JP3096323B2 - Infrared receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit configuration of an infrared light receiver used in a facing infrared intruder detector in which a light emitter and a light receiver are arranged opposite to each other.

[0002]

2. Description of the Related Art Conventionally, a configuration as shown in FIG. 2 has been known as a facing infrared intruder detector in which a light emitter and a light receiver are arranged to face each other. In FIG.
And the light receiving surface of the light receiver 22 are arranged to face each other, and the light projector 21 emits an infrared beam of a predetermined wavelength that blinks at a predetermined cycle. And the floodlight 21
Is received by a light receiving element (not shown) of the light receiver 22 and converted into an electric signal, and a process of detecting the presence or absence of an intruder is performed. However, in the facing infrared intruder detector having a configuration as shown in FIG. 2, since only one infrared beam is used, the infrared intruder may straddle the infrared beam or pass under the infrared beam. In some cases, they could be dived and could not detect intruders. Therefore, as a countermeasure against the above problem, it has been proposed to arrange a plurality of pairs of a light emitter and a light receiver. An example of the configuration is shown in FIG. In FIG.
The four projectors T ₁ , T ₂ , T ₃ , T ₄
Are mounted, and four light receivers R ₁ , R ₂ , R ₃ , R ₄ are mounted on the light receiver mounting support 24 which is arranged to face the light receiver.
Is attached. According to this configuration, since the infrared beam can be projected from a low position to a high position, the above-described problem can be solved.

In general, an infrared beam projected from a light projector has a large spread on the light receiver side. Therefore, in the configuration shown in FIG.
Infrared beam projected from ₁ not only is received by the photodetector R _1, will be received at the same time, even the light receiver R _2, R ₃ and R _4, there is a problem that mutual interference of light occurs . Therefore, in the configuration shown in FIG. 3, the mutual interference of light is avoided by double modulating the infrared light output from each projector at different frequencies. FIG. 4 shows a configuration example for that purpose. FIG. 4A is a diagram showing an example of a circuit configuration of the light projector 1, and FIG.
A relatively high frequency as shown in FIG.
pulsed carrier f _c having a frequency of approximately z is generated, the modulation wave generation circuit 3, as shown in FIG. 5B, frequency sufficiently lower than the carrier frequency f _c, for example 300 to 600
Pulsed modulation wave f _s with a frequency of about Hz is generated. Then, the carrier f _c in the pulse modulator 4 is pulse-modulated by the modulation wave f _s. Now, for example, assuming that pulse amplitude modulation is performed in the pulse modulator 4, a signal as shown in FIG. 5C is obtained. This signal is input to the driving circuit 5, which causes the light emitting element 6
, An infrared pulse-modulated light having a predetermined wavelength is projected, and the infrared light is projected through a reflecting mirror 7 and a visible light cut filter 8 toward a light receiver. Note that, as the light emitting element 6, an LED that emits infrared light having a center wavelength near 900 nm is usually used. FIG. 4B is a diagram illustrating an example of a circuit configuration of the light receiver 10. The infrared beam projected from the light projector 1 illustrated in FIG. The light is received by the light receiving element 13 disposed near the focal position, and is converted into an electric signal (received signal). Receiving wave signals, band-pass filter (hereinafter, referred to as BPF) is input to the 14 carrier frequency f _c
Only the nearby frequency components are extracted and further detected by the detector 15 to extract the modulated wave components, which are then input to the PLL circuit 16. The PLL circuit 16 determines the frequency of the input signal,
It is to compare the frequency of the modulated wave of the infrared beam emitted from the projector arranged opposite to, and to output a signal of a predetermined level according to the result of the comparison, for example,
If the frequency of the input signal matches the modulation wave frequency, a low-level signal is output, for example, and if not, a high-level signal is output. The output signal of the PLL circuit 16 is subjected to predetermined signal processing by a signal processing unit 17, and when there is an intruder, an alarm output unit 18 is activated to output an alarm signal.

[0004]

By the way, in a conventional infrared light receiver used in a conventional facing infrared intruder detector as shown in FIG. 4B, the BPF 14 is usually constituted by an LC circuit. Therefore, it is difficult to make the bandwidth sharp, and the bandwidth must be widened to some extent. And in addition, a frequency which is generally used as the carrier frequency f _c is 9 kHz, 12 kHz, 15 kHz, 20 kHz, 25
It is several kinds of frequencies within a very narrow bandwidth such as kHz, so that although the infrared rays from the corresponding projectors are actually cut off, the infrared rays from the projectors other than the corresponding projectors are received and false alarms are generated. May occur.

[0005] Specifically, it is as follows. Now, the frequency of the modulated wave carrier frequency f _c of the pulse modulated light carrier frequency f _c of the pulse modulated light is projected from the projector T ₁ is being projected 20 kHz, the projector T ₂ is at 15kHz 3 together 300Hz when it is, the light receiver R ₁ is to function properly if they receives infrared rays from the projector T _1, when the infrared radiation from the projector T ₁ is being blocked, is projected from the projector T ₂ When the spectrum of the received signal based on the pulse-modulated light falls within the bandwidth of the BPF 14, the received signal is balanced and demodulated.
Since the signal having a frequency of z is input to the PLL circuit 16, the signal of low level is output indicating that it is receiving correctly infrared as if from the projector T ₁ from the PLL circuit 16. But it is clear that this is nothing more than a misinformation.

As described above, in the prior art, when the carrier frequencies set for the respective light emitters are close to each other, the degree of separation of the received signal in the light receiver deteriorates. It is difficult, and there is a problem that the number is limited even when a plurality of light emitters T and light receivers R are multi-tiered as shown in FIG.

The present invention solves the above-mentioned problems, and can improve the degree of separation of a received signal even when the carrier frequency is close, thereby realizing a multi-channel infrared beam. It is an object of the present invention to provide an infrared light receiver that can be formed and that can be provided with a larger number of light emitters and light receivers in multiple stages.

[0008]

In order to achieve the above object, an infrared receiver of the present invention is an infrared receiver for receiving infrared pulse modulated light projected from a projector,
An infrared receiving optical system, a first bandpass filter for extracting a predetermined band centered on a carrier frequency of the pulse-modulated light from a received signal output from the infrared receiving optical system, and the first bandpass filter A phase comparator having the other input as an input, and an output of a frequency divider for dividing the oscillation frequency of the voltage controlled crystal oscillator at a predetermined frequency division ratio as the other input. A low-pass filter for extracting a frequency signal component; a voltage-controlled crystal oscillator whose oscillation frequency is controlled by an output voltage of the low-pass filter; and an input for receiving the output of the frequency divider and the output of the first bandpass filter. A balanced demodulator for balanced demodulation of the signal; and a second bandpass filter for extracting a predetermined band centered on the modulation wave frequency of the pulse-modulated light from the output of the balanced demodulator. And wherein the Rukoto.

[0009]

[Action] is from the projector, pulse modulation with a pulse modulated signal having a second frequency f _s the pulse carrier lower than with a first frequency f _c, for example, an infrared pulse-modulated light based on a pulse amplitude modulated signal Is projected.

The infrared light receiver has an infrared light receiving optical system for converting a received infrared beam into an electric signal. The received signal output from the infrared light receiving optical system is input to a first bandpass filter, and a predetermined band component having a carrier frequency of the pulse modulated light as a center frequency is extracted. This output is input to a phase comparator, and the phase is compared with a signal obtained by dividing the output of the voltage-controlled crystal oscillator. The output of the phase comparator is input to the voltage-controlled crystal oscillator via the low-pass filter, whereby the output signal of the voltage-controlled crystal oscillator is phase-synchronized with the carrier component in the received signal.

The output of the frequency divider and the output of the first bandpass filter are input to a balanced demodulator, and the output of the balanced demodulator extracts a predetermined band whose center frequency is the modulated wave frequency of the pulse modulated light. Is input to the second bandpass filter.

As a result, the degree of separation of the received signal can be greatly improved as compared with the related art. 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 multi-channel, so that a plurality of projectors and receivers are multi-stacked. It is particularly suitable for use.

[0013]

Embodiments will be described below with reference to the drawings.
FIG. 1 is a diagram showing the configuration of an embodiment of an infrared light 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 an amplifier. , 35 is a BPF, 36 is an amplifier, 37 is a phase comparator,
38 is an LPF, 39 is a voltage controlled crystal oscillator (VC
X), 40 is a frequency divider, 41 is a balanced demodulator, 42 is BP
F and 43 indicate a signal processing unit, and 44 indicates an alarm output unit.

The operation of the circuit configuration shown in FIG. 1 is as follows. The light projector (not shown) has the same configuration as that shown in FIG. 4A. The infrared beam projected from the light projector and reflected by the reflecting mirror 32 via the visible light cut filter 31 is received by the light receiving element 33 arranged near the focal position of the reflecting mirror 32, and is converted into an electric signal. the infrared beam projected from the projector, since it is obtained by pulse amplitude modulating a carrier wave having a predetermined frequency f _c in the modulation wave of a predetermined frequency f _s, the photoelectric conversion output of the light receiving element 33, mf _c
± nf _s (where, m, n are integers) it contains frequency components. The photoelectric conversion output signal is amplified by the amplifier 34, the center frequency is input to BPF35 of f _c, f _c
Only the signal component of ± f _s is extracted.

The output signal of the BPF 35 is input to one input terminal of a phase comparator 37 via an amplifier 36 and to one input terminal of a balanced demodulator 41. The output of the frequency divider 40 is input to the other input terminal of the phase comparator 37. The output of the frequency divider 40 is also input to the other input terminal of the balanced demodulator 41.

The frequency divider 40 has a VCX as a reference oscillator.
The frequency of the output signal 39 is divided and the carrier frequency of the normal received signal, that is, the frequency substantially equal to the carrier frequency of the infrared pulse modulated light emitted from the light emitter arranged opposite to the light receiver 30 is determined. It outputs a signal having the same.
Thus, the carrier frequency f _c of the current example regular received signal
Is 20 kHz and the oscillation frequency of the VCX 39 is 5 MHz, the frequency division ratio of the frequency divider 40 is 1/250.

The phase comparator 37 compares the phase of the carrier component contained in the received signal input via the amplifier 36 with the phase of the carrier frequency signal output from the frequency divider 40, and compares the error with a voltage. The error voltage is input to the VCX 39 via the LPF 38 as a control voltage. The oscillation frequency of the VCX 39 is controlled by the control voltage so that the error voltage becomes zero. By performing the above operation, the phase of the output signal of the frequency divider 40 matches the phase of the carrier component in the received signal.

The balanced demodulator 41 receives the output signal of the BPF 35 and the output signal of the frequency divider 40 and demodulates a pulse modulated wave. The output of the balanced demodulator 41 is input to BPF42 the center frequency is made a frequency f _s of the modulated wave, it is removed unnecessary frequency components only modulated wave component of the frequency f _s is extracted signal processor 43 Is input to

The modulated wave component thus obtained is subjected to predetermined signal processing in a signal processing unit 43, and when it is determined that an intruder is present, an alarm output unit 44 is activated to send the signal to a receiver (not shown). An alarm signal is output. The light receiving element 33 has a center wavelength of 900 nm as in the related art.
A phototransistor or a photodiode having sensitivity in the vicinity is used.

In the configuration shown in FIG. 1, it is very important to use VCX39 as a reference oscillator.
Because the VCX39 uses crystal as an oscillation element, the range of controllable oscillation frequency is very narrow,
Usually, the frequency is about several tens of Hz. Therefore, even if an infrared beam from the opposing projector is shielded and a signal having a frequency component other than the normal carrier frequency is obtained as the output of the BPF 35, the output signal of the frequency divider 40 is obtained. Does not synchronize the phase with the carrier frequency component in the output signal of the amplifier 36. As a result, the output signal cannot be obtained from the balanced demodulator 41, and false alarms which have conventionally occurred can be prevented.

Specifically, it is as follows. In now to Figure 3, projector T _1, the pulse modulated optical carrier frequency is 20kHz, respectively, which is projected from T _2, 16 kHz, the frequency of the modulation wave are both 300 Hz, the light receiver R ₁ is the structure shown in FIG. 1 It is assumed that the range of the oscillation frequency of the VCX 39 is larger than the above controllable range, that is, 5M ± 50 Hz, and the frequency division ratio of the frequency divider 40 is 1/250. At this time, if you receive the infrared beam from the projector T ₁ is, VCX39 the light receiver R ₁ can oscillate a signal synchronized with the phase of the carrier frequency component in the output of the amplifier 36,
As a result, the balanced demodulator 41 demodulates the signal component of the modulated wave. In contrast, when only the infrared beam from the projector T ₁ is being cut off, if the bandwidth of BPF35 is wide, the band of the spectrum of the received signals based on the infrared radiation that is projected from the projector T ₂ is BPF35 may enter within the width, but since the carrier frequency 16kHz used in the projector T ₂ even if is outside the range of the oscillation possible frequencies of VCX39, VCX39 is synchronized with the carrier components in the output signal of BPF35 Therefore, the balanced demodulator 41 does not demodulate the signal component of the modulated wave in the received signal.

[0022]

As is apparent from the above description, in the present invention, a VCX having a very narrow frequency range controllable as a reference oscillator is used. Since the carrier frequency included in the signal can be satisfactorily discriminated as to whether it is a legitimate carrier, the degree of separation of the received signal can be greatly improved as compared with the conventional one, and the frequency separation and discrimination ability can be improved. A high facing infrared intruder detector can be constructed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of an infrared receiver according to the present invention.

FIG. 2 is a diagram illustrating a schematic configuration example of a conventional facing infrared intruder detector.

FIG. 3 is a diagram showing another configuration example of a conventional facing infrared intruder detector.

FIG. 4 is a diagram showing a configuration example of a light projector and a light receiver used in the facing infrared intruder detector shown in FIG. 3;

FIG. 5 is a waveform diagram showing examples of a carrier wave, a signal wave, and a pulse modulation wave.

[Explanation of symbols]

Reference numeral 30: light receiver, 31: visible light cut filter, 32: reflecting mirror, 33: light receiving element, 34: amplifier, 35: BPF,
36 amplifier, 37 phase comparator, 38 LPF, 39
... voltage controlled crystal oscillator (VCX), 40 ... frequency divider, 4
1: balanced demodulator, 42: BPF, 43: signal processing unit, 4
4: Alarm output unit.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G08B 13/181-13/187 G01V 9/04

Claims (1)

(57) [Claims] 1. An infrared receiver for receiving infrared pulse modulated light projected from a projector, comprising: an infrared receiving optical system; and a carrier frequency of the pulse modulated light based on a received signal output from the infrared receiving optical system. A first band-pass filter for extracting a predetermined band having a center frequency as a center frequency, and a frequency divider for dividing the oscillation frequency of the voltage-controlled crystal oscillator at a predetermined frequency-dividing ratio by using the first band-pass filter as one input. A low-pass filter for extracting a predetermined low-frequency signal component from the output of the phase comparator, and a voltage control type in which the oscillation frequency is controlled by the output voltage of the low-pass filter. A crystal oscillator, a balanced demodulator that receives the output of the frequency divider and the output of the first bandpass filter to perform balanced demodulation of the received light signal, and converts the pulse demodulated from the output of the balanced demodulator. An infrared receiver comprising: a second bandpass filter for extracting a predetermined band whose center frequency is a modulated wave frequency of light control.