JPH02281849A - Optical signal transmitter and receiver - Google Patents

Abstract

PURPOSE:To realize the low power consumption by turning on an optical signal by the pulse of extremely narrow width synchronizing with the level variation of a binary input signal. CONSTITUTION:A transmitter 10 is provided a modulating circuit 11 for outputting pulses of first and second width, based on a digital input signal, a driving circuit 12 for turning on/off an optical signal, based on the pulses of first and second width from this modulating circuit 11, and a light emitting element 13. At the time of rise of an input signal and at the time of fall, the pulse of first width and the pulse of second width are outputted, respectively, therefore, the rise and a fall of the input signal are regulated by these pulses. The duration period of these first and second width is much narrower than that of a value for showing one piece of information of the input signal, and the optical signal is turned on only when these pulses of the first and second width are outputted. In such a manner, the power consumption is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical signal transmitting device and receiving device using intensity modulation.

[Prior Art] In recent years, optical communication has been put into practical use as a means of realizing large-capacity digital information transmission, and various improvements are being made. Even in optical communication systems, digital input signals are sent in a modulated format, and direct intensity modulation is widely used as the modulation format.

Simply put, direct intensity modulation is 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. Optical signal on” and “Low level “0””
They are replaced and transmitted in response to the "optical signal off" respectively.

On the other hand, when receiving, the operation is the opposite to the above, that is, when the optical signal is on, a ``high level'' signal is output, and when the optical signal is off, a ``low level'' signal is output. Demodulate.

FIG. 6 is a schematic diagram of a device that implements the above-mentioned optical communication system.

In the light emitting unit 60 of the transmitting device, a drive circuit 61 turns on and off the light emitting element 62 in response to a digital input signal (FIG. 7a) and directly transmits an intensity-modulated optical signal (FIG. 7b). . On the other hand, in the light receiving section 70 of the receiving device, the electric signal obtained by the light receiving element 71 is amplified by the amplifier 72. Upon receiving the amplified signal, the comparator 73 makes a level determination and outputs a digital output signal (FIG. 7C) depending on the high level or low level.

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

■It is difficult to achieve low power consumption.

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

■It is difficult to detect abnormalities in the transmission line or transmitter.

When using general direct intensity modulation, if the input signal continues to be at a "low level", the state of "optical signal off" continues.

On the other hand, on the receiving device side, it is difficult to determine whether the continued state of "optical signal off" is due to the continuation of the input signal's "low level" or whether there is a transmission path error (such as a break in an optical fiber, etc.) or a transmission equipment error (power interruption). etc.) is difficult to determine.

In view of the above drawbacks, the main technical object of the present invention is to provide a transmitting device for optical communication that contributes to reducing power consumption.

Another object of the present invention is to provide a receiving device for optical communications that has a function of distinguishing transmission path abnormalities and transmitting device abnormalities.

[Means for Solving the Problems] According to the present invention, there is provided a means for detecting a rising edge of a binary input signal which is a modulation signal of direct intensity modulation, a means for detecting a falling edge of the input signal, and a means for detecting a falling edge of the input signal, and a means for detecting a falling edge of the input signal. a first pulse generating means that generates one pulse of a first width at the output of the detection means; and a second pulse generating means that generates one pulse of a second width at the output of the fall detecting means. , means for causing the first and second pulse generating means to output pulses corresponding to one of the values when detecting that the input signal has taken one of the values for a predetermined period of time T; An optical signal transmitting apparatus is obtained which includes means for invalidating the detection of the predetermined time T1 when the detection timing of the rise or fall of the signal and the detection timing of the predetermined time T overlap.

According to the present invention, an electric signal obtained by photoelectrically converting a received light signal from the optical signal transmitter is inputted to the first
Alternatively, means for discriminating a pulse of a second width, and a signal having a high level when the pulse has the first width and a signal of the same level when the pulse has the second width according to the discrimination result of the discriminating means. and means for outputting an error detection signal when the electrical signal remains at a low level for a predetermined period of time T2 (where T2>T) is obtained.

[Function] In the transmitting device according to the present invention, a pulse of the first width is outputted at the rising edge of the input signal, and a pulse of the second width is outputted at the falling edge of the input signal. stipulated by. The durations of these first and second widths are very narrow compared to the duration of a value representing one piece of information in the input signal. The optical signal is
It turns on only when a pulse with a width of is output. In addition, when one value of the input signal continues for a predetermined time T, by outputting a pulse with the first or second width corresponding to that one value, one value of the input signal continues for a long time. Please make sure to indicate that this is not abnormal. Further, if the generation of a pulse of the first or second width and the detection timing of the predetermined time T1 overlap, the detection of the predetermined time T1 is invalidated and the first pulse generated by the rising or falling edge of the input signal is invalidated.
Alternatively, priority is given to the pulse output of the second width.

On the other hand, the receiving device outputs a high level when the electrical signal obtained by photoelectric conversion corresponds to a pulse of the first width, and outputs a low level when it corresponds to a pulse of the second width. By outputting the signal, a signal synchronized with the input signal in the transmitting device is reproduced. Further, when the low level state continues for a predetermined time T2 during operation, it is determined that there is an abnormality in the transmitting device or the transmission path, and an error detection signal is output.

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

The transmitting device includes a modulation circuit 11 that outputs pulses of first and second widths based on a digital input signal, and turns on an optical signal based on the pulses of the first and second widths from the modulation circuit 11. Driving concave path 12 and light emitting element 1 for turning off
Contains 3.

The receiving device includes a light receiving element 21 that converts the optical signal sent from the transmitting device 10 through the optical fiber 14 into an electrical signal.
, an amplifier 22 that amplifies this electrical signal, this amplifier 22
It includes a demodulation circuit 23 that reproduces a signal corresponding to a digital input signal in the transmitter based on the output signal of the transmitter, and an abnormality detection circuit 24 that detects an abnormality in the transmitter or the optical fiber.

Next, the transmitter side will be explained with reference to FIGS. 2 and 3.

Regarding the modulation circuit 11, a binary input signal!+(
A rising edge detection circuit 111 that detects the rising edge of the input signal 11 in FIG.
The output of the first pulse generating circuit 113 and the falling detection circuit 112 (Fig. 3 (C)) outputs one pulse with the first width W (Fig. 3 (C)) in Fig. 3 (B)). and the second width W2 (
However, it includes a second pulse generation circuit 114 that outputs one pulse (FIG. 3(g)) of W, >W2).

The clock generation circuit 115 generates a reference clock pulse for limiting the pulse width of the output pulses of the first and second pulse generation circuits 113 and 114.

The timer circuit 116 receives the outputs of the rising edge detection circuit 111 and the falling edge detection circuit 112 via an OR gate OR3, and outputs a timing signal after a certain period of time T1.

The level determination circuit 117 receives the input signal 1. When the timing signal is received from the timer circuit 116 after the level of has risen, the first pulse signal (FIG. 3(d)) is output,
After the level of the input signal I falls, the timer circuit 11
When receiving the timing signal from 6, it outputs a second pulse signal (FIG. 3(e)).

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, and outputs the second pulse signal to the second pulse generation circuit 114 through the OR gate OR2. Output. The condition determination circuit 118 also detects the rise or fall of the input signal 11 and the level determination circuit 11.
When the timing of the output of the first or second pulse signal from the level determination circuit 117 overlaps with the timing of the output of the first or second pulse signal from the level determination circuit 117, the first or second pulse signal from the level determination circuit 117 is It also has the function of invalidating it.

The operation will be explained below.

When the input signal {circle around (2)} rises, the first pulse generating circuit 113 outputs a first pulse having a width W1 based on the output of the rising edge detection circuit 111. Next, when the input signal l falls, the output of the falling detection circuit 112 causes the second pulse generation circuit 1 to
14 outputs a second pulse of width W2. In this way, the first and second pulses are outputted through OR4 in response to the level change between high and low levels of the input signal I. Furthermore, the timer circuit 116 and the level determination circuit 117 determine the input signal 1. When a certain period of time T1 has passed since the level rose or a certain period T1 has elapsed since the level fell, the first or second pulse signal is output, thereby generating the first pulse of width W, or A second pulse of W2 is output. In this way, even if the level of the input signal (2) remains unchanged, the modulation circuit 11 outputs the first or second signal at least every time T.
Since this pulse is output, by monitoring the pulse interval on the receiving device side, it is possible to determine whether there is an abnormality in the transmitting device or the transmission path.

The drive circuit 12 turns on and off the light emitting element 13 based on pulses from the modulation circuit 11. In this way, the optical signal transmitted to the receiving device is an input signal!, as shown in FIG. 3(h). The on-time is very short compared to the high-level time of .

However, the output timings of the first and second pulse signals from the level determination circuit 117 are unrelated to the timing of the level change of the input signal 11, 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, and to invalidate the first and second pulse signals. The condition determination circuit 118 is a rise detection circuit 111
, inputs the detection signal from the falling detection circuit 112 and the first and second pulse signals from the level determination circuit 117,
When these overlap, the first and second pulse signals are OR gated.

Prevent output from OR2.

As described above, the transmitter can output the input signal (1) as an optical signal with a very short on time.
Power consumption in the light emitting section can be significantly reduced. Also,
When an LED is used as a 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 (
Although it is specified by the direct current (direct current) current, it can be driven with a current exceeding the specified maximum current for an extremely short period of time, and as a result, a large amount of light can be obtained.

- As an example, for an LED with a maximum constant current of 100 mA,
When driven with a pulse signal of several μs, the power output is several hundred mA.
It becomes possible to drive with

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

The demodulation circuit 23 receives the pulsed electric signal (FIG. 5(a)) from the amplifier 22 and converts it to a first width WI.

A pulse width identification circuit 231 that identifies a pulse with a second width W2 and outputs the first and second trigger pulses FIG. 5(b) and FIG. 5(C), and a reference clock for this pulse width identification. The reference clock generating circuit 232 generates a reference clock generating circuit 232, and a flip-flop 233 switches an output between a high level and a low level in response to first and second trigger pulses from a pulse width identifying circuit 231.

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 identification circuit 231 determines the first width W of the input signal.
1 or the second width W2, and as shown in FIG. 5(e), when the width is the first width W1, an output is sent to the preset terminal PR of the flip-flop 233. make it high level.

On the other hand, when the width is the second width W2, the flip-flop 23
Send the output to the clear terminal CLR of No. 3 to set it to low level. Note that the transmitting device remains at the same level for a certain period of time T.
1 pulse added when it continues is the flip-flop 23
Does not affect the level change of 3. This is because the level of the flip-flop 233 does not change even if there are successive inputs to the preset terminal PR and the clear terminal CLR.

On the other hand, in the abnormality detection circuit 24, an error detection timer circuit 242 monitors the amplifier output signal during the reception operation. That is, the error detection timer circuit 242 detects a pulse-like signal (FIG. 5(a)) included in the amplifier output signal.
When T2 (T2>T,) is interrupted for a certain period of time, it is determined that the transmitter is abnormal or the transmission path is abnormal, and an error detection signal (fifth
Figure (d)) is output. This is because, as mentioned above, the interval between pulsed signals sent from the transmitting device is time T at most, so if the pulsed signal is interrupted for time T or longer time T2, the transmission This is because it means that there is an abnormality on the side.

In the manner described above, an output signal synchronized with the input signal 11 can be reproduced based on the optical signal with a very short on time output from the transmitter.

[Effects of the Invention] As explained above, according to the present invention, current is supplied to the light emitting element by turning on the optical signal with an extremely narrow pulse synchronized with the level change of the binary input signal. Since the time required to do so is significantly reduced, lower power consumption can be achieved. Conversely, by shortening the time for supplying current to the light emitting element, long-distance transmission becomes possible when the supplied current is increased. Further, abnormalities on the transmitting side including the transmission path can be easily identified.

is the day

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a transmitting side and a receiving 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. Signal waveform diagram for explaining the operation of the modulation circuit shown in Figure 2, TS
4 is a block diagram showing the schematic configuration of the demodulation circuit and 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. 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. 6. In the figure, 11 is a modulation circuit, 23 is a demodulation circuit, 24 is an abnormality detection circuit, 231 is a rising detection circuit, 232 is a falling detection circuit, 113 and 114 are first and second pulse generation circuits, and 117 is a level determination circuit. circuit.

Claims (1)

[Claims] 1. In an apparatus for transmitting an optical signal by intensity modulation, means for detecting a rising edge of a binary input signal that is a modulated signal, means for detecting a falling edge of the input signal, and a means for detecting a falling edge of the input signal; a first pulse generating means that generates one pulse of a first width at the output of the detection means; and a second pulse generating means that generates one pulse of a second width at the output of the fall detecting means. , means for causing the first and second pulse generating means to output a pulse 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; 1. An optical signal transmitting device comprising: means for invalidating the detection of the predetermined time T_1 when the timing of detecting the rise or fall of the signal coincides with the timing of detecting the predetermined time T_1. 2. In a device for receiving an optical signal from a transmitting device according to claim 1, means for inputting an electric signal obtained by photoelectrically converting a received light signal and determining the pulse of the first or second width; means for outputting a high-level signal when the pulse has the first width and a low-level signal when the pulse has the second width according to the discrimination result of the discrimination means;
An optical signal receiving device comprising means for outputting an error detection signal when the electric signal remains at the same level for a predetermined time T_2 (T_2>T_1).