WO2013027768A1 - Detection circuit, and infrared detection device - Google Patents

Abstract

　This detection circuit is provided with a converter circuit and an output circuit. The converter circuit is configured to receive an electric current signal from a pyroelectric element via an input terminal and to convert the received electric current signal into a voltage signal. The output circuit is configured to receive the voltage signal from the converter circuit, compare the size of the received voltage signal to a prescribed threshold value, and output a detection signal via an output terminal when the size of the voltage signal exceeds the prescribed threshold value. The detection signal is a one-shot pulse.

Description

Detection circuit and infrared detection device

The present invention relates to a detection circuit and an infrared detection device using a pyroelectric element.

In recent years, various electrical devices that detect the movement of the human body and perform an efficient operation have been proposed for the purpose of saving energy.

For example, such an electric device incorporates an infrared detector using a pyroelectric element as an infrared detector. A general infrared detection device collects infrared rays from the detection area using a lens or the like into a pyroelectric element, and a current signal output from the pyroelectric element in response to a change in the amount of infrared light received by the pyroelectric element. Changes.

As this type of infrared detection apparatus, an apparatus including a pyroelectric element and an infrared detection circuit that performs signal processing on a detection current signal of the pyroelectric element is known (for example, Reference 1 [Japan Published Patent Publication No. 2003). -227773]]).

In the infrared detection device described in Document 1, the infrared detection circuit includes a current-voltage conversion circuit that converts a current signal from a pyroelectric element into a voltage signal, a voltage amplification circuit, a bandpass filter circuit, and a bandpass filter circuit. And an output circuit connected to the output side.

In Document 1, the current-voltage conversion circuit includes an operational amplifier having a pyroelectric element connected to the inverting input terminal, and a feedback capacitor connected between the output terminal and the inverting input terminal of the operational amplifier. Yes. This current-voltage conversion circuit converts a current signal having a frequency component that is important for detection of a human body, out of the current signal output from the pyroelectric element, into a voltage signal using a capacitor.

The voltage amplification circuit amplifies the voltage signal output from the current-voltage conversion circuit.

The band-pass filter circuit outputs a voltage signal in a frequency band that is important for detecting a human body with a predetermined gain.

The output circuit is composed of, for example, a comparator, compares the voltage signal output from the bandpass filter circuit with a predetermined threshold level, and outputs a detection signal when the voltage signal is equal to or higher than the threshold level.

Incidentally, there is a demand for further downsizing and simplification of the structure of the infrared detection device, and the adverse effect is that the influence of capacitive coupling generated between the input and output of the infrared detection circuit may be a problem. In other words, the infrared detection circuit is caused by the fact that the physical distance between the input and output is shortened with the miniaturization of the entire infrared detection device, and the insulation performance between the input and output is lowered with the simplification of the structure. As a result, the capacitance of capacitive coupling generated between the input and output increases.

Here, in the infrared detection circuit, an inverting amplifier circuit is formed by an operational amplifier and a conversion element (such as a resistor or a capacitor) of the current-voltage conversion circuit and capacitive coupling between the input and output as viewed from the output end. For example, when a current-voltage conversion circuit is configured by using a feedback capacitor as a conversion element, the infrared detection circuit increases Cx / Cf times from the output terminal to the input of the voltage amplification circuit when the capacitance of capacitive coupling increases. Detection signal wraps around. Here, Cx is a capacitance of capacitive coupling, and Cf is a capacitance of a capacitor (conversion element) in the current-voltage conversion circuit.

As described above, when the influence of the capacitive coupling between the input and output of the infrared detection circuit cannot be ignored in the infrared detection device, a signal wraps around from the output end to the input end of the infrared detection circuit. In addition, chattering or oscillation may occur in the detection signal.

In FIG. 16, (a) represents the voltage signal V0 input to the output circuit (that is, output from the bandpass filter circuit), and (b) represents the detection signal S1 output from the output circuit. Yes. In the example of FIG. 16, the output circuit compares the voltage signal V0 with the threshold value using threshold values VH1 and VL1 with hysteresis instead of a fixed threshold value.

The present invention has been made in view of the above reasons, and an object of the present invention is to provide a detection circuit and an infrared detection device capable of suppressing the influence of capacitive coupling generated between the input and output of a circuit portion that receives the output of a pyroelectric element. And

The detection circuit according to the first aspect of the present invention includes a conversion circuit and an output circuit. The conversion circuit is configured to receive a current signal from a sensing element through an input end and convert the received current signal into a voltage signal. The output circuit receives the voltage signal from the conversion circuit, compares the magnitude of the received voltage signal with a predetermined threshold, and passes through the output terminal when the magnitude of the voltage signal exceeds the predetermined threshold. It is comprised so that a detection signal may be output. The detection signal is a one-shot pulse.

In the detection circuit of the second form according to the present invention, in the first form, the conversion circuit is configured to amplify the electric signal which is the current signal or the voltage signal. The conversion circuit has a gain equal to or higher than a predetermined value with respect to a component of the electric signal having a frequency included in a specific frequency band and has a frequency higher than an upper limit value of the specific frequency band. Is configured to have a gain less than a predetermined value. The pulse width of the one-shot pulse is a value corresponding to a frequency higher than the upper limit value.

In the detection circuit according to a third aspect of the present invention, in the first or second aspect, the conversion circuit is configured to determine whether the magnitude of the voltage signal output to the output circuit exceeds the predetermined threshold. During the holding period, a holding operation for holding the magnitude of the voltage signal output to the output circuit at a predetermined value is executed. The length of the holding period is not less than the pulse width of the one-shot pulse.

In the detection circuit of the fourth form according to the present invention, in the third form, the holding period is longer than the pulse width of the one-shot pulse.

In the detection circuit according to a fifth aspect of the present invention, in the third or fourth aspect, the predetermined value is obtained when the magnitude of the voltage signal output to the output circuit exceeds the predetermined threshold. The magnitude of the voltage signal.

In the detection circuit according to a sixth aspect of the present invention, in any one of the third to fifth aspects, the conversion circuit is included in a specific frequency band of the electric signal that is the current signal or the voltage signal. A filter circuit that passes a component having a frequency is provided. The conversion circuit is configured to hold the magnitude of the voltage signal output to the output circuit at the predetermined value by stopping the operation of the filter circuit during the holding period.

In a detection circuit according to a seventh aspect of the present invention, in the sixth aspect, the conversion circuit includes an AD conversion unit that converts the electrical signal into a digital signal and outputs the digital signal. The filter circuit performs arithmetic processing on the digital signal to extract a component having a frequency included in the specific frequency band from a waveform indicated by the digital signal, and generates a digital signal indicating the waveform of the component. This is a digital filter to output.

In the detection circuit according to an eighth aspect of the present invention, in the seventh aspect, the AD conversion unit includes: an integrator that integrates the electrical signal; and a quantizer that quantizes the output of the integrator. It is a ΔΣ type AD converter.

In the detection circuit of the ninth form according to the present invention, in the eighth form, the AD conversion unit is configured to convert the electric signal into a digital signal and output it at a predetermined cycle. The conversion circuit is configured to restart the operation of the filter circuit in accordance with a timing at which the AD conversion unit outputs a digital signal.

In the detection circuit of the tenth aspect according to the present invention, in any one of the first to ninth aspects, the output circuit, when the magnitude of the voltage signal received from the conversion circuit exceeds a predetermined threshold value, A differential value of the magnitude of the voltage signal is obtained, and the pulse width of the one-shot pulse is shortened as the differential value increases.

In the detection circuit of the eleventh aspect according to the present invention, in any of the third to ninth aspects, when the magnitude of the voltage signal received from the conversion circuit exceeds a predetermined threshold value in the output circuit, A differential value of the magnitude of the voltage signal is obtained, and it is configured to determine whether or not the differential value exceeds a specified value. The conversion circuit is configured to end the holding operation when the output circuit determines that the differential value exceeds the specified value.

In the detection circuit according to a twelfth aspect of the present invention, in any one of the first to eleventh aspects, the conversion circuit includes a current-voltage conversion unit that converts the received current signal into a voltage signal. The current-voltage conversion unit includes an operational amplifier and a feedback capacitive element connected to the operational amplifier.

The infrared detection device according to the present invention includes a detection circuit according to any one of the first to twelfth aspects and a detection element connected to the input terminal of the detection circuit. The detection element is a pyroelectric element.

1 is a schematic circuit diagram of an infrared detection device according to Embodiment 1. FIG. 1 is a schematic block diagram of an infrared detection device according to Embodiment 1. FIG. 2 is a schematic circuit diagram of a voltage amplification unit used in the infrared detection device according to Embodiment 1. FIG. 3 is a frequency characteristic diagram of a conversion circuit used in the infrared detection device according to Embodiment 1. FIG. FIG. 3 is an output waveform diagram of a conversion circuit in the infrared detection device according to the first embodiment. It is explanatory drawing of operation | movement of the infrared detection apparatus which concerns on Embodiment 1. FIG. FIG. 3 is an output waveform diagram of a conversion circuit in the infrared detection device according to the first embodiment. It is a schematic circuit diagram which shows the 1st modification of the voltage amplification part used for the infrared rays detection apparatus which concerns on Embodiment 1. FIG. It is a schematic circuit diagram which shows the 2nd modification of the voltage amplification part used for the infrared rays detection apparatus which concerns on Embodiment 1. FIG. 6 is a schematic circuit diagram of an infrared detection device according to Embodiment 2. FIG. 6 is an explanatory diagram of an operation of an AD conversion unit used in an infrared detection device according to Embodiment 2. FIG. FIG. 5 is a schematic circuit diagram of an infrared detection device according to a third embodiment. It is explanatory drawing of operation | movement of the infrared detection apparatus which concerns on Embodiment 3. FIG. It is explanatory drawing of operation | movement of the infrared detection apparatus which concerns on Embodiment 3. FIG. FIG. 6 is a schematic circuit diagram of an infrared detection device according to a fourth embodiment. It is explanatory drawing of operation | movement of a prior art example.

(Embodiment 1)
As shown in FIG. 2, the infrared detection device 1 of the present embodiment includes a pyroelectric element 2 and a detection circuit 10 that performs signal processing on a detection current signal (current signal) of the pyroelectric element 2.

The detection circuit 10 has a conversion circuit 3 that converts a current signal output from the detection element (in this embodiment, the pyroelectric element 2) into a voltage signal, and an output value (a magnitude of the voltage signal) of the conversion circuit 3 as a predetermined value. And an output circuit 4 including a comparator 41 for comparison with the threshold value. Note that the sensing element is not necessarily the pyroelectric element 2.

Here, the detection circuit 10 is integrated into an IC (integrated circuit) without using external components, and is made into one chip.

In this embodiment, an infrared detection device 1 used for a human body detection device that detects a human body in a detection area will be described as an example. However, the infrared detection device 1 is used for purposes other than human body detection such as gas detection. It is not the purpose to prevent.

The pyroelectric element 2 receives infrared rays from the detection area and outputs a current signal according to the change in the amount of received infrared rays.

The detection circuit 10 includes an input terminal T1 and an output terminal T2. The pyroelectric element 2 is connected to the input terminal T1, and an external circuit (not shown) mainly composed of a microcomputer is connected to the output terminal T2.

The detection circuit 10 performs signal processing on the current signal from the pyroelectric element 2, and outputs a detection signal from the output terminal T2 to the external circuit when a human body is detected in the detection area. Thereby, the infrared detection apparatus 1 can output the result of the human body detection to the external circuit, and the external circuit can control the electric device according to the result of the human body detection.

As shown in FIG. 1, the conversion circuit 3 provided in the input stage of the detection circuit 10 includes a current-voltage conversion unit 5 connected to the pyroelectric element 2 and a voltage connected to the output of the current-voltage conversion unit 5. And an amplifying unit 6. Further, in the present embodiment, the conversion circuit 3 has an output holding unit 8 described later.

The current-voltage converter 5 has an operational amplifier 51 whose inverting input terminal is connected to the input terminal T1 of the detection circuit 10. That is, the inverting input terminal of the operational amplifier 51 is connected to the pyroelectric element 2. A capacitor 52 as a capacitive element for AC feedback is connected between the output terminal and the inverting input terminal of the operational amplifier 51. A non-inverting input terminal of the operational amplifier 51 is connected to a reference power supply unit 53 that generates a reference voltage.

According to the current-voltage conversion unit 5 configured as described above, the weak current signal output from the pyroelectric element 2 is converted into a voltage signal using the impedance of the capacitor 52 as the conversion element.

Therefore, the voltage output from the operational amplifier 51 is a value obtained by subtracting the voltage across the capacitor 52 from the reference voltage generated by the reference power supply unit 53. In short, the output of the current-voltage conversion unit 5 changes from the operating point according to the change of the current signal caused by the pyroelectric element 2 receiving infrared rays with the reference voltage as the operating point.

In the following, in order to simplify the description, the output of the current-voltage conversion unit 5 at the above operating point (reference voltage) is assumed to be zero. That is, hereinafter, the output of the current-voltage conversion unit 5 means the amount of change from the operating point of the voltage output from the operational amplifier 51.

The voltage amplifying unit 6 includes a non-inverting amplifier circuit having a two-stage configuration as shown in FIG.

The non-inverting amplifier circuit at the first stage (input terminal T1 side) has an operational amplifier 61 whose non-inverting input terminal is connected to the output of the current-voltage converter 5 (the output terminal of the operational amplifier 51) via the capacitor 62. is doing. A low pass filter composed of a parallel circuit of a resistor 63 and a capacitor 64 is connected between the output terminal and the inverting input terminal of the operational amplifier 61. Further, in the operational amplifier 61, a reference power supply unit 65 that generates a reference voltage is connected to a non-inverting input terminal via a resistor 66, and a reference power supply unit 67 that generates a reference voltage is connected to a resistor 68 at an inverting input terminal. Connected through.

As a result, the non-inverting amplifier circuit in the first stage forms a band-pass filter with the high-pass filter composed of the capacitor 62 and the resistor 66 and the low-pass filter composed of the resistor 63 and the capacitor 64, and gain is obtained for a specific frequency band. To amplify the voltage signal.

In this embodiment, since the infrared detection device 1 is used for human body detection, the pass band of the non-inverting amplifier circuit is set in accordance with the frequency band of the current signal generated by the pyroelectric element 2 when the presence of the human body is detected. Has been.

The second-stage (output terminal T2 side) non-inverting amplifier circuit includes an operational amplifier 71, and capacitors 72, 74 and resistors 73, 76, 78 are connected to the operational amplifier 71. The same circuit as the non-inverting amplifier circuit is constructed.

In FIG. 3, a switch 60 is inserted between the non-inverting input terminal of the first stage operational amplifier 61 and the capacitor 62 and the resistor 66, and the non-inverting input terminal of the second stage operational amplifier 71 and the capacitor 72. A switch 70 is inserted between the resistor 76 and the resistor 76.

These switches 60 and 70 will be described in detail later, but these switches 60 and 70 are on at least during the period when the voltage amplifying unit 6 functions.

Thus, the conversion circuit 3 is configured to receive a current signal from the pyroelectric element 2 through the input terminal T1 and convert the received current signal into a voltage signal.

The conversion circuit 3 is configured to amplify the voltage signal output from the current-voltage conversion unit 5. In particular, the conversion circuit 3 has a gain equal to or higher than a predetermined value with respect to a voltage signal component having a frequency included in a specific frequency band, and converts the voltage signal component having a frequency higher than the upper limit value of the specific frequency band. It is configured to have a gain less than a predetermined value.

As described above, the conversion circuit 3 performs the conversion operation for converting the current signal received from the pyroelectric element 2 into a voltage signal and the amplification operation for amplifying the voltage signal output from the current-voltage conversion unit 5. Configured as follows. In the present embodiment, the conversion operation of the conversion circuit 3 is realized by the current-voltage conversion unit 5, and the amplification operation of the conversion circuit 3 is realized by the voltage amplification unit 6.

Here, in this embodiment, it is assumed that the pyroelectric element 2 is a dual-type pyroelectric element in which two elements are arranged side by side. The pyroelectric element 2 is connected to the detection circuit 10 so that the two elements have different polarities (positive and negative), and both elements are arranged side by side so that the detection areas of the elements are adjacent to each other. Has been.

Thus, when the pyroelectric element 2 detects a change in the amount of infrared rays with one element, the current signal changes in the positive direction, and when a change in the amount of infrared rays is detected with the other element, the current signal changes in the negative direction.

For example, when a person crosses the detection area of one element and the detection area of the other element in order, the conversion circuit 3 receives a current signal that alternately swings in the positive and negative directions with reference to zero. Is done.

Therefore, the frequency band of the current signal generated by the pyroelectric element 2 when the presence of the human body is detected depends on the distance from the person to be detected to the pyroelectric element 2 and the moving speed of the person to be detected. In this embodiment, it is assumed that the frequency is about 0.1 Hz to 1 Hz.

Therefore, the voltage amplifying unit 6 has a gain higher than a predetermined value in a specific frequency band (here, about 0.1 Hz to 1 Hz), and a signal in a specific frequency band among the voltage signals output from the current-voltage conversion unit 5. Is amplified and output. In short, the conversion circuit 3 functions as a filter circuit that allows the voltage amplification unit 6 to pass a signal component in a specific frequency band, so that the conversion circuit 3 has a gain greater than a predetermined value in the specific frequency band as a whole. The output current signal is converted into a voltage signal and output. Note that the two-stage non-inverting amplifier circuit shown in FIG. 3 is merely an example of the specific configuration of the voltage amplifier 6, and the voltage amplifier 6 has the circuit configuration shown in FIG. 3 (two-stage non-inverting amplifier circuit). Is not limited to.

The output circuit 4 receives the voltage signal from the conversion circuit 3 (the voltage signal from the current-voltage conversion unit 5 amplified by the voltage amplification unit 6), and sets the magnitude (voltage value) of the received voltage signal as a predetermined threshold value. In comparison, the detection signal is output through the output terminal T2 when the magnitude of the voltage signal exceeds a predetermined threshold.

In the present embodiment, as shown in FIG. 1, the output circuit 4 includes a comparator (comparator) 41 that compares the output value of the conversion circuit 3 (the output value of the voltage amplification unit 6) with a predetermined threshold value, and an external circuit. And a pulse generator 42 for outputting a detection signal.

The comparator 41 is connected to the output of the conversion circuit 3, and the output value of the conversion circuit 3 when the pyroelectric element 2 is not receiving infrared rays, that is, when the output of the current-voltage conversion unit 5 is zero. The amount of change from zero in this output value is compared with a threshold value as zero.

Here, in this embodiment, since the pyroelectric element 2 is a dual-type pyroelectric element as described above, when the conversion circuit 3 receives a current signal from one element, the output value changes in the positive direction. When a current signal is received from the other element, the output value changes in the negative direction.

For example, when a person crosses the detection area of one element and the detection area of the other element in order, the conversion circuit 3 generates an output that swings alternately in the positive direction and the negative direction with reference to zero.

Therefore, the comparator 41 sets threshold values on both the positive and negative sides with reference to zero so that the change amount from zero of the output value of the conversion circuit 3 can be compared with the threshold value in both the positive and negative directions.

Specifically, the comparator 41 sets a positive threshold value VH1 in the positive direction and a negative threshold value VL1 in the negative direction, and the output value of the conversion circuit 3 swings from zero to the positive direction and exceeds the positive threshold value VH1. Alternatively, it is determined that the output value has exceeded the threshold value when the negative value is exceeded and the negative threshold value VL1 is exceeded. In other words, the comparator 41 determines that the output value is equal to or less than the threshold value when the output value of the conversion circuit 3 is between the positive threshold value VH1 and the negative threshold value VL1, and the output value of the conversion circuit 3 is equal to the positive threshold value VH1. It is determined that the output value has exceeded the threshold when the value deviates from the negative threshold VL1. The absolute value is the same between the positive threshold value VH1 and the negative threshold value VL1.

The comparator 41 of the present embodiment outputs a trigger signal to the subsequent pulse generation unit 42 when the output value of the conversion circuit 3 exceeds the threshold value (positive threshold value VH1, negative threshold value VL1).

Here, the comparator 41 is configured to continue outputting the trigger signal while the output value of the conversion circuit 3 exceeds the threshold value, but is not limited to this configuration. For example, the output value of the conversion circuit 3 exceeds the threshold value. Alternatively, an impulse-like trigger signal may be output at the time point.

The pulse generator 42 receives the trigger signal output from the comparator 41, and outputs a one-shot pulse having a predetermined pulse width as a detection signal to an external circuit. Specifically, the pulse generator 42 generates a one-shot pulse (single pulse) having a fixed time length (fixed pulse width) only once with the rising edge of the trigger signal as a trigger.

Here, the one-shot pulse is unipolar, and the pulse generator 42 has the same polarity and the same polarity when the threshold value is exceeded, regardless of whether the output value of the conversion circuit 3 moves in the positive direction or the negative direction. A one-shot pulse with a pulse width is output.

Here, the one-shot pulse output from the pulse generator 42 is outside a specific frequency band (about 0.1 Hz to 1 Hz) in which the conversion circuit 3 has a gain greater than a predetermined value, and is higher than this frequency band. The pulse width is set so as to be on the side (high frequency side). That is, since the conversion circuit 3 has a gain greater than or equal to a predetermined value in the specific frequency band fb1 as shown in FIG. 4, the pulse generator 42 uses the frequency band fb2 deviating from the specific frequency band fb1 to the high frequency side. The pulse width of the one-shot pulse is set so that

That is, the one-shot pulse has a pulse width corresponding to a frequency included in a frequency band in which the gain of the conversion circuit 3 is less than a predetermined value. In other words, the one-shot pulse is set in the frequency band fb2 where the conversion circuit 3 has little sensitivity.

Therefore, the infrared detection device 1 according to the present embodiment is affected even if a detection signal wraps around from the output terminal T2 to the input terminal T1 through the capacitive coupling 11 (see FIG. 1) generated between the input and output of the detection circuit 10. This prevents chattering and oscillation from occurring in the detection signal. Hereinafter, the chattering and the oscillation phenomenon in which the signal is repeatedly turned on and off are collectively referred to as “chattering or the like”.

That is, the detection circuit 10 is caused by the fact that the physical distance between the input and output is shortened with the miniaturization of the entire infrared detection device 1, and the insulation performance between the input and output is lowered with the simplification of the structure. As a result, the capacitance of the capacitive coupling 11 generated between the input and output increases. In the detection circuit 10, an inverting amplifier circuit is formed by the operational amplifier 51, the capacitor 52, and the capacitive coupling 11 when viewed from the output terminal T 2. Therefore, when the capacitance of the capacitive coupling 11 increases, the output terminal is multiplied by Cx / Cf. The detection signal may circulate from T2 to the input of the voltage amplification unit 6. Here, Cx is the capacitance of the capacitive coupling 11, and Cf is the capacitance of the capacitor 52 in the current-voltage converter 5.

In the present embodiment, the detection signal is a one-shot pulse that is higher than a specific frequency band in which the conversion circuit 3 has a gain greater than or equal to a predetermined value. Therefore, the detection signal wraps around from the output terminal T2 to the input terminal T1. Even in the case of occurrence of chattering, no chattering or the like occurs in the detection signal.

That is, the conversion circuit 3 has almost no sensitivity to the one-shot pulse (detection signal) that wraps around from the output terminal T2 to the input terminal T1, so chattering or the like occurs in the detection signal due to the one-shot pulse. Will not occur.

Therefore, the infrared detection device 1 of the present embodiment can reliably detect a human body even when the capacitance of the capacitive coupling 11 generated between the input and output of the detection circuit 10 increases.

Next, how to determine the pulse width of the one-shot pulse as the detection signal output from the pulse generator 42 will be described with a specific example.

First, if the amplitude (voltage value) of the one-shot pulse is ΔV0 and the gain of the conversion circuit 3 with respect to the frequency f of the one-shot pulse is G, the fluctuation range ΔV1 of the output value of the conversion circuit 3 due to the detection signal wraparound is , ΔV1 = ΔV0 × (Cx / Cf) × G.

When the fluctuation range ΔV1 expressed in this way exceeds a threshold value to be compared in the comparator 41, a one-shot pulse is generated in the pulse generation unit 42 using this as a trigger. Occurs.

Therefore, in the present embodiment, according to the amplitude ΔV0 of the one-shot pulse, the capacitance Cx of the capacitive coupling 11, the capacitance Cf of the capacitor 52, the gain G, and the threshold so that the fluctuation range ΔV1 does not exceed the threshold. Thus, the upper limit value of the pulse width of the one-shot pulse is set.

That is, as the capacitance Cx of the capacitive coupling 11 is larger, the upper limit value of the pulse width is smaller so that the one-shot pulse is set in the high frequency band where the gain G in the conversion circuit 3 is smaller.

The one-shot pulse as a detection signal has a frequency component on the higher frequency side than a specific frequency band by determining the pulse width within a range below the upper limit set in this way.

However, if the pulse width of the one-shot pulse as the detection signal is too small, it is difficult to distinguish the detection signal output from the output circuit 4 from noise in the external circuit connected to the output terminal T2 of the detection circuit 10.

Therefore, the pulse width of the one-shot pulse is determined so as to be within the above-described upper limit value and within a predetermined lower-limit value range. The lower limit here is set according to the internal clock of the microcomputer constituting the external circuit, and is set to, for example, twice the internal clock.

In the present embodiment, as an example, the pulse width of the one-shot pulse is set to 100 ms. Thus, the infrared detection device 1 detects when the one-shot pulse amplitude ΔV0 is 6.0V and the capacitance Cf of the capacitor 52 is several pF, and the capacitance Cx of the capacitive coupling 11 is within several fF. Chattering does not occur in the signal.

By the way, in addition to the structure which outputs the one-shot pulse mentioned above, the infrared rays detection apparatus 1 of this embodiment is detected by the influence of the capacitive coupling 11 by employ | adopting the structure which provided the output holding part 8 in the conversion circuit 3. FIG. It is possible to more reliably prevent chattering and the like from occurring in the signal.

The comparator 41 of the output circuit 4 outputs the trigger signal not only to the pulse generator 42 but also to the output holding unit 8.

The output holding unit 8 uses the trigger signal from the comparator 41 as a trigger to output and convert a control signal from the rising point of the one-shot pulse for at least a holding period having the same length as the pulse width of the one-shot pulse. A holding operation for holding the output value of the circuit 3 constant is performed.

The output holding unit 8 has a function of controlling on / off of the switches 60 and 70 of the voltage amplifying unit 6 shown in FIG. 3. When receiving the trigger signal from the comparator 41, both the switches 60 and 70 over the holding period. 70 is turned off to stop the function of the voltage amplifier 6 as a filter circuit. That is, the output holding unit 8 turns off the switches 60 and 70 over the holding period by the control signal when the output value of the conversion circuit 3 exceeds the threshold, and turns on the switches 60 and 70 when the holding period ends.

In the voltage amplifying unit 6, since the switches 60 and 70 are in the off state during the holding period, the non-inverting input terminals of the first and second operational amplifiers 61 and 71 are opened, and the function of the filter circuit is increased. Stop.

At this time, the conversion circuit 3 holds the output value at a value immediately before the start of the holding period (just before the switches 60 and 70 are turned off) by the input terminal capacitances of the operational amplifiers 61 and 71. In other words, the output holding unit 8 performs a holding operation so as to hold the output value of the conversion circuit 3 at a value immediately before the start of the holding period in the holding period.

That is, when the magnitude of the voltage signal output to the output circuit 4 exceeds a predetermined threshold, the conversion circuit 3 sets the magnitude of the voltage signal output to the output circuit 4 for a predetermined holding period to a predetermined value. It is comprised so that the holding | maintenance operation | movement hold | maintained may be performed. In the present embodiment, the holding operation of the conversion circuit 3 is realized by the output holding unit 8.

As described above, the conversion circuit 3 includes the output holding unit 8 that holds the output value constant over the holding period using the trigger signal from the comparator 41 of the output circuit 4 as a trigger, thereby affecting the influence of the capacitive coupling 11. Thus, chattering and the like can be reliably prevented from occurring in the detection signal.

In short, since the conversion circuit 3 does not change the output value while keeping the output value constant by the holding operation at least during the period in which the pulse generator 42 outputs the one-shot pulse, the one-shot pulse is affected by the capacitive coupling 11 during this period. Even if wraparound occurs, the output value does not change.

Therefore, even if the detection signal wraps around from the output terminal T2 to the input terminal T1, the output value of the conversion circuit 3 does not exceed the threshold value, and the one-shot pulse is generated by the pulse generation unit 42 and the output circuit 4 Chattering or the like does not occur in the output.

As a result, the infrared detection device 1 of the present embodiment can reliably detect a human body no matter how much the capacitance Cx of the capacitive coupling 11 generated between the input and output of the detection circuit 10 increases.

Next, how to determine the length of the retention period will be described with a specific example.

When the pulse generator 42 of the output circuit 4 outputs a one-shot pulse, the charge remains in the capacitance component (capacitor 52, etc.) due to the one-shot pulse, although it is a short time after the fall of the one-shot pulse. Due to this residual charge, a potential difference may occur in the output of the current-voltage converter 5 before and after the application of the one-shot pulse, resulting in output fluctuation.

In this embodiment, in order to suppress the influence of the residual charge due to the one-shot pulse, the time length of the holding period is set longer (larger) than the pulse width of the one-shot pulse. Specifically, the time obtained by adding the time required until the influence of the residual charge from the time when the one-shot pulse falls to the pulse width of the one-shot pulse is the lower limit value of the length of the holding period.

However, since the conversion circuit 3 loses information on the original output (voltage signal) corresponding to the current signal from the pyroelectric element 2 during the holding period, the amount of information lost becomes longer as the holding period becomes longer. The number of holding operations on the output after the end of the holding period is increased.

That is, as shown in FIG. 5, the conversion circuit 3 has a longer output holding performance after the holding operation in the output holding unit 8 ends as the holding period becomes longer. Deviation of waveform from output increases.

As described above, the shorter the holding period, the smaller the influence of the holding operation on the output after the end of the holding period in the conversion circuit 3, so it is desirable that an upper limit value be set for the length of the holding period.

In FIG. 5, the horizontal axis is the time axis, the original output of the conversion circuit 3 when the holding operation is not performed is “V0”, and the output of the conversion circuit 3 when the holding operation is performed while changing the holding time. Are represented as “V1”, “V2”, and “V3” (the retention time increases in the order of V1, V2, and V3).

For example, when information on the original output is lost over a half period of the current signal from the pyroelectric element 2, the conversion circuit 3 does not interfere with human body detection after the end of the holding period. A slight delay occurs in the output with respect to the current signal input from the electric element 2.

Therefore, in the present embodiment, the information of the output of the conversion circuit 3 is not lost over the half cycle of the current signal generated by the pyroelectric element 2 when the presence of the human body is detected. The upper limit of time length is set.

Specifically, the output holding unit 8 performs the holding operation twice when the output value of the conversion circuit 3 exceeds each of the positive threshold value VH1 and the negative threshold value VL1 during one cycle of the current signal. Therefore, the upper limit value of the time length of the holding period is set to ¼ (= ½ × ½) of the wavelength of the current signal.

In this embodiment, the length of the holding period is set to 120 ms as an example with respect to a one-shot pulse width of 100 ms.

In this case, the conversion circuit 3 can ensure the followability of the output after the holding operation in the output holding unit 8 is completed up to a current signal of about 2 Hz generated by the pyroelectric element 2. In other words, in this case, after the output period of the output circuit 4 exceeds the threshold value and the first one-shot pulse is output after the output value of the conversion circuit 3 first exceeds the threshold value, the output value of the conversion circuit 3 reaches the threshold value. Every time it exceeds, the second and subsequent one-shot pulses can be output without delay.

In general, the infrared detecting device 1 generates a current signal in the vicinity of 1 Hz from the pyroelectric element 2 for the purpose of human body detection. For example, when the output followability is ensured up to a current signal of 3 Hz. In this case, it is desirable that the length of the holding period is 80 ms or less.

As described above, the detection circuit 10 takes into consideration the frequency of the current signal to be detected and appropriately sets the pulse width of the one-shot pulse and the time length of the holding period, so that the one-shot after the second shot Pulses can be output without delay.

Hereinafter, the operation of the infrared detection apparatus 1 of the present embodiment will be briefly described with reference to FIG. In FIG. 6, with the horizontal axis as the time axis, (a) represents the output (voltage signal) of the conversion circuit 3, (b) represents the detection signal S1 output from the output circuit 4 (pulse generator 42), c) represents the control signal S2 for determining the holding period. In the example of FIG. 6A, the output circuit 4 compares the voltage signal V0 with the threshold value using threshold values with hysteresis (positive threshold value VH1, negative threshold value VL1) instead of a fixed threshold value.

That is, when the pyroelectric element 2 detects the presence of a human body and a current signal is input to the conversion circuit 3, the conversion circuit 3 converts the current signal received from the pyroelectric element 2 as shown in FIG. The voltage signal is converted into a voltage signal by the current-voltage converter 5 and the voltage signal is amplified by the voltage amplifier 6 and output as a voltage signal (amplified voltage signal) V0.

In the comparator 41, the output circuit 4 compares the output value of the conversion circuit 3 with threshold values (positive threshold value VH1, negative threshold value VL1), and generates a trigger signal when the output value of the conversion circuit 3 exceeds the threshold value. .

The pulse generator 42 outputs a one-shot pulse having a predetermined pulse width as the detection signal S1, as shown in FIG. 6B, with the trigger signal rising as a trigger (that is, when receiving the trigger signal from the comparator 41). .

Further, the output holding unit 8 uses the rising edge of the trigger signal as a trigger (that is, when the trigger signal is received from the comparator 41), and as shown in FIG. 6C, the output holding unit 8 extends over a holding period longer than the pulse width of the one-shot pulse. Thus, the control signal S2 is output to perform a holding operation for holding the output value of the conversion circuit 3 constant.

Thereby, at least while the output circuit 4 outputs the one-shot pulse as the detection signal S1, the output value of the conversion circuit 3 is held at the value immediately before the start of the holding period as shown in FIG. Will be.

The infrared detection device 1 of the present embodiment described above includes a pyroelectric element 2, a conversion circuit 3 that converts a current signal output from the pyroelectric element 2 into a voltage signal, and an output value of the conversion circuit 3 as a predetermined threshold value. And an output circuit 4 including a comparator 41 for comparison. The output circuit 4 includes a pulse generation unit 42 that outputs a one-shot pulse having a predetermined pulse width, triggered by the output value of the conversion circuit 3 exceeding the threshold value.

In other words, the detection circuit 10 in the present embodiment includes the conversion circuit 3 and the output circuit 4. The conversion circuit 3 is configured to receive a current signal from the sensing element (in this embodiment, the pyroelectric element 2) through the input terminal T1, and convert the received current signal into a voltage signal. The output circuit 4 receives the voltage signal from the conversion circuit 3, compares the magnitude of the received voltage signal with a predetermined threshold value, and outputs a detection signal through the output terminal T4 when the magnitude of the voltage signal exceeds the predetermined threshold value. Configured to output. The detection signal is a one-shot pulse.

The infrared detection device 1 according to the present embodiment includes a detection circuit 10 and a detection element connected to the input terminal T1 of the detection circuit 10. The detection element is the pyroelectric element 2.

According to the configuration described above, the output circuit 4 is provided with the pulse generator 42 that outputs a one-shot pulse having a predetermined pulse width triggered by the output value of the conversion circuit 3 exceeding the threshold value. The influence of the capacitive coupling 11 generated between the input and output of the circuit 10 can be suppressed.

Therefore, according to the present embodiment, the influence of capacitive coupling that occurs between the input and output (that is, between the input terminal T1 and the output terminal T2) of the circuit portion that receives the output of the pyroelectric element 2 (that is, the detection circuit 10) is suppressed. There is an advantage that you can.

That is, since the detection signal is a one-shot pulse in the infrared detection device 1 of the present embodiment, even when the detection signal wraps around from the output terminal T2 to the input terminal T1 due to the influence of the capacitive coupling 11, It is possible to prevent chattering and the like and to reliably detect a human body.

In addition, since the detection circuit 10 uses a one-shot pulse with a fixed pulse length as a detection signal, the detection circuit 10 detects the detection signal as compared with a configuration in which the detection signal is continuously output while the output value of the conversion circuit 3 exceeds the threshold value. The power required for output can be kept small.

Further, in the external circuit connected to the output terminal T2 of the detection circuit 10, since the detection signal is a one-shot pulse having a fixed pulse width, it is easy to distinguish the detection signal from noise, and the processing of the detection signal is simple. become.

In addition, according to the infrared detection device 1 having the above-described configuration, hysteresis is not necessary for the threshold values (positive threshold value VH1 and negative threshold value VL1) used in the comparator 41. Therefore, the hysteresis circuit is omitted and the detection circuit can be downsized. You can also plan. That is, since the detection signal is a one-shot pulse having a fixed pulse length, the output value of the conversion circuit 3 falls below or exceeds the threshold value during the output of the one-shot pulse even if no hysteresis is given to the threshold value. Therefore, chattering or the like does not occur in the detection signal.

In the present embodiment, the conversion circuit 3 has a gain greater than a predetermined value in a specific frequency band. The pulse generator 42 outputs a one-shot pulse having a pulse width that is higher than a specific frequency band.

In other words, the conversion circuit 3 is configured to amplify the voltage signal. The conversion circuit 3 has a gain equal to or higher than a predetermined value with respect to a voltage signal component having a frequency included in a specific frequency band, and has a frequency higher than an upper limit value of the specific frequency band. Configured to have a gain less than a predetermined value. The pulse width of the one-shot pulse is a value corresponding to a frequency higher than the upper limit value.

As described above, in this embodiment, the pulse generator 42 outputs a one-shot pulse having a pulse width that is higher than a specific frequency band in which the conversion circuit 3 has a gain equal to or greater than a predetermined value.

Therefore, even if the detection signal wraps around from the output terminal T2 to the input terminal T1 due to the influence of the capacitive coupling 11, the conversion circuit 3 has little sensitivity to the wrapping one-shot pulse (detection signal). Chattering or the like does not occur in the detection signal due to this one-shot pulse. That is, since the pulse generator 42 increases the frequency component of the detection signal, the influence of the detection signal wraparound can be reduced by the attenuation characteristic of the conversion circuit 3.

Note that the conversion circuit 3 may be configured to amplify the current signal received from the pyroelectric element 2. In this case, the conversion circuit 3 has a gain equal to or higher than a predetermined value for a current signal component having a frequency included in a specific frequency band, and has a higher frequency than the upper limit value of the specific frequency band. Is configured to have a gain less than a predetermined value.

That is, the conversion circuit 3 may be configured to amplify an electric signal that is a current signal (current signal from the pyroelectric element 2) or a voltage signal (voltage signal from the current-voltage conversion unit 5). In this case, the conversion circuit 3 has a gain equal to or higher than a predetermined value with respect to the component of the electric signal having a frequency included in the specific frequency band, and the component of the electric signal having a frequency higher than the upper limit value of the specific frequency band. Is configured to have a gain less than a predetermined value.

Further, in the present embodiment, the conversion circuit 3 receives the trigger from the output circuit 4 and outputs an output holding unit 8 that holds the output value constant over a holding period that is at least as long as the pulse width of the one-shot pulse. Have

In other words, when the magnitude of the voltage signal output to the output circuit 4 exceeds a predetermined threshold value, the conversion circuit 3 determines the magnitude of the voltage signal output to the output circuit 4 for a predetermined holding period. It is configured to perform a holding operation that holds the value. The length of the holding period is not less than the pulse width of the one-shot pulse.

As described above, the infrared detection device 1 according to the present embodiment includes the output holding unit 8 that holds the output value of the conversion circuit 3 constant over a holding period that is at least as long as the one-shot pulse. 11 can reliably prevent chattering and the like from occurring in the detection signal. That is, since the conversion circuit 3 does not change the output value while holding the output value constant by the holding operation at least during the period in which the pulse generator 42 outputs the one-shot pulse, the one-shot pulse is affected by the capacitive coupling 11 during this period. Even if wraparound occurs, the output value does not change.

Therefore, the infrared detection device 1 of the present embodiment can reliably detect a human body no matter how large the capacitance Cx of the capacitive coupling 11 generated between the input and output of the detection circuit 10 is.

In this embodiment, the length of the holding period is longer than the pulse width of the one-shot pulse. In other words, the holding period is longer than the pulse width of the one-shot pulse.

As described above, in this embodiment, the output holding unit 8 holds the output value of the conversion circuit 3 constant over a holding period longer than the pulse width of the one-shot pulse. Can be reliably suppressed.

In this embodiment, the output holding unit 8 holds the output value of the conversion circuit 3 at a value immediately before the start of the holding period in the holding period. In other words, the predetermined value is the magnitude of the voltage signal when the magnitude of the voltage signal output to the output circuit 4 exceeds a predetermined threshold.

Thus, since the output holding unit 8 holds the output value of the conversion circuit 3 at the value immediately before the start of the holding period in the holding period, the holding operation to the output of the conversion circuit 3 after the holding period ends. The influence of can be suppressed small.

In short, as shown in FIG. 7, in the conversion circuit 3, the output followability after the holding operation in the output holding unit 8 is changed depending on what value the output value is held in the holding period. In some cases, the deviation of the waveform from the original output when the holding operation is not performed becomes large.

In FIG. 7, with the horizontal axis as the time axis, the original output of the conversion circuit 3 when the holding operation is not performed is “V0”, and the output when the output value is held at the value immediately before the start of the holding period is “V1”. The output when the output value is held at the reference voltage is expressed as “V2”.

Thus, the conversion circuit 3 holds the output value at the value immediately before the start of the holding period in the holding period, thereby reducing the influence of the holding operation on the output after the end of the holding period.

Note that the output holding unit 8 holds the output value of the conversion circuit 3 at a value immediately before the start of the holding period during the holding period, thereby making the output value of the conversion circuit 3 constant as compared with the case of holding at the reference voltage. There is also an advantage that the time required to become shorter can be shortened.

In this embodiment, the conversion circuit 3 includes a filter circuit that allows a signal component in a specific frequency band to pass therethrough. The output holding unit 8 stops the function of the filter circuit during the holding period.

In other words, the conversion circuit 3 includes a filter circuit that passes a component having a frequency included in a specific frequency band in the voltage signal. The conversion circuit 3 is configured to hold the magnitude of the voltage signal output to the output circuit 4 at a predetermined value by stopping the operation of the filter circuit during the holding period.

Furthermore, in this embodiment, the output holding unit 8 turns off both the switches 60 and 70 of the voltage amplification unit 6 over the holding period to stop the function of the voltage amplification unit 6 as a filter circuit, thereby converting the conversion circuit The output value of 3 is held constant. That is, the output holding unit 8 also serves as a part of the voltage amplifying unit 6 as a filter circuit for the holding operation of holding the output value of the conversion circuit 3 constant. Can be simplified.

The conversion circuit 3 may include a filter circuit that allows a component having a frequency included in a specific frequency band in the current signal from the pyroelectric element 2 to pass therethrough. In this case, the conversion circuit 3 is configured to hold the magnitude of the voltage signal output to the output circuit 4 at a predetermined value by stopping the operation of the filter circuit during the holding period.

That is, the conversion circuit 3 only needs to include a filter circuit that allows a component having a frequency included in a specific frequency band in the electric signal that is the current signal or the voltage signal to pass. In this case, the conversion circuit 3 is configured to hold the magnitude of the voltage signal output to the output circuit 4 at a predetermined value by stopping the operation of the filter circuit during the holding period.

In this embodiment, the conversion circuit 3 includes an operational amplifier 51 to which a feedback capacitive element (capacitor) 52 is connected, and the operational amplifier 51 converts a current signal into a voltage signal. In other words, the conversion circuit 3 includes a current-voltage conversion unit 5 that converts the current signal received from the pyroelectric element 2 into a voltage signal. The current-voltage conversion unit 5 includes an operational amplifier 51 and a feedback capacitive element (capacitor) 52 connected to the operational amplifier 51.

In this way, the current-voltage conversion unit 5 constitutes a capacitance conversion type conversion unit that converts the current signal into a voltage signal using the impedance of the capacitor 52, so that it is possible to reduce the size and increase the accuracy by using an IC. There is.

That is, when a current-voltage conversion unit having the same gain as that of the capacitance conversion type is realized using a resistor, a high resistance (for example, 100 GΩ) is required. Therefore, the current-voltage conversion unit can be downsized with an external resistor. In the case of resistors built into ICs, variations in resistance values are large and accuracy is low.

On the other hand, since the capacitance conversion type current-voltage conversion unit 5 can use a capacitor 52 having a small capacity (for example, 2 pF), a small and highly accurate conversion unit is realized by incorporating the capacitor 52 in the IC. In addition, noise due to dielectric loss can be reduced.

The current-voltage conversion unit 5 is not limited to the capacity conversion type, and may be configured using a resistance element instead of the capacitance element for AC feedback (capacitor 52).

By the way, the configuration for the output holding unit 8 to hold the output value of the conversion circuit 3 is not limited to the configuration of FIG. 3 described above, and may be a configuration as shown in FIGS.

FIG. 8 shows a first modification of the voltage amplification unit 6. In FIG. 8, the voltage amplifying unit 6 is between the reference power supply unit 67 and the resistor 68, between the resistor 63 and the operational amplifier 61 output terminal, between the reference power supply unit 77 and the resistor 78, and between the resistor 73 and the operational amplifier 71 output terminal. The switches 60A, 60B, 70A, 70B are inserted in the.

When receiving the trigger signal from the comparator 41, the output holding unit 8 turns off both the switches 60A, 60B, 70A, and 70B over the holding period and stops the function of the voltage amplification unit 6 as a filter circuit.

Thereby, in the voltage amplifying unit 6, since the switches 60A, 60B, 70A, and 70B are in the OFF state during the holding period, the discharge system of the capacitors 64 and 74 is cut off, and the output value of the conversion circuit 3 is set to the holding period. It is held at the value just before the start.

FIG. 9 shows a second modification of the voltage amplification unit 6. In FIG. 9, in the voltage amplifying unit 6, a switch 60C is inserted between the first-stage non-inverting amplifier circuit and the current-voltage converting unit 5, and the first-stage non-inverting amplifier circuit and the second-stage non-inverting amplifier. A switch 70C is inserted between the amplifier circuit.

When receiving the trigger signal from the comparator 41, the output holding unit 8 turns off both the switches 60C and 70C over the holding period to stop the function of the voltage amplification unit 6 as a filter circuit.

Thereby, since the switches 60C and 70C are in the OFF state during the holding period, the voltage amplification unit 6 holds the non-inverting input terminals of the first and second operational amplifiers 61 and 71 at the reference voltage, The output value of the conversion circuit 3 is held at the reference voltage.

In the infrared detection device 1 of the present embodiment, it is not essential for the conversion circuit 3 to have the output holding unit 8, and the output holding unit 8 may be omitted. Even in this case, the infrared detector 1 can suppress the influence of the capacitive coupling 11 generated between the input and output of the detection circuit 10 by the configuration in which the pulse generator 42 generates the one-shot pulse.

In the above embodiment, the frequency band of the current signal generated by the pyroelectric element 2 when the presence of a human body is detected is assumed to be about 0.1 Hz to 1 Hz. However, the present invention is not limited to this example. The element 2 may output a current signal of about 0.1 Hz to 10 Hz, for example, when detecting a human body.

Even when the current signal is about 10 Hz, the detection circuit 10 generates at least one one-shot pulse when the output value of the conversion circuit 3 exceeds the threshold value. Therefore, the external circuit receives this one-shot pulse. It is possible to control electric devices according to the result of human body detection.

(Embodiment 2)
The infrared detection device 1 according to the present embodiment is different from the infrared detection device 1 according to the first embodiment in that the conversion circuit 3 includes an AD conversion unit 91 that converts an analog value into a digital value as illustrated in FIG. To do. Hereinafter, the same configurations as those of the first embodiment are denoted by the same reference numerals as those of the first embodiment, and description thereof will be omitted as appropriate.

In the present embodiment, the voltage amplifying unit 6 subsequent to the current-voltage converting unit 5 includes an AD converting unit 91 and a digital processing unit 92 connected to the output of the AD converting unit 91.

The AD conversion unit 91 converts the voltage value (analog value) input from the current / voltage conversion unit 5 into a digital value, and outputs the digital value to the digital processing unit 92 in a serial manner. That is, the AD conversion unit 91 converts the instantaneous value of the analog signal into a digital serial bit string and outputs it.

In the present embodiment, a ΔΣ (delta sigma) method (ΣΔ method) AD converter (ΔΣ AD converter) is used as the AD conversion unit 91. As a result, a relatively small and highly accurate AD conversion unit 91 can be realized.

Such an AD converter 91 includes an integrator (not shown) that integrates an input signal, a quantizer (not shown) that quantizes the output of the integrator, and an analog output of the quantizer. And a DA converter (not shown) for converting the value.

The integrator performs integration of the input signal from the current-voltage conversion unit 5, and the quantizer converts the analog value into a digital value by comparing the output voltage of the integrator, that is, the integration value, with a predetermined threshold value. To do.

Here, it is assumed that the quantizer converts an analog value into a 1-bit digital value using one threshold value.

The DA converter converts a delay value, which is a value obtained by delaying the digital value converted by the quantizer by one clock, into an analog value and feeds it back to the input of the integrator. As a result, in the AD conversion unit 91, a value obtained by integrating the change (differential value) of the input signal with the passage of time is output from the quantizer as a digital value.

The digital processing unit 92 has a function as a digital filter (digital band pass filter) that passes a signal component in a predetermined frequency band out of the output of the AD conversion unit 91. In the present embodiment, the frequency band of the current signal generated by the pyroelectric element 2 when the presence of a human body is detected (here, about 0.1 Hz to 1 Hz) is set as the pass band of the digital processing unit 92.

Therefore, the conversion circuit 3 functions as a filter circuit that allows the voltage amplification unit 6 to pass a signal component in a specific frequency band, so that the conversion circuit 3 has a gain greater than a predetermined value in the specific frequency band as a whole. The output current signal is converted into a voltage signal and output.

The output circuit 4 compares the output value of the conversion circuit 3 with threshold values (positive threshold value VH1, negative threshold value VL1) based on the digital signal input from the digital processing unit 92, and outputs a detection signal (one-shot pulse). To do. In the present embodiment, since the output of the conversion circuit 3 is a digital signal, the output circuit 4 is configured using a comparator 41 corresponding to the digital signal.

In the infrared detection device 1 of the present embodiment described above, the conversion circuit 3 has an AD conversion unit 91 that converts an analog value into a digital value and outputs it in a serial manner. The filter circuit of the conversion circuit 3 is a digital filter (digital processing unit 92) that passes a signal component in a predetermined frequency band out of the output of the AD conversion unit 91.

In other words, the conversion circuit 3 includes an AD conversion unit 91 that converts an electrical signal into a digital signal and outputs the digital signal. The filter circuit performs arithmetic processing on the digital signal to extract a component having a frequency included in a specific frequency band from the waveform indicated by the digital signal, and generates and outputs a digital signal indicating the waveform of the extracted component. This is a digital filter (digital processing unit 92).

As described above, according to the infrared detection device 1 of the present embodiment described above, since the conversion circuit 3 includes the AD conversion unit 91, the output holding unit 8 simply outputs the output of the conversion circuit 3 when performing the holding operation. It is possible to hold it. Therefore, the infrared detection device 1 has an advantage that the circuit configurations of the conversion circuit 3 and the output holding unit 8 can be simplified.

Further, the infrared detection device 1 of the present embodiment uses the digital filter (digital processing unit 92) as described above, so that no external component is required, and the detection circuit 10 can be easily made into one chip. There are advantages.

On the other hand, when an analog bandpass filter is used, an element such as a capacitor having a relatively large circuit constant is required to pass a signal of about 0.1 Hz to 1 Hz. Since such an element is externally attached to an IC (integrated circuit), in this configuration, it is difficult for the infrared detection device 1 to make the detection circuit 10 into one chip.

In the present embodiment, the AD converter 91 is a ΔΣ type AD converter having an integrator that integrates an analog value and a quantizer that quantizes the output of the integrator.

Thus, in the present embodiment, a ΔΣ type AD converter that can be easily reduced in size is used as the AD conversion unit 91, so that the detection circuit 10 of the infrared detection device 1 is made into an IC, but with relatively high accuracy. The AD conversion unit 91 can be realized.

The AD conversion unit includes an integrator that integrates an electric signal that is a current signal (current signal from the pyroelectric element 2) or a voltage signal (voltage signal from the current-voltage conversion unit 5), and an output of the integrator. It may be a ΔΣ AD converter having a quantizer for quantizing.

Incidentally, since the AD converter 91 is composed of a ΔΣ AD converter, the output value is updated at a predetermined period (for example, 20 ms) as shown in FIG. In short, the AD conversion unit 91 outputs one data (digital value) every predetermined period. In FIG. 11, the horizontal value is the time axis, and the digital value D1 output from the AD conversion unit 91 is conceptually represented so as to have the same form as the analog signal A1 before AD conversion.

Here, if the end timing of the holding operation deviates from the update timing of the digital value D1, the conversion circuit 3 may not be able to update the output data (digital value) or output fluctuation such as an abnormal value output may occur. .

Therefore, the output holding unit 8 matches the timing at which the operation of the filter circuit (digital processing unit 92) is resumed, that is, the timing at which the holding operation is completed, with the timing at which the AD conversion unit 91 updates the digital value D1.

Thus, in this embodiment, the AD conversion unit 41 updates the output value at a predetermined period. The output holding unit 8 matches the timing at which the operation of the filter circuit is resumed with the timing at which the AD conversion unit 41 updates the output value.

In other words, the AD conversion unit 41 is configured to convert an electrical signal (in this embodiment, a voltage signal) into a digital signal and output it at a predetermined cycle. The conversion circuit 3 is configured to restart the operation of the filter circuit in accordance with the timing at which the AD conversion unit 41 outputs a digital signal. The electric signal may be a current signal (current signal from the pyroelectric element 2).

Thereby, since the output data (digital value) is updated at the timing when the output holding unit 8 finishes the holding operation, the conversion circuit 3 can suppress the occurrence of output fluctuation at the end of the holding operation. it can.

In the present embodiment, a ΔΣ type AD converter is exemplified as the AD conversion unit 91, but the AD conversion unit 91 may be an AD converter other than the ΔΣ type.

Other configurations and functions are the same as those in the first embodiment.

(Embodiment 3)
As shown in FIG. 12, the infrared detection apparatus 1 according to the present embodiment is an embodiment in which the output circuit 4 includes a pulse width variable unit 43 that changes the pulse width of the one-shot pulse generated by the pulse generator 42. 1 is different from the infrared detecting device 1 of FIG. Hereinafter, the same configurations as those of the first embodiment are denoted by the same reference numerals as those of the first embodiment, and description thereof will be omitted as appropriate.

In the present embodiment, the comparator 41 is configured to provide the trigger signal to the pulse width variable unit 43 as well.

In the present embodiment, the pulse generator 42 is configured to determine the pulse width of the one-shot pulse according to the instruction value received from the pulse width variable unit 43. For example, the pulse generator 42 shortens the pulse width as the received instruction value is smaller, and lengthens the pulse width as the received instruction value is larger.

The pulse width varying unit 43 is configured to obtain a differential value of the output value (the magnitude of the voltage signal V0) of the conversion circuit 3 when receiving the trigger signal from the comparator 41. The pulse width variable unit 43 is configured to select an instruction value corresponding to the obtained differential value and to supply the selected instruction value to the pulse generation unit 42.

For example, the pulse width variable unit 43 selects a smaller instruction value as the obtained differential value is larger, and selects a larger instruction value as the obtained differential value is smaller.

That is, the pulse width variable unit 43 is configured to control the pulse generating unit 42 so that the pulse width of the one-shot pulse becomes shorter as the differential value is larger. In other words, the pulse width varying unit 43 is configured to control the pulse generating unit 42 so that the pulse width of the one-shot pulse becomes longer as the differential value is smaller.

In this way, the pulse width variable unit 43 obtains a differential value at the time when the output value of the conversion circuit 3 exceeds the threshold value, and sets the differential value so that the pulse width of the one-shot pulse becomes smaller as the differential value becomes larger. Accordingly, the pulse width of the one-shot pulse is changed.

In other words, when the rate of change of the output value of the conversion circuit 3 is large, the pulse width variable unit 43 reduces the pulse width of the one-shot pulse so that the output circuit 4 causes the output value of the conversion circuit 3 to be steep. It is possible to respond to changes.

Here, the pulse width variable unit 43 changes the pulse width of the one-shot pulse within the range between the upper limit value and the lower limit value described in the first embodiment. The differential value of the output value of the conversion circuit 3 can be obtained using a known differential circuit.

For example, when the frequency of the current signal output from the pyroelectric element 2 is relatively low and the change rate of the output value of the conversion circuit 3 is relatively small as shown in FIG. Set the pulse width to the default.

In FIG. 13, with the horizontal axis as the time axis, (a) shows the output (voltage signal V0) of the conversion circuit 3, and (b) shows the detection signal S1. In this case, since the time interval in which the output value of the conversion circuit 3 exceeds the threshold values (positive threshold value VH1, negative threshold value VL1) is relatively long (large), the output circuit 4 is in each time the output value of the conversion circuit 3 exceeds the threshold value. The one-shot pulse is output reliably.

On the other hand, when the frequency of the current signal output from the pyroelectric element 2 is relatively high and the rate of change in the output value of the conversion circuit 3 is relatively large as shown in FIG. No. 4 cannot output a one-shot pulse even if the output value of the conversion circuit 3 exceeds the threshold value.

Therefore, in this case, the pulse width varying unit 43 changes the pulse width of the one-shot pulse so that it is smaller (shorter) than the default, so that the output circuit 4 causes the output value of the conversion circuit 3 to exceed the threshold value. In addition, a one-shot pulse can be output reliably.

In FIG. 14, the horizontal axis is the time axis, (a) shows the output (voltage signal V0) of the conversion circuit 3, (b) shows the detection signal S1 when the pulse width is the default, and (b) shows the pulse. The detection signal S1 when the width is reduced is shown.

In the examples of FIGS. 13 and 14, the output circuit 4 compares the voltage signal V0 with the threshold value using a fixed threshold value (positive threshold value VH1, negative threshold value VL1).

In the infrared detection device 1 of the present embodiment described above, the output circuit 4 obtains a differential value at the time when the output value of the conversion circuit 3 exceeds the threshold value, and the pulse width of the one-shot pulse becomes smaller as the differential value becomes larger. As shown, the pulse width variable unit 43 that changes the pulse width of the one-shot pulse according to the differential value is provided.

In other words, the output circuit 4 obtains a differential value of the magnitude of the voltage signal V0 when the magnitude of the voltage signal V0 received from the conversion circuit 3 exceeds a predetermined threshold value. It is configured to shorten the pulse width.

According to the infrared detection device 1 of the present embodiment described above, even when the change rate of the output value of the conversion circuit 3 is large, the pulse width variable unit 43 reduces the pulse width of the one-shot pulse, thereby reducing the one-shot pulse. It is possible to accurately control the number of pulses and to detect human bodies more reliably.

In short, the infrared detection device 1 outputs the output value of the conversion circuit 3 even when a current signal having a relatively high frequency may be generated in the pyroelectric element 2 when, for example, a person crosses near the pyroelectric element 2. One-shot pulse can be reliably output every time exceeds the threshold. In other words, the detection circuit 10 of the infrared detection device 1 can cope with an input (current signal) in a wider frequency range.

Note that the configuration of the present embodiment can be applied in combination with the configuration of the second embodiment. Other configurations and functions are the same as those of the first embodiment.

(Embodiment 4)
As shown in FIG. 15, the infrared detection device 1 of the present embodiment has the holding invalid unit 44 that invalidates the function (holding operation) of the output holding unit 8. This is different from the detection device 1. Hereinafter, the same configurations as those of the first embodiment are denoted by the same reference numerals as those of the first embodiment, and description thereof will be omitted as appropriate.

In the present embodiment, the comparator 41 is configured to give a trigger signal to the holding unit invalid unit 44 as well.

The holding invalid unit 44 is configured to obtain a differential value of the output value (the magnitude of the voltage signal V0) of the conversion circuit 3 when receiving the trigger signal from the comparator 41. The holding invalid unit 44 is configured to determine whether or not the obtained differential value is larger than a specified value. The holding invalid unit 44 is configured to output an invalid signal to the output holding unit 8 when it is determined that the differential value is larger than the predetermined value.

In the present embodiment, the output holding unit 8 is configured to end the holding operation when receiving the invalid signal from the holding invalid unit 44. For example, when the output holding unit 8 receives the trigger signal from the comparator 41, the output holding unit 8 performs a holding operation of turning off the switches 60 and 70 and holding the voltage signal constant. Thereafter, when receiving an invalid signal from the holding invalid unit 44, the output holding unit 8 turns on the switches 60 and 70, thereby ending the holding operation.

As described above, the holding invalidation unit 44 obtains a differential value at the time when the output value of the conversion circuit 3 exceeds the threshold value, and invalidates the holding operation of the output holding unit 8 if the differential value is larger than the specified value. That is, the output holding unit 8 does not hold the output value (voltage signal V0) of the conversion circuit 3 constant when the rate of change of the output value of the conversion circuit 3 is large, and the voltage amplification unit 6 is also continuously used as a filter circuit. To function.

Thereby, the output circuit 4 can cope with a steep change in the output value of the conversion circuit 3. The differential value of the output value of the conversion circuit 3 can be obtained using a known differential circuit.

Even if the hold invalidating unit 44 invalidates the function of the output holding unit 8 in this way, the conversion circuit 3 has little sensitivity to the output value that changes sharply in the first place. The influence of the capacitive coupling 11 generated between the input and output of the detection circuit 10 can be suppressed.

In the infrared detection device 1 of the present embodiment described above, the output circuit 4 obtains a differential value at the time when the output value of the conversion circuit 3 exceeds the threshold value, and if the differential value is larger than the specified value, the output holding unit 8. A holding invalidation part 44 for invalidating the function of.

In other words, the output circuit 4 obtains a differential value of the magnitude of the voltage signal V0 when the magnitude of the voltage signal V0 received from the conversion circuit 3 exceeds a predetermined threshold, and whether or not the differential value exceeds a specified value. Configured to determine whether or not. The conversion circuit 3 is configured to end the holding operation when the output circuit 4 determines that the differential value exceeds the specified value.

According to the infrared detection device 1 of the present embodiment described above, when the change rate of the output value of the conversion circuit 3 is large, the holding invalidation unit 44 invalidates the holding operation of the output holding unit 8. The original output (voltage signal) information corresponding to the current signal from the pyroelectric element 2 is not lost.

Therefore, even when a current signal having a relatively high frequency may be generated in the pyroelectric element 2 when, for example, a person crosses the pyroelectric element 2, the infrared detection device 1 outputs the output value of the conversion circuit 3. One-shot pulse can be reliably output every time exceeds the threshold. In other words, the detection circuit 10 of the infrared detection device 1 can cope with an input (current signal) in a wider frequency range.

Note that the configuration of the present embodiment can be applied in combination with the configuration of the second embodiment. Other configurations and functions are the same as those of the first embodiment.

Claims (13)

A conversion circuit that receives a current signal from the sensing element through an input terminal and converts the received current signal into a voltage signal;
The voltage signal is received from the conversion circuit, the magnitude of the received voltage signal is compared with a predetermined threshold, and a detection signal is output through an output terminal when the magnitude of the voltage signal exceeds the predetermined threshold. An output circuit;
With
The detection signal is a one-shot pulse. The conversion circuit is configured to amplify the electric signal that is the current signal or the voltage signal,
The conversion circuit has a gain equal to or higher than a predetermined value with respect to a component of the electric signal having a frequency included in a specific frequency band and has a frequency higher than an upper limit value of the specific frequency band. Is configured to have a gain less than the default value for
The detection circuit according to claim 1, wherein a pulse width of the one-shot pulse is a value corresponding to a frequency higher than the upper limit value. When the magnitude of the voltage signal output to the output circuit exceeds the predetermined threshold, the conversion circuit sets the magnitude of the voltage signal output to the output circuit during a predetermined holding period to a predetermined value. Configured to perform a holding action
The detection circuit according to claim 1, wherein a length of the holding period is equal to or greater than a pulse width of the one-shot pulse. The detection circuit according to claim 3, wherein the holding period is longer than a pulse width of the one-shot pulse. The detection circuit according to claim 3, wherein the predetermined value is the magnitude of the voltage signal when the magnitude of the voltage signal output to the output circuit exceeds the predetermined threshold. The conversion circuit includes a filter circuit that passes a component having a frequency included in a specific frequency band of the electric signal that is the current signal or the voltage signal,
The conversion circuit is configured to hold the magnitude of the voltage signal output to the output circuit at the predetermined value by stopping the operation of the filter circuit during the holding period. The detection circuit according to claim 3. The conversion circuit includes an AD conversion unit that converts the electrical signal into a digital signal and outputs the digital signal.
The filter circuit performs arithmetic processing on the digital signal to extract a component having a frequency included in the specific frequency band from a waveform indicated by the digital signal, and generates a digital signal indicating the waveform of the component. The detection circuit according to claim 6, wherein the detection circuit is an output digital filter. The AD converter is a ΔΣ AD converter having an integrator that integrates the electric signal and a quantizer that quantizes the output of the integrator. Detection circuit. The AD converter is configured to convert the electrical signal into a digital signal at a predetermined cycle and output the digital signal,
The detection circuit according to claim 8, wherein the conversion circuit is configured to restart the operation of the filter circuit in accordance with a timing at which the AD conversion unit outputs a digital signal. The output circuit obtains a differential value of the magnitude of the voltage signal when the magnitude of the voltage signal received from the conversion circuit exceeds a predetermined threshold, and the pulse width of the one-shot pulse increases as the differential value increases. The detection circuit according to claim 1, wherein the detection circuit is configured to shorten the length of the detection circuit. The output circuit obtains a differential value of the magnitude of the voltage signal when the magnitude of the voltage signal received from the conversion circuit exceeds a predetermined threshold, and determines whether or not the differential value exceeds a specified value. Configured to
The detection circuit according to claim 3, wherein the conversion circuit is configured to end the holding operation when the output circuit determines that the differential value exceeds the specified value. The conversion circuit includes a current-voltage conversion unit that converts the received current signal into a voltage signal,
The detection circuit according to claim 1, wherein the current-voltage conversion unit includes an operational amplifier and a feedback capacitive element connected to the operational amplifier. A detection circuit according to claim 1;
A sensing element connected to the input end of the sensing circuit;
With
The infrared detection device, wherein the detection element is a pyroelectric element.

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