JP4239385B2 - Infrared detector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an infrared detection device useful for detecting infrared energy radiated from a human body and detecting the presence and movement of the human body.
[0002]
[Prior art]
An example of such a conventional infrared detection device is shown in FIG. In this infrared detector, a pyroelectric element 51 is used as an infrared detector, and a current corresponding to a change in infrared radiation is output. This output current is converted into a voltage via the high resistance of the I / V converter 52 and is amplified by the voltage amplifier circuit 531. The amplified voltage is compared with a predetermined set value through the detection unit 532, and a detection signal is output when the amplified value is exceeded. That is, when the output of the voltage amplification circuit 531 exceeds the detection level, it is detected that the human body exists and has moved.
[0003]
In addition, the frequency characteristics with respect to the overall gain increase sensitivity to the human body and suppress malfunctions of other signals by using a bandpass filter centered at approximately 1 Hz that matches the movement of the human body.
[0004]
However, the pyroelectric element 51 may generate a single noise called popcorn noise. As a countermeasure for that, since the output from the pyroelectric element 51 due to popcorn noise rises much faster than the output from the human body or the like, the popcorn noise detection unit 54 detects popcorn noise as a separate system, According to the detection signal, the pop-up noise is generated by prohibiting the output from the detection unit 532 on the side of detecting the human body for a certain period of time or reducing the gain of the I / V conversion unit 52 or the voltage amplification circuit 531. It tries to eliminate the malfunction caused by. (See JP-A-11-248532)
[0005]
[Problems to be solved by the invention]
By the way, the actual popcorn noise has a pulse width of several ms or less, and the signal for the human body motion is around 1 Hz. Therefore, it can be seen that the signal for the human body motion and the popcorn noise have a considerable difference in the frequency band. ing. Due to this difference, when popcorn noise is not generated, the timer circuit 55 in the popcorn noise detection unit 54 of another system is naturally not used, and when popcorn noise occurs, a signal for the movement of the human body is a voltage amplification circuit. Since the output from the detection unit 532 is prohibited before being amplified by the 531, the voltage amplification circuit 531 on the side for detecting the human body is substantially unused.
[0006]
The present invention has been made in view of the above-described reasons, and an object of the present invention is to provide an infrared ray whose circuit configuration can be reduced in size by sharing a voltage amplification circuit and a timer circuit on the human body detection side. It is to provide a detection device.
[0007]
[Means for Solving the Problems]
In order to solve the above-described problem, an infrared detection device according to claim 1 is a pyroelectric element, an I / V conversion unit that converts a current output from the pyroelectric element into a voltage, and outputs the voltage. A signal detection unit that detects a signal to be detected from the output voltage of the conversion unit; and a popcorn noise detection unit that detects popcorn noise from the output voltage of the I / V conversion unit. The signal detection unit includes a voltage amplification circuit that amplifies and outputs the output voltage of the I / V conversion unit, and a plurality of switches for switching to a timer circuit are provided in the voltage amplification circuit. . The infrared detection device further includes a control unit for converting the voltage amplification circuit to the timer circuit when the popcorn noise detection unit detects the popcorn noise, and returning the voltage amplification circuit to the voltage amplification circuit again after a predetermined time. It is characterized by that.
[0008]
According to this infrared detection device, when popcorn noise is detected by the popcorn noise detection unit, the control unit switches the switch in the voltage amplification circuit to function as the timer circuit. Thereafter, after a lapse of a certain time, the control unit switches the switch again to restore the voltage amplification circuit serving as the timer circuit. That is, by switching the switch by the control unit, the circuit configurations of the voltage amplifier circuit and the timer circuit can be converted to each other, and each function can be performed as necessary. Thus, by making the voltage amplifier circuit and the timer circuit common, the circuit configuration of the entire apparatus can be reduced.
[0009]
The infrared detection device according to claim 2 is the infrared detection device according to claim 1, wherein the voltage amplification circuit includes a filter including a capacitor and a resistor, and the capacitor and the resistor are connected to the timer circuit. The switch is provided so as to play the role of setting the time as the capacitor, and the capacitor and the resistor serve as the filter and the time as the timer circuit. Thus, the circuit configuration can be reduced in size.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described. FIG. 1 is a circuit block diagram of an infrared detector according to an embodiment of the present invention.
[0011]
This infrared detection device outputs pyroelectric element 1 that outputs a current corresponding to the amount of change in infrared radiation radiated from a predetermined detection area, and converts the current output from pyroelectric element 1 into a voltage for output. V converter 2 is provided.
[0012]
In addition, the infrared detection apparatus includes a signal detection unit 3 that detects a signal to be detected from an output voltage obtained by converting the output of the pyroelectric element 1 by the I / V conversion unit 2. In this embodiment, the human body is mainly used. It is set to detect infrared rays radiated from. The signal detection unit 3 includes a voltage amplification circuit 31 that amplifies the output voltage of the I / V conversion unit 2 and a comparator. The fluctuation range of the output voltage of the voltage amplification circuit 31 is a predetermined reference width for detecting a human body signal. If it is larger, the detection unit 32 is configured to output a detection signal indicating detection of a human body. Further, in the present embodiment, the voltage amplification circuit 31 has a BPF (band pass filter) that selects and outputs a frequency component around 1 Hz that matches the moving speed of the human body, for example, and a switch for conversion to the timer circuit 31 ′ Are provided. By switching this switch, the voltage amplification circuit 31 and the timer circuit 31 ′ can be converted to each other.
[0013]
Further, the infrared detection device includes a popcorn noise detection unit 4 that detects popcorn noise from the output voltage obtained by converting the output of the pyroelectric element 1 by the I / V conversion unit 2. The popcorn noise detection unit 4 is for amplifying the output voltage of the I / V conversion unit 2 and has, for example, a BPF (several tens to several hundreds Hz) that outputs only components in a predetermined frequency range for popcorn noise extraction. And a popcorn noise detector 42 that detects the detection of popcorn noise if the fluctuation range of the output voltage of the voltage amplifier circuit 41 is larger than a predetermined reference width for detecting popcorn noise. Yes.
[0014]
Further, in this infrared detection device, when popcorn noise is detected by the popcorn noise detection unit 4, a signal for switching a switch in the voltage amplification circuit 31 is output and converted to the timer circuit 31 ', and at the same time, the detection unit 32 In order to inhibit the detection signal from the control unit 5, a control unit 5 is provided for switching the output changeover switch 6 that cuts off the circuit and outputs a constant voltage instead.
[0015]
The operation of the infrared detection device will be described. The current output by the pyroelectric element 1 is converted into a voltage by the I / V converter 2 and output. The output voltage from the I / V converter 2 is extracted by the BPF having the voltage amplification circuit 31 and only the value necessary for human body detection (around 1 Hz) is output and the fluctuation range of this output voltage is for detecting human body signals. If it is larger than the predetermined reference width, the detection unit 32 outputs a detection signal indicating detection of a human body.
[0016]
Next, let us consider a case where the voltage amplification circuit 41 in the popcorn noise detection unit 4 outputs a popcorn noise extraction BPF (several tens to several hundreds of Hz). If the fluctuation range of the output voltage selected and amplified by the voltage amplifier circuit 41 is larger than a predetermined reference width for detecting popcorn noise determined by the popcorn noise detector 42, a popcorn noise detection signal is output. ing. At this time, the control unit 5 that has received the popcorn noise detection signal outputs a signal for switching the switch to the voltage amplification circuit 31 to convert the voltage amplification circuit 31 to the timer circuit 31 ′, and at the same time to the output changeover switch 6. A switching signal is output to prohibit the detection operation of the signal detector 3.
[0017]
Here, an example in which the voltage amplification circuit 31 is converted to the timer circuit 31 ′ by switching the switch in the voltage amplification circuit 31 according to the output signal from the control unit 5 will be described with reference to FIGS. FIG. 2 is a circuit diagram showing a general example of a voltage amplifier circuit, and FIG. 3 is a circuit diagram showing a general example of a timer circuit. FIG. 4 is a block diagram showing an example of a voltage amplifier circuit to which a switch according to this embodiment is added, and FIG. 5 is a block diagram showing an example of a timer circuit to which a switch according to this embodiment is added.
[0018]
In FIG. 2, the cut-off frequencies of the high-pass filter and the low-pass filter are the cut-off frequencies of the high-pass filter: fc = 1 / (2 * π * C1 * R1)
Cut-off frequency of the low-pass filter: fc = 1 / (2 * π * C2 * R3)
Therefore, it is determined by the capacitors and resistors that make up the filter.
[0019]
In FIG. 3, the voltage of C1 is
VC1 = (1-exp (-t / R1 * C1)) * VCC
And when VC1 exceeds Vref voltage, the output of AMP1 is inverted.
[0020]
FIG. 4 is obtained by adding switches SW1 to SW4 to the voltage amplifier circuit of FIG. 2, and when a popcorn noise detection signal is not output, that is, when a normal detection operation is performed in the signal detection unit 3. The switches SW1 to SW4 are on the A side (state shown in FIG. 4) and function as the voltage amplifier circuit 31. Next, when the popcorn noise detection signal is output, the output signal from the control unit 5 is received, and the switches SW1 to SW4 are switched to the B side. If it does so, it will become a structure as shown in FIG. 5, and it will function as timer circuit 31 '. As described above, the timer circuit 31 ′ is a circuit that inverts the output of the AMP1 when VC1 exceeds the Vref voltage, and the time until the inversion is set as a time for prohibiting the detection operation of the signal detection unit 3. It has established. Further, as shown in the above equation, this time can be determined by the capacitor and resistor values (in this case C1 and R1) constituting the timer circuit 31 '. It also defines the bandwidth of the filter in the circuit 31.
[0021]
Thereafter, when the time determined by the timer circuit 31 ′ elapses, the control unit 5 returns the switches SW 1 to SW 4 to the A side to make the voltage amplifier circuit 31 again. During the period when the timer circuit 31 'is functioning, the switching signal is also output from the control unit 5 to the output changeover switch 6 at the same time, and the detection operation from the signal detection unit 3 is prohibited by cutting off the circuit. At the same time, a constant voltage is output.
[0022]
In the present embodiment, the capacitor C1 and the resistors R1 and ANP1 are used in common. However, the capacitors and resistors used in common can be freely changed by changing the number of switches provided in the voltage amplification circuit 31 and the arrangement location. Can be selected.
[0023]
Further, FIG. 6 is a configuration diagram showing a modification of the resistor R1 according to the present embodiment. As shown in this figure, the resistor R1 is replaced by resistors R1.1 to R1. n connected in series, and switches sw1.1 to sw1. n is provided, and the magnitude of the resistance can be changed by switching the switch. That is, the time determined by the timer circuit 31 ′ can be set to an arbitrary value.
[0024]
【The invention's effect】
As described above, in the infrared detection device of the present invention, when popcorn noise is detected, the voltage amplification circuit on the signal detection unit side can function as a timer circuit, so the voltage amplification circuit and the timer circuit are shared. This circuit configuration can be realized. Therefore, the circuit configuration of the entire apparatus can be reduced.
[Brief description of the drawings]
FIG. 1 is a circuit block diagram of an infrared detection device according to an embodiment of the present invention.
FIG. 2 is a circuit diagram showing a general example of a voltage amplifier circuit.
FIG. 3 is a circuit diagram showing a general example of a timer circuit.
FIG. 4 is a configuration diagram illustrating an example of a voltage amplifier circuit to which a switch according to the present embodiment is added.
FIG. 5 is a configuration diagram showing an example of a timer circuit to which a switch according to the present embodiment is added.
FIG. 6 is a configuration diagram showing a modified example of a resistor R1 according to the present embodiment.
FIG. 7 is a circuit block diagram of a conventional infrared detection device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Pyroelectric element 2 I / V conversion part 3 Signal detection part 31 Voltage amplification circuit 31 'Timer circuit 4 Popcorn noise detection part 5 Control part

Claims (2)

A pyroelectric element, an I / V converter that converts the current output from the pyroelectric element into a voltage and outputs the signal, and a signal detector that detects a signal to be detected from the output voltage of the I / V converter And a popcorn noise detector for detecting popcorn noise from the output voltage of the I / V converter,
The signal detection unit has a voltage amplification circuit that amplifies and outputs the output voltage of the I / V conversion unit, and a plurality of switches for switching to a timer circuit are provided in the voltage amplification circuit,
Infrared detection comprising a control unit for converting the voltage amplification circuit into the timer circuit when the popcorn noise detection unit detects popcorn noise, and returning the voltage amplification circuit to the voltage amplification circuit again after a predetermined time. apparatus. The voltage amplification circuit includes a filter including a capacitor and a resistor, and the switch is provided so that the capacitor and the resistor play a role of setting a time as the timer circuit. The infrared detection device according to claim 1.

Images