JPH0424475Y2 - - Google Patents

Description

[Detailed explanation of the invention] <Field of industrial application> This invention is designed to detect the amount of infrared energy emitted from moving objects such as human bodies and the amount of infrared energy emitted from the floor of buildings in the background of the set detection area. High frequency noise in infrared moving object detection devices that detect the difference between the amount of infrared energy and the amount of infrared energy used to control the opening and closing of automatic doors, etc., especially in car phones, personal radios, etc.
Alternatively, the present invention relates to a high frequency noise prevention circuit for preventing malfunction due to high frequency noise generated by a high frequency treatment device or the like.

<Conventional technology> All objects at temperatures above absolute zero (-273°C) emit infrared rays corresponding to their temperature, but human bodies and buildings at room temperature emit far infrared rays with a wavelength of around 10 μm. There is. Infrared moving object detection equipment sets a predetermined detection area on the floor of a building, etc., and constantly monitors the infrared rays emitted from this detection area using an optical system. When the human body moves, the amount of infrared energy that enters the infrared detection element changes by the difference between the amount emitted by the human body and the amount emitted by the floor surface, etc. Therefore, from this change in the amount of infrared energy, the amount of infrared energy that enters the infrared detection element changes. The device is configured to detect the movement of the door and output an opening signal for an automatic door or an alarm signal for a security alarm device.

<Problems to be solved by the invention> By the way, the electronic circuits of these infrared moving object detection devices, especially the electronic circuits where the signal level between the infrared detection element and the amplifier circuit is relatively low and are easily affected by high frequency noise. When a high-frequency radio wave enters from the outside, it is detected by an IC such as an operational amplifier in the amplifier circuit and becomes a false signal.This false signal may turn on the switching circuit and cause it to malfunction. For example, amateur radios and police radios in the 140 to 150 MHz band, amateur radios and other professional radios in the 40 MHz band, car phones and personal radios in the 800 to 900 MHz band, and even high frequency treatment devices of 2 GHz or more are the main high frequency radios. It is the source.
When the high frequencies emitted by these devices jump into semiconductor elements such as transistors, ICs, diodes, and FETs in the electronic circuit of the infrared detection device, they are detected by the nonlinearity of the semiconductor elements and become false signals, which is the cause. Malfunctions may occur.

Conventionally, as a measure to prevent malfunctions caused by such high-frequency noise, that is, as a means for reducing high-frequency noise within an electronic circuit, a method has been adopted in which a shield case and a feedthrough capacitor are used to electrically interrupt the electronic circuit.

However, the space required to install the shielding case not only impedes the miniaturization of the equipment, but also reduces the noise level by only about 10 to 20 dB, which is not so much considering the high cost. No effect.

Further, the method using a bypass capacitor is effective against voltage mode radio waves, but has the disadvantage that it is ineffective against current mode radio waves and is less effective against high frequencies. Furthermore, attempts have been made to apply radio wave absorbers, but the effective frequency band is narrow, so sufficient effects have not been achieved.

Furthermore, it is possible to exclude the effects of high frequency noise by using a low pass filter consisting of a resistor and a capacitor, but if the zero frequency is within the passband and the infinite frequency is within the attenuation range, A general low-pass filter, whose cutoff frequency is the boundary between the Can not.

The present invention has been developed in view of these conventional problems, and its technical objective is to provide a high-frequency noise prevention circuit for an infrared detection device that can reliably prevent malfunctions caused by various high-frequency noises. It is something.

<Means for Solving the Problems> In the present invention, as a technical means for achieving the above-mentioned problems, a high frequency noise prevention circuit of an infrared detection device is configured as follows. That is, the infrared light flux emitted from a predetermined detection area is focused by an optical system and incident on an infrared detection element, and this infrared detection element converts the amount of incident infrared energy into an electrical signal proportional to the amount of variation in the amount of infrared energy. A high frequency noise absorption circuit disposed between the infrared detection element and the amplifier circuit in a high frequency noise prevention circuit in an infrared detection device that detects entry of an object into a detection area when a signal exceeds a predetermined detection level. A capacitor with a self-resonant frequency near or higher than the frequency of the high-frequency noise to be reduced and a capacitance of 5 to 100 pF and a resistance value of 100 Ω2 to several
KΩ resistor, and the high frequency noise absorbing circuit section is integrated into the integrated circuit constituting the amplifier circuit by being connected to the input terminal of the integrated circuit. The length of the wiring pattern in the capacitor is set to 1 mm or less, and the length of the lead wire of the capacitor is set to 2 mm or less.

<Function> Since the high-frequency noise absorption circuit section is integrated into the IC that constitutes the amplifier circuit, which has a relatively low signal level and is easily affected by high-frequency noise,
The lead wire of the capacitor in the high frequency noise absorption circuit can be made as short as possible to a length of 2 mm or less, and its capacitance can be reduced to about 5 to 100 pF, and the wiring can act as an antenna against high frequency noise. Since the length of the pattern can be shortened to 1 mm or less, the self-resonant frequency of the capacitor can be set extremely high, and high-frequency noise below this self-resonant frequency can be reliably cut out.

<Example> Hereinafter, a preferred example of the present invention will be described in detail with reference to the drawings.

Since the figure shows only the essential parts of an embodiment of the present invention, first, an infrared detection device to which the present invention is applied will be explained. For example, in an infrared moving object detection device, far infrared rays emitted from a predetermined detection area are collected by an optical system and incident on an infrared detection element such as a pyroelectric detector, a thermistor bolometer, or a thermoelectric pile. The infrared detection element outputs a signal corresponding to the amount of variation in the incident infrared energy, and this output signal is amplified by an amplifier circuit such as an operational amplifier and output to a subsequent switching circuit. The switching circuit monitors fluctuations in the amount of infrared energy, and when it detects fluctuations exceeding a predetermined range, it turns on and conducts an electronic switch such as a MOSFET, sending a door opening signal to the controller that controls the opening and closing of the automatic door. It is designed to output.

In such an infrared moving object detection device, as described above, the electronic circuit between the infrared detection element and the amplifier circuit has a low signal level and is easily affected by high frequency noise. Therefore, as shown in the figure, the present invention includes a high frequency noise absorbing circuit section consisting of a resistor R ₃ and a capacitor C ₃ , a resistor R ₄ and a capacitor C ₄ in the operation amplifier integrated circuit 2 that constitutes the amplifier circuit. It is integrated and connected to the input terminal of the operational amplifier.

Furthermore, the capacitors C ₃ and C ₄ are set to have self-resonant frequencies near or higher than the high frequency frequency that is the noise to be removed.

That is, the high frequency noise absorption circuit section is connected to the capacitor C ₃ ,
At frequencies higher than the self-resonant frequency of _C4 , the impedance increases and the high-cut effect worsens. On the other hand, the self-resonant frequency is the capacitor C ₃ ,
It is not determined only by the value of _C4 , but by the length of the pattern of the high frequency noise absorption circuit,
This is determined as the self-resonant frequency of the entire high-frequency noise absorption circuit section in relation to the length of the C ₃ and C ₄ lead wires and the combined impedance of inductance and capacitance.Increasing the self-resonance frequency , it is necessary to reduce the length of the above-mentioned pattern, the length of the lead wire, the inductance, and the capacitance as much as possible. According to actual measurement results, 140M, which is the target of exclusion in infrared moving object detection equipment,
For high frequency noise from Hz to 2GHz, capacitor
The capacitance of C ₃ , C ₄ is 5 to 100 pF, the capacitor C ₃ ,
C ₄ lead wire length is approximately 2 mm or less, resistance R ₃ , R ₄
It is necessary to set the pattern length appropriately within the range of 100Ω to several KΩ, and the length of the pattern to be 1 mm or less.

Therefore, in this invention, the high frequency noise absorption circuit section is
By integrating the capacitors C 3 and C 4 into the integrated circuit 2 that constitutes the amplifier circuit, the lead wires of the capacitors C ₃ and C ₄ can be made as short as possible, and their capacitance can be made as small as possible. The length of the wiring pattern that acts as an antenna can also be shortened to satisfy the above-mentioned values. Therefore, the self-resonant frequency can be set extremely high, and high-frequency noise below the self-resonant frequency can be reliably cut out and prevented from entering the operational amplifier. Therefore, false signals caused by high frequency noise can be completely eliminated and malfunctions can be prevented.

Moreover, since the high-frequency noise absorption circuit section is integrally provided on the substrate of the integrated circuit 2, it not only functions as a means for reducing high-frequency noise, but also eliminates static electricity caused by static electricity accumulated in the human body when assembling and adjusting equipment. This also has the secondary effect of preventing the substrate of the integrated circuit 2 from being damaged by electric breakdown.

In the above embodiment, an infrared type moving object detection device was explained, but it goes without saying that the same effect can be obtained by applying the present invention to other infrared passive type infrared detection devices such as an infrared type security alarm device. be.

<Effects of the invention> As described above, according to the high-frequency noise prevention circuit of the infrared detection device of the present invention, a high-frequency noise absorption circuit with a simple circuit configuration consisting of a capacitor and a resistor is placed in an integrated circuit that constitutes an amplifier circuit. By inserting the input terminal into the connected state and integrating it, the lead wire of the capacitor, which is a component of the high-frequency noise absorption circuit, can be made as short as possible to 2 mm or less, and its quietness can be minimized. Since the capacitance can be as small as 5 to 100 pF and the wiring pattern can be shortened to 1 mm or less, the self-resonant frequency of the high-frequency noise absorption circuit can be set extremely high, and high-frequency noise below this self-resonant frequency can be reliably cut out. Therefore, unlike a general low-pass filter, the 140MHz that needs to be excluded in an infrared detection device
It can reliably absorb high frequency noise over a wide range of ~2GHz.

Actual measurement results show that conventional high-frequency noise prevention means malfunction when the distance between the personal radio and the infrared detection device is around 3 meters against the high-frequency noise emitted by a 900MHz, 5W personal radio. In the case of an infrared detection device to which a high-frequency noise prevention circuit was applied, no malfunction occurred even at the aforementioned close distance of 30 cm. Therefore, the present invention can significantly alleviate the restrictions on the installation environment conditions for an infrared detection device.

[Brief explanation of the drawing]

The figure is a schematic circuit diagram of an embodiment of the present invention. 2...Integrated circuit, _R3 , _R4 ...Resistor, _C3 , _C4 ...
...capacitor.

Claims (1)

[Scope of utility model registration request] The infrared light flux emitted from a predetermined detection area is focused by an optical system and incident on an infrared detection element, and this infrared detection element converts the amount of incident infrared energy into an electrical signal proportional to its variation, and this electrical signal is In a high frequency noise prevention circuit in an infrared detection device that detects entry of an object into a detection area by exceeding a predetermined detection level, the high frequency noise absorption circuit section is provided between the infrared detection element and the amplifier circuit. , a capacitor with a self-resonant frequency near or higher than the frequency of the high-frequency noise to be reduced and a capacitance of 5 to 100 pF and a resistance value of
It consists of a resistance of 100Ω2 to several KΩ, and
The high frequency noise absorption circuit section is integrated into the integrated circuit constituting the amplifier circuit by being connected to the input terminal thereof, and the length of the wiring pattern in the high frequency noise absorption circuit section is 1 mm. Below, and the length of the lead wire of the capacitor is 2mm.
A high frequency noise prevention circuit for an infrared detection device characterized by the following settings.