JP2011217080A - Current-voltage conversion circuit and smoke detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify a device for preventing incidence of disturbance light on a light receiving part.SOLUTION: This current-voltage conversion circuit converts an input current converted by a photodiode into voltage according to a light receiving amount of emitted light of a light emitting diode by the photodiode, and performs control so as to cancel DC components by converting first input current which is input into output voltage to be output, converting second input current which is input into output voltage to be output, receiving each output voltage which are output to output average voltage equivalent to average value components of each output voltage, and canceling drain current equivalent to the DC components according to each output average voltage when the DC components are contained in the current output by the photodiode.

Description

  The present invention relates to a current-voltage conversion circuit that converts a current into a voltage and outputs the voltage, and a smoke detector including the current-voltage conversion circuit.

  Conventionally, in order to detect a change in current amount as a change in voltage value, a current-voltage conversion circuit that converts a current into a voltage and outputs the voltage is used. As shown in FIG. 10, such a current-voltage conversion circuit is used in, for example, a smoke detector 1 that detects and reports smoke generated during a fire. FIG. 10 is a schematic circuit diagram of a smoke detector 2 using a conventional current-voltage conversion circuit. Hereinafter, a schematic configuration of the smoke detector 1 shown in FIG. 10 will be described.

  As shown in FIG. 10 (a), the smoke detector 1 has a detection space K in the housing 3, a light emitting diode LD that intermittently outputs light toward the detection space K, and the light emitting diode LD. And a photodiode PD that is arranged at a position where no direct light is incident and converts received light into current (see, for example, Patent Document 1). In the smoke detector 1, when smoke flows into the detection space K, light from the light emitting diode LD is diffusely reflected by the smoke in the detection space K, so that light from the light emitting diode LD is received by the photodiode PD. The amount increases, and the amount of current output from the photodiode PD increases.

  The light emitting diode LD and the photodiode PD constitute an optical block 5 together with a light projecting lens 4a disposed in front of the light emitting diode LD and a light receiving lens 4b disposed in front of the photodiode PD. The housing 3 includes a body 6 that houses an optical block 5 so that an opening is formed on the lower surface and light from the light emitting diode LD is emitted toward the opening, and a bottomed cylindrical body that has an upper surface opening. 6 and a cover 7 coupled to the body 6 so as to cover the opening of 6.

  An opening window for taking in smoke is formed on the peripheral wall of the cover 7, and the detection space K described above is formed in the cover 7. Here, in the cover 7, an insect net 8 that prevents the insects from entering the detection space K and a labyrinth L that prevents disturbance light from entering the detection space K are disposed so as to surround the detection space K. Yes. In the labyrinth L, various disturbance lights such as a fluorescent lamp or an incandescent lamp are prevented from entering, and light from the light emitting diode LD is prevented from entering the photodiode PD in the absence of smoke in the detection space K. A complex structure with intricate light paths is used.

  In this type of smoke detector 1, as shown in FIG. 10 (b), a current-voltage conversion that converts the input current from the photodiode PD into a voltage and outputs it to the circuit block 9 housed in the housing 3. A circuit (IV conversion circuit) 23 is provided. Further, the output voltage of the current-voltage conversion circuit 23 is input to the alarm determination circuit 26 which is a determination processing unit through the amplifier circuit 24 and the filter circuit 25, and the change amount of the output voltage Vout described above exceeds a predetermined fire determination level. And a notification circuit 27 (buzzer or the like). The circuit block 9 includes a power supply circuit 28 for supplying power to each circuit, an interlocking circuit 29 for interlocking with other reporting means, and a transistor Tr10 (see FIG. 11) connected in series with the light emitting diode LD. An LED drive circuit 22 that periodically emits light from the light emitting diode LD is provided. FIG. 11 is an explanatory diagram showing a schematic circuit diagram of a conventional current-voltage conversion circuit 23.

  The current-voltage conversion circuit 23 used here has a conversion unit 33 formed by connecting a conversion resistor R20 between an inverting input terminal and an output terminal of an operational amplifier OP10 as shown in FIG. 11, for example. When the input current Iin is input to the terminal, the output voltage Vout whose voltage value varies according to the variation of the input current Iin is output to the output terminal Tout. In the example of FIG. 11, since the reference voltage Vs is applied to the non-inverting input terminal, if the resistance value of the conversion resistor R20 is r20, the output voltage Vout is expressed by Vout = Vs− (Iin × r20). . In short, the current-voltage conversion circuit 23 uses the output voltage Vout in a steady state where the photodiode PD does not receive light from the light-emitting diode LD as an operating point, and outputs the output voltage based on the operating point according to the fluctuation of the input current Iin. Vout is changed.

  In recent years, since the installation is simple, the demand for the smoke detector 1 using a battery as a power source is increasing. When a battery is used as the power source of the smoke detector 1, it is necessary to drive the smoke detector 1 intermittently in order to suppress the average power consumption of the smoke detector 1 and extend the life of the battery.

  FIG. 12 is a timing chart showing the operation of the conventional current-voltage conversion circuit 23, where (a) is a timing chart of the power supply circuit, (b) is a timing chart of the light emitting diode, and (c) is a timing chart of the output voltage. is there. In this case, the power supply to the current-voltage conversion circuit 23 shown in FIG. 12A is also intermittently performed. Therefore, the light emitting diode LD outputs pulsed light while power is supplied to the current-voltage conversion circuit 23 as shown in FIG. Here, when smoke flows into the detection space K and the photodiode PD receives light from the light emitting diode LD, a change amount ΔV of the output voltage Vout of the current-voltage conversion circuit 23 as shown by a solid line in FIG. Becomes larger and reaches the fire judgment level in FIG. On the other hand, if there is no smoke in the detection space K, the change amount ΔV of the output voltage becomes small as shown by the broken line in FIG. 12C, and does not reach the fire determination level.

  In the current-voltage conversion circuit 23 as shown in FIG. 11, the dynamic range of the operational amplifier OP10 is defined between the power supply voltage VDD of the operational amplifier OP10 and the ground GND as shown in FIG. The aforementioned output voltage Vout varies within this dynamic range. Therefore, when the input current Iin exceeds a certain level, the output voltage Vout is saturated.

  For example, in the smoke detector 1 described above, although the labyrinth L is provided, since the detection space K cannot be completely blocked from the outside, a slight disturbance light may enter the photodiode PD. . Normally, disturbance light has a small temporal variation, and when the photodiode PD receives the disturbance light, a current (hereinafter referred to as “DC component”) having a small temporal variation is output from the photodiode PD. . In the following description, the symbol indicating the current of the DC component is indicated by “Idc”.

  When the low frequency component included in the input current Iin exceeds a certain level, the output voltage Vout may be saturated. In particular, when the battery is used as the power source of the smoke detector A as described above, the output voltage Vout tends to be saturated because the power supply voltage of the operational amplifier OP1 is low and the dynamic range of the operational amplifier OP1 is relatively narrow.

  13A and 13B are explanatory diagrams showing the output voltage of the conventional current-voltage conversion circuit 23, where FIG. 13A shows a state in which the input current Iin does not contain a DC component, and FIG. 13B shows a state in which the input current Iin has a little DC component. (C) is a state in which the input current Iin contains a large amount of DC component.

  That is, if the input current Iin does not contain a direct current component, the operating point of the output voltage Vout becomes the reference voltage Vs as shown in FIG. 13A. Therefore, if the input current Iin varies, the output voltage Vout also becomes this In contrast to this, when the input current Iin includes a DC component, the operating point of the output voltage Vout decreases as shown in FIG. 13B, and the input current Iin becomes smaller. When it increases, there is a possibility that the output voltage Vout is saturated in the middle. In particular, when the DC component is large and the operating point of the output voltage Vout is lowered to near the ground GND as shown in FIG. 13C, the output voltage Vout is saturated regardless of the fluctuation of the input current Iin. Yes, the output voltage Vout does not follow the increase in the input current Iin.

  For example, if the resistance value r20 of the conversion resistor R20 is 1 MΩ and the reference voltage Vs is 1 V, the input current Iin is 1 μA and the voltage drop across the conversion resistor R20 is 1 V. As a result, the output voltage Vout of the current-voltage conversion circuit 23 Saturates to 0V. In this state, even if the photodiode PD receives light from the light emitting diode LD and the pulsed input current Iin is input to the current-voltage conversion circuit 23, the output voltage Vout of the current-voltage conversion circuit 23 is saturated. Therefore, there is a possibility that the change amount ΔV of the output voltage Vout does not reach the fire determination level and becomes a false alarm.

  Therefore, as the current-voltage conversion circuit 23, when the input current Iin contains a DC component, feedback can be applied between the output terminal Tout and the input terminal Tin to suppress saturation of the output voltage Vout due to the DC component. Something like this has been proposed.

  In addition to the conversion unit 33 described above, the current-voltage conversion circuit 23 receives an output voltage Vout of the conversion unit 33 and outputs an integration voltage Vdc corresponding to the integral value component of the output voltage Vout as shown in FIG. The circuit 38 includes a shunt resistor R31 inserted between the output of the integrating circuit 38 and the input terminal Tin of the converter 33. FIG. 14 is a schematic circuit diagram of another conventional current-voltage conversion circuit. As a result, the influence of the integrated value component on the output voltage Vout can be suppressed by drawing a current corresponding to the magnitude of the integrated voltage Vdc from the input current Iin and flowing it through the shunt resistor R31. When a direct current component is included in the input current Iin, the influence of the direct current component on the output voltage Vout can be suppressed by subtracting the direct current component from the input current Iin.

  In the current-voltage conversion circuit 23, the magnitude of the current flowing through the shunt resistor R31 is determined by the potential difference between both ends of the shunt resistor R31 and the resistance value of the shunt resistor R31. Since the potential difference between both ends of the shunt resistor R31 changes according to the magnitude of the DC component included in the input current Iin, the DC component that is larger as the output voltage Vout of the conversion unit 33 is saturated is included in the input current Iin. In this case, the potential difference between both ends of the shunt resistor R31 is also saturated, so that no more current can flow through the shunt resistor R31. The current at this time becomes the upper limit of the magnitude of the low frequency component that can suppress the influence on the output voltage Vout.

  However, in the smoke detector 1 described above, the disturbance light is prevented from entering the detection space K by the labyrinth L. Therefore, the disturbance light that is stronger as the direct current component included in the input current Iin exceeds the upper limit described above. If the current-voltage conversion circuit 23 having the above configuration is employed, saturation of the output voltage Vout can be sufficiently prevented.

Japanese Patent No. 2783945 (page 1-2)

  By the way, in the current-voltage conversion circuit 23 having the above-described configuration, when an input current Iin including a DC component exceeding the above-described upper limit is input, as illustrated in FIG. 13B or 13C. In addition, the operating point of the output voltage Vout may be lowered and the output voltage Vout may be saturated. If a resistor having a small resistance value is used as the shunt resistor R31, the upper limit of the magnitude of the direct current component that can suppress the influence on the output voltage Vout can be widened by drawing a large amount of current through the shunt resistor R31. However, the thermal noise of the shunt resistor R31 itself increases. If the thermal noise of the shunt resistor R31 increases, the input conversion noise of the current-voltage conversion circuit 23 also increases, which causes a problem that the SN ratio, which is the ratio between the noise and the signal component to be detected, is reduced. The resistance value of the shunt resistor R31 must be set large to some extent. As a result, there is a possibility that the output voltage Vout is saturated, and the following problems occur, for example.

  That is, in the smoke detector 1 described above, the structure of the labyrinth L that prevents the incidence of ambient light into the detection space K is complicated, and the cost for manufacturing the labyrinth L is reduced in the overall cost of the smoke detector 1. Therefore, it is desired to reduce the cost of the smoke detector 1 by simplifying the structure of the labyrinth L as much as possible or omitting the labyrinth L itself. However, if the labyrinth L is simplified or omitted, the disturbance light received by the photodiode PD becomes strong, and the direct current component included in the input current Iin has a magnitude of a low frequency component that can suppress the influence on the output voltage Vout. The upper limit may be exceeded, and as a result, the output voltage Vout may be saturated.

  Therefore, the present invention has been made in view of the above-described conventional circumstances, and provides a current-voltage conversion circuit and a smoke detector capable of simplifying means for preventing disturbance light from entering the light receiving unit. With the goal.

  In order to achieve the above-described object, the current-voltage conversion circuit of the present invention is a current that converts an input current output by conversion of a photodiode into a voltage according to the amount of light received by the photodiode with respect to light emitted from the light emitting diode. A voltage conversion circuit, which converts a first input current output from a photodiode into a first output voltage and outputs the first input current, and outputs a second input current output from the photodiode. A second operational amplifier that converts the output voltage to a second output voltage and outputs a first average voltage corresponding to an average value component of the first output voltage output by the first operational amplifier; 1 feedback circuit unit, a second feedback circuit unit that outputs a second average voltage corresponding to an average value component of the second output voltage output by the second operational amplifier unit, and a first feedback circuit Output by In accordance with the first average voltage, the first transistor unit that controls the flow of the current according to the current drawn from the first operational amplification unit, and the second output from the second feedback circuit unit And a second transistor unit that controls to flow a current according to a current flowing into the second operational amplifier according to the average voltage.

  The current-voltage conversion circuit according to the present invention includes a first feedback circuit portion, a gate electrode of the first transistor portion, and a gate electrode of the first transistor portion between the terminal of the first feedback circuit portion and the gate electrode of the first transistor portion. A first sample-and-hold circuit including a first switch unit that is conductive or non-conductive between the first switch unit and a first capacitor that is connected in parallel with the first switch unit. Between the terminal and the gate electrode of the second transistor part, a second switch part for conducting or non-conducting between the second feedback circuit part and the gate electrode of the second transistor part, and a second switch It is preferable that a second sample and hold circuit configured by a second capacitor connected in parallel with the unit is provided.

  Next, the current-voltage conversion circuit of the present invention is a current-voltage conversion circuit that converts an input current output by conversion of a photodiode into a voltage according to the amount of light received by the photodiode with respect to light emitted from the light-emitting diode, A third operational amplifier that converts the third input current output from the photodiode into a third output voltage and outputs the third input current, and converts the fourth input current output from the photodiode into a fourth output voltage A fourth operational amplifier for outputting, a third feedback circuit for outputting a third average voltage corresponding to an average value component of the fourth output voltage output by the fourth operational amplifier, A third transistor section for controlling to flow a current corresponding to a current flowing into the fourth operational amplifier section according to the third average voltage output by the third feedback circuit section; and a third feedback circuit Output by Depending on the third average voltage, and a current mirror circuit for the third transistor arranged to control the electric current corresponding to the current drawn from the third operational amplifying unit.

  The current-voltage conversion circuit according to the present invention includes a third feedback circuit section, a gate electrode of the third transistor section, and a gate electrode of the third transistor section between the terminal of the third feedback circuit section and the gate electrode of the third transistor section. It is preferable to provide a third sample-and-hold circuit including a third switch unit that conducts or non-conducts between and a third capacitor that is connected in parallel with the third switch unit.

  Next, the current-voltage conversion circuit of the present invention is a current-voltage conversion circuit that converts an input current output by conversion of a photodiode into a voltage according to the amount of light received by the photodiode with respect to light emitted from the light-emitting diode, A fifth operational amplifier that converts the fifth input current output from the photodiode into a fifth output voltage and outputs the fifth input current, and converts the sixth input current output from the photodiode into a sixth output voltage And outputs an output voltage obtained by amplifying the difference between the fifth and sixth output voltages output by the sixth operational amplification unit and the fifth and sixth operational amplification units, respectively, according to a predetermined gain. A differential amplifier; a fourth feedback circuit unit that receives the amplified output voltage output from the differential amplifier and outputs an average voltage corresponding to an average value component of the output voltage; and a fourth feedback circuit unit. In accordance with the average voltage output, the fourth transistor unit that controls to flow a current corresponding to the current flowing into the sixth operational amplifier unit, and the average voltage output by the fourth feedback circuit unit, A current mirror circuit unit for the fourth transistor unit that controls to flow a current corresponding to the current drawn from the fifth operational amplifier unit.

  The current-voltage conversion circuit according to the present invention includes a fourth feedback circuit section, a gate electrode of the fourth transistor section, and a gate electrode of the fourth transistor section between the terminal of the fourth feedback circuit section and the gate electrode of the fourth transistor section. It is preferable to provide a fourth sample-and-hold circuit including a fourth switch unit that conducts or non-conducts between and a fourth capacitor that is connected in parallel with the fourth switch unit.

  The current-voltage conversion circuit according to the present invention includes the first, second, third, and fourth terminals corresponding to the terminal of the feedback circuit unit and the feedback circuit unit among the first, second, third, and fourth. Any one of the first, second, third and fourth of the sample-and-hold circuit among the first, second, third and fourth between the gate electrode of any of the transistor portions. Any one of the first, second, third, and fourth capacitors due to leakage current from any one of the first, second, third, and fourth capacitors when the switch portion is non-conductive. It is preferable that a resistor that compensates for a decrease in voltage between the two terminals is connected in parallel to any one of the first, second, third, and fourth switch units.

  The smoke detector according to the present invention includes any one of the current-voltage conversion circuits described above, a light emitting unit that emits light intermittently toward a predetermined detection space, and direct light emitted from the light emitting unit is not incident. The photoelectric conversion unit that is disposed at the position and converts the amount of light received when the light output from the light emitting unit diffusely reflected by the smoke flowing into the detection space into current, and the output voltage output by the current-voltage conversion circuit A determination unit that determines whether or not a predetermined fire determination level is exceeded, and a determination unit that determines that the amount of change in the output voltage level exceeds a predetermined fire determination level according to the amount of change in the level of A warning unit that fires a warning sound that suggests the possibility of a predetermined fire, and the photoelectric conversion unit outputs a current to any one of the first to sixth input terminals of the current-voltage conversion circuit. It is characterized by that.

  According to the current-voltage conversion circuit and the smoke detector according to the present invention, it is possible to simplify the means for preventing the disturbance light from entering the light receiving unit.

The block diagram which shows the internal structure of the smoke detector containing the current voltage conversion part of each embodiment. Schematic circuit diagram showing the configuration of the current-voltage conversion unit and the amplification unit of the first embodiment The schematic circuit diagram which shows the structure of the current-voltage conversion part and amplification part of the modification of 1st Embodiment Explanatory diagram showing the time transition of the current output by the conversion of the photodiode and the average voltage output by the feedback circuit, (a) the time transition of the current output by the conversion of the photodiode, (b) by the feedback circuit Temporal transition of output average voltage Schematic circuit diagram showing the configuration of the current-voltage conversion unit and the amplification unit of the second embodiment The schematic circuit diagram which shows the structure of the current-voltage conversion part and amplification part of the modification of 2nd Embodiment Schematic circuit diagram showing the configuration of the current-voltage conversion unit and the amplification unit of the third embodiment The schematic circuit diagram which shows the structure of the current-voltage conversion part and amplification part of the modification of 3rd Embodiment The schematic circuit diagram which shows the structure of the current-voltage conversion part and amplification part in the further modification of the modification of 2nd Embodiment Explanatory drawing which shows the outline | summary of the smoke detector using the conventional current voltage conversion circuit, (a) is a schematic block diagram of a smoke detector, (b) is a block diagram which shows an internal structure. Schematic circuit diagram of a conventional current-voltage conversion circuit Timing chart showing operation of a conventional current-voltage conversion circuit, (a) is a timing chart of a power supply circuit, (b) is a timing chart of a light emitting diode, and (c) is a timing chart of an output voltage. An explanatory diagram showing an output voltage of a conventional current-voltage conversion circuit, (a) is a state in which a DC component is not included in the input current Iin, (b) is a state in which a DC component is slightly included in the input current Iin, ( c) The input current Iin contains a large amount of DC component. Schematic circuit diagram of another conventional current-voltage conversion circuit

  Hereinafter, each embodiment of the present invention will be described with reference to the drawings.

(First embodiment)
1. Description on Configuration and Operation of Smoke Detector FIG. 1 is a block diagram showing an internal configuration of the smoke detector 1 including a current-voltage conversion unit 13 which is a current-voltage conversion circuit of the first embodiment. In FIG. 1, the smoke detector 1 includes a timing generation unit 11, a light emission control unit 12, a light emitting diode LD, a photodiode PD, a current-voltage conversion unit 13, an amplification unit 14, a signal processing unit 15, A determination unit 16, an output unit 17, and a power supply circuit unit 18 are provided. Hereinafter, each part 11-18 of the smoke detector 1 and the operation | movement content of the said smoke detector 1 are demonstrated.

  The timing generation unit 11 includes a clock or the like, generates a timing signal related to the operation start and operation end of each unit 12 to 18 of the smoke detector 1, and outputs the generated timing signal to each unit 12 to 18 The respective units 12 to 18 are operated.

  The light emission control unit 12 is configured by a dedicated electronic circuit for controlling the operation of the light emitting diode LD, and starts or ends the operation based on the timing signal generated by the timing generation unit 11. The light emission control unit 12 preferably causes the light emitting diode LD to emit light periodically. In addition, the light emission control unit 12 emits light by applying a predetermined voltage generated in a circuit constituting the light emission control unit 12 to the light emitting diode LD based on the timing signal generated by the timing generation unit 11. The operation of starting or stopping the light emission of the diode LD is controlled. As an example of a specific circuit configuration of the light emission control unit 12, Patent Document 1 (see FIG. 14) can be referred to. For example, the light-emitting diode LD shown in FIG. 1 is connected in series to a collector electrode and an emitter electrode of a bipolar transistor (not shown), and turns on the bipolar transistor by applying a constant voltage across the series circuit. The pulse width of light emitted from the light emitting diode LD is determined by the pulse width.

  The current-voltage conversion unit 13 starts or ends operation based on the timing signal generated by the timing generation unit 11 and also according to the amount of light received by the photodiode PD with respect to the light emitted from the light-emitting diode LD based on the timing signal. The input current output by the conversion of the photodiode PD is converted into a voltage. A detailed configuration of the current-voltage converter 13 will be described later.

The amplifying unit 14 is configured by a differential amplifier or the like, and starts or ends the operation based on the timing signal generated by the timing generating unit 11. Further, the amplifier 14 is based on the timing signal output from the timing generation unit 11, and the difference (V ⁺⁺ −V ⁻⁻ ) between the two output voltages (V ⁺⁺ , V ⁻⁻ ) output from the current / voltage conversion unit 13. ) In accordance with a predetermined gain, and the amplified output voltage Vout is output to the signal processing unit 15. Here, when the predetermined gain is k, the relationship of Vout = k (V ^{++ −} V−−) is established.

  The signal processing unit 15 is configured by a filter circuit or the like for efficiently passing the signal output from the amplification unit 14, and starts or ends the operation based on the timing signal generated by the timing generation unit 11. It is preferable that the filter circuit constituting the signal processing unit 15 is set so that a signal having a frequency equal to or lower than a preset frequency or a predetermined frequency range is extracted from the signal output from the amplification unit 14. . The signal processing unit 15 outputs the extracted signal of the output voltage Vout to the determination unit 16.

  The determination unit 16 is configured by a dedicated electronic circuit, software, or the like, and starts or ends the operation based on the timing signal generated by the timing generation unit 11. Further, the determination unit 16 is based on the timing signal generated by the timing generation unit 11, and the detection space K provided in advance in the smoke detector 1 according to the signal of the output voltage Vout output by the signal processing unit 15. It is determined whether smoke has flowed into the room.

  Specifically, the determination unit 16 compares the signal of the output voltage Vout extracted by the signal processing unit 15 with a threshold signal of the output voltage that suggests the possibility of fire set in the determination unit 16 in advance. . When it is determined by this comparison that the signal of the output voltage Vout is larger than the threshold signal described above, the determination unit 16 outputs a control signal for reporting to the output unit 17 to the output unit 17. When it is determined by the above-described comparison that the signal of the output voltage Vout is smaller than the above-described threshold signal, the determination unit 16 does not output a control signal for reporting to the output unit 17 to the output unit 17.

  The output unit 17 includes a buzzer that issues a warning sound for suggesting the possibility of a fire, and is based on the timing signal generated by the timing generation unit 11 and the control signal for notification by the determination unit 16. The operation starts or ends.

  The power supply circuit unit 18 supplies power necessary for the operation of each unit 11 to 17 in the smoke detector 1.

2. Description on Configuration of Current-Voltage Conversion Unit 13 FIG. 2 is a schematic circuit diagram illustrating configurations of the current-voltage conversion unit 13 and the amplification unit 14 of the first embodiment. As shown in FIG. 2, the current-voltage converter 13 of the first embodiment includes at least an operational amplifier OP1, an operational amplifier OP2, a feedback circuit A1, a feedback circuit B1, a transistor Tr1, and a transistor Tr2. .

In the operational amplifier OP1, a conversion resistor R is connected between the input terminal T3 connected to the inverting input terminal of the operational amplifier OP1 and the output terminal T5 of the operational amplifier OP1, and the operational amplifier OP1 is connected to the non-inverting input terminal of the operational amplifier OP1. The reference voltage Vs is applied. The inverting input terminal of the operational amplifier OP1 has an input current Iac output according to the net amount of light received by the light emitting diode LD received by the photodiode PD via the terminal T3, and the photodiode PD. A combined current (Iac + Idc) with the DC component Idc output according to the amount of received disturbance light is supplied as an input current Iin ⁺ to the operational amplifier OP1. The operational amplifier OP1 outputs an output voltage V ⁺ satisfying V ⁺ = R · Iin ⁺ with respect to the supplied input current Iin ⁺ .

In the operational amplifier OP2, a conversion resistor R is connected between the input terminal T4 connected to the inverting input terminal of the operational amplifier OP2 and the output terminal T6 of the operational amplifier OP2, and the operational amplifier OP2 is connected to the non-inverting input terminal of the operational amplifier OP2. The reference voltage Vs is applied. The inverting input terminal of the operational amplifier OP2 has an input current Iac output according to the net amount of light received by the light emitting diode LD received by the photodiode PD via the terminal T4, and the photodiode PD. combined current of the direct current component Idc outputted in response to the received light amount of ambient light received (Iac + Idc) is the input current Iin to the operational amplifier OP2 ^- supplied as. The operational amplifier OP2 outputs an output voltage V ⁻ that satisfies V ⁻ = −R · Iin ⁻ with respect to the supplied input current Iin ⁻ .

The feedback circuit A1 inputs the output voltage V ⁺ output from the operational amplifier OP1 via the terminal T7 at the start, and inverts and amplifies the input output voltage V ^+, and the inverted and amplified output voltage V ^+. Integrate ⁺ . As an example of a specific circuit configuration of the feedback circuit A1, Patent Document 1 (see FIG. 1) can be referred to. Specifically, the feedback circuit A1 includes an inverting amplifier circuit for inverting and amplifying the output voltage V ⁺ output from the operational amplifier OP1, and an integration circuit for integrating the inverting and amplified output voltage V ^+. Has been. In this integration circuit, a predetermined time constant is determined by a capacitor and a resistor constituting the integration circuit. In particular, in the integrating circuit included in the feedback circuit A1, at least the photodiode PD is in a predetermined described above to have a cutoff frequency f ₁ for blocking a pulsed input current Iac generated upon receiving light from the light emitting diode LD A time constant is preferably set.

Feedback circuit A1 by inverting amplifying and integrating the outputted output voltage V ⁺ by the operational amplifier OP1, and outputs the average voltage Vdca corresponding to the average value component of the output voltage V ^+. Therefore, when the input current Iin ⁺ of the operational amplifier OP1 includes the pulsed input current Iac and the DC component Idc generated when the photodiode PD receives light from the light emitting diode LD, the feedback circuit The average voltage Vdca output from A1 is a voltage corresponding to the DC component Idc.

Feedback circuit B1, an output voltage V that is output by the operational amplifier OP2 via the terminal T8 ^- inputs the at starting, the output voltage V which is the input ^- inverting amplifying, said inverted amplified output voltage V ^- integrating the. As an example of a specific circuit configuration of the feedback circuit B1, Patent Document 1 (see FIG. 1) can be similarly referred to. Specifically, the feedback circuit B1, an output output voltage V by the operational amplifier OP2 ^- constituted by an integrating circuit for integrating an ^- an inverting amplifier circuit for inverting and amplifying a corresponding inverted amplified output voltage V Has been. In this integration circuit, a predetermined time constant is determined by a capacitor and a resistor constituting the integration circuit. In particular, in the integrating circuit included in the feedback circuit B1, at least the photodiode PD is in a predetermined described above to have a cutoff frequency f ₁ for blocking a pulsed input current Iac generated upon receiving light from the light emitting diode LD A time constant is preferably set.

Feedback circuit B1 outputs output voltage V by the operational amplifier OP2 ^- by inverting amplifying and integrating, the output voltage V ^- outputs an average voltage Vdcb corresponding to the average value components. Therefore, the photodiode PD and pulsed input current Iac generated upon receiving light from the light emitting diode LD and the DC component Idc input current Iin of the operational amplifier OP2 ^- if included in the feedback circuit The average voltage Vdcb output from B1 is a voltage corresponding to the DC component Idc.

The transistor Tr1 is composed of, for example, an NMOS (Metal Oxide Semiconductor) transistor in which an N-type channel is formed, a gate electrode connected to the terminal of the feedback circuit A1, and a power supply voltage by the power supply circuit unit 18 shown in FIG. And a source electrode connected to a terminal T1 connected to the current path of the input current Iin ⁺ . Further, when the average voltage Vdca output from the feedback circuit A1 is applied to the gate electrode, the transistor Tr1 is connected between the drain electrode and the source electrode of the transistor Tr1 from the operational amplifier OP1 corresponding to the average voltage Vdca. Control is performed so that a drain current Itr1 which is a current corresponding to the drawn current flows. This average voltage Vdca is assumed to be equal to or higher than the threshold voltage Vth of the transistor Tr1. As described above, when the average voltage Vdca is applied to the gate electrode of the transistor Tr1, the transistor Tr1 has a drain current that satisfies the relationship Itr1 = Idc between the drain current Itr1 and the DC component Idc. It is controlled to flow Itr1.

Transistor Tr2 is, for example, an NMOS transistor N-type channel is formed, a gate electrode connected to the end of the feedback circuit B1, the input current Iin ^- is connected to the terminal T2 connected to the current path A drain electrode and a grounded source electrode. In addition, when the average voltage Vdcb output from the feedback circuit B1 is applied to the gate electrode, the transistor Tr2 is connected to the operational amplifier OP2 between the drain electrode and the source electrode of the transistor Tr2 corresponding to the average voltage Vdcb. Control is performed so that a drain current Itr2 which is a current corresponding to the flowing-in current flows. This average voltage Vdcb is assumed to be equal to or higher than the threshold voltage Vth of the transistor Tr2. As described above, when the average voltage Vdcb is applied to the gate electrode of the transistor Tr2, the transistor Tr2 has a drain current that satisfies the relationship Itr2 = Idc between the drain current Itr2 and the DC component Idc. It controls to flow Itr2.

3. Next, the operation of the current / voltage conversion unit 13 will be described. First, when the photodiode PD receives light emitted by the light emitting diode LD, a pulsed input current output when the photodiode PD receives light from the light emitting diode LD is provided at both ends of the photodiode PD. A combined current (Idc + Iac) of Iac and the DC component Idc output when the photodiode PD receives disturbance light flows.

At this time, since a voltage equal to or higher than the threshold voltage Vth has not yet been applied to the gate electrode of the transistor Tr1, no drain current flows between the drain electrode and the source electrode of the transistor Tr1. For this reason, the input current Iin ⁺ flowing through the inverting input terminal of the operational amplifier OP1 becomes the above-described combined current (Idc + Iac). That is, the relationship of Iin ⁺ = Idc + Iac is established.

Similarly, since a voltage equal to or higher than the threshold voltage Vth has not yet been applied to the gate electrode of the transistor Tr2, no drain current flows between the drain electrode and the source electrode of the transistor Tr2. Therefore, the input current Iin ⁻ flowing to the inverting input terminal of the operational amplifier OP2 is also the above-described combined current (Idc + Iac). In other ^words, Iin - = Idc + Iac relationship is established.

In the operational amplifier OP1, the input current Iin ⁺ input to the inverting input terminal of the operational amplifier OP1 is amplified and the output voltage V ⁺ is output to the output terminal T5. Feedback circuit A1 receives the output voltage V ^+, as described above, integrates the inverted amplified output voltage V ⁺ while the inverting amplifier output voltage is the input V ^+. The feedback circuit A1 applies the average voltage Vdca obtained by this integration to the gate electrode of the transistor Tr1. The transistor Tr1 controls the drain current Itr1 to flow between the drain electrode and the source electrode according to the average voltage Vdca applied to the gate electrode. Therefore, by applying the first Kirchhoff's law at terminal T1, relationship Idc + ^Iac = Iin + + Itr1 is established. Here, since the relationship of the drain current Itr1 = Idc is established as described above, the transistor Tr1 supplies the drain current by the application of the average voltage Vdca output by the feedback circuit A1, and thereby the inverting input of the operational amplifier OP1. An input current Iac in which the DC component Idc is canceled is input to the terminal. Accordingly, the drain current Itr1 output by the transistor Tr1 according to the average voltage Vdca output by the feedback circuit A1 is amplified by the operational amplifier OP1 to which the input current Iin ⁺ (= Iac) is supplied to the output terminal T5. Output voltage V ⁺⁺ is output.

In the operational amplifier OP2, the input current Iin ⁻ input to the inverting input terminal of the operational amplifier OP2 is amplified and the output voltage V ⁻ is output to the output terminal T6. Feedback circuit B1, the output voltage V ^- type a, as described above, the input output voltage V ^- integrating ^- the inverted amplified output voltage V with inverted amplifying. The feedback circuit B1 applies the average voltage Vdcb obtained by this integration to the gate electrode of the transistor Tr2. The transistor Tr2 controls the drain current Itr2 to flow between the drain electrode and the source electrode according to the average voltage Vdcb applied to the gate electrode. Therefore, by applying the first law of Kirchhoff in the terminal T2, Idc + Iac ⁼ Iin - relationship + ITR2 is established. Here, as described above, since the drain current Itr2 = Idc is established, the transistor Tr2 supplies the drain current by the application of the average voltage Vdcb output from the feedback circuit B1, and thereby the inverting input of the operational amplifier OP2. An input current Iac in which the DC component Idc is canceled is input to the terminal. Accordingly, the drain current Itr2 output from the transistor Tr2 according to the average voltage Vdcb output from the feedback circuit B1 is amplified by the operational amplifier OP2 to which the input current Iin ⁻ (= Iac) is supplied to the output terminal T6. output voltage ^{V -} is output.

Amplifying section 14 is constituted by a differential amplifier, the output output voltage V ⁺⁺ and V by the current-voltage converter 13 ^- the type, respectively, the output voltage V ⁺⁺ and V in accordance with the predetermined gain ^- in The difference is amplified and the output voltage Vout is output to the output terminal T9.

  As described above, the current-voltage conversion unit 13 of the first embodiment corresponds to the net conversion amount of light of the light emitting diode LD to the current output by the photodiode PD by receiving light by the light emission of the light emitting diode LD. Even when the input current Iac and the DC component Idc corresponding to the amount of disturbance light conversion are included, the average voltage corresponding to the DC component is output from the output obtained by amplifying the current from two directions, A current that appropriately cancels the DC component is generated according to the average voltage. Specifically, as described above, the combined current of the current Iac and the DC component Idc is supplied to the operational amplifiers OP1 and OP2, respectively, and the feedback circuits A1 and B1 invert and amplify the output voltages of the operational amplifiers OP1 and OP2. And integrate. The average voltages Vdca and Vdcb obtained by the inversion amplification and integration are applied to the gate electrodes of the transistors Tr1 and Tr2, so that the transistors Tr1 and Tr2 have the average voltages Vdca and Vdcb applied to the gate electrodes. Accordingly, a drain current corresponding to the DC component Idc is passed through the current paths of the input currents of the operational amplifiers OP1 and OP2. As a result, the DC component Idc is canceled out of the input current flowing through the operational amplifiers OP1 and OP2.

  Therefore, according to the current-voltage conversion unit 13 of the first embodiment, the current output by receiving light by the light emission of the light emitting diode LD of the photodiode PD corresponds to the net conversion amount of light of the light emitting diode LD. Even when the current Iac and the direct current component Idc corresponding to the amount of disturbance light conversion are included, the output voltage Vout that operates stably without being saturated can be output. Furthermore, in the smoke detector 2 including the current-voltage converter 13 of the first embodiment, the structure of the detection region K provided in the smoke detector 2 can be simplified.

(Modification of the first embodiment)
4). Description on Configuration and Operation of Current-Voltage Conversion Unit 13a FIG. 3 is a schematic circuit diagram illustrating configurations of a current-voltage conversion unit 13a and an amplification unit 14 according to a modification of the first embodiment. As shown in FIG. 3, the current-voltage conversion unit 13a according to the modification of the first embodiment includes an operational amplifier OP1, an operational amplifier OP2, a feedback circuit A1, a feedback circuit B1, a transistor Tr1, and a transistor Tr2. , At least a sample-and-hold circuit SH1 and a sample-and-hold circuit SH2. Hereinafter, only a difference in configuration from the current-voltage conversion unit 13 of the first embodiment will be described, and the description of the same content in the configuration will be omitted. The difference in configuration from the current-voltage conversion unit 13 of the first embodiment is that sample hold circuits SH1 and SH2 are further provided.

  The sample hold circuit SH1 includes a switch unit Sw1 having one end connected to the terminal of the feedback circuit A1 and the other end connected to the gate electrode of the transistor Tr1, and a capacitor C1 connected in parallel to the switch unit Sw1. Note that one electrode of the capacitor C1 is connected to the gate electrode of the transistor Tr1, and the other electrode of the capacitor C1 is grounded. In the sample hold circuit SH1, the average voltage Vdca output by the feedback circuit A1 is applied to both ends of the capacitor C1 when the contact of the switch unit Sw1 is in a conductive state.

  The sample hold circuit SH1 opens and closes the contact of the switch unit Sw1 according to the timing signal output from the timing generation unit 11 shown in FIG. Specifically, when the contact of the switch unit Sw1 is in an OFF state (non-conduction state), the sample hold circuit SH1 turns on the contact of the switch unit Sw1 (conduction state) based on the timing signal. To. Further, when the contact of the switch unit Sw1 is in a conductive state, the sample hold circuit SH1 sets the contact point of the switch unit Sw1 in a non-conductive state based on the timing signal. In addition, it is preferable that the timing generation unit 11 manages whether the contact of the switch unit Sw1 is in a conductive state or a non-conductive state.

  When the contact of the switch unit Sw1 is in a conductive state, the timing generation unit 11 does not connect the contact of the switch unit Sw1 of the sample hold circuit SH1 substantially in synchronization with the timing signal for starting the light emitting operation of the light emitting diode LD. A timing signal that is a control signal for conducting is output. In the switch unit Sw1 of the sample hold circuit SH1, the contact of the switch unit Sw1 is made non-conductive based on the output timing signal. Note that the timing generator 11 outputs a timing signal that is a control signal for turning off the contact of the switch unit Sw1 of the sample hold circuit SH1 immediately before outputting the timing signal for starting the light emitting operation of the light emitting diode LD. It may be output.

  In addition, when the contact of the switch unit Sw1 is in a non-conductive state, the timing generation unit 11 substantially synchronizes with the timing signal for stopping the light emission operation of the light emitting diode LD, and the switch unit Sw1 of the sample hold circuit SH1. A timing signal which is a control signal for conducting the contact is output. In the switch unit Sw1 of the sample hold circuit SH1, the contact of the switch unit Sw1 is brought into conduction based on the output timing signal. The timing generator 11 outputs a timing signal that is a control signal for conducting the contact of the switch unit Sw1 of the sample hold circuit SH1 immediately after outputting the timing signal for stopping the light emitting operation of the light emitting diode LD. You may do it. Therefore, while the light emitting diode LD is emitting light, the contact of the switch unit Sw1 of the sample hold circuit SH1 is in a non-conductive state.

  FIG. 4A is an explanatory diagram showing the temporal transition of the current output by the conversion of the photodiode PD. FIG. 4B is an explanatory diagram showing temporal transitions of the average voltages Vdca and Vdcb output by the feedback circuits A1 and B1, respectively. As shown in FIG. 4A, when the light emitting diode LD emits light, the photodiode PD has a pulse-like shape due to the net light reception of the light from the light emitting diode LD in addition to the direct current component Idc due to the reception of ambient disturbance light. The current Iac is output. As described above, in the integrating circuit in the feedback circuit A1, the time constant is set so that the photodiode PD blocks the pulsed current Iac due to the net reception of light from the light emitting diode LD. However, when the light emitting diode LD emits light while the terminal of the feedback circuit A1 is electrically connected to the gate electrode of the transistor Tr1, and the current Iac corresponding to the emitted light amount is further input to the feedback circuit A1. In the integrating circuit of the feedback circuit A1, a part of the component of the pulsed current Iac may be integrated. In this case, as shown in FIG. 4B, the average voltage Vdca output by the feedback circuit A1 increases by an average voltage ΔVdc corresponding to Iac that is not blocked by the integration circuit of the feedback circuit A1. For this reason, since the drain current due to the transistor Tr1 increases, an excess current greater than or equal to the DC component Idc is supplied to the terminal T1, and Iac reduced by the excess current is supplied to the operational amplifier OP1. This is not preferable as the current conversion efficiency of the current-voltage conversion unit 13a.

  Therefore, in the current-voltage conversion unit 13a of the modification of the first embodiment, the switch unit Sw1 of the sample hold circuit SH1 is in a non-conductive state immediately before the light emission of the light emitting diode LD in accordance with the timing signal output from the timing generation unit 11. During the light emission of the light emitting diode LD, the switch part Sw1 is maintained in a non-conductive state, and immediately after the light emission of the light emitting diode LD, the switch part Sw1 is brought into a conductive state. Thereby, during light emission of the light emitting diode LD, the average voltage Vdca between both ends of the capacitor C1 applied when the switch unit Sw1 is in a conductive state is released, and the feedback circuit A1 immediately before light emission of the light emitting diode LD. An average voltage Vdca that is an output can be applied to the gate electrode of the transistor Tr1. Therefore, the feedback circuit A1 can apply a more accurate average voltage Vdca to the gate electrode of the transistor Tr1 than the current-voltage conversion unit 13 of the first embodiment, and noise can also be applied to the inverting input terminal of the operational amplifier OP1. The current Iac canceled by the direct current component Idc can be supplied. As a result, the current-voltage conversion unit 13a according to the modification of the first embodiment can perform current-voltage conversion that is less susceptible to disturbance light than the current-voltage conversion unit 13 of the first embodiment. .

  On the other hand, the sample hold circuit SH2 includes a switch unit Sw2 having one end connected to the terminal of the feedback circuit B1 and the other end connected to the gate electrode of the transistor Tr2, and a capacitor C2 connected in parallel to the switch unit Sw2. Prepare. Note that the electrode on one side of the capacitor C2 is connected to the gate electrode of the transistor Tr2, and the electrode on the opposite side of the capacitor C2 is grounded. In the sample hold circuit SH2, the average voltage Vdcb output by the feedback circuit B1 is applied to both ends of the capacitor C2 when the contact of the switch unit Sw2 is conductive.

  The sample hold circuit SH2 opens and closes the contact of the switch unit Sw2 in accordance with the timing signal output by the timing generation unit 11 shown in FIG. Specifically, when the contact of the switch unit Sw2 is in a non-conductive state, the sample hold circuit SH21 sets the contact point of the switch unit Sw2 in a conductive state based on the timing signal. In addition, when the contact of the switch unit Sw2 is in a conductive state, the sample hold circuit SH2 sets the contact point of the switch unit Sw2 in a non-conductive state based on the timing signal. In addition, it is preferable that the timing generation unit 11 manages whether the contact of the switch unit Sw2 is in a conductive state or a non-conductive state.

  When the contact of the switch unit Sw2 is in a conductive state, the timing generation unit 11 does not connect the contact of the switch unit Sw2 of the sample hold circuit SH2 almost in synchronization with the timing signal for starting the light emitting operation of the light emitting diode LD. A timing signal that is a control signal for conducting is output. In the switch unit Sw2 of the sample hold circuit SH2, the contact of the switch unit Sw2 is made non-conductive based on the output timing signal. Note that the timing generator 11 outputs a timing signal, which is a control signal for turning off the contact of the switch unit Sw2 of the sample hold circuit SH2, immediately before outputting the timing signal for starting the light emitting operation of the light emitting diode LD. It may be output.

  Further, when the contact of the switch unit Sw2 is in a non-conductive state, the timing generation unit 11 substantially synchronizes with the timing signal for stopping the light emission operation of the light emitting diode LD, and the switch unit Sw2 of the sample hold circuit SH2 A timing signal which is a control signal for conducting the contact is output. In the switch unit Sw2 of the sample hold circuit SH2, the contact of the switch unit Sw2 is brought into conduction based on the output timing signal. The timing generation unit 11 outputs a timing signal that is a control signal for conducting the contact of the switch unit Sw2 of the sample hold circuit SH2 immediately after outputting the timing signal for stopping the light emitting operation of the light emitting diode LD. You may do it. Therefore, while the light emitting diode LD is emitting light, the contact of the switch unit Sw2 of the sample hold circuit SH2 is in a non-conductive state.

  Similarly, in the integrating circuit in the feedback circuit B1, the time constant is set so that the photodiode PD blocks the pulsed current Iac due to the net reception of light from the light emitting diode LD. However, when a current Iac corresponding to the amount of light emitted from the light emitting diode LD is input to the feedback circuit B1 in a state where the terminal of the feedback circuit B1 and the gate electrode of the transistor Tr2 are conductive, the integration of the feedback circuit B1. In the circuit, a part of the component of the pulsed current Iac may be integrated. In this case, as shown in FIG. 4B, the average voltage Vdcb output by the feedback circuit B1 is The voltage increases by an average voltage ΔVdc corresponding to Iac that is not blocked by the integrating circuit of the feedback circuit B1. For this reason, since the drain current due to the transistor Tr1 increases, an excess current greater than or equal to the DC component Idc is supplied to the terminal T2, and the current Iac reduced by the excess current is supplied to the operational amplifier OP2. That is, it is not preferable as the current conversion efficiency of the current-voltage converter 13a.

  Therefore, in the current-voltage conversion unit 13a of the modification of the first embodiment, the switch unit Sw2 of the sample-and-hold circuit SH2 is in a non-conductive state immediately before the light emitting diode LD emits light according to the timing signal output from the timing generation unit 11. During the light emission of the light emitting diode LD, the switch unit Sw2 is maintained in a non-conductive state, and immediately after the light emission of the light emitting diode LD, the switch unit Sw2 is brought into a conductive state. Thereby, during light emission of the light emitting diode LD, the average voltage Vdcb between both ends of the capacitor C2 applied when the switch unit Sw2 is in a conductive state is released, and the feedback circuit B1 immediately before light emission of the light emitting diode LD. An average voltage Vdcb as an output can be applied to the gate electrode of the transistor Tr2. Therefore, the feedback circuit B1 can apply a more accurate average voltage Vdcb to the gate electrode of the transistor Tr2 than the current-voltage converter 13 of the first embodiment, and noise can also be applied to the inverting input terminal of the operational amplifier OP2. The current Iac canceled by the direct current component Idc can be supplied. As a result, the current-voltage conversion unit 13a according to the modification of the first embodiment can perform current-voltage conversion that is less susceptible to disturbance light than the current-voltage conversion unit 13 of the first embodiment. .

(Second Embodiment)
5. Description on Configuration of Current-Voltage Conversion Unit 13b FIG. 5 is a schematic circuit diagram illustrating configurations of the current-voltage conversion unit 13 and the amplification unit 14 of the second embodiment. As shown in FIG. 5, the current-voltage converter 13b of the second embodiment includes an operational amplifier OP1, an operational amplifier OP2, a feedback circuit B2, a transistor Tr2, a transistor Tr2a, a transistor Tr2b, and a transistor Tr2c. And at least a current mirror circuit. Hereinafter, only a difference in configuration from the current-voltage conversion unit 13 of the first embodiment will be described, and the description of the same content in the configuration will be omitted. The difference in configuration from the current-voltage converter 13 of the first embodiment is that the feedback circuit A1 is not provided and a current mirror circuit for the transistor Tr2 is provided.

Transistor Tr2 is, for example, an NMOS transistor N-type channel is formed, a gate electrode connected to the end of the feedback circuit B2, the input current Iin ^- is connected to the terminal T2 connected to the current path A drain electrode and a grounded source electrode. In addition, when the average voltage Vdcb output from the feedback circuit B2 is applied to the gate electrode, the transistor Tr2 is connected to the operational amplifier OP2 between the drain electrode and the source electrode of the transistor Tr2 corresponding to the average voltage Vdcb. Control is performed so that a drain current Itr2 which is a current corresponding to the flowing-in current flows. This average voltage Vdcb is assumed to be equal to or higher than the threshold voltage Vth of the transistor Tr2. As described above, when the average voltage Vdcb is applied to the gate electrode of the transistor Tr2, the transistor Tr2 has a drain current that satisfies the relationship Itr2 = Idc between the drain current Itr2 and the DC component Idc. It controls to flow Itr2.

  The transistor Tr2a is composed of, for example, an NMOS transistor in which an N-type channel is formed. The gate electrode connected to the terminal of the feedback circuit B2, the drain electrode connected to the source electrode of the transistor Tr2b, and the ground A source electrode. Further, when the average voltage Vdcb output from the feedback circuit B2 is applied to the gate electrode, the transistor Tr2a is connected between the drain electrode and the source electrode of the transistor Tr2 from the operational amplifier OP1 corresponding to the average voltage Vdcb. Control is performed so that a drain current Itr2, which is a current corresponding to the current drawn, flows. As described above, when the average voltage Vdcb is applied to the gate electrode of the transistor Tr2a, the transistor Tr2a has a drain current that satisfies the relationship Itr2 = Idc between the drain current Itr2 and the DC component Idc. It controls to flow Itr2.

  The transistor Tr2b is composed of, for example, an NMOS transistor in which an N-type channel is formed, and has a gate electrode connected to the gate electrode of the transistor Tr2c, and a drain to which a power supply voltage is applied by the power supply circuit unit 18 shown in FIG. And a source electrode connected to a connection node between the gate electrode of the transistor Tr2b and the gate electrode of the transistor Tr2c and connected to the drain electrode of the transistor Tr2a. Further, since the source electrode of the transistor Tr2b and the drain electrode of the transistor Tr2a are connected, the same drain current Itr2 as the drain current Itr2 flowing in the transistor Tr2a flows in the transistor Tr2b.

The transistor Tr2c is composed of, for example, an NMOS transistor in which an N-type channel is formed, and has a gate electrode connected to the gate electrode of the transistor Tr2b and a drain to which a power supply voltage is applied by the power supply circuit unit 18 shown in FIG. An electrode, and a source electrode connected to a terminal T1 connected to a current path of an input current Iin ⁺ . Further, as described above, the transistors Tr2a, Tr2b, and Tr2c constitute a current mirror circuit for the transistor Tr2, so that the current Itr2 having the same magnitude as the drain current Itr2 of the transistor Tr2 is supplied to the drain electrode of the transistor Tr2c and the transistor Tr2c. It will flow between the source electrodes. Therefore, when the average voltage Vdcb output from the feedback circuit B2 is applied to the gate electrode of the transistor Tr2, the transistor Tr2a performs an operation corresponding to the average voltage Vdcb between the drain electrode and the source electrode of the transistor Tr2. Control is performed so that a drain current Itr2, which is a current corresponding to the current drawn from the amplifier OP1, flows. This average voltage Vdcb is assumed to be equal to or higher than the threshold voltage Vth of the transistor Tr2a. As described above, when the average voltage Vdcb is applied to the gate electrode of the transistor Tr2, the transistor Tr2a has a drain current that satisfies the relationship Itr2 = Idc between the drain current Itr2 and the DC component Idc. It controls to flow Itr2.

6). Next, the operation of the current / voltage conversion unit 13b will be described. First, when the photodiode PD receives light emitted by the light emitting diode LD, a pulsed input current output when the photodiode PD receives light from the light emitting diode LD is provided at both ends of the photodiode PD. A combined current (Idc + Iac) of Iac and the DC component Idc output when the photodiode PD receives disturbance light flows.

At this time, since a voltage equal to or higher than the threshold voltage Vth has not yet been applied to the gate electrode of the transistor Tr2c, no drain current flows between the drain electrode and the source electrode of the transistor Tr2c. For this reason, the input current Iin ⁺ flowing through the inverting input terminal of the operational amplifier OP1 becomes the above-described combined current (Idc + Iac). That is, the relationship of Iin ⁺ = Idc + Iac is established.

Similarly, since a voltage equal to or higher than the threshold voltage Vth has not yet been applied to the gate electrode of the transistor Tr2, no drain current flows between the drain electrode and the source electrode of the transistor Tr2. Therefore, the input current Iin ⁻ flowing to the inverting input terminal of the operational amplifier OP2 is also the above-described combined current (Idc + Iac). In other ^words, Iin - = Idc + Iac relationship is established.

In the operational amplifier OP1, the input current Iin ⁺ input to the inverting input terminal of the operational amplifier OP1 is amplified and the output voltage V ⁺ is output to the output terminal T5. However, as will be described later, the drain current Itr2 of the transistor Tr2 is provided between the drain electrode and the source electrode of the transistor Tr2c constituting the current mirror circuit for the transistor Tr2 in accordance with the average voltage Vdcb applied to the gate electrode of the transistor Tr2. A drain current Itr2 having the same magnitude as that flows. Therefore, the relationship of Idc + Iac = Iin ⁺ + Itr2 is established by applying Kirchhoff's first law at the terminal T1. Here, as described above, since the drain current Itr2 = Idc is established, the transistor Tr2c supplies the drain current by the application of the average voltage Vdcb output from the feedback circuit B2, so that the inverting input of the operational amplifier OP1. An input current Iac in which the DC component Idc is canceled is input to the terminal. The output voltage V ⁺⁺ amplified by the operational amplifier OP1 to which the input current Iin ⁺ (= Iac) is supplied is output to the output terminal T5.

In the operational amplifier OP2, the input current Iin ⁻ input to the inverting input terminal of the operational amplifier OP2 is amplified and the output voltage V ⁻ is output to the output terminal T6. Feedback circuit B2 is the output voltage V ^- type a, as described above, the input output voltage V ^- integrating ^- the inverted amplified output voltage V with inverted amplifying. The feedback circuit B2 applies the average voltage Vdcb obtained by this integration to the gate electrode of the transistor Tr3. The transistor Tr2 controls the drain current Itr2 to flow between the drain electrode and the source electrode according to the average voltage Vdcb applied to the gate electrode. Therefore, by applying the first law of Kirchhoff in the terminal T2, Idc + Iac ⁼ Iin - relationship + ITR2 is established. Here, as described above, since the drain current Itr2 = Idc is established, the transistor Tr2 supplies the drain current by the application of the average voltage Vdcb output from the feedback circuit B2, thereby inverting the input of the operational amplifier OP2. An input current Iac in which the DC component Idc is canceled is input to the terminal. Accordingly, the drain current Itr2 output from the transistor Tr2 according to the average voltage Vdcb output from the feedback circuit B2 is amplified by the operational amplifier OP2 to which the input current Iin ⁻ (= Iac) is supplied to the output terminal T6. output voltage ^{V -} is output.

Amplifying section 14 is constituted by a differential amplifier, the output output voltage ^{V ++} and ^V by the current-voltage converter 13b ^- the type, respectively, the output voltage ^{V ++} and ^V in accordance with the predetermined gain ^- in The difference is amplified and the output voltage Vout is output to the output terminal T9.

  As described above, the current-voltage conversion unit 13b of the second embodiment corresponds to the net conversion amount of light of the light emitting diode LD to the current output by the photodiode PD by receiving light by the light emission of the light emitting diode LD. Even when the input current Iac and the DC component Idc corresponding to the amount of disturbance light conversion are included, the average voltage corresponding to the DC component is output from the output obtained by amplifying the current from two directions, A current that appropriately cancels the DC component is generated according to the average voltage. Specifically, as described above, a combined current of the current Iac and the DC component Idc is supplied to each operational amplifier OP1 and OP2, and the feedback circuit B2 inverts and amplifies and integrates the output voltage of the operational amplifier OP2. The average voltage Vdcb obtained by the inverting amplification and integration is applied to the current mirror circuit for the transistor Tr2 and the transistor Tr2, so that the current mirror circuit for the transistor Tr2 and the transistor Tr2 is applied to the gate electrode. According to the average voltage Vdcb, a drain current corresponding to the DC component Idc is passed through the current paths of the input currents of the operational amplifiers OP1 and OP2. As a result, the DC component Idc is canceled out of the input current flowing through the operational amplifiers OP1 and OP2.

  Therefore, according to the current-voltage conversion unit 13b of the second embodiment, the current output by receiving light by the light emission of the light emitting diode LD of the photodiode PD corresponds to the net conversion amount of light of the light emitting diode LD. Even when the current Iac and the direct current component Idc corresponding to the amount of disturbance light conversion are included, the output voltage Vout that operates stably without being saturated can be output. Furthermore, in the smoke detector 2 including the current-voltage converter 13 of the first embodiment, the structure of the detection region K provided in the smoke detector 2 can be simplified. Furthermore, according to the current-voltage conversion unit 13b of the second embodiment, since only one feedback circuit included in the current-voltage conversion unit 13 of the first embodiment is required, the overall configuration of the current-voltage conversion unit 13b is as follows. Since it can be realized with a very simple configuration, it can be manufactured at low cost.

(Modification of the second embodiment)
7). Description on Configuration and Operation of Current-Voltage Conversion Unit 13c FIG. 6 is a schematic circuit diagram illustrating configurations of a current-voltage conversion unit 13c and an amplification unit 14 according to a modification of the second embodiment. As shown in FIG. 6, the current-voltage conversion unit 13c according to the modification of the second embodiment includes an operational amplifier OP1, an operational amplifier OP2, a feedback circuit B3, a transistor Tr2, a transistor Tr2a, a transistor Tr2b, and a transistor Tr2c. And at least a sample-and-hold circuit SH3. Hereinafter, only a difference in configuration from the current-voltage conversion unit 13b of the second embodiment will be described, and the description of the same content in the configuration will be omitted.

  The sample hold circuit SH3 includes a switch unit Sw3 having one end connected to the terminal of the feedback circuit B3 and the other end connected to the gate electrode of the transistor Tr2, and a capacitor C3 connected in parallel to the switch unit Sw3. Note that one electrode of the capacitor C3 is connected to the gate electrode of the transistor Tr2, and the other electrode of the capacitor C3 is grounded. In the sample hold circuit SH22, when the contact of the switch unit Sw3 is conductive, the average voltage Vdcb output by the feedback circuit B3 is applied across the capacitor C3.

  The timing for opening and closing the contact of the sample hold circuit SH3 is the same as that of the sample hold circuits SH1 and SH2 shown in FIG. Therefore, while the light emitting diode LD is emitting light, the contact of the switch unit Sw3 of the sample hold circuit SH3 is in a non-conductive state.

  Therefore, in the current-voltage conversion unit 13c of the modification of the second embodiment, the switch unit Sw3 of the sample hold circuit SH3 is non-conducting immediately before the light emission of the light emitting diode LD according to the timing signal output from the timing generation unit 11. When the light emitting diode LD emits light, the switch unit Sw3 is maintained in a non-conductive state, and immediately after the light emitting diode LD emits light, the switch unit Sw3 is brought into a conductive state. Thereby, during light emission of the light emitting diode LD, the average voltage Vdcb between both ends of the capacitor C3 applied when the switch unit Sw3 is in a conductive state is released, and the feedback circuit B3 immediately before light emission of the light emitting diode LD. An average voltage Vdcb as an output can be applied to the gate electrode of the transistor Tr2. At this time, since the average voltage Vdcb that is the output of the feedback circuit B3 is also applied to the gate electrode of the transistor Tr2a, the current mirror circuit configured by the transistors Tr2a, Tr2b, and Tr2c is used to connect the drain electrode and the source electrode of the transistor Tr2c. The same drain current Itr2 (= Idc) as the drain current Itr2 of the transistor Tr2 flows.

  Therefore, the current-voltage conversion unit 13c according to the modification of the second embodiment has a more accurate average voltage Vdcb than the current-voltage conversion unit 13b of the second embodiment, even during light emission of the light emitting diode LD. Can be applied to the gate electrode of the transistor Tr2, and the current Iac with the DC component Idc canceled can be supplied to the inverting input terminal of the operational amplifier OP1. As a result, the current-voltage conversion unit 13c according to the modification of the second embodiment can perform current-voltage conversion that is less susceptible to disturbance light than the current-voltage conversion unit 13b of the second embodiment. .

(Third embodiment)
8). Description on Current-Voltage Conversion Unit 13d FIG. 7 is a schematic circuit diagram showing the configuration of the current-voltage conversion unit 13d of the third embodiment. The current-voltage conversion unit 13d according to the third embodiment includes an operational amplifier OP1, an operational amplifier OP2, a feedback circuit B4, a transistor Tr2, a current mirror circuit including a transistor Tr2a, a transistor Tr2b, and a transistor Tr2c. And a dynamic amplifier 14a. Hereinafter, a difference in configuration from the current-voltage conversion unit 13b of the second embodiment will be described, and the description of the same content in the configuration will be omitted. The difference in configuration from the current-voltage converter 13 of the second embodiment is that the feedback circuit B4 receives the output voltage Vout output by the differential amplifier 14a.

As described above, the current-voltage conversion portion 13d of the third embodiment, the output voltage V ⁺⁺ respectively outputted to the output terminal T5, ^T6, V ^- the difference to amplify according to a difference between the predetermined gain A dynamic amplifier 14a is further included. In the current-voltage conversion unit 13d of the third embodiment, the feedback circuit B4 receives the output voltage Vout amplified by the differential amplifier 14a, and performs the inversion amplification and integration with respect to the output voltage Vout to thereby output the output voltage Vout. Is applied to the gate electrodes of the transistors Tr2 and Tr2a. Since other configurations and operations are the same as those of the second embodiment, description of the contents is omitted.

  Therefore, according to the current-voltage converter 13d of the third embodiment, the input current Iac corresponding to the net conversion amount of the light is converted into the current output by receiving the light from the light emitting diode LD of the photodiode PD. Even when the DC component Idc corresponding to the amount of disturbance light conversion is included, the output voltage Vout that operates stably without being saturated can be output. Furthermore, in the smoke detector 2 including the current-voltage conversion unit 13d of the third embodiment, the structure of the detection region K provided in the smoke detector 2 can be simplified. Furthermore, according to the current-voltage conversion unit 13d of the third embodiment, since only one feedback circuit included in the current-voltage conversion unit 13 of the first embodiment is required, the overall configuration of the current-voltage conversion unit 13d is as follows. Since it can be realized with a very simple configuration, it can be manufactured at low cost.

Furthermore, according to the current-voltage conversion portion 13d of the third embodiment, the output voltage V of the feedback circuit B4 is amplified by the operational amplifier OP2 ^- not for the amplified output voltage Vout by the differential amplifier 14a Is supplied to the transistor Tr2 and the current mirror circuit for the transistor Tr2 according to the average voltage Vdcc obtained by inverting amplification and integration. Therefore, compared to the current-voltage conversion unit 13b of the second embodiment, input currents Iin ⁺ and Iin ⁻ with less noise due to the differential amplifier 14a can be supplied to the operational amplifiers OP1 and OP2.

(Modification of the third embodiment)
9. Description of Current-Voltage Conversion Unit 13e FIG. 8 is a schematic circuit diagram illustrating a configuration of a current-voltage conversion unit 13e according to a modification of the third embodiment. As shown in FIG. 8, the current-voltage conversion unit 13e according to the modification of the third embodiment includes an operational amplifier OP1, an operational amplifier OP2, a feedback circuit B5, a transistor Tr2, a transistor Tr2a, a transistor Tr2b, and a transistor Tr2c. And at least a sample and hold circuit SH4. The difference in configuration from the current-voltage conversion unit 13d of the third embodiment shown in FIG. 7 is that a sample hold circuit SH4 is further provided. Since the other configuration is the same as that of the current-voltage conversion unit 13d of the third embodiment shown in FIG. 7, the description regarding the same content is omitted.

  The sample hold circuit SH4 includes a switch unit Sw4 having one end connected to the terminal of the feedback circuit B5 and the other end connected to the gate electrode of the transistor Tr2, and a capacitor C4 connected in parallel to the switch unit Sw4. The electrode on one side of the capacitor C4 is connected to the gate electrode of the transistor Tr2, and the electrode on the opposite side of the capacitor C4 is grounded. In the sample hold circuit SH4, when the contact of the switch unit Sw4 is in a conductive state, the average voltage Vdcc output by the feedback circuit B5 is applied across the capacitor C4.

  The timing for opening and closing the contacts of the sample and hold circuit SH4 is the same as that of the sample and hold circuits SH1 and SH2 shown in FIG. Therefore, while the light emitting diode LD is emitting light, the contact of the switch unit Sw4 of the sample hold circuit SH4 is in a non-conductive state.

  Therefore, in the current-voltage conversion unit 13e of the modification of the third embodiment, the switch unit Sw4 of the sample hold circuit SH4 is non-conducting immediately before the light emission of the light emitting diode LD according to the timing signal output from the timing generation unit 11. When the light emitting diode LD emits light, the switch unit Sw4 is maintained in a non-conductive state, and immediately after the light emitting diode LD emits light, the switch unit Sw4 is brought into a conductive state. Thus, during the light emission of the light emitting diode LD, the average voltage Vdcc across the capacitor C4 applied when the switch unit Sw4 is in a conductive state is released, and the feedback circuit B5 immediately before the light emission of the light emitting diode LD emits light. An average voltage Vdcc that is an output can be applied to the gate electrode of the transistor Tr2. At this time, since the average voltage Vdcc, which is the output of the feedback circuit B5, is also applied to the gate electrode of the transistor Tr2a, the current mirror circuit configured by the transistors Tr2a, Tr2b, and Tr2c is used to connect the drain electrode and the source electrode of the transistor Tr2c. The same drain current Itr2 (= Idc) as the drain current Itr2 of the transistor Tr2 flows.

  Therefore, the current-voltage conversion unit 13e according to the modification of the third embodiment has a more accurate average voltage Vdcc than the current-voltage conversion unit 13d of the third embodiment even during light emission of the light emitting diode LD. Can be applied to the gate electrode of the transistor Tr2, and the current Iac with the DC component Idc canceled can be supplied to the inverting input terminal of the operational amplifier OP1. As a result, the current-voltage conversion unit 13e according to the modification of the third embodiment can perform current-voltage conversion that is less susceptible to disturbance light than the current-voltage conversion unit 13c of the second embodiment. .

(Further modified example for the current-voltage converter having the sample-and-hold circuit)
10. FIG. 9 shows a parallel connection of the leakage current correction resistor Ra and the switch unit Sw2 of the sample hold circuit SH2 with respect to the current / voltage conversion unit 13c shown in FIG. It is the schematic circuit diagram of the current-voltage conversion part 13f performed. 9 shows an example in which a leakage current correction resistor Ra is provided for the current-voltage conversion unit 13c shown in FIG. 6 as a representative, the leakage current correction resistor Ra is shown in FIGS. 8 may be connected in parallel to the switch units of the sample and hold circuits of the current-voltage conversion units 13a and 13c shown in FIG. 8, respectively, and the same operation is performed.

  In FIG. 9, the leakage current correction resistor Ra has a high resistance value and is connected in parallel with the switch unit Sw2 of the sample hold circuit SH2. In the sample hold circuit SH2 shown in FIG. 6, when the contact of the switch unit Sw2 is made non-conductive based on the timing signal output by the timing generation unit 11 immediately before the light emission of the light emitting diode LD, the leakage current from the capacitor C2 May flow. When a leakage current flows from the capacitor C2, the average voltage Vdcb applied to both ends of the capacitor C2 decreases, so that the average voltage Vdcb applied to both ends of the capacitor C2 can be appropriately applied to the gate electrodes of the transistors Tr2 and Tr2a. It may not be possible.

  Therefore, the leakage current correction resistor R connected in parallel with the switch unit Sw2 reduces the average voltage Vdcb between both ends of the capacitor C2 caused by the leakage current from the capacitor C2 after the switch unit Sw2 is turned off. By compensating, the average voltage Vdcb can be appropriately applied to the gate electrodes of the transistors Tr2 and Tr2a.

  Although various embodiments have been described with reference to the accompanying drawings, it goes without saying that the current-voltage conversion circuit and the smoke detector 1 of the present invention are not limited to such examples. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

Note that a capacitor C may be connected in parallel to the conversion resistor R in each of the operational amplifiers OP1 and OP2 in the above-described embodiments. In this case, the capacitor C functions as a low-pass filter (LPF), and the circuit constants of the conversion resistor R and the capacitor C are set so as to pass only the input currents Iin ⁺ and Iin ⁻ having a predetermined cutoff frequency f ₁ or less. The This cut-off frequency f ₁ can be expressed as f ₁ = 1 / (2π × r × c) by using the resistance value r of the conversion resistor R and the constant c of the capacitor C, and at least the photodiode PD is It is set so as to pass pulsed input currents Iin ⁺ and Iin ⁻ generated when light from a light emitting diode LD as a light emitting unit is received.

  In addition, although it has been described that the transistors Tr1 to Tr6 in each of the embodiments described above can be configured with NMOS transistors, the transistors Tr1 to Tr6 may be configured with PMOS transistors in which a P-type channel is formed. Is possible. In this case, the “drain electrode” and “source electrode” in the above-described embodiments may be read as “source electrode” and “drain electrode”, respectively.

  The products to which the above-described current-voltage conversion units 13 to 13f are applied are not limited to the smoke detector 1 shown in FIG.

DESCRIPTION OF SYMBOLS 1 Smoke detector 11 Timing generation part 12 Light emission control part 13 Current voltage conversion part 14 Amplification part 14a Differential amplifier 15 Signal processing part 16 Determination part 17 Output part 18 Power supply circuit part A1, B1-B6 Feedback circuit C1-C4 Capacitor Iac , Iin ⁺ , Iin ^— Input current Idc DC component Itr1, Itr2 Drain current LD Light emitting diode OP1, OP2 Operational amplifier PD Photodiode R, Ra Resistors SH1-SH4 Sample hold circuits Sw1-Sw4 Switches T1-T9 Terminals Tr1, Tr2, Tr2a , Tr2b, Tr2c Transistor Vdd Power supply voltage Vs Reference voltage

Claims (8)

A current-voltage conversion circuit that converts an input current output by conversion of the photodiode into a voltage according to an amount of light received by the photodiode with respect to light emitted from the light-emitting diode,
A first operational amplifier that converts the first input current output from the photodiode into a first output voltage and outputs the first output current;
A second operational amplifier that converts the second input current output by the photodiode into a second output voltage and outputs the second output current;
A first feedback circuit unit that outputs a first average voltage corresponding to an average value component of the first output voltage output by the first operational amplification unit;
A second feedback circuit unit that outputs a second average voltage corresponding to an average value component of the second output voltage output by the second operational amplification unit;
A first transistor unit that controls to flow a current corresponding to a current drawn from the first operational amplifier unit according to the first average voltage output by the first feedback circuit unit;
A second transistor unit that controls to flow a current corresponding to a current flowing into the second operational amplifier unit according to the second average voltage output by the second feedback circuit unit;
A current-voltage conversion circuit comprising: The current-voltage conversion circuit according to claim 1,
Between the termination of the first feedback circuit section and the gate electrode of the first transistor section,
A first switch unit that conducts or non-conducts between the first feedback circuit unit and the gate electrode of the first transistor unit, and a first capacitor connected in parallel to the first switch unit. A first sample and hold circuit is provided,
Between the termination of the second feedback circuit section and the gate electrode of the second transistor section,
A second switch unit that conducts or non-conducts between the second feedback circuit unit and the gate electrode of the second transistor unit, and a second capacitor that is connected in parallel to the second switch unit. A current-voltage conversion circuit, characterized in that a second sample-and-hold circuit is provided. A current-voltage conversion circuit that converts an input current output by conversion of the photodiode into a voltage according to an amount of light received by the photodiode with respect to light emitted from the light-emitting diode,
A third operational amplifier that converts the third input current output by the photodiode into a third output voltage and outputs the third output voltage;
A fourth operational amplifier that converts the fourth input current output by the photodiode into a fourth output voltage and outputs the fourth output current;
A third feedback circuit unit that outputs a third average voltage corresponding to an average value component of the fourth output voltage output by the fourth operational amplification unit;
A third transistor unit that controls to flow a current corresponding to a current flowing into the fourth operational amplifier according to the third average voltage output by the third feedback circuit unit;
A current for the third transistor unit that controls to flow a current according to a current drawn from the third operational amplifier unit according to the third average voltage output by the third feedback circuit unit. A mirror circuit section;
A current-voltage conversion circuit comprising: The current-voltage conversion circuit according to claim 3,
Between the termination of the third feedback circuit section and the gate electrode of the third transistor section,
A third switch unit that conducts or non-conducts between the third feedback circuit unit and the gate electrode of the third transistor unit, and a third capacitor that is connected in parallel to the third switch unit. And a third sample-and-hold circuit provided. A current-voltage conversion circuit that converts an input current output by conversion of the photodiode into a voltage according to an amount of light received by the photodiode with respect to light emitted from the light-emitting diode,
A fifth operational amplifier that converts the fifth input current output by the photodiode into a fifth output voltage and outputs the fifth output current;
A sixth operational amplifier that converts the sixth input current output by the photodiode into a sixth output voltage and outputs the sixth output voltage;
A differential amplifier that outputs an output voltage obtained by amplifying a difference between the fifth and sixth output voltages output by the fifth and sixth operational amplifiers according to a predetermined gain;
A fourth feedback circuit unit that outputs an average voltage corresponding to an average value component of the amplified output voltage output by the differential amplifier;
A fourth transistor unit that controls to flow a current according to a current flowing into the sixth operational amplifier unit according to the average voltage output by the fourth feedback circuit unit;
A current mirror circuit unit for the fourth transistor unit that controls to flow a current corresponding to a current drawn from the fifth operational amplifier unit according to the average voltage output from the fourth feedback circuit unit When,
A current-voltage conversion circuit comprising: The current-voltage conversion circuit according to claim 5,
Between the end of the fourth feedback circuit section and the gate electrode of the fourth transistor section,
A fourth switch unit that conducts or non-conducts between the fourth feedback circuit unit and the gate electrode of the fourth transistor unit, and a fourth capacitor that is connected in parallel to the fourth switch unit. And a fourth sample-and-hold circuit provided. The current-voltage converter according to any one of claims 2, 4, and 6,
The terminal of any one of the first, second, third, and fourth feedback circuit sections and the transistor section of any one of the first, second, third, and fourth corresponding to the feedback circuit section. Between the gate electrode,
When any one of the first, second, third, and fourth switch sections of the first, second, third, and fourth sample hold circuits is non-conductive, the first A resistor that compensates for a decrease in voltage across one of the first, second, third, and fourth capacitors due to leakage current from the first, second, third, and fourth capacitors; A current-voltage converter circuit connected in parallel with any one of the first, second, third, and fourth switch units. The current-voltage conversion circuit according to any one of claims 1 to 7,
A light emitting unit that emits light intermittently toward a predetermined detection space;
A photoelectric device that is disposed at a position where direct light emitted by the light emitting unit is not incident, and that converts the amount of light received when the light output from the light emitting unit is diffusely reflected by smoke flowing into the detection space into a current. A conversion unit;
A determination unit that determines whether or not a predetermined fire determination level is exceeded according to an amount of change in the level of the output voltage output by the current-voltage conversion circuit;
A reporting unit that fires a warning sound indicating the possibility of the predetermined fire when the determination unit determines that the amount of change in the level of the output voltage exceeds the predetermined fire determination level; ,
The photoelectric conversion unit outputs the current to any one of the first to sixth input terminals of the current-voltage conversion circuit.

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