JPH0687832U - Pyroelectric infrared detector - Google Patents

Abstract

(57) [Abstract] [Purpose] An object of the present invention is to obtain a pyroelectric infrared detector with little malfunction even when high-frequency electric field noise with a large transmission output is incident. A bias resistor R is connected in parallel to pyroelectric elements 11 and 12 wired in series so that the spontaneous polarization characteristics are opposite to each other, and one end of these parallel circuits is connected to the gate of an FET Tr for impedance conversion. The other end is connected to the ground terminal G. The source terminal of the FET Tr is connected to the ground terminal G via the capacitor C. This ground terminal is grounded.
The capacitance of the capacitor C is set to 10 pF or less.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a pyroelectric infrared detector used in a human body detection system or the like, and more particularly to a pyroelectric infrared detector that eliminates the influence of external noise as much as possible.

[0002]

[Prior art]

 As is well known, when a pyroelectric material receives infrared rays, it absorbs its heat energy and causes a temperature change, spontaneous polarization changes, and a charge is generated on the surface. In this way, an electric charge is induced on the surface in proportion to a slight temperature change, and this electric charge is detected as an electric current or voltage by an external circuit. The pyroelectric infrared detector utilizes such a pyroelectric effect and is used for human body detection and the like.

A configuration example of a conventional pyroelectric infrared detector will be described with reference to FIG. Three lead terminals 731, 732, 733 are projected on the upper surface of a metal base 73, a printed wiring board 72 is supported at three points on these lead terminals, and a circuit component 721 is provided on the upper and lower surfaces of this board. , 722 and supports 761 and 762 are mounted to support the pyroelectric element 71 on this support. The optical filter 75 on the flat plate is joined to the metallic cap 74 having the light incident window, and the cap 74 covers each of these parts. The optical filter 75 has a non-insulating substrate made of a conductor such as a silicon wafer or a semiconductor as a substrate, and a frequency-selective insulating film (not shown) for transmitting infrared rays is formed on at least one of the front and back surfaces thereof. Then, it is obtained by cutting into a predetermined size and shape. Since a conductor or a semi-conductor portion is exposed at this cut surface (that is, a side surface), the cap 74 and the optical filter are made conductive by the conductive bonding material S including the cut surface. Conducts, and can be electrically shielded.

[0004]

[Problems to be solved by the device]

 Not only infrared rays but also other electromagnetic waves emitted from various electric devices enter the infrared detector as described above through an optical filter. These other electromagnetic waves became harmful noises for the infrared detector and were a factor that caused malfunction in infrared detection. By performing the above electric shield, other electromagnetic waves are grounded from a specific lead terminal through a metal cap and a metal base. Therefore, it has been possible to reduce the malfunction to a certain level.

However, recently, the number of mobile communication and the like has rapidly increased, and the high frequency electric field noise (electromagnetic wave) generated from them has a large transmission output, and the shield may be insufficient in some cases. That is, since the conductor or semiconductor portion exposed on the cut surface of the optical filter has a small surface area and the surface tension is difficult to obtain, sufficient conduction may not be obtained in some cases. In such a case, high frequency electric field noise may infiltrate into the detector and may be transmitted as high frequency noise on the connection line between each electronic component, which may be amplified by a transistor etc. and output, which may cause malfunction. Was there.

The present invention has been made in order to solve the above-mentioned problems, and a pyroelectric red line detector with less malfunction even when high frequency electric field noise with a large transmission output is incident on this infrared detector. It is intended to be provided.

[0007]

[Means for Solving the Problems]

 In order to solve the above problems, the pyroelectric infrared detector according to the present invention is connected in parallel with a pyroelectric element that detects infrared rays that are selectively incident by an optical filter. Bias resistor, a transistor having a gate terminal connected to one end of the parallel circuit, and a ground terminal connected to the other end of the parallel circuit, and the output terminal of the transistor is connected to the bypass capacitor via a bypass capacitor. The bypass capacitor is connected to the ground terminal and the capacitance of the bypass capacitor is set to 10 pF or less. The capacitor used here may be a feedthrough type capacitor, in which the output terminal of the transistor passes through the feedthrough type bypass capacitor and is electrically connected, and the other end of this bypass capacitor is electrically connected to the ground terminal. The configuration may be changed.

In addition, a pyroelectric element that detects infrared rays selectively incident by an optical filter, a bias resistor that is connected in parallel to these pyroelectric elements, and a gate that is connected to one end of these parallel circuits. In a pyroelectric infrared detector including a transistor having a terminal and a ground terminal connected to the other end of the parallel circuit, the input capacitance of the transistor may be 10 pF or less.

[0009]

[Action]

 According to claim 1, since a bypass capacitor having a capacitance of 10 pF or less is provided between the output terminal of the transistor and the ground terminal, high-frequency electromagnetic waves that become noise for the infrared detector pass through the bypass capacitor. Then grounded. Therefore, no high frequency noise is output, and only an output corresponding to an electromagnetic wave (that is, an infrared ray) having a desired frequency component is obtained. Further, as described in claim 2, a hollow ring-shaped feedthrough type bypass capacitor is used, and the bypass capacitor is pierced and electrically connected to the output terminal of the transistor, and the other end of the bypass capacitor is connected to the ground terminal. By electrically connecting, the capacitor can be installed with an extremely simple structure, and even if the lead terminal of the inner lead part serves as an antenna and absorbs high frequency noise, this noise can be blocked by the feedthrough capacitor.

FIGS. 6 and 7 show the circuit configuration shown in FIG. 3 (the configuration shown in FIG. 1 is used for the pyroelectric infrared detector) to intermittently interrupt high-frequency electromagnetic waves near the pyroelectric infrared detector. 6 is a graph showing an output waveform from a circuit output end when a signal is transmitted in a static manner. Fig. 6 shows the output waveform when an electromagnetic wave of 980 MHz is output at 2.5 V at a distance of 50 cm from the detector, and Fig. 7 is an electromagnetic wave of 600 MHz with an output of 1.5 V, which is the same for the detector. The output waveform when the signal is transmitted at a distance of 50 cm from is shown. In each figure, P indicates the transmission status of electromagnetic waves, and the transmission is turned on and off several times. In the figure, A is the output waveform when the bypass capacitor is not attached, B is the output waveform when the 20 pF bypass capacitor is attached, and C is the output waveform when the 10 pF bypass capacitor is attached. D in the figure is an output waveform when a 1 pF bypass capacitor is attached. From each of these graphs, it can be understood that when a bypass capacitor of about 10 pF or less is inserted, high frequency noise is removed and a stable output is obtained.

According to the third aspect, since the input capacitance of the transistor is set to a value of 10 pF or less, high-frequency electromagnetic waves that become noise for the infrared detector are grounded as in the above configuration. Therefore, the high frequency noise is not output, and only the output corresponding to the electromagnetic wave (that is, infrared ray) of the desired frequency component is obtained. FIG. 8 shows comparative data with this configuration. Fig. 8 shows the circuit configuration shown in Fig. 3 in which high-frequency electromagnetic waves are emitted intermittently near the pyroelectric infrared detector by using FETs with different input capacitances without installing bypass capacitors. It is a graph which shows the output waveform from the circuit output end in the case. FIG. 8 shows an output waveform when an electromagnetic wave of 980 MHz at 2.5 V is emitted at a distance of 50 cm from the detector. In the figure, P indicates the transmission status of the electromagnetic wave, and the transmission is turned on and off several times. In the figure, A is the output waveform when an FET with an input capacitance of 20 pF is used, B in the figure is the output waveform when an FET with an input capacitance of 10 pF is used, and C in the figure is the case where a 1 pF bypass capacitor is attached. Is an output waveform of. From this graph, it can be understood that when an FET having an input capacitance of about 10 pF or less is used, high frequency noise is removed and a stable output is obtained.

[0012]

【Example】

 An embodiment according to the present invention will be described with reference to the drawings, taking a pyroelectric infrared detector as an example. FIG. 1 is a sectional view of a pyroelectric infrared detector. The pyroelectric substrate 1 is made of lead titanate-based pyroelectric ceramic, is polarized in the plate thickness direction, and is cut into a rectangular shape. Although not shown, two metal film electrodes (Cr or Ni—Cr, etc.) for light reception are provided at a predetermined interval on the surface of the pyroelectric substrate 1, and the metal film electrodes for light reception are provided on the back surface. A metal film electrode (Ag or the like) corresponding to the film electrode is provided. The electrodes for receiving light are commonly connected.

The pyroelectric substrate 1 is mounted on a printed wiring board 2 on which printed wiring is provided, with supports 61 and 62 interposed therebetween. Further, on the back surface of the printed wiring board 2, circuit components 21 and 22 such as FETs and resistors forming an external circuit are attached, and necessary electrical connection is made with the pyroelectric substrate. In the base 3, lead terminals 31 and 32 are planted in a metallic shell 3a via insulating glass, and a lead terminal 33 is planted in a state of being electrically connected to the shell 3a. The lead terminal 33 becomes a ground terminal. The lead terminal 32 serves as an output terminal of a transistor which will be described later, and a bypass capacitor is attached to a protruding portion of the lead terminal 32 from the base. This bypass capacitor is a hollow ring-shaped through type, and electrodes are formed on the inner peripheral portion and the outer peripheral portion, respectively, and the inner peripheral portion is a lead terminal 32 and the outer peripheral portion is a shell 3a (conducts with the lead terminal 33). Are connected to each other). An example of connection of this feedthrough type bypass capacitor is shown in the perspective view of FIG. After the bypass capacitors are mounted on the lead terminals, the printed wiring board is mounted on the lead terminals to make the necessary electrical connections. It should be noted that the bypass capacitor may be configured such that a chip capacitor or the like is mounted on the printed wiring board.

The cap 4 that seals each of these components is made of metal, and a light incident window 41 is provided on the upper surface. Although not shown, the optical filter 5 mounted inside the light incident window 41 has a frequency for transmitting only infrared rays to the front and back surfaces of a non-insulating substrate (conductor or semiconductor) such as silicon. This is a structure in which a selective insulating film is formed on at least the surface. Then, the cap 4 and the optical filter 5 are brought into contact with each other, and the conductive bonding material S1 is applied to electrically and mechanically connect the cap 4 and the optical filter. In order to improve airtightness, the cap and the optical filter may be pre-bonded with an insulative bonding material and then bonded with a conductive bonding material, if necessary. An epoxy-based bonding material S2 or the like may be applied to the upper portion of the lever conductive bonding material to enhance mechanical bonding or airtightness. As described above, the pyroelectric infrared detector is completed by mounting the printed wiring board on which the pyroelectric substrate is mounted on the base and hermetically sealing with the cap.

FIG. 3 is a circuit diagram of the pyroelectric infrared detector described above. The bias resistor R is connected in parallel to the pyroelectric elements 11 and 12 that are wired in series so that the spontaneous polarization characteristics are opposite to each other. , One end of these parallel circuits is connected to the gate terminal of the FET Tr for impedance conversion, and the other end is connected to the ground terminal G. The source terminal of the FET Tr is connected to the ground terminal G via the capacitor C. This ground terminal is grounded. By setting the capacitance of the capacitor C to 10 pF or less, the high frequency component that becomes noise is grounded and is not output from the FET Tr.

Further, in the circuit configuration shown in FIG. 3, even when the bypass capacitor is not attached, by setting the input capacitance of the FET Tr to 10 pF or less, the high frequency component which also becomes noise is grounded and is not output from the FET Tr. .

As shown in FIG. 4, the optical filter attached to the pyroelectric infrared detector is notched on the pyroelectric element side in the vicinity of the outer periphery thereof, and the non-insulating substrate 51 under the insulating film 52 is It is also possible to form a notch 5a that is exposed and has a thin portion and a thick portion, and apply a conductive bonding material to this portion. With this configuration, it is possible to more effectively prevent the intrusion of high frequency noise, and further prevent malfunctions in combination with the action of the high frequency noise filter by the capacitor or the like. Further, if the capacitance of the bypass capacitor or the input capacitance of the transistor is approximately 10 pF or less, high frequency noise can be reduced, but if this value is 1 pF or less, for example, approximately 0.5 pF, the same effect can be expected.

[0018]

[Effect of device]

 According to the present invention, the high-frequency electromagnetic wave that becomes noise for the infrared detector passes through this bypass capacitor and is grounded, so that high-frequency noise is not output and it corresponds to the electromagnetic wave of the desired frequency component (that is, infrared rays). Only output is available. As a result, unnecessary electromagnetic waves that become noise can be sufficiently grounded, and even when high-frequency electric field noise with a large transmission output from mobile communication equipment, which has been rapidly increasing in recent years, is incident on this infrared ray detector. Therefore, a pyroelectric infrared detector with few malfunctions can be obtained.

Further, when the bypass capacitor is a hollow ring-shaped through type as described in claim 2, the bypass capacitor can be installed with a very simple structure in manufacturing, and the inner capacitor can be installed. Even if the lead terminal of the lead part serves as an antenna and absorbs high frequency noise, this noise can be blocked by a through-type capacitor. Therefore, a pyroelectric infrared detector with less malfunction can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a pyroelectric infrared detector according to the present invention.

FIG. 2 is a perspective view showing an installation example of a capacitor.

FIG. 3 is a diagram showing a pyroelectric infrared detection circuit according to the present invention.

FIG. 4 is a sectional view showing another embodiment according to the present invention.

FIG. 5 is a sectional view showing a conventional example.

FIG. 6 is a diagram showing comparative data.

FIG. 7 is a diagram showing comparative data.

FIG. 8 is a diagram showing comparative data.

[Explanation of symbols]

1, 71 Pyroelectric substrate 2, 72 Printed wiring board 3, 73 Base 31, 32, 33, 731, 732, 733 Lead terminal 4, 74 Cap 5, 75 Optical filter 5a Cutout portion BC Bypass capacitor

Claims (3)

[Scope of utility model registration request] 1. A pyroelectric element for detecting infrared rays selectively incident by an optical filter, a bias resistor connected in parallel to these pyroelectric elements, and a gate terminal connected to one end of these parallel circuits. In a pyroelectric infrared detector consisting of a transistor and a ground terminal connected to the other end of the parallel circuit, the output terminal of the transistor is connected to the ground terminal via a bypass capacitor, and the bypass capacitor 10p capacity
A pyroelectric infrared detector characterized by being set to F or less. 2. The bypass capacitor is a hollow ring-shaped feedthrough type, the output terminal of the transistor penetrates the feedthrough type bypass capacitor and is electrically connected, and the other end of the bypass capacitor is electrically connected to the ground terminal. The pyroelectric infrared detector according to claim 1, wherein the pyroelectric infrared detector is registered as a utility model. 3. A pyroelectric element for detecting infrared rays selectively incident by an optical filter, a bias resistor connected in parallel to these pyroelectric elements, and a gate terminal connected to one end of these parallel circuits. A pyroelectric infrared detector comprising a transistor and a ground terminal connected to the other end of the parallel circuit, wherein the input capacitance of the transistor is 10 pF or less.