JPH0262063B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an infrared communication device used for data communication between one computer and a large number of terminal devices indoors, for example, by optical signals using infrared rays.

Generally, in an indoor data communication system using an optical signal using infrared rays, an indoor infrared communication device configured as shown in FIG. 1, for example, is used. That is, a polling signal output from the computer 11 is supplied to a modem (modulator/demodulator) 13 via a transmission line 12 and modulated into a high frequency signal of frequency fd. The polling signal modulated by this modem 13 is sent to a large number of satellites 1 installed on the ceiling etc. via coaxial cables 14a, 14b, .
5a, 15b, . . . and converted into a high frequency optical signal of the frequency fd. This large number of satellites 1
The optical signals from the transceivers 16a, 15b, . . . are diffused into the room as shown by the broken line a, and are received by the transceivers 16a, 16b, .
The optical signals received by the transceivers 16a, 16b, . . . are demodulated as polling signals from the computer 11.
7b, . . to the terminal devices 18a, 18b, .

As a result, each terminal device 18a, 18
b, ... check whether the supplied polling signal is their designated address or not, and if it is their own address, output the response data signal, and from these terminal devices 18a, 18b, ... The data signals are again supplied to the transceivers 16a, 16b, . . . via the transmission lines 17a, 17b, . The data signals supplied to the transceivers 16a, 16b, . . . are modulated at a frequency fu and then converted into optical signals. , 15b, . . . and converted into an electrical signal. This satellite 15a, 15
The data signals converted into electrical signals by the signals b, . . . are supplied to the modem 13 via the coaxial cables 14a, 14b, . The electrical data signals demodulated by the modem 13 from the terminal devices 18a, 18b, . . . are supplied to the computer 11 via the transmission line 12 and subjected to signal processing. In this way, one computer 11 and a large number of terminal devices 18a, 18
It is designed to perform mutual communication with b,...

Here, FIG. 2 shows the configuration of the satellite 15a of the indoor infrared communication device in FIG. The signal is supplied to the drive amplifier circuit 23 via 22. As a result, the light emitting element 24 blinks at the frequency fd in response to the polling signal, and diffuses and radiates the optical signal into the room.

Furthermore, the transceiver 16a in FIG.
The optical signal corresponding to the response data signal from is converted into an electrical signal of a predetermined voltage by the light receiving element 25 and the preamplifier circuit 26, and is again outputted to the coaxial cable 14a via the duplexer 22 and the splitter 21.

However, satellite 15 configured in this way
a, 15b, . . . do not receive optical signals from, for example, the transceivers 18a, 18b, . Even in this case, noise signals are output to the coaxial cables 14a, 14b, . . . . That is, noise signals similar to those described above are added from a large number of satellites 15a, 15b, . . . to the coaxial cables 14a,
14b,..., and modem 1
3, when demodulating data signals from the terminal devices 18a, 18b, . . . , it becomes very difficult to distinguish between the noise signal and the data signal.

Each part A~ in the satellite 15a in this case
The signal waveform of C is shown in FIG. Here, T _O has no response from the terminal device 18a, and the transceiver 16a
The time during which no optical signal is emitted from T _D
There is a response from the terminal device 18a, and the transceiver 1
It shows the time during which the optical signal of frequency fu is emitted from 6a. That is, a noise signal is added to the waveform A received by the light receiving element 25 via the light receiving element 25 and the preamplifier circuit 26 as shown in the waveform B, and furthermore, to this waveform B, the noise signal is added to the waveform A received by the light receiving element 25.
On 4a, other satellites 15a, 15b,
Noise signals from ... are also added to form a random signal like waveform C.

Therefore, for example, the coaxial cables 14a, 14
Many satellites 15a, 15b,... on b,...
When connected, the received signal from the satellite near the tip will be significantly attenuated due to the above-mentioned noise signal and loss due to the coaxial cables 14a, 14b, etc., and the satellite will inevitably The number must be limited. This makes it extremely difficult to expand the communication range.

This invention was made in view of the above-mentioned problems. For example, even when a large number of satellites are connected, the infrared rays enable accurate demodulation without adding noise signals to the data signal. The purpose is to provide communication equipment.

That is, the infrared communication device according to the present invention outputs the optical signal from the satellite to the coaxial cable only when the light receiving element receives the optical signal output from the transceiver as response data.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 4 shows an extracted satellite 31a of this communication device, in which the modem 13 uses a frequency fd
A polling signal modulated by the computer 11 is input via the coaxial cable 14a. A polling signal input from this coaxial cable 14a is supplied to a drive amplifier circuit 23 via a branching device 21 and a branching filter 22. This drive amplification circuit 23 amplifies the polling signal that is supplied and causes the light receiving element 24 to blink in accordance with the frequency fd.Thereby, the light receiving element 24 transmits an optical signal corresponding to the polling signal of the frequency fd into the room. radiate diffusely.

On the other hand, the frequency fu has a signal waveform as shown in FIG. 5A, for example, corresponding to the response data signal from the terminal device 18a output from the transceiver 16a.
The optical signal is received by the light receiving element 25. The response data signal converted into an electrical signal by this light receiving element 25 is amplified by a preamplifier 26.
The response data signal amplified by the preamplifier 26 becomes a signal waveform with added noise signals as shown in FIG. 5B due to the influence of unnecessary light incident on the light receiving element 25, thermal noise, etc. . Then, the response data signal with added noise from the preamplifier circuit 26 is passed through the amplitude limiting circuit 32 to the fifth
As shown in FIG. C, when a response signal is supplied from the transceiver 16a, the amplitude is limited to a constant width and is supplied to the high frequency switch circuit 33. At the same time, the response data signal from the preamplifier circuit 26 is passed through the detection circuit 34 into a positive pulse signal corresponding to the response signal supplied from the transceiver 16a, as shown in FIG. Convert. Furthermore, this positive pulse signal is converted into a pulse shaping circuit 3.
5 through a constant voltage level as shown at E in the same figure.
The pulse is shaped by V _P and supplied to the high frequency switch circuit 33. In other words, the detection circuit 34 and the pulse shaping circuit 35 operate at a constant voltage level only when the optical signal corresponding to the response data signal from the transceiver 16a is received by the light receiving element 25.
It outputs a pulse signal higher than V _P and supplies it to the high frequency switch circuit 36.

This high frequency switch circuit 36 is turned on only when the pulse signal from the pulse shaping circuit 35, that is, the light receiving element 25 receives a high frequency optical signal from the transceiver 16a. The response data signal from the amplitude limiting circuit 32 is supplied to the output amplifier circuit 36 only during operation. This output amplification circuit 36 amplifies the supplied response data signal, and then outputs it to the coaxial cable 14a via the duplexer 22 and the splitter 21. This coaxial cable 14
The response data signal output to a is demodulated by the modem 13 and supplied to the computer 11.

That is, the detection circuit 34 and the pulse shaping circuit 35 cause the transceiver 1 to be
Since the reception of the optical signal from the satellite 6a is detected and a response data signal whose amplitude is limited is output via the high frequency switch circuit 33 only when the light is received, the so-called satellite 31a outputs the response data signal to the coaxial cable 14a. The response data signal transmitted from the terminal device 18a has a signal waveform as shown in FIG. 5F. That is, the terminal device 18a responds to the polling signal from the computer 11,
When the response data signal becomes an optical signal from the transceiver 16a and is received by the light receiving element 25
Only at T _D , the satellite 31a outputs a response data signal limited to a constant amplitude, and when there is no response data signal from the terminal device 18a, T _O
At this time, the high frequency switch circuit 33 is turned off and does not output any signal at all.

Therefore, even if, for example, unnecessary light such as indoor lighting light is incident on the light receiving element 25, or thermal noise is generated in the preamplifier circuit 26, etc., there is no response signal from the terminal device 18a. Sometimes, it is possible to completely prevent noise signals from being output to the coaxial cable 14a. Furthermore, since the response signal is outputted with a limited amplitude, a response signal of a constant level can be obtained without being greatly affected by the length of the optical signal transmission distance. As a result, the terminal device 18
It is possible to clarify the presence or absence of response signals from a, 18b, .

As described above, according to the present invention, when no optical signal is supplied from the transceiver, the transmission of noise signals is completely prevented and the presence or absence of response data signals is made clear. Even when connected in series, accurate demodulation can be performed without noise signals being added to the response data signal, making it possible to significantly expand the communication range.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an indoor infrared communication device, FIG. 2 is a block diagram showing a conventional satellite of the indoor infrared communication device, FIG. 3 is a diagram showing signal waveforms of each part in the conventional satellite, and FIG. This figure is a diagram showing an extracted satellite of an infrared communication device according to an embodiment of the present invention, and FIG. 5 is a diagram showing signal waveforms of various parts in the satellite of FIG. 4. 13...Modem (modulator/demodulator), 16a, 16b
... Transceiver, 25 ... Light receiving element, 31a,
31b...satellite, 32...amplitude limiting circuit,
33... High frequency switch circuit, 34... Detection circuit, 35... Pulse shaping circuit.

Claims (1)

[Claims] 1 A light receiving element that receives a high frequency optical signal output from a transceiver, an amplifier that amplifies the output signal from this light receiving element, and a device that maintains the amplitude of the high frequency signal received by the light receiving element and output via the amplifier. an amplitude limiting circuit for limiting the amplitude; a high frequency switch circuit for outputting the high frequency signal whose amplitude has been limited by the amplitude limiting circuit only when the light receiving element receives the optical signal; and a detection circuit and a pulse shaping circuit for driving the high frequency switch circuit. , a duplexer and branching device for coupling the high-frequency signal output from the high-frequency switch circuit to the coaxial cable, a light-emitting element for transmitting the high-frequency optical signal to the transceiver, and the light-emitting element and the duplexer. An infrared communication device comprising an amplifier interposed between the infrared communication device and the amplifier.