JPH0843201A - Pyroelectric infrared sensor circuit - Google Patents

Abstract

PURPOSE:To improve both the detection sensitivity and speed of response of an infrared sensor circuit. CONSTITUTION:One end of the pyroelectric infrared sensor S1 is connected to a DC power source E1 which supplies a first reference potential VREF1 and the noninverting input terminal of an operational amplifier OP1. The other end of the sensor S1 is connected to the inverting input terminal of the amplifier OP1 and one end of a series circuit composed of a series resistance R2 and the phototransistor Tr1 of a photocoupler 11. The other end of the series circuit is connected to a variable DC power source E2 which supplies a second reference potential VREF2. The phototransistor Tr1 is connected with a parallel resistance R1. Between the output terminal of the amplifier OP1 and a variable DC power source E3 which supplies a third reference potential, a resistor R3 for deciding amplification factor and the light-emitting diode LED of the photocoupler 11 are connected. Therefore, the detection sensitivity of the sensor S1 can be improved by adjusting the resistor 3. In addition, the speed of response of the sensor S1 can be also improved by reducing the value of the series resistance R2 to a relatively small value. This sensor S1 is suitable for the human body detecting sensor fixed to automobiles, robot arms, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pyroelectric infrared sensor circuit, and more particularly to a pyroelectric infrared sensor circuit capable of achieving both detection sensitivity and high-speed response.

[0002]

2. Description of the Related Art FIG. 3 is a circuit diagram showing an example of a conventional pyroelectric infrared sensor circuit. In this pyroelectric infrared sensor circuit 500, one end of the pyroelectric infrared sensor S1 is connected to the reference potential VREF and the non-inverting input terminal of the operational amplifier OP1, and the other end of the pyroelectric infrared sensor S1 is the inverse of the operational amplifier OP1. It is connected to the input terminal.
The reference potential VREF is a voltage dividing resistor R for dividing the power supply voltage VCC.
4, obtained by partial pressure with R5. A feedback resistor R22 is connected between the inverting input terminal and the output terminal of the operational amplifier OP1. Incidentally, C1 is a stray capacitance C1 existing between the inverting input terminal and the output terminal of the operational amplifier OP1.

Next, the pyroelectric infrared sensor circuit 500 described above.
Will be described. When there is a change in infrared rays, the pyroelectric infrared sensor S1 is approximately 10
^-Emits an electric charge of ⁸ C / K · cm ² . For example, the size of the detection element of the pyroelectric infrared sensor S1 is 0.1 cm × 0.
When the temperature change of the detection element is 0.001K at 1 cm, it is approximately 10 ^-8 C / K · cm ² × 0.01 cm ² × 0.00
It releases a charge of 1K = 10 ⁻¹³ C. Then, through the feedback resistor R22 and the stray capacitance C1, the operational amplifier OP1
The current corresponding to the electric charge is fed back from the output terminal of the above to the inverting input terminal. As a result, the detection signal So according to the intensity of infrared rays is output from the operational amplifier OP1.

The pyroelectric infrared sensor circuit 500 has a high-frequency cutoff type filter characteristic because of the stray capacitance C1. The high cutoff frequency fp is defined by fp = 1 / (2π · C1 · R22).

[0005]

In the conventional pyroelectric infrared sensor circuit 500, in order to increase the detection sensitivity, the value of the feedback resistor R22 may be increased and the amplification factor may be increased. However, if the value of the feedback resistor R22 is increased,
The high cutoff frequency fp becomes low and the high speed response is lost. For example, when the stray capacitance C1 is about several pF,
When the feedback resistor R22 is set to about 10 ¹¹ Ω, the high cutoff frequency fp becomes about several tens Hz, and the high speed response is lost. That is, the above conventional pyroelectric infrared sensor circuit 5
In No. 00, there is a trade-off between detection sensitivity and high-speed response, and there is a problem that it is difficult to achieve compatibility. Therefore, an object of the present invention is to provide a pyroelectric infrared sensor circuit that can achieve both detection sensitivity and high-speed response.

[0006]

According to a first aspect of the present invention, one end of a pyroelectric infrared sensor is connected to a first reference potential point and a non-inverting input terminal of a differential amplifier. The other end of the infrared sensor is connected to the inverting input terminal of the differential amplifier, and the light receiving element of the photocoupler and the series circuit of the series resistor are connected between the inverting input terminal of the differential amplifier and the second reference potential point. A parallel resistor is connected in parallel with the light receiving element, and a light emitting element of the photocoupler and a gain determining resistor are connected between the output terminal of the differential amplifier and a third reference potential point. Provided is a pyroelectric infrared sensor circuit.

According to a second aspect of the present invention, in the pyroelectric infrared sensor circuit according to the first aspect, the second reference potential DC power supply or the third reference potential for applying the second reference potential is used. There is provided a pyroelectric infrared sensor circuit characterized in that at least one of a third DC power supply for reference potential is provided.

According to a third aspect of the present invention, in the pyroelectric infrared sensor circuit according to the second aspect, at least one of the second reference potential DC power supply and the third reference potential DC power supply has a zero volt output. A pyroelectric infrared sensor circuit is provided which is a variable DC power supply.

[0009]

In the pyroelectric infrared sensor circuit according to the first aspect, the amplification factor is increased and the detection sensitivity can be increased by adjusting the amplification factor determining resistor to reduce the feedback amount by the photocoupler. . Therefore, it is not necessary to increase the value of the series resistance so much (10 ¹⁰ Ω or less). On the other hand, for the high cutoff frequency fp, the value of the series resistance is R
2, and stray capacitance is C0, then fp = 1 / (2π · C0 · R2). Since it is not necessary to increase the value R2 of the series resistance so much as described above, the high cutoff frequency fp becomes high. For example, if R2 = 10 ⁸ Ω and C0 = several pF,
fp becomes about 1 kHz. Therefore, both detection sensitivity and high-speed response can be achieved. The parallel resistance is for applying the second reference potential to the inverting input terminal of the differential amplifier even when the light receiving element of the photocoupler is off.

In the pyroelectric infrared sensor circuit of the second aspect, the degree of freedom of the offset amount given to the differential amplifier can be improved by giving the second reference potential by the second reference potential DC power supply. Further, since the current flowing through the light emitting element of the photocoupler is changed by applying the third reference potential from the third DC power supply for the reference potential, the feedback amount by the photocoupler can be set to be suitable.

In the pyroelectric infrared sensor circuit according to the third aspect, since at least one of the second reference potential DC power supply and the third reference potential DC power supply is a variable DC power supply capable of producing a zero volt output, an offset amount and a feedback are provided. The degree of freedom in adjusting the amount can be further improved, and the second reference potential and the third reference potential can be set to the ground potential.

[0012]

EXAMPLES The present invention will be described in more detail with reference to the examples shown in the drawings. The present invention is not limited to this.

First Embodiment FIG. 1 is a circuit diagram of a pyroelectric infrared sensor circuit according to the first embodiment of the present invention. In the pyroelectric infrared sensor circuit 100, one end of the pyroelectric infrared sensor S1 is connected to a DC power source E1 that supplies a first reference potential VREF1 and a non-inverting input terminal of an operational amplifier OP1. The first reference potential VREF1 amplifies the sensor signal (positive direction or negative direction) from the pyroelectric infrared sensor S1 without departing from the operating range of the operational amplifier OP1 (determined by the power supply voltages VCC and VSS). Give the amount of offset that can be done.

The other end of the pyroelectric infrared sensor S1 is connected to the inverting input terminal of the operational amplifier OP1. Further, the series resistance R2 (preferably about 10 ⁶ Ω or more and about 1
0 ¹⁰ Ω or less) and the phototransistor Tr1 of the photocoupler 11 are connected to one end of a series circuit. Further, the other end of the series circuit is connected to a variable DC power source E2 that gives a second reference potential VREF2. The offset amount can be adjusted by setting the voltage of the variable DC power source E2. The variable DC power source E2 basically supplies a positive reference potential VREF2, but the reference potential VREF2 can be set to be substantially the ground potential by setting a zero volt output.

A parallel resistor R1 is connected in parallel to the phototransistor Tr1. The current flowing through the parallel resistance R1 when the phototransistor Tr1 is on is 1% of the emitter current of the phototransistor Tr1.
If it is set to be equal to or less than that, a sufficient amount of feedback can be obtained by the operational amplifier OP1. The parallel resistor R1 stabilizes the operation of the operational amplifier OP1 when it rises, and its value is preferably about 10 ¹⁰ Ω or more.

C0 is a stray capacitance between the collector and emitter of the phototransistor Tr1.

The output terminal of the operational amplifier OP1 is connected to one end of the amplification factor determining resistor R3, and the other end of the amplification factor determining resistor R3 is connected to the anode of the light emitting diode LED of the photocoupler 11. Light emitting diode L
The cathode of ED is connected to a variable DC power supply E3 that provides a third reference potential VREF3. Variable DC power source E
3 basically gives a positive reference potential VREF3, but the reference potential VREF3 can be set to be substantially the ground potential by setting a zero volt output.

Next, the pyroelectric infrared sensor circuit 100
Will be described. When there is no change in the infrared rays incident on the pyroelectric infrared sensor S1, an offset voltage is applied from the variable DC power source E2 to the operational amplifier OP1 to stabilize the rising operation of the operational amplifier OP1. When the infrared ray changes, the pyroelectric infrared sensor S1 emits a charge of about 10 ⁻⁸ C / K · cm ² in accordance with the temperature change caused by the change. For example, when the size of the detection element of the pyroelectric infrared sensor S1 is 0.1 cm × 0.1 cm and the temperature change of the detection element is 0.001 K, it is approximately 10 ⁻⁸ C / K · cm ² ×
A charge of 0.01 cm ² × 0.001K = 10 ⁻¹³ C is released. This charge changes the voltage at the inverting input terminal of the operational amplifier OP1. That is, when the voltage of the sensor signal from the pyroelectric infrared sensor S1 is Vs, (Vs +
The potential VREF2) is applied to the inverting input terminal of the operational amplifier OP1. Then, the output voltage of the operational amplifier OP1 changes according to the change of the voltage of the inverting input terminal of the operational amplifier OP1. This change in the output voltage is caused by the amplification factor determining resistor R3 and the light emitting diode L of the photocoupler 11.
The current flowing through the ED is changed, and further the photocoupler 1
The resistance value between the collector and the emitter of the first phototransistor Tr1 is changed. This phototransistor Tr1
The change in the resistance value between the collector and the emitter of the series resistor R
2 is transmitted to the inverting input terminal of the operational amplifier OP1. Thus, as a result of the output voltage of the operational amplifier OP1 being fed back to the inverting input terminal, the detection signal So according to the intensity of infrared rays is output from the operational amplifier OP1.

In the pyroelectric infrared sensor circuit 100,
By adjusting the amplification factor determining resistor R3 to reduce the feedback amount by the photocoupler 11, the amplification factor can be increased and the detection sensitivity can be increased. On the other hand, the high cutoff frequency fp is fp = 1 / (2π · C0 · R2) when the value of the series resistance is R2 and the stray capacitance is C0. For example, if R2 = 10 ⁸ Ω and C0 = several pF, then fp is about 1 kHz. The feedback amount can be adjusted by setting the voltage of the variable DC power source E3. For example, by increasing the voltage of the variable DC power source E3,
If the reference potential VREF3 of the
The current flowing through the ED is reduced, and the feedback amount is reduced.
Therefore, both detection sensitivity and high-speed response can be achieved.

-Second Embodiment- FIG. 2 is a circuit diagram of a pyroelectric infrared sensor circuit according to a second embodiment of the present invention. This pyroelectric infrared sensor circuit 200
Shows that the connection between the series resistor R2 and the phototransistor Tr1 is opposite to that in the first embodiment. Further, the connection between the amplification factor determining resistor R3 and the light emitting diode LED is opposite to that in the first embodiment. The directions of the variable DC power supplies E2 'and E3' are opposite to those of the first embodiment. Even with such a connection, the same effect as the pyroelectric infrared sensor circuit 100 of the first embodiment can be obtained.

[0021]

According to the pyroelectric infrared sensor circuit of the present invention, the amplification factor is increased and the detection sensitivity is increased by adjusting the amplification factor determining resistor to reduce the feedback amount by the photocoupler. I can. For this reason, the value of the series resistance may be made relatively small. However, if this is done, the high cutoff frequency determined by the value of the series resistance and the stray capacitance becomes high, so that high-speed response can be obtained. That is, both detection sensitivity and high-speed response can be achieved. Therefore, it is suitable for use in detecting a human body by being attached to a high-speed moving object (automobile, robot arm, etc.).

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a pyroelectric infrared sensor circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a pyroelectric infrared sensor circuit according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing an example of a conventional pyroelectric infrared sensor circuit.

[Explanation of symbols]

 100 Pyroelectric infrared sensor circuit 11 Photocoupler S1 Pyroelectric infrared sensor R1 Parallel resistance R2 Series resistance R3 Amplification factor determining resistance Tr1 Phototransistor LED Light emitting diode C0, C1 Floating capacitance VREF1 First reference potential VREF2 Second reference Potential VREF3 Third reference potential OP1 Operational amplifier VCC, VSS Power supply voltage So Detection signal E1, E1 'DC power supply E2, E2' Variable DC power supply E3, E3 'Variable DC power supply

Claims (3)

[Claims] 1. A pyroelectric infrared sensor has one end connected to a first reference potential point and a non-inverting input terminal of a differential amplifier, and the other end of the pyroelectric infrared sensor has an inverting input terminal of the differential amplifier. And an inverting input terminal of the differential amplifier and a second
Between the light receiving element of the photocoupler and the series circuit of the series resistor between the reference potential points, and the parallel resistor connected in parallel with the light receiving element, and between the output terminal of the differential amplifier and the third reference potential point. A pyroelectric infrared sensor circuit characterized in that a light emitting element of the photocoupler and a gain determining resistor are connected to the. 2. The pyroelectric infrared sensor circuit according to claim 1, wherein a second reference potential DC power supply for providing a second reference potential or a third reference potential for supplying a third reference potential.
A pyroelectric infrared sensor circuit comprising at least one of a DC power supply for reference potential. 3. The pyroelectric infrared sensor circuit according to claim 2, wherein at least one of the second reference potential DC power supply and the third reference potential DC power supply is a variable DC power supply capable of providing a zero volt output. Characteristic pyroelectric infrared sensor circuit.