JPH0777386B2 - Optical signal transmission device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical signal transmission device for transmitting an optical signal by intensity modulation.

[Prior Art] In recent years, optical communication has been put into practical use as a means for realizing large-capacity digital information transmission, and various improvements have been made. Also in the optical communication system, the digital input signal is sent in a modulated form, and direct intensity modulation is widely used as a modulation form.

Direct intensity modulation is simply a method of transmitting digital information, that is, the level of a binary input signal in correspondence with the presence or absence of an optical signal. For example, “high level“ 1 ”” of the input signal is “Optical signal on” and “low level“ 0 ”” are replaced with “optical signal off” and transmitted. On the other hand, at the time of reception, the reverse operation to the above, that is, when the "optical signal is on", "high level" is output, and when the "optical signal is off", "low level" signal is output, respectively, to generate an electrical signal. Demodulate.

FIG. 6 is a schematic diagram of an apparatus that realizes the above-described optical communication system.

In the light emitting section 60 of the transmitter, the drive circuit 61 turns on and off the light emitting element 62 according to the digital input signal (FIG. 7A) to directly transmit the intensity-modulated optical signal (FIG. 7B). . On the other hand, in the light receiving section 70 of the receiving device, the light receiving element 71
The electric signal obtained in (1) is amplified by the amplifier 72. Upon receiving the amplified signal, the comparator 73 determines the level, and the digital output signal (the seventh level) corresponding to the high level and the low level is determined.
Output Figure c).

[Problems to be Solved by the Invention] The above-described optical signal transmitter / receiver using direct intensity modulation has the following problems.

It is difficult to realize low power consumption.

In the optical communication transmitter, the light emitting unit requires the most power consumption. Usually, the current supplied to the light emitting unit depends on the transmission distance, but in the case of an LED, a maximum of about 100 mA is required. This value cannot be said to be small, and moreover, if the "high level" of the input signal continues in the direct intensity modulation system,
In the light emitting section, it is necessary to constantly consume a current of 100 mA to drive the light emitting element, resulting in a large power consumption.

It is difficult to detect an abnormality in the transmission line or an abnormality in the transmitter.

Generally, when direct intensity modulation is used, if the "low level" of the input signal continues, the state of "optical signal off" continues.
On the other hand, on the receiving device side, whether the continuation of "optical signal off" is due to the continuation of "low level" of the input signal, transmission line abnormality (breakage of optical fiber etc.) or transmission device abnormality (power cut) It is difficult to determine whether it is due to the above).

In view of the above drawbacks, a main technical problem of the present invention is to provide an optical signal transmission device that contributes to reduction of power consumption.

Another object of the present invention is to provide an optical signal transmission device having a function of easily discriminating a transmission line abnormality or a transmission device abnormality.

[Means for Solving the Problems] According to the present invention, means for detecting the rising of a binary input signal, which is a modulated signal of direct intensity modulation, on the transmitting device side,
Means for detecting the falling edge of the input signal, and a first pulse for generating one pulse having a first width at the output of the rising edge detecting means.
Pulse generating means, second pulse generating means for generating one pulse of the second width by the output of the fall detecting means, and the time when the input signal takes one of the values for a predetermined time.
When it is detected that T _{1 has} continued, a means for outputting a pulse from the first and second pulse generating means corresponding to one of the values, detection of rising or falling of the input signal and detection of the predetermined time T ₁ An optical signal transmission device having means for invalidating the detection of the predetermined time T ₁ when the timings overlap can be obtained.

[Operation] In the transmitter of the optical signal transmission device according to the present invention, the pulse of the first width is output when the input signal rises, and the pulse of the second width is output when the input signal falls, whereby the input signal rises and rises. The fall is defined by these pulses. The duration of these first and second widths is equal to 1 of the input signal.
It is very narrow compared to the duration of the value that represents one piece of information. The optical signal is turned on only when the pulses of the first and second widths are output. In addition, one value of the input signal is T ₁
When it continues, the pulse of the first or second width corresponding to one of the values is output to indicate that one value of the input signal is not abnormal even if the value continues for a long time. Further, when the pulse generation of the first or second width and the detection timing of the predetermined time T ₁ overlap, the detection of the predetermined time T ₁ is invalidated and the first or the first due to the rising or falling of the input signal. Priority is given to the pulse output of the width of 2.

On the other hand, the receiving device outputs a high level when the electric signal obtained by photoelectric conversion corresponds to the pulse of the first width and outputs a low level when the electric signal corresponds to the pulse of the second width. By outputting, a signal synchronized with the input signal in the transmitter is reproduced. Further, when the low level state continues for a predetermined time T ₂ during operation, it is determined that the transmitter is abnormal or the transmission line is abnormal, and an error detection signal is output.

[Embodiment] FIG. 1 shows a schematic configuration of an optical signal transmitter and receiver according to the present invention.

The transmitter includes a modulation circuit 11 that outputs pulses of first and second widths based on a digital input signal, and the modulation circuit 11.
It includes a drive circuit 12 and a light emitting element 13 for turning on and off an optical signal based on the first and second width pulses from 11.

The receiving device includes a light receiving element 21 for converting an optical signal sent from the transmitting device 10 through the optical fiber 14 into an electric signal, an amplifier 22 for amplifying the electric signal, and a digital signal in the transmitting device based on an output signal of the amplifier 22. It includes a demodulation circuit 23 for reproducing a signal corresponding to an input signal, and an abnormality detection circuit 24 for detecting an abnormality in a transmitter or an optical fiber.

Next, the transmitter side will be described with reference to FIG. 2 and FIG.

As for the modulation circuit 11, a rising edge detection circuit 111 for detecting the rising edge of a binary input signal I ₁ (FIG. 3 (a)),
A first pulse generation circuit 113 for outputting one pulse (FIG. 3 (f)) having a first width W ₁ at the output of the falling detection circuit 111 of the input signal I ₁ (FIG. 3 (b)), Fall detection circuit 1
With 12 outputs (Fig. 3 (c)), the second width W ₂ (W ₁ >
It includes a second pulse generation circuit 114 for outputting one pulse of W ₂ ) (FIG. 3 (g)).

The clock generation circuit 115 includes the first and second pulse generation circuits 11
A reference clock pulse for limiting the pulse width of the output pulse of 3, 114 is generated. The timer circuit 116 OR gates the outputs of the rising edge detection circuit 111 and the falling edge detection circuit 112.
When it is received via OR ₃ , a timing signal is output after a fixed time T ₁ .

The level determination circuit 117 outputs the first pulse signal (FIG. 3 (d)) when the timing signal is received from the timer circuit 116 after the level of the input signal I ₁ rises and the input signal I ₁ When the timing signal from the timer circuit 116 is received after the level has fallen, the second pulse signal (FIG. 3 (e)) is output.

The condition determination circuit 118 outputs the first pulse signal from the level determination circuit 117 to the first pulse generation circuit 113 through the OR gate OR ₁ , and the second pulse signal through the OR gate OR ₂ to the second pulse generation circuit 114. Output to. When the rising edge detection or the falling edge detection of the input signal I ₁ and the timing of the first or second pulse signal output from the level determination circuit 117 coincide with _each other, the condition determination circuit 118 also raises the input signal I ₁ . To prioritize the fall,
It also has a function of invalidating the first or second pulse signal from the level determination circuit 117.

The operation will be described below.

When the input signal I ₁ rises, the output of the rise detection circuit 111 causes the first pulse generation circuit 113 to output the first pulse having the width W ₁ . Next, when the input signal I ₁ falls, the output of the fall detection circuit 112 causes the second pulse generation circuit 114 to output the second pulse of the width W ₂ .
The pulse of is output. In this way, the first and second signals are changed according to the level change of the input signal I ₁ between high level and low level.
Pulse is output through OR gate OR ₄ . Also,
Timer circuit 116, the input signal a predetermined time T ₁ from the level rises in I _1, or when the level drops a predetermined time T ₁ elapses after standing by the level determining circuit 117, the first or second pulse signal is output As a result, the first pulse having the width W ₁ or the second pulse having the width W ₂ is output. In this way, even if the level of the input signal I ₁ remains unchanged, the modulation circuit 11 outputs the first or second pulse at least every time T _1. By monitoring, it is possible to determine a transmitter abnormality or a transmission path abnormality.

The drive circuit 12 turns on and off the light emitting element 13 based on the pulse from the modulation circuit 11. In this way, the optical signal to be transmitted to the receiving device is represented by an ON time which is very short as compared with the high level time of the input signal I ₁ , as shown in FIG. 3 (h).

However, the output timings of the first and second pulse signals from the level determination circuit 117 are irrelevant to the timing of the level change of the input signal I ₁ , and it is expected that their generation timings will overlap. In this case, it is necessary to give priority to the timing of the level change of the input signal I ₁ and invalidate the first and second pulse signals. The condition determination circuit 118 inputs the detection signals from the rising detection circuit 111 and the falling detection circuit 112 and the first and second pulse signals from the level determination circuit 117, and when they overlap, the first and second pulse signals are input. Do not output the pulse signal of to OR gates OR ₁ and OR ₂ .

As described above, the input signal I ₁ can be expressed and output as an optical signal having a very short on-time from the transmitting device, and power consumption in the light emitting unit can be significantly reduced. Further, when an LED is used as the light emitting element, a larger amount of light can be obtained and the transmission distance can be extended. The reason is that the maximum current that can be passed through the LED is continuous (DC).
Although it is specified by the current, if the time is extremely short, it can be driven with a current exceeding the specified maximum current, and as a result, a large amount of light can be obtained.

As an example, in the case of an LED with a maximum constant-path current of 100 mA, driving with a pulse signal of several μs enables driving with several hundred mA.

Next, the demodulation circuit 23 and the abnormality detection circuit 24 will be described with reference to FIGS. 4 and 5.

The demodulation circuit 23 receives the pulse-shaped electric signal (FIG. 5 (a)) from the amplifier 22 and discriminates the pulses of the first width W ₁ and the second width W ₂ , and determines the _first and second widths W ₁ and W 2. A pulse width identification circuit 231 that outputs a trigger pulse shown in FIGS. 5B and 5C, a reference clock generation circuit 232 that generates a reference clock for identifying the pulse width, and a pulse width identification circuit 231 It includes a flip-flop 233 that switches between high level and low level output in response to the first and second trigger pulses.

On the other hand, the abnormality detection circuit 24 includes a carrier detection circuit 241 and an error detection timer circuit 242.

The pulse width discriminating circuit 231 discriminates whether the input signal has the first width W ₁ or the second width W ₂ , and as shown in FIG. 5 (e), the first width W ₁ When it is W ₁ , the output is sent to the preset terminal PR of the flip-flop 233 to make it high level. On the other hand, when the width is the second width W ₂ , the output is sent to the clear terminal CLR of the flip-flop 233 to be set to the low level. It should be noted that the same level status is maintained for a certain time in the transmitter.
The pulse added when T ₁ continues is flip-flop 233.
Does not affect the level change. This is a flip flop
This is because the level of 233 does not change even if the preset terminal PR and the clear terminal CLR are continuously input.

On the other hand, in the abnormality detection circuit 24, the error detection timer circuit 242 monitors the amplifier output signal during the reception operation. In other words, the error detection timer circuit 242 determines that the transmission device abnormality or the transmission path abnormality occurs when the pulse-shaped signal (FIG. 5 (a)) included in the amplifier output signal is interrupted for a certain time T ₂ (T ₂ > T ₁ ). Judgment and error detection signal (Fig. 5 (d))
Is output. This means that, as described above, the interval between the pulsed signals sent from the transmitter is at most time T ₁ , and therefore, when the pulsed signal is interrupted for a time T ₂ longer than time T ₁ , , It means that there was something wrong with the sender.

As described above, the output signal synchronized with the input signal I ₁ can be reproduced based on the optical signal having a very short on-time output from the transmitter.

[Effect of the Invention] As described above, according to the present invention, the time for supplying the current to the light emitting element by turning on the optical signal by the pulse having an extremely narrow width in synchronization with the level change of the binary input signal. Is significantly reduced, so that low power consumption can be realized. On the contrary, by shortening the current supply time to the light emitting element, long-distance transmission becomes possible when the supply current is increased. Further, it is possible to easily identify the abnormality on the transmission side including the transmission path.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a transmission side and a reception side for realizing optical communication according to the present invention, FIG. 2 is a block diagram showing a schematic configuration of the modulation circuit shown in FIG. 1, and FIG. FIG. 4 is a signal waveform diagram for explaining the operation of the modulation circuit shown in FIG.
FIG. 5 is a block diagram showing a schematic configuration of the demodulation circuit and the abnormality detection circuit shown in FIG. 1, FIG. 5 is a signal waveform diagram for explaining the operation of the circuit shown in FIG. 4, and FIG. FIG. 7 is a schematic configuration diagram for explaining a conventional optical communication system, and FIG. 7 is a signal waveform diagram for explaining the operation of the configuration shown in FIG. In the figure, 11 is a modulation circuit, 23 is a demodulation circuit, 24 is an abnormality detection circuit, 231 is a rise detection circuit, 232 is a fall detection circuit,
113 and 114 are first and second pulse generation circuits, and 117 is a level determination circuit.

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Claims (1)

[Claims] 1. In an optical signal transmission device for transmitting an optical signal by intensity modulation, means for detecting the rise of a binary input signal, which is a modulation signal, and the fall of the input signal are detected on the side of the transmission device. Means, first pulse generating means for generating one pulse of a first width at the output of the rising edge detecting means, and second pulse generating means for generating a pulse of a second width at the output of the falling edge detecting means. Pulse generating means and means for outputting a pulse from the first and second pulse generating means corresponding to one of the values when it is detected that the input signal takes one of the values for a predetermined time T ₁ when the optical signal transmission apparatus rise or the fall detection means when said timing of the predetermined time T ₁ detected overlap is characterized in that it comprises a means for disabling the detection of said predetermined constant-time T ₁ of the said input signal .