JPH09105671A - Photosensor circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect the illuminance of a wide area by providing a converting means for converting the output current of photodetecting element to a voltage, a means for switching the output of the element to the input of the converting means, and a control means for controlling the operations of the switching means and inputting the output of the conversion means. SOLUTION: The photosensor circuit comprises a photodetecting element PD1 and a controller 1. The controller 1 has a switching means 2 connected with the output of the element PD1 , an operational amplifier OP1 for converting the current IS to be input via the means 2 into a voltage, a conversion means having a resistor connected to the amplifier, and an amplifying means such as an operational amplifier OP2 for amplifying the output of the conversion means. The circuit detects the current IS of the element PD1 with the two modes of an offset detecting mode and photodetecting mode as one period. The operation for subtracting the value from the value of the voltage V2 detected by the offset detecting mode in the case of the current IS=0 is conducted, the value proportional to the current IS excluding offset amount is detected, and an accurate detection having no error is conducted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical sensor circuit suitable for use in a vehicle air conditioner, a light controller, and the like.

[0002]

2. Description of the Related Art In an automatic air-conditioning control device mounted on an automobile or the like, various control parameters such as an air flow rate and a blowout temperature are corrected according to the detected intensity of outdoor sunlight (outside the vehicle compartment). Similarly, as a control that is performed according to the brightness of the surroundings, there is automatic lighting control of a light that lights up when the surroundings become dark and turns off when it becomes bright. The configuration of a system for detecting insolation for air conditioning control and illuminance detection for lighting control by a single photodetector is described in Japanese Patent Application Laid-Open No. 6-344754 "Automobile Air Conditioning and Light Control Device". .

Further, there is an example of a problem and a solution thereof in performing the solar radiation detection for the air conditioning control and the illuminance detection for the lighting control of the light by one photodetector.
No. 1994626, “Optical sensor circuit”. FIG. 4 is a circuit diagram showing an optical sensor circuit including a photodetector and an output amplifier circuit thereof described in this publication. The photosensor circuit shown in FIG. 4 includes an operational amplifier 10 and a photodetector element 1 provided to detect outdoor illuminance.
1. A series resistor Rf ₁ provided in the negative feedback portion of the operational amplifier 10.
And diode 1 connected in parallel with Rf ₂ and resistor Rf ₂
2 and a reference voltage source 13 (V _REF ).

Generally, when the illuminance detection for automatic air conditioning control and the illuminance detection for light control are performed using one photodetector, the output from a photodiode or the like used as the detector is not suitable for automatic air conditioning control. For example, a region with an output current of about several mA is a region required for control, and a region with a weak output current of about several μA for write control is a region required for control. Therefore, for example, when the output current of such a photodetector is converted into a voltage with a constant amplification factor to obtain an output, the output voltage value when the illuminance for light control is detected is the value for automatic air conditioning control. On the other hand, the value becomes about one thousandth, and there is a problem that the signal-to-noise ratio (S / N ratio) deteriorates. Therefore, the photodetector and the output amplifier circuit thereof used under such operating conditions are required to detect and amplify both different output regions without lowering the S / N ratio.

The optical sensor circuit shown in FIG.
It is a circuit that converts the output of the detection element 11 into current-voltage at two conversion rates by switching the value of the negative feedback resistance of 0 in two steps. FIG. 5 is a diagram showing an operation example of the circuit shown in FIG. 4, in which the horizontal axis represents the output current I _Sh of the photodetector 11, and the vertical axis represents the output voltage V _out between the terminals 14 and 15 shown in FIG. 4, respectively. Shows. In FIG. 5, as one operation example, the photodetector 11 shown in FIG. 4 outputs a current of 1 to 5 μA when performing illuminance detection for light control, and outputs 1 to 5 μA when performing illuminance detection for automatic air conditioning control. It is assumed that a current of 2 mA is output, and the total value of the on-voltages of the reference voltage source 13 and the diode 12 is 3.2 to 3.4V.

As shown in FIG. 5, according to the optical sensor circuit shown in FIG. 4, for example, an output voltage of about 0.5V to 3V can be obtained at the time of illuminance detection necessary for light control, and automatic air conditioning control is possible. It is possible to obtain an output voltage near 4 V even when detecting the illuminance. In this case, the resistance Rf ₁
Has a resistance of about 600 kΩ, and the resistance of resistor Rf ₂ is about 3 kΩ.
It is.

[0007]

By the way, in the above-mentioned conventional photosensor circuit, the weak output current from the photodetection element 11 in the region used for the light control is set to a predetermined level such that the problem of the S / N ratio can be ignored. Several hundred kΩ to convert the voltage to
A feedback resistor having a large resistance value is used. Therefore, the influence of the variation of the bias current of the operational amplifier and the temperature change on the output voltage increases accordingly. A high-precision operational amplifier with a small bias current or offset current is expensive, or even if the desired characteristics can be obtained at room temperature, the operating temperature range of automobiles is wide and the environment such as temperature and vibration is severe. However, there is a problem that it cannot be used or the characteristics cannot be obtained.

The present invention has been made under such a background, and it is possible to accurately detect the illuminance in a wide area even if an inexpensive general-purpose photodetector, a circuit element such as an operational amplifier is used. An object is to provide an optical sensor circuit.

[0009]

In order to solve the above-mentioned problems, the invention according to claim 1 is a photo-detecting element, and a converting means for inputting an output current of the photo-detecting element, converting it into a voltage and outputting it. , Switching means interposed between the output of the photodetection element and the input of the conversion means for switching the connection and disconnection state between the output of the photodetection element and the input of the conversion means, and at predetermined intervals. The control means controls the switching operation of the switching means, and controls the fetching of the output of the converting means in each switching operation state.

According to a second aspect of the present invention, the conversion means receives the output current of the photodetection element, converts the output current into a voltage with a predetermined amplification factor, and outputs the voltage, and the voltage conversion means. Is further configured to be amplified by a predetermined amplification factor and output.

According to a third aspect of the present invention, the photodetector element, switching means for switching and outputting the connected and disconnected states of the output of the photodetector element, and the first output means for amplifying the output of the switching means. An operational amplifier, a second operational amplifier that amplifies the output of the first operational amplifier, and a bias voltage corresponding to the offset voltage of the first and second operational amplifiers is generated and input to the first operational amplifier. Bias voltage generating means and control means for controlling the switching operation of the switching means for each predetermined cycle and for fetching the outputs of the first and second operational amplifiers in each switching operation state. I am trying.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a configuration of an optical sensor circuit according to an embodiment of the present invention when applied to an automobile. PD in Figure 1
₁ cabin dashboard a photodiode or the like that choice to provided the light detecting element, 1 denotes a control unit, the optical sensor circuit of the present invention the case shown in this figure, the light detecting element PD ₁ and Control And part 1. In the control unit 1, the output current of the photo-detecting element PD ₁ is converted into a voltage signal having a voltage of a predetermined magnitude and then input to the 1-chip microprocessor (MPU) IC ₁ . And
The 1-chip microprocessor IC ₁ performs a signal for controlling solar radiation of an automatic air conditioner (automatic air conditioning control device) according to a program stored therein, and an automatic light control for turning on / off a headlight and a small light. To output a signal or the like.

In this case, the one-chip microprocessor IC ₁ is provided with a storage circuit such as RAM and ROM, an analog / digital conversion circuit, a timer circuit, etc., and has a 5V DC power source from a vehicle-mounted battery (not shown). Works with power. The signals for controlling solar radiation are signals for controlling the blower motors for air conditioners and the step motors for controlling the wind direction, while the signals for auto light control drive relays that connect and disconnect headlights and small lights. It is a signal for controlling. The form of output from the one-chip microprocessor IC ₁ is not limited to that shown in this figure, and various control signals other than the solar radiation control and the auto light control are output, or they are used as communication signals to other control devices. It is also possible to output the signal of.

The control section 1 includes a switching means 2 to which the output of the photodetector PD ₁ is connected, and an operational amplifier O for converting the current I _S input via the switching means 2 into a voltage.
It is composed of a conversion means composed of P ₁ and a resistor connected to it, and an amplification means composed of an operational amplifier OP ₂ etc. for amplifying the output of the conversion means. In this case, the switching means 2 comprises an analog switch, a relay, etc. 2
It is composed of individual switches S ₁ and S ₂ . One switch S ₁ is connected so as to intermittently connect between the output terminals of the photodetector PD ₁ , and the other switch S ₂ is connected between _one terminal of the photodetector PD ₁ and the inverting input terminal of the operational amplifier OP _1. Are connected to be intermittent. And the switch S
₁ and S ₂ respectively correspond to the output of the inverter IN ₁ whose input is connected to the output terminal P _O1 of the microprocessor IC _{1 and} the output from the terminal P _O1 (ON at the output “H”). As shown in, they operate in a mutually opposite phase. That is, when the switch S ₂ is open, between the output terminals of the photodetector element PD ₁ is adapted to be shorted by the switch S _1.

The operational amplifier OP ₁ has a resistor R ₁ between its output terminal and its inverting input terminal and a resistor R ₁ at its non-inverting input terminal.
₂ , the output terminal is connected to the resistor R ₇ and the non-inverting input terminal of the operational amplifier OP ₂ . The other terminal of the resistor R ₂ is connected to a connection point of a resistor R ₅ whose other end is connected to a DC 5V power source and a resistor R ₆ whose other end is grounded. The other terminal of the resistor R ₇ is connected to the anode of the diode D ₁ to the input terminal AD ₁ and the cathode of the analog / digital converter of the microprocessor IC ₁ is connected to a 5V power supply.

The operational amplifier OP ₂ has a resistor R ₄ between its output terminal and its inverting input terminal, and a ground resistance R _{3 at} its inverting input terminal.
However, the resistor R ₈ is connected to each output terminal. The other terminal of the resistor R ₈ is connected to the input terminal AD ₂ of the analog / digital conversion circuit of the microprocessor IC ₁ and the anode of the diode D ₂ whose cathode is connected to the 5V power supply.

Further, in this case, the operational amplifier OP ₁ and the operational amplifier OP ₂ are constructed so as to be operated by the power source V _cc of the single power source of DC 12V.

Next, the operation of the optical sensor circuit shown in FIG. 1 will be described. Here, each of the resistors R _{1 to} R ₈ described above is, as an example, R ₁ = R ₂ = 1.2 kΩ, R ₃ = 1 kΩ,
R ₄ = 100 kΩ, R ₅ = 15 kΩ, R ₆ = 47 Ω, R ₇ =
It is assumed that it has a resistance value of R ₈ = 10 kΩ. Further, the output current of the photodetector PD ₁ is I _S , the voltage of the output terminal of the operational amplifier OP ₁ is V ₁ , the offset voltage is V _OS1 , the voltage of the output terminal of the operational amplifier OP ₂ is V ₂ , and the offset voltage is V.
_OS2, the voltage at the node between the resistor R ₅ resistors R ₆ and V _SS.

The voltage V _SS is equal to the operational amplifier OP ₁
Of the offset voltage V _OS1 and the offset voltage V _OS2 of the operational amplifier OP ₂ are set to a value larger than the absolute value of the sum of the maximum values of the standard values in the negative direction.

As shown in FIG. 3, the optical sensor circuit shown in FIG. 1 detects an offset voltage generated due to a variation in characteristics of the operational amplifiers OP ₁ and OP ₂ and a temperature change, and an error component such as the change. The output current I _S of the photodetector element PD ₁ is detected by repeating the two modes of the offset detection mode and the photodetection mode for actually detecting the output of the photodetector element PD ₁ as one cycle. FIG. 3 is a timing chart showing changes in the output signal SW of the output terminal P _O1 of the microprocessor IC ₁ and the timing of sampling the output of the internal analog / digital conversion circuit. In FIG. 3, time t ₁ is the sampling timing in the offset detection mode, and time t ₂ is the sampling timing in the light detection mode. These times t ₁
It is desirable that the time t ₂ and the time t ₂ be set at the time when at least half the time has elapsed in each cycle, in which the state of each mode is stable. Further, it is necessary to set the time for one cycle at intervals such that the difference in operating conditions such as the temperature of each circuit element can be ignored. For example, each mode is set to a time of about 50 ms.

Next, the details of each of the offset detection mode and the light detection mode will be described. First, in the offset detection mode, the output signal SW from the output terminal P _O1 of the microprocessor IC ₁ becomes "L", and the switch S ₁ is turned on and the switch S ₂ is turned off. Therefore, the output terminals of the photodetector element PD ₁ are short-circuited, and the circuits on the switches S ₁ and S ₂ side of the operational amplifier OP ₁ are opened. In this case, the output voltage V of the operational amplifier OP _1
1 is

V ₁ = V _OS1 + V _SS

The voltage obtained by the above becomes, and the operational amplifier OP
Output voltage V ₂ of _2,

V ₂ = (V _OS2 + V ₁ ) · (1 + R ₄ / R ₃ ).

That is, the voltage V ₂ (t ₁ ) at time t ₁ is

V ₂ (t ₁ ) = (V _OS2 + V _OS1 + V _SS ).
(1 + R ₄ / R ₃ )

## EQU1 ## As described above, the voltage V _SS is set to a value larger than the value obtained by adding the estimated maximum values of the offset voltage V _OS1 and the offset voltage V _{OS 2 in} the negative direction. Therefore, the value of V _OS2 + V _OS1 + V _SS It is always a positive value. Therefore, the value V ₂ (t ₁ ) of the voltage V ₂ detected at the time t ₁ includes a value corresponding to the offset voltage of the operational amplifiers OP ₁ and OP ₂ at that time, and the output of the photodetector PD ₁ The value that does not include the current I _S is taken into the microprocessor IC ₁ .

The output voltages V ₁ and V ₂ of the operational amplifiers OP ₁ and OP ₂ are diode D ₁ or D _{2 at} a voltage value of 5V.
When the voltage exceeds the ON voltage of, resistance R ₇ ,
The voltage input to the terminals AD ₁ and AD ₂ is clamped by the clamp circuit composed of R ₈ and the diodes D ₁ and D ₂ . This clamp circuit makes the output voltage of each operational amplifier OP ₁ and OP ₂ higher than the operating voltage of the microprocessor IC ₁ in order to prevent the output saturation of each operational amplifier OP ₁ and OP ₂ in the normal illuminance detection region. It is provided to prevent the application of an overvoltage to the microprocessor IC ₁ due to the above.

Further, the switch S ₁ is short-circuited in the offset detection mode because when only the switch S ₂ is turned off, a high impedance state is high between the output terminals of the photodetector PD ₁ which is a current source. This is to prevent generation of voltage. Thus, even when the switch S ₂ is composed of a semiconductor switch such as a MOS analog switch, it is possible to prevent an increase in the leak current of the switch S ₂ due to the voltage generated between the output terminals of the photodetector element PD ₁ .

On the other hand, in the light detection mode, the output signal SW from the output terminal P _O1 of the microprocessor IC ₁ becomes "H", the switch S ₁ is turned off and the switch S ₂ is turned on. Therefore, the output terminal of the photodetector element PD ₁ is connected to each input terminal of the operational amplifier OP ₁ . In this case, the output voltage V ₁ of the operational amplifier OP ₁ is

V ₁ = V _OS1 + V _SS + I _S · (R ₁ + R ₂ )

The voltage is obtained by The output voltage V ₂ of the operational amplifier OP ₂ is

V ₂ = (V _OS2 + V ₁ ) · (1 + R ₄ / R ₃ )

Since it is the same as the above case, the voltage V ₂ (t ₂ ) at time t ₂ is

V ₂ (t ₂ ) = (V _OS2 + V _OS1 + V _SS + I _S
・ (R ₁ + R ₂ )) ・ (1 + R ₄ / R ₃ )

It becomes Therefore, the value V ₂ (t ₂ ) of the voltage V ₂ detected at the time t ₂ is the value corresponding to the offset voltage of the operational amplifiers OP ₁ and OP ₂ at that time and the output current I _{S of the} photodetector element PD _1. Is taken into the microprocessor IC ₁ as a value including both the values according to.

Here, the microprocessor IC ₁ performs a subtraction of V ₂ (t ₂ ) -V ₂ (t ₁ ) according to a predetermined program, and the total offset voltage value V _OS3 (= V _OS2 + V)
A value corresponding to the output current I _S not including _OS1 + V _SS ) is obtained. Then, the microprocessor IC ₁ uses the V ₂ (t
₂₎ a detection value corresponding to the illuminance obtained by -V ₂ (t ₁₎ comprising subtraction, in accordance with the detected value of the voltage V _1, the output process is performed for each signal for light control and solar control.

[0038] A light detection device PD ₁ of the output current I _S and the relationship between the operational amplifiers OP ₁ and OP ₂ output voltages V ₁ and V ₂ in the steady state in the above-mentioned condition in FIG. On the other hand, as shown in this figure, the output current I for light control
_In the region where _S is several μA (in this case, 1 to 5 μA), the voltage V ₂ has an output of several V (in this case, 1 to 3 V), while on the other hand, several mA for solar radiation control (in this case, 1 to 2 mA). In this region, the voltage V ₁ has an output of several V (in this case, 2 to 5 V). For example, when the value of the current I _{S at} the illuminance for determining whether to turn on or off the light is 1 μA and 5 μA, the magnitude of the determination voltage when the light is turned on is V _TL , and the determination voltage when the light is turned off. Is V _TH , and each judgment is V ₂ (t ₂ ) −V ₂ (t ₁ ).
Can be done by comparison with.

The offset voltages V _OS1 and V _{OS1 of the} operational amplifiers OP ₁ and OP _{2 depend on} variations in elements and temperature changes.
_{Since OS2} changes, the voltage V _{OS3 obtained} by adding the voltage V _SS and the voltages V _OS1 and V _{OS 2} shown in FIG. 2 changes. However, according to the present embodiment, the value when the current I _S = 0 is detected in the offset detection mode and the voltage V ₂ detected in the light detection mode is detected.
The calculation is performed by subtracting the value from the value of, and a value proportional to the current I _S excluding the offset is detected. Therefore,
Even if a general-purpose operational amplifier having a relatively large offset voltage is used, highly accurate detection without error can be performed. Further, since the feedback resistor R ₁ and the input resistor R ₂ in the circuit for converting the current I _S into the voltage V ₁ can be set to several kΩ or less, the detection accuracy is deteriorated due to the offset current of the operational amplifier and the bias current itself. Can be kept low.

Further, as shown in FIG. 2, each operational amplifier O
The saturation point of the output voltage of P ₁ and OP ₂ is set higher than the detection region of the normal current I _S , and their power supply voltage is set higher than the operating voltage of the microprocessor IC _1, that is, the analog / digital conversion circuit. Thus, the characteristics of the current I _{S and the} voltages V ₁ and V _{2 having} a wide operating range are obtained.

In the above embodiment, each operational amplifier is operated by one power supply (single power supply), but the configuration of the power supply and the operational amplifier itself are changed so as to be of both power supplies. May be. In this case, the circuit for forming the bias voltage V _SS composed of the resistor R ₅ and the resistor R ₆ shown in FIG. 1 may be omitted, and the resistor R ₂ may be directly grounded.

[0042]

As described above, according to the present invention, the output of the conversion means or the operational amplifier which does not include the output component of the photodetector and the output of the conversion means or the operational amplifier which includes the output component of the photodetector. Since the control unit repeatedly takes in every predetermined period, the control unit can remove the error component based on both outputs. Therefore, it is possible to perform highly accurate photodetection even by using a conversion unit or an operational amplifier that produces an error component.

According to the invention described in claim 3, the first
Also, the second operational amplifier can be operated with a single power source, and the circuit configuration can be simplified and the cost of the components can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a circuit configuration of an optical sensor circuit according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing one operation characteristic of the optical sensor circuit shown in FIG.

FIG. 3 is a timing chart for explaining the operation of the optical sensor circuit shown in FIG.

FIG. 4 is a circuit diagram showing a conventional optical sensor circuit.

5 is a characteristic diagram showing operating characteristics of the circuit shown in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 control part 2 switching means PD ₁ photodetector OP ₁ , OP ₂ operational amplifier IC ₁ microprocessor S ₁ , S ₂ switch R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ , R ₇ , R ₇ , R ₈ resistance

Front page continued (72) Inventor Yoshinori Otsubo, 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda Co., Ltd. (72) In-house, No. 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda Corporation

Claims (3)

[Claims] 1. A photo-detecting element, a converting means for inputting an output current of the photo-detecting element to convert it into a voltage and outputting the voltage, and an intervening device between the output of the photo-detecting element and the input of the converting means. Switching means for switching the connection and non-connection state of the output of the photodetector and the input of the converting means, and controlling the switching operation of the switching means at every predetermined cycle, and the converting means in each switching operation state. And a control means for taking in the output of the optical sensor circuit. 2. The voltage converting means, wherein the converting means inputs the output current of the photo-detecting element, converts the output current into a voltage at a predetermined amplification rate, and outputs the voltage, and the output of the voltage converting means further has a predetermined amplification rate. 2. The optical sensor circuit according to claim 1, wherein the optical sensor circuit comprises: an amplifying unit that amplifies and outputs. 3. A photo-detecting element, a switching means for switching and outputting the output of the photo-detecting element by switching between connected and non-connected states, a first operational amplifier for amplifying the output of the switching means, and the first operational amplifier. A second operational amplifier for amplifying the output of the operational amplifier; a bias voltage generating means for generating a bias voltage according to the offset voltage of the first and second operational amplifiers and inputting the bias voltage to the first operational amplifier; And a control means for controlling the switching operation of the switching means for each cycle and for fetching the outputs of the first and second operational amplifiers in each switching operation state.