacitor 31, and the period during which the signal current J flows from the photodetection element 10 to the smoothing capacitor 42, may or may not overlap.

[0044] As charge accumulation progresses in the voltage-holding capacitor 31 and the smoothing capacitor 42, the voltages across the voltage-holding capacitor 31 and the voltages across the smoothing capacitor 42 gradually cease to change. The first signal voltage V1, output by the photodetection circuit 1A, is used outside the photodetection circuit 1A after the switching point, i.e., at the point when the voltages across the voltage-holding capacitor 31 and the voltages across the smoothing capacitor 42 are hardly changing anymore.

[0045] At the switching time, the control unit 50 switches the first switching element 32 so that no current flows from the photodetection element 10 to the voltage-holding capacitor 31. This allows the voltage across the voltage-holding capacitor 31 to be determined based on the magnitude of the low-frequency component at the switching time and maintained at a constant value even after the switching time. The voltage across the voltage-holding capacitor 31 is applied to the control terminal 33a of the first transistor 33. Consequently, the first transistor 33 extracts, as shown in Fig. Figure 1 shows the first current J1, with a magnitude corresponding to the voltage across the voltage-holding capacitor 31, derived from the signal current J. The control unit 50 maintains the state of the first switching element 32 such that no current flows from the photodetection element 10 to the voltage-holding capacitor 31, while the first signal voltage V1 is used outside the photodetection circuit 1A.

[0046] At the switching time or at another time, the control unit 50 switches the second switching element 45 so that no current flows from the photodetection element 10 to the smoothing capacitor 42. Therefore, the smoothing capacitor 42 can perform the smoothing of the second signal voltage V2. As in Fig. As shown in Figure 1, the second transistor 43 extracts the second current J2 from the signal current J, with a magnitude corresponding to the smoothed second signal voltage V2. The control unit 50 maintains the state of the second switching element 45 such that no current flows from the photodetection element 10 to the smoothing capacitor 42, while the first signal voltage V1 is used outside the photodetection circuit 1A.

[0047] The effects achieved by the photodetection circuit 1A described above, according to the present embodiment, are described. According to the photodetection circuit 1A, a certain fraction of the low-frequency component contained in the signal current J, i.e., the first current J1, is extracted from the signal current J by the first current removal unit 30. The remaining fraction of the low-frequency component contained in the signal current J, i.e., the second current J2, is extracted from the signal current J by the second current removal unit 40. The second current J2 is a fluctuation of the low-frequency component after the switching time at which the first switching element 32 is switched.With this configuration, the low-frequency component to be removed by the second current removal unit 40, which performs a feedback operation on the low-frequency component, is reduced compared to a case where the first current removal unit 30 is not provided. Therefore, the transconductance of the second transistor 43 decreases, and the loop gain decreases. As a result, the frequency band of the low-frequency component extracted from the signal current J in the second current removal unit 40, i.e., the frequency band of the second current J2, becomes narrower. Furthermore, since the charge to be accumulated in the smoothing capacitor 42 is reduced, the time required for charge accumulation in the smoothing capacitor 42 is shortened. Therefore, the settling time of the feedback process can be shortened.Thus, according to the photodetection circuit 1A of the present embodiment, it is possible to shorten the settling time of the feedback process and at the same time to keep the frequency band of the low frequency component extracted from the signal current J small.

[0048] Most photodetection elements that generate a large dark current have a central sensitivity in the near- to mid-infrared wavelength range. Therefore, when a photodetection element with a central sensitivity in the near- to mid-infrared wavelength range is used as photodetection element 10 in the present embodiment, the effects described above become even more pronounced. Furthermore, most photodetection elements that generate a large dark current are compound semiconductors. Therefore, when a photodetection element containing a compound semiconductor as the semiconductor material is used as photodetection element 10 in the present embodiment, the effects described above become even more pronounced. Representative examples of semiconductor materials used in photodetection elements that generate a large dark current are Ge, InGaAs, and InAsSb.The central sensitivity of a photodetection element using Ge is 1.6 µm or less. The central sensitivity of a photodetection element using InGaAs is 2.6 µm or less. The central sensitivity of a photodetection element using InAsSb is 12 µm or less. A photodetection element containing one of these semiconductor materials is primarily used in the near- to mid-infrared wavelength range. The effects described above become even more pronounced when using a photodetection element containing one of these semiconductor materials.

[0049] As in the present embodiment, the first current removal unit 30 can comprise the voltage-holding capacitor 31, the first switching element 32, and the first transistor 33. The voltage-holding capacitor 31 is configured to be charged by the current from the photodetection element 10. The first switching element 32 is configured to switch a current flow from the photodetection element 10 to the voltage-holding capacitor 31 on and off. The first transistor 33 has the control terminal 33a, the first current terminal 33b, and the second current terminal 33c. A voltage based on the voltage across the voltage-holding capacitor 31 is applied to the control terminal 33a. The first current terminal 33b is connected to the photodetection element 10. The second current terminal 33c is connected to the reference potential line 62.Since the first current distance unit 30 has such a configuration, the magnitude of the first current J1 can, for example, be determined based on the magnitude of the low-frequency component at a predetermined time, i.e., the switching time.

[0050] As in the present embodiment, the second current removal unit 40 can include the second switching element 45. The second switching element 45 is connected in series between the photodetection element 10 and the smoothing capacitor 42 and switches the current flow from the photodetection element 10 to the smoothing capacitor 42 on / off. In this case, the charge in the smoothing capacitor 42 can be accumulated in advance before the first signal voltage V1 is used outside the light detection circuit 1A. Therefore, the settling time of the feedback process in the second current removal unit 40 can be further reduced.

[0051] As in the present embodiment, the resistive element 421 can be arranged in series with the smoothing capacitor 42 between node N6 and the reference potential line 62. In this case, the phase delay at high frequencies can be reduced by the resistive element 421. Therefore, the stability of the feedback process of the second current removal unit 40 can be improved. [First modification]

[0052] (a) to (c) in Fig. 3, (a) and (b) in Fig. 4, (a) to (c) in Fig. 5 and (a) to (d) in Fig. Figure 6 shows circuit diagrams illustrating the configurations of the first current distance units 30A to 30M according to a modification of the above embodiment. The photodetection circuit 1A according to the above embodiment can include any of the first current distance units 30A to 30M instead of the first current distance unit 30.

[0053] The first current removal unit 30A, which is in (a) in Fig. Figure 3, in addition to the configuration of the first current removal unit 30 in the embodiment above, includes a first amplifier 34A. The first amplifier 34A is configured to amplify the current flowing from the photodetection element 10 to the voltage-holding capacitor 31. Alternatively, the first amplifier 34A can be configured to amplify the voltage applied from the photodetection element 10 to the voltage-holding capacitor 31. In particular, the first amplifier 34A is connected in series with the first switching element 32 between node N3 and node N2. In the example shown, the first amplifier 34A is connected between node N3 and the first switching element 32, but the first amplifier 34A can also be connected between the first switching element 32 and node N2. In this case, the first amplifier 34A can have a control terminal to select whether or not an output should be made.By setting the output terminal of the first amplifier 34A to a high impedance state, leakage current through the first amplifier 34A can be prevented. The input terminal of the first amplifier 34A is connected to the photodetection element 10 via node N3 and node N1. The output terminal of the first amplifier 34A is connected to the voltage-holding capacitor 31 via node N2. According to the first current removal unit 30A, the charge caused by the signal current J can be accumulated more quickly in the voltage-holding capacitor 31, thus reducing the time required for charge accumulation. In the above embodiment, the time required for charge storage in the voltage-holding capacitor 31 is the time during which the first signal voltage V1, corresponding to the light intensity of the signal light L, cannot be output, i.e., the dead time.According to the first current removal unit 30A, it is possible to shorten the dead time.

[0054] As in (b) in Fig. As shown in Figure 3, the first current removal unit 30B has a first amplifier 34B instead of the first amplifier 34A of the first current removal unit 30A. The first amplifier 34B is also configured to amplify the current flowing from the photodetection element 10 to the voltage-holding capacitor 31 or the voltage applied from the photodetection element 10 to the voltage-holding capacitor 31. The first amplifier 34B has an inverting input terminal and a non-inverting input terminal, the non-inverting input terminal being connected to node N3. A predetermined reference voltage Vref1 is applied to the inverting input terminal of the first amplifier 34B. Alternatively, as in the first current removal unit 30C in Figure (c), Fig. As shown in Figure 3, the inverting input terminal of the first amplifier 34B is connected to node N2. These first current removal units 30B and 30C can also achieve the same effects as the first current removal unit 30A described above. Furthermore, according to the first current removal unit 30B, the voltage at node N3 can be set to any reference voltage, regardless of the magnitude of the current input to the first current removal unit 30B. Therefore, the error in the magnitude of the first current J1 caused by the channel length modulation effect of the first transistor 33 can be reduced.

[0055] The first current removal unit 30D, which is in (a) in Fig. As shown in Figure 4, a first switching element 32A replaces the first switching element 32 of the first current removal unit 30 in the embodiment above. The first switching element 32A comprises an amplifier 321 and is configured to amplify the current flowing from the photodetection element 10 to the voltage-holding capacitor 31 or the voltage applied from the photodetection element 10 to the voltage-holding capacitor 31. The first switching element 32A has a control terminal 321a for selecting whether or not an output is to be made. The first switching element 32A can switch between a first state and a second state. The first state is a state in which a current (or voltage) input to the input terminal is amplified, and the amplified current (or voltage) is output from the output terminal.The second state is one in which the output terminal is in a high-impedance state and a signal at the input terminal is not transmitted to the output terminal. The control terminal of amplifier 321 for switching is connected to the control unit 50. The control unit 50 controls the switching operation of the first switching element 32A in the same way as the first switching element 32 in the embodiment above. As in that modification, the first switching element can have a function for amplifying a current (or a voltage).

[0056] The first current removal unit 30E, which is in (b) in Fig. As shown in Figure 4, the first switching element 32 of the first current removal unit 30 in the above embodiment has a first resistive element 35. The first resistive element 35 is provided along the path of a current flowing from the photodetection element 10 to the voltage-holding capacitor 31. In particular, one end of the first resistive element 35 is connected to the photodetection element 10 via node N3 and node N1. The other end of the first resistive element 35 is connected to an electrode of the voltage-holding capacitor 31 via node N2. The resistance value of the first resistive element 35 is relatively high, for example, 100 kΩ or more and 10 MΩ or less.

[0057] If the photodetection circuit 1A includes the first current removal unit 30E, the photodetection circuit 1A operates, for example, as follows. Initially, during a period in which the first signal voltage V1 output by the photodetection circuit 1A (see Fig. 1) When not used outside of the photodetection circuit 1A, a portion of the signal current J from the photodetection element 10 flows through the first resistor element 35 to the voltage-holding capacitor 31. This stores charge in the voltage-holding capacitor 31 to increase the voltage across it. The first signal voltage V1 output by the photodetection circuit 1A is used outside of the photodetection circuit 1A after the point at which the voltage across the voltage-holding capacitor 31 is no longer changing significantly. If the period during which the first signal voltage V1 is used is sufficiently short, the voltage across the voltage-holding capacitor 31 is determined based on the magnitude of the low-frequency component at that point and maintained at an approximately constant value during this period. The voltage across the voltage-holding capacitor 31 is applied to the control terminal 33a of the first transistor 33.As a result, the first transistor 33 extracts the first current J1 from the signal current J (see . Fig. 1) with a value corresponding to the voltage across the voltage-holding capacitor 31. In this way, the magnitude of the first current J1 can also be determined in this modification based on the magnitude of the low-frequency component at a predetermined time.

[0058] As in (a) in Fig. As shown in Figure 4, the first switching element 32A can include the amplifier 321 with the control terminal 321a for selecting whether or not an output should be made. In this case, the charge can accumulate more quickly in the voltage-holding capacitor 31 due to the signal current J. Therefore, the time required for charge accumulation can be reduced. The time required for charge accumulation in the voltage-holding capacitor 31 is the time during which the first signal voltage V1, corresponding to the light intensity of the signal light L, cannot be output, i.e., the dead time. According to the diagram in (a) in Fig. In the first current removal unit 30D shown in Figure 4, it is possible to shorten the dead time. Furthermore, by equipping the amplifier 321 with a function for switching the current flow from the photodetection element 10 to the voltage-holding capacitor 31 on and off, the number of components can be further reduced compared to the case where an amplifier is provided separately from the first switching element 32.

[0059] The first current distance units 30F to 30H, which are shown in (a) to (c) in Fig. Figure 5 shows a first transistor 36 instead of the first transistor 33 in the embodiment above. The first transistor 36 in this modification is a P-channel MOSFET. The first transistor 36 is configured to extract the first current J1 from the signal current J, the magnitude of which corresponds to the voltage across the voltage-holding capacitor 31. The first transistor 36 has a control terminal 36a (Gate), a first current terminal 36b (Source), and a second current terminal 36c (Drain).

[0060] In the first current distance unit 30F, which is in (a) in Fig. As shown in Figure 5, one electrode of the voltage-holding capacitor 31 is connected to node N1 between the photodetection element 10 and the first transistor 36. The other electrode of the voltage-holding capacitor 31 is connected to one end of the first switching element 32. The other end of the first switching element 32 is connected to the reference potential line 62. In this way, the first switching element 32 is connected in series between the voltage-holding capacitor 31 and the reference potential line 62. As in the embodiment above, the first switching element 32 switches the current flow from the photodetection element 10 to the voltage-holding capacitor 31 on and off.

[0061] The control terminal 36a of the first transistor 36 is connected to node N8 between the other electrode of the voltage-holding capacitor 31 and the first switching element 32. A voltage based on the voltage across the voltage-holding capacitor 31, for example, the voltage across the voltage-holding capacitor 31 itself, is applied to the control terminal 36a. The first current terminal 36b is connected to node N9 between the voltage-holding capacitor 31 and node N1, and via nodes N9 and N1 to the photodetection element 10. The second current terminal 36c is connected to the reference potential line 62. The connection shown in (a) in Fig. The photodetection circuit 1A shown in Figure 5 with the first current removal unit 30F can achieve the same effects as in the embodiment above.

[0062] The first current removal unit 30G, which is in (b) in Fig. 5, in addition to the configuration of the first current removal unit 30F shown in (a) in Fig. Figure 5 shows a first amplifier 37A. The first amplifier 37A is configured to amplify the current flowing from the photodetection element 10 to the voltage-holding capacitor 31 or the voltage applied from the photodetection element 10 to the voltage-holding capacitor 31. Specifically, the first amplifier 37A is connected in series with the first switching element 32 between nodes N9 and N8. In this embodiment, the other end of the first switching element 32 is connected to the output terminal of the first amplifier 37A instead of the reference potential line 62. In the example shown, the first amplifier 37A is connected between node N9 and the first switching element 32, but the first amplifier 37A can also be connected between the first switching element 32 and node N8.In this case, the first amplifier 37A can have a control terminal for selecting whether or not an output should be made, like the first switching element 32A shown in (a) in . Fig. Figure 4 shows that by setting the output terminal of the first amplifier 37A to a high impedance state, it is possible to prevent charge leakage through the first amplifier 37A. The input terminal of the first amplifier 37A is connected to the photodetection element 10 via node N1. According to the first current removal unit 30G, the charge can accumulate more quickly in the voltage-holding capacitor 31 due to the signal current J. Therefore, the time required for charge accumulation can be reduced. The time required for charge accumulation in the voltage-holding capacitor 31 is thus the time during which the first signal voltage V1, corresponding to the light intensity of the signal light L, cannot be output, i.e., the dead time. According to the first current removal unit 30G, it is possible to shorten the dead time.

[0063] The in (c) in Fig. The first current removal unit 30H shown in Figure 5 has a first amplifier 37B instead of the first amplifier 37A of the first current removal unit 30G.

[0064] The first amplifier 37B is also configured to amplify the current flowing from the photodetection element 10 to the voltage-holding capacitor 31, or the voltage applied from the photodetection element 10 to the voltage-holding capacitor 31. The first amplifier 37B has an inverting input terminal and a non-inverting input terminal, and the inverting input terminal is connected to nodes N1 and N9. A predetermined reference voltage Vref2 is applied to the non-inverting input terminal of the first amplifier 37B. The first current removal unit 30H can also achieve the same effects as the first current removal unit 30G described above. In addition, the voltage at node N9 can be set to any reference voltage, independent of the magnitude of the current applied to the first current removal unit 30H.Therefore, the error in the magnitude of the first current J1 caused by the channel length modulation effect of the first transistor 36 can be reduced.

[0065] In the first current distance unit 30J, which is in (a) in Fig. As shown in Figure 6, both the second current terminal 33c of the first transistor 33 and the other electrode of the voltage-holding capacitor 31 are connected to a common third constant-potential line 64, which has a different potential than the reference potential line 62. The potential of the third constant-potential line 64 is lower than the potential of the bias line 61. In a first current-distance unit 30K, shown in (b) in Fig. As shown in Figure 6, the second current terminal 33c of the first transistor 33 is connected to a fourth constant potential line 65, which has a different potential than the reference potential line 62. The other electrode of the voltage-holding capacitor 31 is connected to a fifth constant potential line 66, which has a different potential than the reference potential line 62 and the fourth constant potential line 65. The photodetection circuit 1A, which includes either the first current removal unit 30J or 30K, can achieve the same effect as in the embodiment above.

[0066] The in (c) in Fig. The first current removal unit 30L shown in Figure 6 comprises, in addition to the configuration of the first current removal unit 30 in the embodiment above, a transistor 38. The transistor 38 is connected in series with the first transistor 33 between the photodetection element 10 and the reference potential line 62. The transistor 38 has a control terminal 38a, a first current terminal 38b, a second current terminal 38c, and a control terminal 38a. The first current terminal 38b is connected to the second current terminal 38c of the first transistor 33. The second current terminal 38c is connected to the reference potential line 62. A voltage based on the voltage across the voltage-holding capacitor 31 is applied to the control terminal 38a.In the example shown, the control terminal 38a is short-circuited with the first current terminal 38b, and the voltage of the second current terminal 33c of the first transistor 33 is applied to the control terminal 38a.

[0067] As in this modification, by connecting transistor 38 in series with the first transistor 33, it is possible to adjust the magnitude of the gate voltage required to turn on the first transistor 33. That is, by connecting transistor 38 between the first transistor 33 and the reference potential line 62, as in the example shown, the gate voltage required to turn on the first transistor 33 can be increased by the gate-source voltage of transistor 38. Similarly, in the second current removal unit 40, another transistor can be connected in series with the second transistor 43. In this case, for example, if the output voltage range of the second amplifier 44 is limited, the magnitude of the gate voltage required to turn on the second transistor 43 can be adjusted to match the output voltage range of the second amplifier 44.

[0068] The in (d) in Fig. The first current removal unit 30M shown in Figure 6 comprises, in addition to the configuration of the first current removal unit 30 in the embodiment above, a source follower circuit 39. The source follower circuit 39 comprises a transistor 391 and a current source 392. The transistor 391 is, for example, a FET. The gate of the transistor 391 is connected to node N2, and the source of the transistor 391 is connected to the reference potential line 62 via the current source 392. The control terminal 33a of the first transistor 33 is connected to a node N10 between the transistor 391 and the current source 392 and is connected to node N2 via the transistor 391.

[0069] With this modification, the magnitude of the voltage across the voltage-holding capacitor 31 required to switch on the first transistor 33 can be adjusted. That is, by connecting the source-follower circuit 39 between the first transistor 33 and one electrode of the voltage-holding capacitor 31, as shown in the example, the voltage across the voltage-holding capacitor 31 required to switch on the first transistor 33 can be increased by the gate-source voltage of transistor 391. If the source-follower circuit 39 is provided, the first transistor 33 can be a bipolar transistor. [Second modification]

[0070] (a) and (b) in Fig. 7, (a) and (b) in Fig. 8 and (a) and (b) in Fig. Figure 9 shows circuit diagrams illustrating the configurations of the second current removal units 40A to 40F according to a modification of the above embodiment. The photodetection circuit 1A according to the above embodiment can include any of the second current removal units 40A to 40F instead of the second current removal unit 40.

[0071] The second current distance unit 40A, which is in (a) in Fig. Figure 7 shows a feedback circuit section 41A instead of the feedback circuit section 41 in the embodiment above. The configuration, apart from the feedback circuit section 41A, is the same as that of the second current removal unit 40 in the embodiment above. The feedback circuit section 41A in this modification includes a second amplifier 46. The second amplifier 46 comprises an input terminal 46a and an output terminal 46b. The input terminal 46a is connected to the signal output terminal 22 of the current-to-voltage conversion unit 20. The output terminal 46b is connected via node N6 to an electrode of the smoothing capacitor 42. The second amplifier 46 outputs the second signal voltage V2 at the output terminal 46b, the magnitude of which is proportional to the voltage applied to the input terminal 46a.As in this modification, an amplifier forming the feedback circuit section can have a single input terminal.

[0072] The in (b) in Fig. The second current removal unit 40B shown in Figure 7 has the same configuration as the second current removal unit 40 in the embodiment above, except for the following points. Specifically, in the second current removal unit 40B, the first input terminal 44a of the second amplifier 44 in the feedback circuit section 41 is not connected to the terminal shown in Figure 7. Fig. The second current removal unit 40B is not connected to node N5, but receives a reference voltage Vref3. The same effects can be achieved with the second current removal unit 40 described above.

[0073] The in (a) in Fig. Figure 8 shows a second current removal unit 40C having a feedback circuit section 41C instead of the feedback circuit section 41 in the embodiment above. The configuration, except for the feedback circuit section 41C, is the same as that of the second current removal unit 40 in the embodiment above. The feedback circuit section 41C in this modification includes a second resistive element 47. One end of the second resistive element 47 is connected to the signal output terminal 22 of the current-to-voltage conversion unit 20. The other end of the second resistive element 47 is connected via node N6 to an electrode of the smoothing capacitor 42. The resistance value of the second resistive element 47 is, for example, 100 kΩ or more and 10 MΩ or less. The feedback circuit section 41C outputs the second signal voltage V2 with a magnitude equal to the first signal voltage V1.According to the second current removal unit 40C, it is possible to achieve the same effects as with the second current removal unit 40 described above.

[0074] The second current removal unit 40D, which is shown in (b) in Fig. 8, in addition to the configuration of the second current removal unit 40A shown in (a) in Fig. Figure 7 shows a third amplifier 48. The third amplifier 48 is configured to amplify the current flowing from the photodetection element 10 to the smoothing capacitor 42, or the voltage applied from the photodetection element 10 to the smoothing capacitor 42. In this modification, the third amplifier 48 is connected in series with the second switching element 45 between nodes N7 and N6. In the example shown, the third amplifier 48 is connected in series between node N7 and the second switching element 45, but the third amplifier 48 can also be connected between the second switching element 45 and node N6. In this case, the third amplifier 48 can have a control terminal to select whether or not an output is made. By setting the output terminal of the third amplifier 48 to a high impedance state, leakage current through the third amplifier 48 can be prevented.According to this modification, charge can accumulate more quickly in the smoothing capacitor 42. Therefore, the time required for charge accumulation can be reduced. The time required for charge accumulation in the smoothing capacitor 42 is the time during which the first signal voltage V1, corresponding to the light intensity of the signal light L, cannot be output, i.e., the dead time. According to the second current removal unit 40D, it is possible to reduce the dead time. The second current removal unit 40D can replace the second amplifier 46 with the second resistive element 47 (see (a) in ). Fig. 8) exhibit.

[0075] The third amplifier 48 can have an inverting input terminal and a non-inverting input terminal. In this case, the non-inverting input terminal is connected to node N7, and a predetermined reference voltage is applied to the inverting input terminal. The voltage at node N7 can then be adjusted to any desired reference voltage, independent of the magnitude of the current applied to the second current removal unit 40D. Therefore, the error in the magnitude of the second current J2 caused by the channel length modulation effect of the second transistor 43 can be reduced. Alternatively, the inverting input terminal can be connected to node N6.

[0076] Alternatively, instead of the second switching element 45 and the third amplifier 48, a second switching element with an amplifier can be provided. In this case, the amplifier of the second switching element is configured to amplify the current flowing from the photodetection element 10 to the smoothing capacitor 42 or the voltage applied from the photodetection element 10 to the smoothing capacitor 42. Furthermore, the amplifier has a control terminal for selecting whether or not an output is provided. The amplifier can switch between a first state and a second state. The first state is a state in which a current (or voltage) applied to the input terminal is amplified, and the amplified current (or voltage) is output from the output terminal.The second state is one in which the output terminal is in a high-impedance state and a signal at the input terminal is not transmitted to the output terminal. The amplifier's control terminal for switching is connected to the control unit 50. The control unit 50 controls the switching operation of the amplifier in the same way as the second switching element 45 in the embodiment described above. As described above, the second switching element can have a function for amplifying the current (or voltage).

[0077] The in (a) in Fig. Figure 9 shows a second current removal unit 40E, which has a feedback circuit section 41B instead of the feedback circuit section 41 in the embodiment above. The configuration, except for the feedback circuit section 41B, is the same as that of the second current removal unit 40 in the embodiment above. The feedback circuit section 41B includes a second amplifier 49. The second amplifier 49 comprises an input terminal 49a, an output terminal 49b, and a control terminal 49c. The input terminal 49a is connected to the signal output terminal 22 of the current-to-voltage conversion unit 20. The output terminal 49b is connected via node N6 to an electrode of the smoothing capacitor 42. The second amplifier 49 outputs the second signal voltage V2 via the output terminal 49b, the magnitude of which is proportional to the voltage applied to the input terminal 49a.Control terminal 49c is used to select whether or not the output voltage, i.e., the second signal voltage V2, is output. Depending on a control signal input to control terminal 49c, the second amplifier 49 is in either a first state or a second state. The first state is a state in which the second signal voltage V2 is output. The second state is a state in which output terminal 49b is in a high-impedance state, and a signal at input terminal 49a is not transmitted to output terminal 49b. Control terminal 49c is connected to control unit 50, and a control signal is output from control unit 50 to control terminal 49c. According to this modification, the second amplifier 49 can be controlled, after prior accumulation of charge in the smoothing capacitor 42, so that it does not output the second signal voltage, i.e., V2.This prevents some of the current from flowing from the photodetection element 10 into the second amplifier 49, and the charge can be efficiently stored in the smoothing capacitor 42. Although the above description depicts the case where the second amplifier has a single input terminal, the second amplifier can also have a differential input, i.e., an inverting input terminal and a non-inverting input terminal.

[0078] The second amplifier 49 can be a transconductance amplifier that outputs a current from its output terminal 49b, the magnitude of which is proportional to the voltage applied to its input terminal 49a. In this case, the control terminal 49c is used to select whether or not a current is output. Depending on a control signal applied to the control terminal 49c, the second amplifier 49 is in either a first state or a second state. The first state is a state in which a current with a magnitude proportional to the input voltage is output. The second state is a state in which the output terminal 49b is in a high-impedance state and a signal at the input terminal 49a is not transmitted to the output terminal 49b. Again, the second amplifier 49 can be controlled so that it does not output a current if the charge is accumulated in advance in the smoothing capacitor 42.This prevents some of the current from flowing from the photodetection element 10 into the second amplifier 49, and the charge can be efficiently accumulated in the smoothing capacitor 42.

[0079] The second current distance unit 40F, which is shown in (b) in Fig. 9, in addition to the configuration of the second current removal unit 40A shown in (a) in Fig. Figure 7 shows a third switching element 71. The third switching element 71 is connected in series between the second amplifier 46 and the smoothing capacitor 42. The third switching element 71 switches the connection between the second amplifier 46 and the smoothing capacitor 42 between a connected state and a disconnected state. In one example, the third switching element 71 includes a switch 71a. The switch 71a can be a mechanical switch or a semiconductor switch such as a transistor. The switching operation of the third switching element 71 is controlled by the control unit 50. According to this modification, the third switching element 71 can be put into a disconnected state after the charge has been accumulated in the smoothing capacitor 42. This prevents some of the current from flowing from the photodetection element 10 to the second amplifier 46, and the charge can be efficiently stored in the smoothing capacitor 42.Although the above description depicts the case where the second amplifier has a single input terminal, the second amplifier can also have a differential input, i.e., an inverting input terminal and a non-inverting input terminal. [Third modification]

[0080] (a) and (b) in Fig. 10, Fig. 11 and (a) in Fig. Figure 12 are circuit diagrams, each showing the configurations of the current-to-voltage converter units 20A to 20D according to a modification of the embodiment described above. The photodetection circuit 1A according to the embodiment described above can include any of the current-to-voltage converter units 20A to 20D instead of the current-to-voltage converter unit 20. Each of the current-to-voltage converter units 20A to 20D is configured to switch the input of the signal current J to the signal input terminal 21 on and off.

[0081] Each of the in (a) and (b) in Fig. In Figure 10, the current-to-voltage converter units 20A and 20B shown have a resistor 25 instead of the capacitor 24 in the embodiment above. This means that the current-to-voltage converter units 20A and 20B are transimpedance amplifiers. One end of the resistor 25 is connected to the input terminal of the amplifier 23, and the other end of the resistor 25 is connected to the output terminal of the amplifier 23. The current-to-voltage converter unit 20A has a fourth switching element 26, and the current-to-voltage converter unit 20B has a fourth switching element 27. The fourth switching element 26 of the current-to-voltage converter unit 20A is connected in series between node N4 and both the amplifier 23 and the resistor 25. The fourth switching element 26 switches the relationship between node N4 and both amplifier 23 and resistor 25 of the current-voltage converter unit 20B between a connected state and a disconnected state.The fourth switching element 27 of the current-to-voltage converter unit 20B is connected in series with resistor 25 between the input terminal and the output terminal of amplifier 23. In the example shown, the fourth switching element 27 is connected between the input terminal of amplifier 23 and resistor 25, but it can also be connected between resistor 25 and the output terminal of amplifier 23. The fourth switching element 27 switches the connection between the input terminal and the output terminal of amplifier 23 between a connected state and a disconnected state. In this modification, the fourth switching elements 26 and 27 each have switches 26a and 27a, respectively. Switches 26a and 27a can be mechanical switches or semiconductor switches such as transistors.

[0082] According to these current-to-voltage converter units 20A and 20B, when charge accumulates prematurely in the smoothing capacitor 42, the fourth switching elements 26 and 27 are put into a disconnected state, so that the signal current J is not fed into the signal input terminal 21. This prevents part of the current from flowing from the photodetection element 10 to the current-to-voltage converter unit, and the charge can be efficiently stored in the smoothing capacitor 42.

[0083] The in Fig. Figure 11 shows a current-to-voltage converter unit 20C with a resistor 25 instead of the capacitor 24 in the embodiment above. That is, the current-to-voltage converter unit 20C is a transimpedance amplifier. Furthermore, the current-to-voltage converter unit 20C has an amplifier 28 instead of the amplifier 23. In addition to an input terminal and an output terminal, the amplifier 28 has a control terminal 28a. The control terminal 28a is a terminal for receiving a control signal to select whether the output terminal should be set to a high impedance state or not. In response to a control signal input to the control terminal 28a, the amplifier 28 is in either a first state or a second state. The first state is a state in which the first signal voltage V1 is output.The second state is one in which the output terminal is in a high-impedance state and a signal at the input terminal is not transmitted to the output terminal. Control terminal 28a is connected to control unit 50, and a control signal is input from control unit 50 to control terminal 28a.

[0084] According to the current-to-voltage converter unit 20C, prior charge accumulation in the smoothing capacitor 42 can cause the output terminal of the amplifier 28 to enter a high-impedance state. This prevents the signal current J from being fed into the signal input terminal 21. Since a portion of the current from the photodetection element 10 is thus prevented from flowing to the current-to-voltage converter unit, the charge can be efficiently stored in the smoothing capacitor 42.

[0085] The in (a) in Fig. The current-to-voltage converter unit 20D shown in Figure 12 is a charge amplifier with a capacitor 24 and has an amplifier 28 instead of the amplifier 23. The configuration of the amplifier 28 is similar to that in Figure 12. Fig. 11 Current-to-voltage converter unit 20C shown. This current-to-voltage converter unit 20D is used in combination with the one shown in (a) in Fig. Figure 8 shows a second current removal unit, 40C, which uses a resistive element as a feedback circuit section. The current-to-voltage converter unit 20D can also achieve the same effects as the current-to-voltage converter unit 20C. [Fourth modification]

[0086] (am Fig. 12 and Fig. Figure 13 are circuit diagrams, each showing the configurations of the second current removal units 40H and 40J according to a modification of the above embodiment. The photodetection circuit 1A according to the above embodiment can include one of the second current removal units 40H and 40J instead of the second current removal unit 40.

[0087] The second current distance unit 40H, which is in (b) in Fig. 12, in addition to the configuration of the second current removal unit 40C shown in (a) in Fig. Figure 8 shows a third switching element 73. The third switching element 73 is connected in series with the second resistor 72 between the signal output terminal 22 of the current-to-voltage conversion unit 20 and the smoothing capacitor 42, more precisely between the signal output terminal 22 and node N6. The third switching element 73 switches the connection between the signal output terminal 22 and the smoothing capacitor 42 between a connected state and a disconnected state. In the example shown, the third switching element 73 is connected between the signal output terminal 22 and the second resistor 72, but the third switching element 73 can also be connected between the second resistor 72 and node N6. In one example, the third switching element 73 includes a switch 73a. The switch 73a can be a mechanical switch or a semiconductor switch, such as a transistor.The switching process of the third switching element 73 is controlled by the control unit 50.

[0088] According to the second current removal unit 40H, the third switching element 73 can be placed in a disconnected state when charge accumulates prematurely in the smoothing capacitor 42. This prevents some of the current from flowing from the photodetection element 10 through the second resistive element 72. Therefore, the charge can be stored efficiently in the smoothing capacitor 42.

[0089] The in Fig. Figure 13 shows a second current removal unit 40J having a feedback circuit section 41D instead of the feedback circuit section 41 in the embodiment above. The configuration, except for the feedback circuit section 41D, is the same as that of the second current removal unit 40 in the embodiment above. The feedback circuit section 41D in this modification includes a transistor 74. The transistor 74 is, for example, a MOSFET. One current terminal (for example, a source) of the transistor 74 is connected to the signal output terminal 22 of the current-to-voltage converter unit 20. The other current terminal (for example, a drain) of the transistor 74 is connected via node N6 to an electrode of the smoothing capacitor 42. The control terminal (gate) of the transistor 74 is electrically connected to the control unit 50 and receives a control signal from the control unit 50.Depending on a control signal applied to its control terminal, transistor 74 is in either a first state or a second state. The first state is a state in which the second signal voltage V2 is output. The second state is a state in which the output terminal is in a high-impedance state and a signal at the input terminal is not transmitted to the output terminal. According to this modification, after prior charge accumulation in the smoothing capacitor 42, it is possible to control transistor 74 such that the output terminal is set to a high-impedance state and the signal at the input terminal is not transmitted to the output terminal. This prevents some of the current from the photodetection element 10 from flowing through transistor 74, and the charge can be efficiently accumulated in the smoothing capacitor 42. [Fifth modification]

[0090] Fig. Figure 14 is a circuit diagram showing the configuration of a photodetection circuit 1B according to a modification of the embodiment above. In this modification, the configuration of the current-to-voltage converter unit 20 is similar to that in the embodiment above. In the photodetection circuit 1B according to this modification, the wiring 63 is connected to the cathode of the photodetection element 10, and the bias line 61 is connected to the anode of the photodetection element 10. The photodetection circuit 1B includes a first current removal unit 30N instead of the first current removal unit 30 in the embodiment above. The photodetection circuit 1B includes a second current removal unit 40P instead of the second current removal unit 40 in the embodiment above.

[0091] In this modification, the first current removal unit 30N comprises a voltage-holding capacitor 31, a first switching element 32, and a first transistor 36. The voltage-holding capacitor 31 is configured to be charged by a current from the photodetection element 10. Specifically, one electrode of the voltage-holding capacitor 31 is connected to the photodetection element 10 via the first switching element 32 and a node N1. The other electrode of the voltage-holding capacitor 31 is connected to a sixth constant-potential line 68. The potential of the sixth constant-potential line 68 is higher than the potential of the bias line 61. The first switching element 32 is connected in series between node N1 and the voltage-holding capacitor 31. The first switching element 32 switches the current flow from the photodetection element 10 to the voltage-holding capacitor 31 on and off.

[0092] The first transistor 36 is configured to extract the first current J1 from the signal current J, with a magnitude corresponding to the voltage across the voltage-holding capacitor 31. The first transistor 36 has a control terminal 36a (gate), a first current terminal 36b (drain), and a second current terminal 36c (source). In this modification, the first transistor 36 is a P-channel MOSFET. The control terminal 36a is connected to node N2 between an electrode of the voltage-holding capacitor 31 and the first switching element 32. A voltage based on the voltage across the voltage-holding capacitor 31, for example, the voltage across the voltage-holding capacitor 31 itself, is applied to the control terminal 36a. The first current terminal 36b is connected to node N3 between the first switching element 32 and node N1, and via nodes N3 and N1, to the photodetection element 10.The second power terminal 36c is connected to a seventh constant potential line 69. The potential of the seventh constant potential line 69 is higher than the potential of the bias line 61. The potential of the seventh constant potential line 69 can be equal to or different from the potential of the sixth constant potential line 68.

[0093] The second current removal unit 40P in this modification includes a feedback circuit section 41B, a smoothing capacitor 42, and a second transistor 81. The configuration of the feedback circuit section 41B is similar to the configuration of the feedback circuit section 41B of the second current removal unit 40E shown in (a) in Fig. 9 is shown.

[0094] The smoothing capacitor 42 smooths the second signal voltage V2. In this modification, the other electrode of the smoothing capacitor 42 is connected to a constant potential line 82. The potential of the constant potential line 82 is higher than the potential of the bias line 61.

[0095] The second transistor 81 is configured to extract the second current J2 from the signal current J, the magnitude of which corresponds to the second signal voltage V2 smoothed by the smoothing capacitor 42. The second transistor 81 has a control terminal 81a, a first current terminal 81b, and a second current terminal 81c. In this modification, the second transistor 81 is a P-channel MOSFET. The control terminal 81a is connected to node N6 between an electrode of the smoothing capacitor 42 and the feedback circuit section 41b. The second signal voltage V2, smoothed by the smoothing capacitor 42, is applied to the control terminal 81a. The first current terminal 81b is connected to node N4 and, via node N4, to the photodetection element 10. The second current terminal 81c of transistor 81 is connected to a constant potential line 83.The potential of the constant potential line 83 can be the same or different from the potential of the constant potential line 82. The gain of the second transistor 81 is lower than the gain of the first transistor 36, for example 1 / 10 or less of the gain of the first transistor 36.

[0096] The photodetection circuit 1B according to this modification can also achieve the same effects as the photodetection circuit 1A according to the above embodiment. [Sixth modification]

[0097] The Fig. Figures 15 to 20 are circuit diagrams, each showing the configurations of the photodetection circuits 1C to 1H according to a modification of the above embodiment.

[0098] The in Fig. The photodetection circuit 1C shown in Figure 15 comprises a second current removal unit 40K instead of the second current removal unit 40 in the embodiment above. The second current removal unit 40K differs from the second current removal unit 40 in the following points, but is identical to the second current removal unit 40 in other points. The second current removal unit 40K has a second switching element 75 instead of the second switching element 45 of the second current removal unit 40. The second switching element 75 is connected in series with the first switching element 32 between the photodetection element 10 and the smoothing capacitor 42. That is, the second switching element 75 is connected in series between node N2 and node N6. The second switching element 75, together with the first switching element 32, switches the current flow from the photodetection element 10 to the smoothing capacitor 42 on and off.The second switching element 75 in this modification includes a switch 75a. The switch 75a can be a mechanical switch or a semiconductor switch such as a transistor. The switching operation of the second switching element 75 is controlled by the control unit 50. As in this second current removal unit 40K, the current supplied by the photodetection element 10 to the smoothing capacitor 42 can flow through the first switching element 32. Even in this case, the same effects as in the embodiment above can be achieved. The photodetection circuit 1C can include one of the first current removal units 30 and 30A to 30N described above and one of the current-to-voltage converter units 20 and 20A to 20D described above.

[0099] The in Fig. The photodetection circuit 1D shown in Figure 16 includes a first current removal unit 30P instead of the first current removal unit 30 in the embodiment above. The first current removal unit 30P differs from the first current removal unit 30 in the following points, but is identical to the first current removal unit 30 in other points. The first current removal unit 30P has a first switching element 76 instead of the first switching element 32 of the first current removal unit 30. The first switching element 76 is connected in series with the second switching element 45 between the photodetection element 10 and the voltage-holding capacitor 31. That is, the first switching element 76 is connected in series between node N6 and node N2. The first switching element 76, together with the second switching element 45, switches the current flow from the photodetection element 10 to the voltage-holding capacitor 31 on and off.The first switching element 76, in this modification a switch 76a. The switch 76a can be a mechanical switch or a semiconductor switch such as a transistor. The switching operation of the first switching element 76 is controlled by the control unit 50. As in this first current removal unit 30P, the current supplied by the photodetection element 10 to the voltage-holding capacitor 31 can flow through the second switching element 45. In this case as well, the same effects as in the embodiment above can be achieved. The photodetection circuit 1D can include one of the second current removal units 40 and 40A to 40J described above and one of the current-to-voltage converter units 20 and 20A to 20D described above.

[0100] The in Fig. The photodetection circuit 1E shown in Figure 17 comprises any first current removal unit from the first current removal unit 30A shown in (a) in Fig. 3 shows the first current removal unit 30B, which is shown in (b) in Fig. 3 is shown, and the first current removal unit 30C, which is shown in (c) in Fig. Figure 3 shows the second current removal unit 40L instead of the first current removal unit 30 in the embodiment above. Furthermore, the photodetection circuit 1E includes a second current removal unit 40L instead of the second current removal unit 40 in the embodiment above. The second current removal unit 40L differs from the second current removal unit 40 in the following respects, but is identical to the second current removal unit 40 in other respects. The second current removal unit 40L has a second switching element 77 instead of the second switching element 45 of the second current removal unit 40. The second switching element 77 is connected in series between node N11, between the first amplifier 34A (or the first amplifier 34B) and the first switching element 32, and node N6. The second switching element 77 switches the current flow from the photodetection element 10 to the smoothing capacitor 42 on and off.The second switching element 77 in this modification includes a switch 77a. The switch 77a can be a mechanical switch or a semiconductor switch such as a transistor. The switching operation of the second switching element 77 is controlled by the control unit 50.

[0101] As in this second current removal unit 40L, the first amplifier 34A (or the first amplifier 34B) of the first current removal units 30A to 30C can also be used to amplify the current (or voltage) from the photodetection element 10 to the smoothing capacitor 42. In this case, both the current through the first current removal units 30A to 30C, shown in (a) to (c) in Fig. 3 shown, the effect achieved as well as that achieved by the second current distance unit 40D, which is shown in (b) in Fig. As shown in Figure 8, the effect achieved can be obtained with a smaller circuit. Similar effects can also be achieved by using one of the first current removal units (30A to 30C) with the circuit shown in Figure 8. Fig. The second current removal unit shown in section 15 is combined with 40K, as shown in the diagram. Fig. 18 photodetection circuit shown 1F.

[0102] The in Fig. The photodetection circuit 1G shown in Figure 19 has, instead of the first current removal unit 30 in the above embodiment, the one shown in Figure 19. Fig. 4 (b) shows the first current removal unit 30E. Furthermore, the photodetection circuit 1G, instead of the second current removal unit 40 in the above embodiment, has the one shown in Fig. The second current removal unit 40K shown in Figure 15 is used. As in this photodetection circuit 1G, the current supplied from the photodetection element 10 to the smoothing capacitor 42 can flow through the first resistor element 35. In this case, too, the same effects as in the embodiment above can be achieved.

[0103] The in Fig.The photodetection circuit 1H shown in Figure 20 has a first current removal unit 30Q instead of the first current removal unit 30 in the embodiment above. In addition to the configuration of one of the first current removal units 30 and 30A to 30P, the first current removal unit 30Q has a first short-circuit switch 78. The first short-circuit switch 78 is connected in parallel with the voltage-holding capacitor 31 between node N2 and the reference potential line 62. When the first current removal unit 30Q is not in use, the electrode pair of the voltage-holding capacitor 31 can be short-circuited via the first short-circuit switch 78. Therefore, it is possible to prevent a malfunction of the first transistor 33 due to unnecessary charge accumulation in the voltage-holding capacitor 31.

[0104] The photodetection circuit 1H has a second current removal unit 40M instead of the second current removal unit 40 in the embodiment above. In addition to the configuration of one of the second current removal units 40 and 40A to 40L, the second current removal unit 40M has a second short-circuit switch 79. The second short-circuit switch 79 is connected in parallel to the smoothing capacitor 42 between node N6 and the reference potential line 62. When the second current removal unit 40M is not in use, the electrode pair of the smoothing capacitor 42 can be short-circuited via the second short-circuit switch 79. Since the control terminal 43a of the second transistor 43 is connected to the reference potential line 62 via the second short-circuit switch 79, a malfunction of the second transistor 43 can be prevented.

[0105] The photodetection circuit according to the present disclosure is not limited to the embodiment described above, and various other modifications can be made. For example, the respective modifications described above can be combined according to the desired purpose and effect. The second switching element of the second current removal unit can be omitted depending on the situation. [Additional note]

[0106] In the photodetection circuit, the feedback circuit must shorten the settling time of the feedback process when extracting a low-frequency component from the signal stream. Therefore, the photodetection circuit can have the following configuration.

[0107] A photodetection circuit, including: a photodetection element that outputs a signal current in response to the incidence of signal light; a current-to-voltage converter unit having a signal input terminal and a signal output terminal, which converts the signal current input to the signal input terminal into a first signal voltage and outputs the first signal voltage from the signal output terminal, the signal input terminal being connected to the photodetection element; and a current removal unit connected to the photodetection element, wherein the signal stream contains a signal component and a low-frequency component with a lower frequency than the signal component or with a constant magnitude, and The current distance unit includes: a feedback circuit section that is connected to the signal output terminal of the current-to-voltage converter unit and outputs a second signal voltage whose magnitude corresponds to the first signal voltage; a smoothing capacitor configured to smooth the second signal voltage; a second transistor configured to extract the low-frequency component from the signal current with a magnitude corresponding to the second signal voltage smoothed by the smoothing capacitor; and a switching element that is connected in series between the photodetection element and the smoothing capacitor and is configured to switch a current flow from the photodetection element to the smoothing capacitor on and off.

[0108] The photodetection circuit operates as follows. First, during a period when the initial signal voltage output by the photodetection circuit is not used outside the circuit, the switching element allows current to flow from the photodetection element to the smoothing capacitor. This stores charge in the smoothing capacitor, increasing the voltage across it. Then, the initial signal voltage output by the photodetection circuit is used outside the circuit. At this point, the switching element is switched so that no current flows from the photodetection element to the smoothing capacitor. Therefore, the smoothing capacitor can smooth the second signal voltage. Thus, according to the photodetection circuit described above, the charge in the smoothing capacitor can be accumulated in advance before the initial signal voltage is used outside the circuit.Therefore, the settling time of the feedback process in the current removal unit can be shortened. List of reference symbols

[0109] 1A to 1H: Photodetection circuit, 10: Photodetection element, 20, 20A to 20D: Current-voltage- Converter unit, 21: Signal input terminal, 22: Signal output terminal, 23: Amplifier, 24: Capacitor, 25: Resistor, 26, 27: Fourth switching element, 26a, 27a: Switch, 28: Amplifier, 28a: Control terminal, 30, 30A to 30H, 30J to 30N, 30P, 30Q: First current removal unit, 31: Voltage holding capacitor, 32, 76: First switching element, 32a, 76a: Switch, 32A: First switching element, 33, 36: First transistor, 33a, 36a: Control terminal, 33b, 36b: First current terminal, 33c, 36c: Second current terminal, 34A, 34B: First amplifier, 35: First resistor element, 37A, 37B: first amplifier, 38: transistor, 38a: control terminal, 38b: first current terminal, 38c: second current terminal, 39: source follower circuit, 40, 40A to 40F, 40H, 40J to 40M, 40P: second current removal unit, 41, 41A to 41D: feedback circuit section, 42: smoothing capacitor, 43, 81: second transistor, 43a, 81a: control terminal, 43b, 81b: first current terminal, 43c, 81c: second current terminal44, 46: second amplifier, 44a: first input terminal, 44b: second input terminal, 44c: output terminal, 45, 75, 77: second switching element, 45a, 75a, 77a: switch, 46, 49: second amplifier, 46a, 49a: input terminal, 46b, 49b: output terminal, 47: second resistive element, 48: third amplifier, 49c: control terminal, 50: control unit, 61: bias line, 62: reference potential line, 63: wiring, 64: third constant potential line, 65: fourth, Constant potential line, 66: fifth Constant potential line, 68: sixth Constant potential line, 69: seventh constant potential line, 71, 73: third switching element, 71a, 73a: switch, 72: second resistive element, 74: transistor, 78: first short-circuit switch, 79: second short-circuit switch, 82, 83: constant potential line, 311: resistive element, 321: amplifier, 391: transistor, 392: current source, 421: resistive element, J: signal current, J1: first current, J2: second current, L: signal light, N1 to N11: node, V1: first signal voltage, V2: second signal voltage, Vref1, Vref2, Vref3: reference voltage. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP H4-142416 A

[0002]

Claims

[1] Photodetection circuit, comprising: a photodetection element configured to output a signal stream in response to the incident signal light; a current-to-voltage converter unit with a signal input port and a signal output port, configured to convert the signal current input to the signal input port into a first signal voltage and output the first signal voltage from the signal output port, the signal input port being connected to the photodetection element; a first current removal unit connected to the photodetection element and configured to extract a first current from the signal current; and a second current removal unit connected to the photodetection element and configured to extract a second current from the signal current, wherein the signal stream comprises a signal component and a low-frequency component with a lower frequency than the signal component or with a constant magnitude, wherein the first current distance unit is configured to determine a first current magnitude based on the magnitude of the low-frequency component at a predetermined time and to maintain the first current magnitude, and The second current distance unit includes: a feedback circuit section connected to the signal output terminal of the current-to-voltage converter unit and configured to output a second signal voltage of a magnitude corresponding to the first signal voltage; a smoothing capacitor configured to smooth the second signal voltage; and a second transistor configured to extract from the signal current a second current of a magnitude corresponding to the second signal voltage smoothed by the smoothing capacitor. [2] Photodetection circuit according to claim 1, wherein the first current removal unit comprises: a voltage-holding capacitor configured to be charged by a current from the photodetection element; a first switching element configured to switch a current flow from the photodetection element to the voltage-holding capacitor on and off; and a first transistor with a control terminal, a first current terminal and a second current terminal, wherein a voltage based on a voltage across the voltage-holding capacitor is applied to the control terminal, the first current terminal is connected to the photodetection element and the second current terminal is connected to a constant potential line. [3] Photodetection circuit according to claim 2, wherein the first switching element is an amplifier with a control terminal for selecting whether or not an output should be made. [4] Photodetection circuit according to claim 1, wherein the first current removal unit comprises: a voltage-holding capacitor configured to be charged by a current from the photodetection element; a first resistive element provided in a current path from the photodetection element to the voltage-holding capacitor; and a first transistor with a control terminal, a first current terminal and a second current terminal, wherein a voltage based on a voltage at the voltage-holding capacitor is applied to the control terminal, the first current terminal is connected to the photodetection element and the second current terminal is connected to a constant potential line. [5] Photodetection circuit according to claim 2 or 4, wherein the first current removal unit further comprises a first amplifier configured to amplify a current flowing from the photodetection element to the voltage-holding capacitor or a voltage applied from the photodetection element to the voltage-holding capacitor. [6] Photodetection circuit according to one of claims 2 to 4, wherein the first current removal unit further comprises a transistor connected in series with the first transistor between the photodetection element and the constant potential line and has a control terminal to which a voltage is applied which is based on a voltage at the voltage-holding capacitor. [7] Photodetection circuit according to one of claims 2 to 4, wherein the first current removal unit further comprises a first short-circuit switch connected in parallel to the voltage-holding capacitor. [8] Photodetection circuit according to any one of claims 1 to 7, wherein the second current removal unit further comprises a second switching element which is connected in series between the photodetection element and the smoothing capacitor and is configured to switch on and off a current flow from the photodetection element to the smoothing capacitor. [9] Photodetection circuit according to claim 8, wherein the feedback circuit section comprises a second amplifier with an input terminal and an output terminal, the input terminal being connected to the signal output terminal of the current-to-voltage converter unit and the output terminal being connected to the smoothing capacitor, and The second amplifier also has a control connection that allows you to select whether or not an output should be made. [10] Photodetection circuit according to claim 8, wherein the feedback circuit section comprises a second amplifier with an input terminal and an output terminal, the input terminal being connected to the signal output terminal of the current-to-voltage converter unit and the output terminal being connected to the smoothing capacitor, and The second current removal unit further comprises a third switching element which is connected in series between the second amplifier and the smoothing capacitor and switches a relationship between the second amplifier and the smoothing capacitor between a connected state and a disconnected state. [11] Photodetection circuit according to claim 8, wherein the feedback circuit section comprises a second resistive element with one end and another end, the one end being connected to the signal output terminal of the current-to-voltage converter unit and the other end being connected to the smoothing capacitor, and The second current removal unit further comprises a third switching element which is connected in series with the second resistive element between the signal output terminal of the current-to-voltage converter unit and the smoothing capacitor and switches a relationship between the signal output terminal and the smoothing capacitor between a connected state and a disconnected state. [12] Photodetection circuit according to claim 8, wherein the second current removal unit further comprises a third amplifier configured to amplify a current flowing from the photodetection element to the smoothing capacitor or a voltage applied from the photodetection element to the smoothing capacitor. [13] Photodetection circuit according to claim 8, wherein the second switching element is an amplifier with a control terminal for selecting whether or not to make an output. [14] Photodetection circuit according to claim 8, wherein the current-to-voltage conversion unit is configured to be able to switch the input of the signal current into the signal input terminal on and off. [15] Photodetection circuit according to claim 2 or 3, wherein the second current removal unit further comprises a second switching element which is connected in series between a node between the first switching element and the voltage-holding capacitor and the smoothing capacitor and is configured to switch on and off a current flow from the photodetection element to the smoothing capacitor together with the first switching element. [16] Photodetection circuit according to claim 2 or 3, wherein the second current removal unit further comprises a second switching element connected in series between the photodetection element and the smoothing capacitor and configured to switch a current flow from the photodetection element to the smoothing capacitor on and off, and The first switching element is connected in series between a node between the second switching element and the smoothing capacitor and the voltage-holding capacitor, and is configured to switch a current flow from the photodetection element to the voltage-holding capacitor on and off together with the second switching element. [17] Photodetection circuit according to any one of claims 1 to 16, wherein the second current removal unit further comprises a second short-circuit switch connected in parallel to the smoothing capacitor.

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