JPH07254882A - Optical modulator for data transmission - Google Patents

Abstract

PURPOSE:To provide the optical modulator for data transmission which surely transmits the optical signal of a light emitting part to a light reception part even in unfavorable circumstances of mixture of external disturbing lights and has high S/N and high reliability. CONSTITUTION:This device is provided with a coding part 12 which generates binarized data to be transmitted in series, a first modulating means 13 which generates a square wave having two kinds of frequencies f1 and f2 correspondingly to this binarized data, a high frequency generator 19 which generates a pulse train having a prescribed duty factor a second modulating means (gate 20) which generates a pulse train having a high frequency only in half cycles of the square wave having frequencies f1 and f2' and a light emitting element 21 which is driven to emit light by the output of the second modulating means.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical modulator for data transmission for transmitting digital information, which is usually binarized, by light such as infrared rays, visible rays, and laser beams to a light receiver side by turning on and off a light emitter. .

[0002]

2. Description of the Related Art Conventionally, in an apparatus that uses light emission by an LED (solid-state light emitting diode) to monitor the passage or approach of a person, a vehicle, or other moving objects, the emission intensity of the LED is made larger than a continuous rated value. In addition, for the purpose of suppressing power consumption, pulse-modulated light with a duty of about 1/10 is adopted, for example.

FIG. 1 shows a circuit configuration of a conventional example disclosed in, for example, Japanese Patent Publication No. 59-21132, and FIG. 2 shows a waveform diagram of each part. Low-frequency oscillator 1 outputs a square wave, such for example 500H _Z as shown in FIG. 2b. High-frequency oscillator 2, for example 20 kHz _Z as shown in Figure 2a, a duty 1 /
It outputs 10 pulse trains. The AND gate 3 allows the high frequency pulse train to pass only while the low frequency square wave is at a high level. As a result, the light emitting element 4 has the following structure as shown in FIG.
It is driven to emit light by a high frequency signal which is low frequency modulated.

By receiving such modulated light, a reflecting object,
Since the light receiver that determines the presence or absence of a light-shielding object continuously receives pulsed light, the PLL (phase synchronization) detection method is used to increase the S / N and extend the maximum reach of optical signals. There is.

[0005]

However, for example, when a plurality of sensors are arranged and used in a light-shielding type infrared sensor or the like, in the PLL detection method, mutual interference is prevented by switching the set frequency and the like. (Because it is necessary to prepare many different frequencies), there is a limit to the number. In the case of transmitting a plurality of pieces of information from a human body detector or the like arranged on a ceiling or a wall surface, that is, in data transmission or the like, depending on the code form (system), S / N may be used.
This will lead to deterioration of the ratio. On the other hand, the present invention provides a highly reliable data transmission device having a high S / N ratio in any code form (system).

[0006]

An optical modulator for data transmission according to the present invention comprises coding means for serially generating binary data (0/1) to be transmitted, and the binary data (0
/ 1) corresponding to the first modulation means for frequency-modulating the binarized data by generating square waves of two kinds of frequencies (f ₁ / f ₂ ) and the two kinds of frequencies (f ₁ / f) ₂ ) A high-frequency generator that generates a pulse train having a frequency higher than that of ₂ ) and a _second high-frequency pulse train that generates the high-frequency pulse train only during a half-cycle period of a square wave of the above frequency (f ₁ / f ₂ ). It is characterized in that it has a modulator and a projector which is driven to emit light by an output signal of the second modulator.

The first modulation means of the present invention is preferably constituted by an FSK (Frequency Shift Keying) low frequency oscillator.

[0008]

The first modulation means is the (O) of the data to be transmitted.
To the frequency (f ₁ ), and the data (1) to the frequency (f ₂ ). The frequencies f ₁ and f ₂ are, for example, 5
00H is a _Z to several KH _Z. The second modulating means outputs the square wave modulated by the frequencies f ₁ and f ₂ to, for example,
0KH _Z, modulated by a high frequency pulse duty 1/10.

[0009]

FIG. 3 shows a circuit block diagram of a light projecting section 10 embodying the present invention. For example, the human body detector 11 arranged on a ceiling, a wall surface or the like detects that a human body is present in a predetermined detection area and inputs a detection signal to the coding unit 12.
The coding unit 12 forms, for example, the number of the human body detector, information indicating that the human body is detected, and the like into a formalized digital signal of one frame, and repeatedly outputs a predetermined number of frames. The low frequency modulation circuit 13 includes two different low frequency oscillators 14 and 15 of f ₁ and f _2, an AND gate 16 that opens when the digital output of the coding unit 12 is at a high level, and a low digital output of the coding unit 12. It is provided with an AND gate 17 which opens at the time of level and an OR gate 18 which allows the digital output of any of the gates 16 and 17 to pass. The low frequency modulation circuit 13 can be composed of an FSK oscillator. The high frequency oscillator 19 is, for example, f _H = 100 KH
A pulse train with _Z and a duty of 1/10 is output. AND
The gate 20 outputs the palace train of the high frequency oscillator 19 only when the output of the low frequency modulation circuit 13 is at a high level. According to the output waveform of the AND gate 20, the LED element 2
1 is driven to emit light.

FIG. 4 shows the waveform of each part of the light projecting section 10. When coding unit 12 is a digital signal as shown in (A) FIG., The low frequency modulation circuit 13, (B) in accordance with the output of the coding unit 12 as shown in FIG., A square wave of frequency f ₁ or frequency f _2, Outputs a square wave of. The high frequency oscillator 19 continuously outputs a high frequency pulse train having a fundamental frequency f _H as shown in FIG. AND gate 2
0 outputs the high frequency pulse train modulated by the square wave output of the low frequency modulation circuit 13, and the LED is output according to this output waveform.
The element 21 is driven to emit light.

FIG. 5 shows a circuit block diagram of the light receiving section 30 which receives the optical signal of the light projecting section 10. The photoelectric conversion signal of the light receiving element 31 passes through the tuning amplifier 32 of high frequency f _H , then the low frequency component is demodulated, and the low frequency component is amplified by the amplifier 34. Next, the FSK detection unit 35 discriminates between the low frequency f ₁ component and the low frequency f ₂ component, and the decoding unit 36 demodulates the input signal of the coding unit 12 of the light projecting unit 10 and outputs through the output circuit 37. To be done.

[0012]

According to the present invention, predetermined low frequencies f ₁ , f
_The digital signal coded by ₂ is modulated, and then further modulated by a pulse train of a predetermined high frequency f _H to emit and output light, so that it is hardly affected by external noise and the reliability of optical data transmission is improved. Greatly improved.

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing a conventional example.

FIG. 2 is an operation explanatory view of the conventional example shown in FIG.

FIG. 3 is a circuit block diagram showing an embodiment of the present invention.

FIG. 4 is an operation explanatory view of the embodiment shown in FIG.

5 is a circuit block diagram showing an embodiment of a light receiving section 30 used in cooperation with the light projecting section 10 shown in FIG.

[Explanation of symbols]

10 Light emitting unit 11 Human body detecting unit 12 Coding unit 13 Low frequency modulation circuit (FSK oscillator) 14 Low frequency f ₁ oscillator 15 Low frequency f ₂ oscillator 19 High frequency oscillator

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location G02F 2/02 3/00 H01H 35/00 A H01S 3/10 A H04L 27/12 Z 9297-5K

Claims (2)

[Claims] 1. A coding means for serially generating binary data (0/1) to be transmitted, and two types of frequencies (f ₁ / f ₂ ) corresponding to the binary data (0/1). ) A first modulating means for frequency-modulating the binarized data by generating a square wave, and a pulse train having a frequency higher than the two kinds of frequencies (f ₁ / f ₂ ) and having a predetermined duty. A high frequency generator for generating, a second modulating means for generating the high frequency pulse train only for a half cycle period of a square wave of the above frequency (f ₁ / f ₂ ), and a light emission drive by an output signal of the second modulating means. Optical modulator for data transmission having a floodlight. 2. The optical modulator for data transmission according to claim 1, wherein said first modulating means is an FSK (Frequency Shift Keying) low frequency oscillator.