Pyroelectric infrared detector and integrated circuit

Abstract

A pyroelectric infrared detector (10) comprising: a housing (11); one or more pyroelectric elements (21) housed in the housing (11); and an integrated circuit (25) housed in the housing (11) and performing processing of a detection signal based on an output of the pyroelectric element (21), the pyroelectric infrared detector (10) being characterized in that: the integrated circuit (25) comprises: a converter (27) which converts the detection signal from analog to digital; a signal processor (29) which performs signal processing by means of a digital filter for the detection signal converted into a digital signal; and an input-output controller (32) which supplies output data from the signal processor (29) to an external device (15) via serial data communication, and wherein a The cutoff frequency of the digital filter can be adjusted and changed by applying a voltage to the integrated circuit (25) or by a command supplied by the external device (15) via serial data communication.

Description

Technical field

[0001] The present invention relates to infrared (IR) detection, and more particularly to a pyroelectric infrared detector including an integrated circuit (IC) and the integrated circuit. background

[0002] In recent years, due to the development of wireless communication technologies, various electronic devices have been equipped with wireless communication functions. Furthermore, devices with wireless communication functions, which can be miniaturized and battery-operated, have become remarkably popular. A pyroelectric infrared detector is often incorporated into such an electronic device so that the electronic device can operate only when a person or animal that the electronic device is intended to detect is present, in order to save energy. A pyroelectric infrared detector is a device in which a pyroelectric element is housed in a housing equipped with a window for transmitting infrared rays.The pyroelectric infrared detector installed in such an electronic device is often equipped with an integrated circuit, as disclosed in Patent Documents 1 to 4. By incorporating an integrated circuit, it is possible to achieve miniaturization of the electronic device equipped with a pyroelectric infrared detector. Furthermore, a signal processing circuit is arranged inside the pyroelectric infrared detector, which is made of a metal casing, thus reducing the influence of external electromagnetic noise. Pyroelectric infrared detectors with built-in integrated circuits are used in a wide variety of devices and systems, in addition to devices with wireless communication functions.

[0003] The integrated circuits built into pyroelectric infrared detectors include, for example, a converter that converts the detection signal received from the pyroelectric element into an analog-to-digital signal, and a signal processor that noise-reduces and processes the detection signal converted into a digital signal. Noise reduction is achieved, for example, by digital filtering with a specific cutoff frequency. Another type of integrated circuit includes an amplifier that amplifies the detection signal received from the pyroelectric element with a constant gain; and a converter that performs analog-to-digital conversion of the detected signal after amplification. The integrated circuit performs noise reduction and calculation according to a fixed rule on the detection signal converted into a digital signal and outputs the result to the outside world.

[0004] As an output form of the integrated circuit, there is one in which the detection signal is converted into a digital signal and then signal-processed. A constant detection determination threshold is applied to the converted and signal-processed detection signal to determine whether an object to be detected, such as a human body or an animal, is detected or not. Then, only the information of whether it has been detected or not is output as a binary signal. Alternatively, there is another form in which the detection signal, converted into a digital signal and signal-processed, is output in accordance with an interface standard specific to the manufacturer of the pyroelectric infrared detector.These output forms allow the external device to which the pyroelectric infrared detector is connected to receive and use the detection signal in digital form without providing an analog circuit to process the detection signal.

[0005] KR 10 2000 0 067 627 A describes a signal processing circuit for a thermal imaging detector element. Citation listPatent literature Patent Document 1: JP 2012-225763A Patent Literature 2: JP 2013-524178A Patent Document 3: JP 2016-70694A Patent Document 4: JP 2016-186478A Summary of the inventionTechnical problem

[0006] In a pyroelectric infrared detector, it is necessary to perform filtering on the detection signal based on the output of the pyroelectric element to filter out only the signal components of the object to be detected. Pyroelectric infrared detectors detect various objects such as human bodies, animals, machinery, or flames that move at different speeds and emit infrared wavelengths. Therefore, to extract only the signal components of a detected object, it is necessary to set an appropriate cutoff frequency during filtering according to the object to be detected and the application. However, conventional pyroelectric infrared detectors with digital output have a fixed cutoff frequency, which is unsuitable for some applications.In addition, with the conventional pyroelectric infrared detectors with digital output, it is necessary to provide an input / output (I / O) port for each of the pyroelectric infrared detectors individually when multiple pyroelectric infrared detectors are connected to an external device containing an external integrated circuit.

[0007] The object of the present invention is to provide a pyroelectric infrared detector that can cope with various objects to be detected and various applications and that can prevent an increase in the number of input / output terminals in an external device that is a connection target even when a plurality of pyroelectric infrared detectors are used, and an integrated circuit that can be used in such a pyroelectric infrared detector. Solution to the problem

[0008] The pyroelectric infrared detector according to the present invention comprises: a housing; one or more pyroelectric elements housed in the housing; and an integrated circuit housed in the housing and performing processing of a detection signal based on an output of the pyroelectric element, the pyroelectric infrared detector being characterized in that the integrated circuit comprises: a converter that performs analog-to-digital conversion of the detection signal; a signal processor that performs signal processing by means of a digital filter for the detection signal converted into a digital signal;and an input-output controller that supplies output data from the signal processor to an external device via serial data communication, and wherein a cutoff frequency of the digital filter is adjustable and variable by applying a voltage to the integrated circuit or by a command supplied from the external device via serial data communication;

[0009] The integrated circuit according to the present invention is an integrated circuit that performs input and signal processing of a detection signal based on an output of a pyroelectric infrared detector, characterized in that the integrated circuit comprises: a converter that performs analog-to-digital conversion of the detection signal; a signal processor that performs signal processing by means of a digital filter for the detection signal converted into a digital signal; and an input-output controller that supplies output data from the signal processor to an external device via serial data communication, and a cutoff frequency of the digital filter is adjustable and changeable by applying a voltage to the integrated circuit or by a command supplied from the external device via serial data communication. Advantageous effects of the invention

[0010] In the present invention, since the cutoff frequency in the digital filter can be adjusted and changed by applying a voltage to the integrated circuit or by a command supplied from an external device via serial data communication, it becomes possible to adapt a single pyroelectric infrared detector to various objects to be detected and various applications. Since the pyroelectric infrared detector can communicate with an external device via serial data communication, it is possible to prevent an increase in the number of input / output terminals in an external device that is a connection target by using a technique capable of connecting a plurality of devices to a single bus line generally used in serial data communication, even when a plurality of pyroelectric infrared detectors are used. Brief description of the drawings Fig. 1 is a diagram showing the configuration of a pyroelectric infrared detector according to a first embodiment; Fig. 2 is a diagram showing an example of the frequency characteristics in digital filter processing; Fig. 3 is a timing chart for explaining the operation of a maximum value holding unit; Fig. 4 is a timing diagram for explaining the operation of a detection discriminator; and Fig. 5 is a diagram showing the connection of a plurality of pyroelectric infrared detectors in the second embodiment. Description of the Embodiments[First Embodiment]

[0011] Embodiments of the present invention will be described below with reference to the drawings. Fig. Figure 1 shows an internal configuration of a pyroelectric infrared detector according to a first embodiment of the present invention. This pyroelectric infrared detector 10 is used to detect an object to be detected and transmit the detection result to an external device 15. The external device 15 is located outside the pyroelectric infrared detector 10 and is, for example, an integrated circuit or various devices.

[0012] The pyroelectric infrared detector 10 is a device in which one or more pyroelectric elements 21 and an integrated circuit 25 for processing the detection signal received from the pyroelectric element 21 are hermetically housed in a housing 11 made of, for example, metal. A window 12 is formed in the housing 11 to allow infrared rays to pass into the interior of the housing 11. The pyroelectric element 21 is arranged to receive the infrared rays transmitted through the window 12. In the illustrated example, a pyroelectric element 21 is provided. A resistor 22 with a high resistance value is connected in parallel with the pyroelectric element 21.Furthermore, an impedance converter element 23 is connected to one end of the pyroelectric element 21, and a filter circuit 24, which is an analog low-pass filter for reducing high-frequency noise, is provided between the impedance converter element 23 and the integrated circuit 25. In the example shown, a source-follower circuit with a field-effect transistor is used as the impedance converter element.

[0013] The integrated circuit 25 includes: an amplifier 26 that amplifies the detection signal supplied by the pyroelectric element 21 via an impedance converter element 23, and a filter circuit 24; a converter 27 that performs analog-to-digital conversion of the detection signal after amplification; a signal processor 29 that digitally filters the detection signal converted into a digital signal; and an input / output controller 32 that supplies the output data of the signal processor 29 to an external device 15 via serial data communication. In the example shown, two input / output terminals 33 and 34, called "Pin A" and "Pin B," are provided in the pyroelectric infrared detector 10 for serial data communication. The input / output terminals 33 and 34 are both connected to the input / output controller 32.If the detection signal provided by the pyroelectric element 21 is sufficiently large or if a ΔΣ converter is used for analog-to-digital conversion, the amplifier 26 is not necessarily required. Furthermore, the pyroelectric infrared detector 10 is equipped with: a power supply terminal 35 that supplies the integrated circuit 25 with the supply voltage VDD; and a ground terminal 36 that connects the integrated circuit 25 to the ground potential GND and is electrically connected to the housing 11.

[0014] Here, the serial data communication used for connection with the external device 15 will be described. As the communication scheme of the serial data communication in the present invention, various types of schemes such as synchronous serial data communication and asynchronous serial data communication can be used, but a communication scheme capable of connecting a plurality of slave devices to a bus line used for serial data communication is preferably used. An example of such a system is the I2C (Inter-Integrated Circuit) system. "I2C" may also be referred to as "I 2C". When using the I2C system, the external device 15 is used as the master device, the pyroelectric infrared detector 10 is used as the slave device, one of the input / output ports 33 and 34 is used as a port for bidirectional serial data transmission, and the other is used to receive a serial clock (SCL) from the master device. Unlike the I2C system, there is a scheme in which one of the input / output ports 33 and 34 is used for serial data communication, and the other is used to transmit a trigger signal or an interrupt signal from the pyroelectric infrared detector 10 to the external device 15.

[0015] The digital filtering in the signal processor 29 serves to extract only the components of the object to be detected from the detection signal of the pyroelectric element 21. External electromagnetic noise and sudden noise due to an abrupt change in ambient temperature are also eliminated by this digital filtering process. Various objects such as a human body, an animal, a machine, or a flame are considered to be the object to be detected by the pyroelectric infrared detector 10, and these objects differ in the moving speed and the wavelength of the emitted infrared rays. The object to be detected may not be detected correctly if the cutoff frequency of the digital filtering processing is not adjusted or changed according to the application of the pyroelectric infrared detector 10.Therefore, the pyroelectric infrared detector 10 according to the present embodiment is configured so that the cutoff frequency in the digital filter processing can be set and changed by applying a voltage to a setting input pin (not shown) provided in the integrated circuit 25 or by a command supplied to the input-output controller 32 via serial data communication from the external device 15. When the cutoff frequency is set and changed by applying a voltage to the integrated circuit 25, it can be configured so that the cutoff frequency can be set and changed in multiple stages depending on the applied voltage.When the serial data communication scheme is the I2C system, it is easy to send and receive commands to set and change the cutoff frequency, and it is possible to set any cutoff frequency characteristics based on the command. In the example shown in . Fig. 1, the command sent by the serial data communication of the I2C system is converted into a set value in the input / output controller 32, and then the set value is supplied to the signal processor 29.

[0016] Fig. 2 shows an example of the frequency characteristics of the digital filter implemented by the signal processor 29. As shown, it is advantageous that the cutoff characteristic 41 on the lower frequency side and the cutoff characteristic 42 on the upper frequency side can be set and changed independently of each other. By individually setting the cutoff characteristics 41 in the lower frequency range and the cutoff characteristic 42 in the upper frequency range in accordance with the application of the pyroelectric infrared detector 10, it is possible to improve the detection performance of the object to be detected and suppress false alarms due to the detection of an object that is not the object to be detected.

[0017] In the pyroelectric infrared detector 10, the level of the detection signal generated when the pyroelectric element 21 receives infrared rays largely depends on the shape of a light-receiving electrode provided in the pyroelectric element 21 and the amount of energy of the received infrared rays. Therefore, if the dynamic range of the analog-to-digital conversion in the converter 27 is too large compared to the level of the detection signal, the resolution of the analog-to-digital conversion is effectively reduced. This leads to a reduction in detection performance when attempting to detect a minute movement with a small change in the amount of infrared energy or when detecting an object to be detected at an ambient temperature corresponding to the surface temperature of the object to be detected.To improve detection performance, it is necessary that the dynamic range in analog-to-digital conversion correspond to the level of the detection signal and the amount of its change. Therefore, in the pyroelectric infrared detector 10 according to the present embodiment, it is advantageous that the gain of the detection signal in the amplifier 26 and / or the dynamic range of the analog-to-digital conversion by the converter 27 can be changed by applying a voltage to a setting input pin (not shown) provided in the integrated circuit 25 or by a command supplied to the input-output controller 32 via serial data communication from the external device 15. In the embodiment shown in FIG. Fig. In the device shown in Figure 1, the command sent via the serial data communication of the I2C system is converted into a setting value in the input-output controller 32. The integrated circuit 25 is equipped with an adjustment unit 28 to adjust and change the gain of the amplifier 26 and the dynamic range of the converter 27 based on the set value.

[0018] By making the gain of amplifier 26 and / or the dynamic range of converter 27 variable and adjustable, the resolution of the analog-to-digital conversion for the detection signal will not be insufficient even when the infrared energy incident on pyroelectric element 21 is small or even when the movement of the object to be detected is minute, and the detection signal can be converted into a digital signal without deteriorating the detection resolution regardless of the size of the detection signal. Thus, the detection performance can be maintained or improved, and high detection performance can be achieved for fine movements of the object to be detected.

[0019] When the I2C system is used as a communication scheme of serial data communication, the external device 15 becomes a master device and the pyroelectric infrared detector 10 becomes a slave device, the external device 15 sends a data request to the pyroelectric infrared detector 10, and in response to the data request, the integrated circuit 25 of the pyroelectric infrared detector 10 transmits the detection data to the external device 15. Since an interval of the data request is determined by software or the like executed by the external device 15, if the data request interval is too long, the transmission of the detection signal by an object to be detected to the external device 15 side may fail.When the pyroelectric infrared detector 10 is installed in a battery-powered device, it is effective to reduce the frequency of data requests from an external integrated circuit, which is the external device 15, to the pyroelectric infrared detector 10 for energy saving. However, by reducing the frequency of data requests, it is possible to miss an originally required detection signal, that is, there is a possibility of alarm loss. Energy saving and alarm loss are in conflict. Therefore, it is advantageous that the integrated circuit 25 be provided with a maximum value hold unit 30 for holding the maximum oscillation width of the detection signal processed by the signal processor 29 during a period when there is no data request and the oscillation direction of the detection signal at that time.

[0020] Fig. Figure 3 describes the operation of the maximum value hold unit 30. Although the temporal change of the detection signal 43 processed by the signal processor is represented by a graph here, the detection signal 43 is actually in the form of time-varying digital data. The maximum value 44 of the detection signal 43 is stored in the maximum value hold unit 30. When the data request 45 is supplied from the external device 15, the transmission of the maximum value data 46 to the external device 15 is performed at the time of the data request 45. By providing a maximum value hold unit 30 that holds the maximum value of the detection signal in this way, it is possible to confirm the maximum value of the detection signal due to the detection of the object to be detected even if the interval of the data request from the external device 15 is long, and it is possible to save power and prevent the loss of an alarm.Here, the maximum value holding unit 30 holds the maximum value 44 at the time when the detection signal changes in a positive direction, that is, the detection signal oscillates in the positive direction. Since the detection signal 43 may change in the negative direction when the object to be detected is detected, the maximum oscillation width in the positive direction or the maximum oscillation width in the negative direction of the detection signal is processed into an absolute value, and then the absolute value and oscillation direction of the direction signal at this time are held in the maximum value holding unit 30.

[0021] From the perspective of energy saving of the device in which the pyroelectric infrared detector 10 is installed, it is effective to keep the device in a sleep state during normal hours and operate the device only when the pyroelectric infrared detector 10 has determined that the object to be detected is detected. To realize such operation, it is advantageous for the integrated circuit 25 to be provided with a detection discriminator 31 that compares the detection signal processed by the signal processor 29 with a threshold value to make a detection determination of the object to be detected. The detection discriminator 31 outputs a trigger signal or an interrupt signal to the external device 15 via the input / output controller 32 when the detection discriminator 31 determines that the object to be detected has been detected.

[0022] Fig. Figure 4 is a diagram illustrating the operation of the detection discriminator 31. The detection signal of the pyroelectric element 21 can change not only in the positive direction but also in the negative direction, depending on the movement direction of the object to be detected. Therefore, an upper limit threshold value 51 and a lower limit threshold value 52 are set in the detection discriminator 31 for the detection signal 43 processed by the signal processor 29. The detection discriminator 31 compares the detection signal 43 with the threshold values 51 and 52 and outputs the trigger signal 53 or the interrupt signal when the detection signal 43 exceeds the upper limit threshold value 51 or falls below the lower limit threshold value 52.Preferably, the threshold values 51 and 52 can be changed by applying a voltage to a setting input pin (not shown) provided in the integrated circuit 25 or by a command supplied to the input-output controller 32 from the external device 15 through serial data communication. When the external device 15 to which the pyroelectric infrared detector 10 is connected is an integrated circuit or the like serving as a connection interface with the pyroelectric infrared detector 10 in a device in which the pyroelectric infrared detector 10 is installed, it is possible to restart the device from the sleep state only when the trigger signal or the interrupt signal from the detection discriminator 31 is present. In this way, the power consumption of the device in which the pyroelectric infrared detector 10 is installed can be reduced.When the integrated circuit 25 is equipped with a maximum value holding unit 30, the external device 15, which has been restarted from the sleep state by the trigger signal or the interrupt signal, can send a data request to the pyroelectric infrared detector 10 and obtain the absolute value of the maximum oscillation width and the oscillation direction of the detection signal stored in the maximum value holding unit 30. [Second embodiment]

[0023] Since the pyroelectric infrared detector 10 according to the first embodiment can be connected to the external device 15 via a serial data communication bus line, a plurality of pyroelectric infrared detectors 10 can be connected to one external device 15. Fig.5 shows an example in which a plurality of pyroelectric infrared detectors 10 according to the first embodiment are connected to an external device 15. Here, it is assumed that the I2C system is used as the communication scheme for serial data communication. In the illustrated example, an external device 15, which is a master device, is connected to the bus line 54 of the I2C system, and three pyroelectric infrared detectors 10, which are slave devices, are connected to the bus line. The bus line 54 consists of a serial data signal line (SDA) and a serial clock signal line (SCL). Each pyroelectric infrared detector 10 is assigned a unique access address according to the I2C standard.To facilitate individual identification when the pyroelectric infrared detector 10 is installed, the access address of the pyroelectric infrared detector 10 is printed or marked on the casing 11 of the pyroelectric infrared detector 10 so that it is visible. The number of pyroelectric infrared detectors 10 that can be connected to the bus line 54 at the same time is not limited to three, and more pyroelectric infrared detectors 10 can be connected to the bus line 54. By using the pre-stored access address of the pyroelectric infrared detector 10, the external device 15 can perform individual identification of the pyroelectric infrared detector 10 connected to the bus line 54 to access the desired pyroelectric infrared detector 10.

[0024] Even if the I2C system is used as the serial data communication scheme, the external device 15 can receive the trigger signal or the interrupt signal via the bus line 54 at the time when one of the pyroelectric infrared detectors 10 connected to the bus line 54 detects an object to be detected. The external device 15 can send a data request 45 to each pyroelectric infrared detector 10 in such a way that the access addresses are scanned to detect the data held in the maximum value holding unit 30 of each pyroelectric infrared detector 10.

[0025] According to the second embodiment, in each pyroelectric infrared detector 10, it is possible to remove external electromagnetic noise or the like without affecting the quality of the detection signal from the pyroelectric element 21, and to process the detection signal appropriately. A plurality of pyroelectric infrared detectors 10 can be connected to the same bus line 54. Therefore, an inexpensive component with a reduced number of input / output terminals, i.e., pins, can be used as the external device 15 for connection to the pyroelectric infrared detectors 10. Reference character list 10 Pyroelectric infrared detector; 11 housings; 12 windows; 15 External device; 21 Pyroelectric element; 23 Impedance converter element; 25 Integrated circuit; 26 amplifiers; 27 converters; 28 adjustment unit; 29 signal processor; 30 maximum value holding unit; 31 detection discriminator; and 32 Input-output control.

Claims

[1] A pyroelectric infrared detector (10) comprising: a housing (11); one or more pyroelectric elements (21) housed in the housing (11); and an integrated circuit (25) housed in the housing (11) and performing processing of a detection signal based on an output of the pyroelectric element (21), the pyroelectric infrared detector (10) characterized by is that: the integrated circuit (25) comprises: a converter (27) which converts the detection signal from analog to digital; a signal processor (29) which performs signal processing by means of a digital filter for the detection signal converted into a digital signal; and an input-output controller (32) which supplies output data from the signal processor (29) to an external device (15) via serial data communication, and wherein a The cutoff frequency of the digital filter can be adjusted and changed by applying a voltage to the integrated circuit (25) or by a command supplied by the external device (15) via serial data communication. [2] Pyroelectric infrared detector (10) according to claim 1, wherein the cutoff frequency of the digital filter on a high frequency side and the cutoff frequency of the digital filter on a low frequency side are individually adjustable. [3] Pyroelectric infrared detector (10) according to claim 1 or 2, wherein a dynamic range of the analog-to-digital conversion in the converter (27) is variable by applying a voltage to the integrated circuit (25) or by a command supplied from the external device (15) via the serial data communication. [4] Pyroelectric infrared detector (10) according to one of claims 1 to 3, wherein the integrated circuit (25) includes an amplifier (26) provided in a front stage of the converter (27) and amplifying the detection signal, and wherein a gain of the amplifier (26) can be changed by applying a voltage to the integrated circuit (25) or by a command supplied by the external device (15) via the serial data communication. [5] Pyroelectric infrared detector (10) according to one of claims 1 to 4, wherein the integrated circuit (25) includes a maximum value holding unit (30) which holds an absolute value of a maximum oscillation width in a positive or negative direction of the detection signal processed by the signal processor (29) and a polarity of the detection signal according to the absolute value, and wherein the integrated circuit (25) transmits a current value of the detection signal and the maximum value held in the maximum value holding unit (30) to the external device (15) in response to a data request from the external device (15). [6] Pyroelectric infrared detector (10) according to one of claims 1 to 5, wherein the integrated circuit (25) includes a detection discriminator (31) which compares the detection signal processed by the signal processor (29) with a threshold value to perform a detection discrimination of an object to be detected, and supplies a trigger signal or an interrupt signal to the external device (15) according to a result of the detection discrimination, and wherein the threshold value can be changed by applying a voltage to the integrated circuit (25) or by a command supplied by the external device (15) via serial data communication. [7] Pyroelectric infrared detector (10) according to one of claims 1 to 6, wherein an access address for specifying the pyroelectric infrared detector (10) is set in the serial data communication and the access address is visibly printed or stamped on the pyroelectric infrared detector (10). [8] Pyroelectric infrared detector (10) according to claim 7, wherein the serial data communication is an I2C type serial data communication and individual identification of the pyroelectric infrared detector (10) is possible by the access address when a plurality of pyroelectric infrared detectors (10) are connected to a single I2C bus line (54). [9] A pyroelectric infrared detector (10) according to claim 6, wherein the serial data communication is an I2C type serial data communication and the trigger signal or interrupt signal supplied from the detection discriminator (31) is supplied to the external device (15) using a single I2C bus line (54). [10] Integrated circuit (25) which performs the input and signal processing of a detection signal based on an output of a pyroelectric infrared detector (10), characterized by , that the integrated circuit (25) comprises: a converter (27) which converts the detection signal from analog to digital; a signal processor (29) which performs signal processing by means of a digital filter for the detection signal converted into a digital signal; and an input-output controller (32) which supplies output data from the signal processor (29) to an external device (15) via serial data communication, and wherein a The cutoff frequency of the digital filter can be adjusted and changed by applying a voltage to the integrated circuit (25) or by a command supplied by the external device (15) via serial data communication.

Images