Current-voltage conversion circuit

Abstract

To provide a current-voltage conversion circuit which can realize a low power consumption by reducing the influence of noise.SOLUTION: The current-voltage conversion circuit is connected to a detection element (20) and converts a current output as a detection signal of a detection element to a voltage. The current-voltage conversion circuit includes: a first inverter (11) for inputting a current and outputting a voltage; and a second inverter (12) for outputting a reference voltage to the detection element. The first inverter and the second inverter are connected to a supply circuit (10) directly connected to a common power source and supplying a potential which does not depend on the common power source.SELECTED DRAWING: Figure 1

Description

Technical Field

[0004] ,

[0001] The present disclosure relates to a current-voltage conversion circuit.

Background Art

[0002] Infrared rays with a wavelength of 2 μm or more are used in human body detection sensors, non-contact thermometers, gas sensors, etc. that detect the human body due to their thermal effects and the effects of infrared absorption by gases. For example, an infrared sensor used in a non-contact thermometer detects temperature based on the amount of infrared rays incident from a measurement target. Further, an infrared sensor may be provided in a small battery-driven electronic device and may be used for controlling the operation of the electronic device. For example, Patent Document 1 discloses an infrared sensor provided in an earphone and used for determining whether the earphone is worn or not in order to adjust the volume.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Here, particularly when provided in a small battery-driven electronic device, the infrared sensor is required to have low power consumption. The infrared sensor includes, for example, a photodiode that outputs a current according to the amount of incident infrared rays, and a current-voltage conversion circuit that converts the current into a voltage and amplifies it (see the left diagram of FIG. 9). For example, by replacing the operational amplifier included in the current-voltage conversion circuit with an inverter (see the right diagram of FIG. 9), the number of elements constituting the current-voltage conversion circuit can be reduced, and the power consumption can be reduced. When replaced with an inverter, it is preferable to drive the inverter under a driving source such as a regulator. However, when driving the inverter under a driving source, there is a problem that the noise of the driving source rides on the output and the detection accuracy of the infrared sensor decreases.

[0005] In view of these circumstances, the purpose of this disclosure is to provide a current-voltage conversion circuit that can reduce the effects of noise and achieve low power consumption. [Means for solving the problem]

[0006] (1) A current-voltage conversion circuit according to one embodiment of the present disclosure is: A current-voltage conversion circuit connected to a detection element, which converts the current output as a detection signal from the detection element into a voltage, A first inverter that takes the current as input and outputs the voltage, The detection element is further provided with a second inverter that outputs a reference voltage, The first inverter and the second inverter are connected to a supply circuit that is directly connected to a common power supply and supplies a potential independent of the common power supply.

[0007] (2) A current-voltage conversion circuit according to one embodiment of the present disclosure is A current-voltage conversion circuit connected to a detection element, which converts the current output as a detection signal from the detection element into a voltage, A first inverter that takes the current as input and outputs the voltage, The detection element is further provided with a second inverter that outputs a reference voltage, The first inverter and the second inverter are connected to a supply circuit that is directly connected to a common ground and supplies a potential independent of the common ground.

[0008] (3) As one embodiment of the present disclosure, in (1), The aforementioned supply circuit is a regulator or a current source.

[0009] (4) In one embodiment of the present disclosure, in any of (1) to (3), The aforementioned detection element is a photodiode that detects light.

[0010] (5) As one embodiment of the present disclosure, in (4), the light is infrared light.

Advantages of the Invention

[0011] According to the present disclosure, it is possible to provide a current-voltage conversion circuit capable of reducing the influence of noise and achieving low power consumption.

Brief Description of the Drawings

[0012] [Figure 1] FIG. 1 is a diagram showing a configuration example of a current-voltage conversion circuit according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a diagram for explaining the effect of the current-voltage conversion circuit of FIG. 1. [Figure 3] FIG. 3 is a diagram showing another configuration example of a current-voltage conversion circuit according to an embodiment of the present disclosure. [Figure 4] FIG. 4 is a diagram showing another configuration example of a supply circuit. [Figure 5] FIG. 5 is a diagram showing another configuration example of a supply circuit. [Figure 6] FIG. 6 is a diagram showing another configuration example of a current-voltage conversion circuit. [Figure 7] FIG. 7 is a diagram showing another configuration example of a current-voltage conversion circuit. [Figure 8] FIG. 8 is a diagram showing another configuration example of a current-voltage conversion circuit. [Figure 9] FIG. 9 is a diagram for explaining a method for reducing power consumption. <000008​​​​​​​​​​FIG. 1 is a circuit diagram showing a configuration example of a current-voltage conversion circuit according to the present embodiment. The current-voltage conversion circuit is connected to a detection element 20 and converts a current output as a detection signal of the detection element 20 into a voltage. Further, the current-voltage conversion circuit constitutes a detection device together with the detection element 20 and a subsequent-stage circuit. In the present embodiment, the detection element 20 is a photodiode that detects light. The light detected by the photodiode is infrared light. The photodiode converts the intensity of the incident infrared light into a current and outputs it. Here, the detection element 20 is not limited to a photodiode for infrared detection. The detection element 20 connected to the current-voltage conversion circuit described below may be, for example, a photodiode that detects light other than infrared light, or a phototransistor.

[0015] The current-voltage conversion circuit includes a first inverter 11 and a second inverter 12. The first inverter 11 inputs a current that is a detection signal of the detection element 20 and outputs a voltage. In the example of FIG. 1, a feedback resistor (R) is provided in the first inverter 11, and the output voltage of the first inverter 11 directly becomes the output (OUT) of the current-voltage conversion circuit. As described above, it is possible to reduce power consumption by replacing the operational amplifier included in the conventional current-voltage conversion circuit with an inverter (see FIG. 9), but the first inverter 11 corresponds to a circuit that replaces the operational amplifier.

[0016] The second inverter 12 outputs a reference voltage to the detection element 20. In the present embodiment, the output of the second inverter 12 is connected to the anode of the photodiode, and the input of the first inverter 11 is connected to the cathode of the photodiode. However, the connection polarity is not limited to that shown in FIG. 1.

[0017] In this embodiment, the current-voltage conversion circuit is connected to the supply circuit 10. The supply circuit 10 is directly connected to the common power supply (VDD), but supplies a potential independent of VDD to the current-voltage conversion circuit and the like. Here, the common power supply (VDD) is the power supply used in the circuits downstream of the current-voltage conversion circuit. The supply circuit 10 may be a regulator, as will be described later. The output of the supply circuit 10 is used to power the first inverter 11 and the second inverter 12.

[0018] As described above, in a conventional current-voltage conversion circuit, simply replacing the operational amplifier with an inverter resulted in noise from the supply circuit 10 being transmitted, leading to a problem of reduced detection accuracy as a detection device. In the current-voltage conversion circuit according to this embodiment, the circuit that outputs a reference voltage to the detection element 20 is composed of a second inverter 12. Furthermore, the power supply for the second inverter 12 is shared with the power supply (supply circuit 10) for the first inverter 11.

[0019] Figure 2 illustrates the effect of the current-voltage conversion circuit according to this embodiment on reducing the noise influence of the supply circuit 10. Let n1 be the node where the output of the supply circuit 10 is connected to the power supply of the first inverter 11. Let n2 be the node where the output of the supply circuit 10 is connected to the power supply of the second inverter 12. In Figure 2, the photodiode is replaced with an equivalent circuit including a current source and a resistor (R0). The gain from n1 to OUT, which is the output of the current-voltage conversion circuit, is given by equation (1) below. The gain from n2 to OUT is given by equation (2) below.

[0020]

number

[0021] Here, in equations (1) and (2), R0 is the resistance value of the resistor in the equivalent circuit of the photodiode. R is the resistance value of the feedback resistor of the first inverter 11. P1 is the power supply rejection ratio (PSRR) of the first inverter 11. P2 is the power supply rejection ratio (PSRR) of the second inverter 12. Since the path to OUT is common, the gain as a current-voltage conversion circuit can be obtained by combining equations (1) and (2). In addition, the power supply for the first inverter 11 and the power supply for the second inverter 12 both use the output of the supply circuit 10. Therefore, by designing them so that the power supply rejection ratio is the same (P1=P2) when noise occurs in the supply circuit 10, the terms for R / R0 in equations (1) and (2) cancel each other out. Thus, the current-voltage conversion circuit according to this embodiment can reduce the influence of noise from the supply circuit 10.

[0022] In the example shown in Figure 1, the circuit configuration reduces noise in the supply circuit 10, which is referenced to a common power supply (VDD). However, a circuit configuration referenced to a common ground (GND) is also possible. The common ground (GND) is used as the ground in the circuit after the current-voltage conversion circuit. As shown in Figure 3, the supply circuit 10 is directly connected to the common ground (GND), but it supplies a potential that is independent of the common ground (GND). The output of the supply circuit 10 is used as the ground for the first inverter 11 and the second inverter 12. The current-voltage conversion circuit shown in Figure 3, like Figure 1, can achieve low power consumption by replacing the operational amplifier used in the conventional configuration with the first inverter 11. Furthermore, the current-voltage conversion circuit shown in Figure 3, like Figure 1, can reduce the impact of noise from the supply circuit 10.

[0023] Here, for example, the supply circuit 10 may be a constant current regulator as shown in Figure 4. Alternatively, for example, the supply circuit 10 may be a current source as shown in Figure 5.

[0024] Furthermore, the current-voltage conversion circuit is not limited to a configuration in which a feedback resistor (R) is provided in the first inverter 11. For example, as shown in Figure 6, a capacitor (C) may be provided instead of the feedback resistor (R).

[0025] Furthermore, the current-voltage conversion circuit may include an operational amplifier to enhance its function as an amplification circuit. For example, as shown in Figure 7, the current-voltage conversion circuit may be configured to include an operational amplifier connected in series with the outputs of the first inverter 11 and the second inverter 12, respectively.

[0026] Furthermore, the current-voltage conversion circuit may be equipped with additional circuits to enable control over the detection element 20. For example, as shown in Figure 8, the current-voltage conversion circuit may be configured to include a so-called auto-zero mechanism that sets the potential difference across the photodiode, which is the detection element 20, to zero. In this case, a chopper switch may be added to the connection point with the photodiode.

[0027] As described above, the current-voltage conversion circuit according to this embodiment, with the above configuration, reduces the effects of noise and enables low power consumption.

[0028] While embodiments of this disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art will find it easy to make various modifications or alterations based on this disclosure. Therefore, it should be noted that these modifications or alterations are within the scope of this disclosure. For example, the functions included in each component can be rearranged in a logically consistent manner, and multiple components can be combined into one or separated. [Explanation of symbols]

[0029] 10 Supply circuit 11. First Inverter 12. Second Inverter 20 detection elements

Claims

1. A current-voltage conversion circuit connected to a detection element, which converts the current output as a detection signal from the detection element into a voltage, A first inverter that takes the current as input and outputs the voltage, The detection element is further provided with a second inverter that outputs a reference voltage, The first inverter and the second inverter are connected to a current-voltage conversion circuit that is directly connected to a common power supply and to a supply circuit that supplies a potential independent of the common power supply.

2. A current-voltage conversion circuit connected to a detection element, which converts the current output as a detection signal from the detection element into a voltage, A first inverter that takes the current as input and outputs the voltage, The detection element is further provided with a second inverter that outputs a reference voltage, The first inverter and the second inverter are connected to a supply circuit that is directly connected to a common ground and supplies a potential independent of the common ground, forming a current-voltage conversion circuit.

3. The current-voltage conversion circuit according to claim 1, wherein the supply circuit is a regulator or a current source.

4. The current-voltage conversion circuit according to any one of claims 1 to 3, wherein the detection element is a photodiode for detecting light.

5. The current-voltage conversion circuit according to claim 4, wherein the light is infrared.

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