JPH04100197A - Infrared detector - Google Patents

Abstract

PURPOSE:To realize multi-channel photodetection by using infrared beams by providing an infrared photodetection part, a phase synchronizing circuit which generates a carrier signal with the output of a band-pass filter whose center frequency is equal to a carrier frequency, and a balanced demodulator which demodulates a modulated signal with the output of the circuit and the output of a band-pass filter. CONSTITUTION:The infrared beam projected by a projector is obtained by imposing pulse width modulation upon a carrier of frequency fc with a modulating wave of frequency fs, so the photoelectric conversion output of a photodetecting element 33 contains a frequency component of mfc+ or -nfs (m, n; integer). The photoelectric conversion output signal is amplified by an amplifier 34 and then inputted to the band-pass filter BPF 35 which has the center frequency fc to extract a signal component fc+ or -fs. A PLL circuit 36 outputs a continuous wave which has the frequency fc and is synchronized with the carrier with the output of the BPF 35. The balanced demodulator 37 inputs the output signal of the BPF 35 and the output signal of the PLL circuit 36 to modulate the pulse modulating wave. Consequently, infrared beams is usable for the multichannel photodetection.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention particularly relates to an infrared receiver suitable for application to a facing type infrared intruder detector in which a projector and a receiver are arranged facing each other. It is something.

[Prior Art] Conventionally, a configuration as shown in FIG. 2 has been known as a facing type infrared intruder detector in which a light projector and a light receiver are arranged facing each other. In FIG. 2, the projection surface of the light emitter 21 and the light receiving surface of the light receiver 22 are arranged to face each other, and the light emitter 21 is arranged to face the light receiving surface of the light receiver 22.
1 projects an infrared beam of a predetermined wavelength that blinks at a predetermined period. The infrared beam projected from the light projector 21 is received by a light receiving element (not shown) of the light receiver 22 and converted into an electrical signal, thereby detecting the presence or absence of an intruder.

However, in the two-way infrared intruder detector with the configuration shown in Figure 2, since only one infrared beam is used, there is a risk of being crossed over the infrared beam or under the infrared beam. In some cases, the intruder could be hidden and the intruder could not be detected.

Therefore, as a countermeasure to the above-mentioned problem, it has been proposed to arrange a plurality of pairs of a light projector and a light receiver. An example of its configuration is shown in FIG. In Figure 3, the floodlight mounting post 2
3 has 4 floodlights TI, T + T 2 + T J
is attached, and four receivers R+, Re
, Rs, and R4 are attached. According to this configuration, the infrared beam can be projected from a low position to a high position, so the above-mentioned problem can be solved.

By the way, since the infrared beam projected from the projector for boat fishing has a large spread on the receiver side, in the configuration shown in FIG. There is a problem that not only the light is received, but also the light receivers R2+ Rs and R4 simultaneously, causing mutual interference of light.As a result, even if a person passes near the emitter side, the light receiver side However, there was a problem in that it could not be detected and the alarm would be missed.

This is the floodlight T2. The same applies to T 3 and T 4.

Therefore, in the configuration shown in FIG. 3, mutual interference of light is avoided by doubly modulating the infrared rays output from each projector at different frequencies. An example of a configuration for this purpose is shown in FIG.

FIG. 4(a) is a diagram showing an example of the circuit configuration of the projector 1, and the carrier wave generation circuit 2 generates a relatively high frequency as shown in FIG. 5(a), for example, a frequency f0 of about 10 KHz.
A pulsed carrier wave having a frequency f0 is generated, and the modulated wave generation circuit 3 has a carrier wave frequency f0 as shown in FIG.
A pulse-like modulated wave having a sufficiently lower frequency, for example, a frequency f3 of several hundred Hz, is generated. Then, the carrier wave is pulse-modulated by a modulated wave in a pulse modulator 4. For example, if pulse amplitude modulation is performed in the pulse modulator 4, a modulated signal as shown in FIG. 5(C) is obtained. This modulated wave is input to the drive circuit 5, whereby the light emitting element 6 emits infrared rays having a predetermined wavelength, and the infrared rays are projected toward the light receiver via the reflecting mirror 7 and the visible light cut filter 8. . Note that as the light emitting element 6, an infrared light emitting LED with a center wavelength of around 900 nm is normally used.

FIG. 4(b) is a diagram showing an example of the circuit configuration of the light receiver 10, and the infrared beam projected from the projector 1 shown in FIG. 4(a) passes through the visible light cut filter 11 to the reflecting mirror 1.
2, is received by a light receiving element 13 disposed near the focal point of the reflecting mirror 12, and is converted into an electrical signal. The received signal is input to a band pass filter (hereinafter referred to as BPF) 14 to extract only frequency components near the carrier frequency f0, and further detected by a detector IS to separate the carrier wave, and then passed through a phase locked circuit ( PLL) 1B separates the modulated wave components.

The modulated wave component extracted in this way is transmitted to the signal processing section 17.
, predetermined signal processing is performed to determine the presence or absence of an intruder, and if it is determined that there is an intruder, the alarm output unit 18
is activated and a predetermined alarm operation is performed.

[Problems to be Solved by the Invention] By the way, in the infrared receiver used in the conventional two-way infrared intruder detector as shown in FIG. 4(b), the BPF 14 is composed of an LC circuit. , whose center frequency is fixed. Therefore, in the past, only a signal with a predetermined frequency component was extracted using a BPF with a fixed center frequency, and the presence or absence of the signal was detected by amplitude detection. Therefore, it is very difficult to create multiple channels of infrared beams, and even when multiple emitters T and receivers R are stacked in multiple stages as shown in Fig. 3, the number is limited. There was a problem.

The present invention solves the above-mentioned problems, and is a facing type infrared trespasser that can realize multi-channel infrared beams in a container, and can therefore stack more emitters and receivers in multiple stages. The purpose is to provide a detector.

[Means for Solving the Problems] In order to achieve the above object, an infrared receiver of the present invention receives infrared pulse modulated light projected from a projector. A bandpass filter having a center frequency of It is characterized by

[The working light from the projector has a first frequency f0. Infrared rays and NH pulse dimming are projected based on a signal obtained by pulse modulating a <7 less carrier wave with a pulse modulated signal having a second frequency f lower than that, for example, i<7 less amplitude modulation.

The infrared receiver includes an infrared receiver that converts the received infrared beam into an electrical signal, a bandpass filter whose center frequency is the carrier frequency, a phase synchronization circuit that generates a carrier signal from the output of the bandpass filter, and a phase synchronization circuit that generates a carrier signal from the output of the bandpass filter. A balanced demodulator is provided for demodulating a modulated signal from the output of the circuit and the output of the bandpass filter. Therefore, in the output signal of the infrared light receiving section, the carrier wave is separated by a bandpass filter and a phase synchronization circuit, and the modulated signal is further demodulated and separated by a balanced demodulator.

As a result, the ability to separate modulated signals can be greatly improved compared to the conventional method. Therefore, when the infrared receiver according to the present invention is applied to a facing type infrared intruder detector, it is possible to easily realize multiple channels. Particularly suitable for use.

[Example code] Examples will be described below with reference to the drawings.

FIG. 1 is a diagram showing the configuration of an embodiment of an infrared receiver according to the present invention. In the figure, 30 is a light receiver, 31 is a visible light cut filter, 32 is a reflecting mirror, 33 is a light receiving element, and 34 is a light receiving element. 35 is a BPF, 36 is a PLL circuit, 37 is a balanced demodulator, and 38 is a BPF.

39 indicates an alarm output section.

The operation of the circuit configuration shown in FIG. 1 is as follows.

Note that the projector (not shown) has the same configuration as shown in FIG. 4(a).

The infrared beam projected from the projector and reflected by the reflector 32 via the visible light filter 31 is reflected by the reflector 32.
The light is received by a light receiving element 33 arranged near the focal position of
Although converted into an electrical signal, the infrared beam projected from the projector has a frequency f. Since the carrier wave is pulse-amplitude modulated with a modulated wave of frequency f1, the photoelectric conversion output of the light receiving element 33 includes frequency components of m f a±nfs (where mln is an integer). This photoelectric conversion output signal is amplified by an amplifier 34 and then passed through a BPF with a center frequency f0.
35, and only the signal components of f0±f are extracted.

The PLL circuit 36 outputs a continuous wave having a frequency fo from the output of the BPF 35 and synchronized with the carrier wave.

The balanced demodulator 37 receives the output signal of the BPF 35 and the output signal of the PLL circuit 36 and demodulates the pulse modulated wave.

The output of the balanced demodulator 37 is BP whose center frequency is f.
The signal is input to F38, unnecessary frequencies are removed, only the modulated wave component having frequency f is extracted, and is input to the alarm output section 39. In other words, the BPF 38 is arranged to improve the degree of separation of modulated wave components.

The alarm output unit 39 receives the output of the BPF 3B, determines whether the modulated wave component is absent, drives a relay, etc., and sends an alarm signal to the outside when it is determined that there is an intruder.

Note that as the light-receiving element 33, a phototransistor having sensitivity around the center wavelength of 900 nm is used as in the conventional case.

Now, for example, a pulse with a frequency f0 = 9 KHz is used as a carrier wave, a pulse with a frequency f = 500 Hz is used as a modulating wave, pulse amplitude modulation is performed, and the center frequency of the BPF 35 and BPF 38 of the light receiver 30 is set as follows. When set to 9 K)lz and 500 Hz, respectively, f, = 500 Hz was detected as the output of the BPF38. However, when the light receiver 530 is set under the above conditions, the frequency projected from the light emitter 21 is set to fo=a
KHz, rs=soo)lz+=,
When f,=12 KHz, f,=500 Hz, and f. =12 KHz, f, = [ioo
Hz, the output signal of BPF'38 was found to be greatly attenuated, and it was confirmed that the resolution ability to correctly detect the modulated wave frequency f was 30 dB or more.

As described above, in the present invention, the resolution ability of the modulated wave frequency f3 is much higher than that of the conventional method, so for example, as the carrier wave frequency f al + f a2 +...+
m frequencies of foe are used, and f is the modulation wave frequency.
When n frequencies of s++ f s2 +...1fsn are used, mX
It is now possible to set n types of channels, and the fourth
As shown in the figure, this is very effective when multiple emitters and receivers are stacked in multiple stages.

As is clear from the above explanation, it is required that the center frequencies of the BPFs 3S and 38 can be easily changed, and for this purpose, the BPFs 35 and 38 must be able to change the center frequencies to the desired center frequencies using externally input clock frequencies. A switched gear pantograph that can vary the frequency may be used, and the desired center frequency may be obtained by changing the dip switch.

Hereinafter, one embodiment of the present invention has been described, but it will be obvious to those skilled in the art that the present invention is not limited to the above embodiment, and that various modifications can be made. For example, −
1- In the embodiment described above, a balanced double F is used to separate the modulated waves.
Although the BPF 3B is placed after the L filter 37, it is clear to those skilled in the art that a PLL circuit may be used in the same way as for carrier wave separation.

However, the output frequency of the balanced demodulator 38 is about several hundred Hz, and the Q value of the BPF can be set high, so there is no need to intentionally use a PLL circuit, and a BPF is sufficient.

[Effects of the invention] As is clear from the above explanation, conventionally carrier waves are separated using a BPF and a detector with the carrier frequency f0 as the center frequency, and modulated waves are separated using a PLL circuit. , in the present invention, carrier wave separation is performed using BPF35 and P
The L L circuit 36 separates the modulated wave, and the balanced demodulator 3 separates the modulated wave.
7 and BPF38, the following effects can be obtained.

■Generally, BPF used to separate carrier waves has poor frequency separation because the carrier wave frequency 10 is high and the Q value of the filter cannot be high. However, in the present invention, the separation of carrier wave frequency f0 is performed using Since a synchronous detection circuit is used, the Q value of the filter can be increased isometrically, and the degree of frequency separation can be improved.

■Carrier frequency f. is usually set within the range of 10 KHz to 30 KHz due to the response speed of the light receiving element, etc., but since the degree of frequency separation is good in this frequency band, there is no need to move the carrier frequency f0 far away, and the channel You can take a large number.

(2) Since the center frequency of the BPF is electrically variable and a PLL circuit is used to separate carrier waves, it is easy to follow even if the carrier frequency is slightly different, making adjustment easy.

As described above, by using the infrared receiver according to the present invention, it is possible to construct a two-way infrared intruder detector with high frequency separation discrimination ability, so it is extremely effective for use in a multi-channel infrared intruder detector.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an embodiment of an infrared receiver according to the present invention, FIG. 2 is a diagram showing a schematic configuration example of a conventional facing-type infrared intruder detector, and FIG. 3 is a diagram showing a schematic configuration example of a conventional facing-type infrared intruder detector. A diagram showing another configuration example of an infrared intruder detector, FIG. 4 is a diagram showing a configuration example of a projector and a light receiver used in the facing type infrared intruder detector shown in FIG. 3, and FIG. 5 is a diagram showing a carrier wave, FIG. 3 is a waveform diagram showing an example of a signal wave and a pulse modulated wave. 30... Light receiver, 31... Visible light cut filter,
32... Reflector, 33... Light receiving element, 34... Amplifier, 35... BPF, 3B... PLL circuit, 37
...Balanced demodulator, 38...BPFl 39...Alarm output section. Applicant: Ammi Electric Co., Ltd. Agent Patent Attorney: Hideo Sugai (7 others) Figure 4 (b)

Claims (1)

[Claims] (1) An infrared receiver that receives infrared pulse modulated light projected from a projector includes an infrared receiver, a bandpass filter whose center frequency is a carrier frequency, and a phase synchronization circuit that generates a carrier signal from the output of the bandpass filter. and,
An infrared light receiver comprising a balanced demodulator that demodulates a modulated signal from the output of the phase synchronization circuit and the output of the bandpass filter.