JPS61163735A - Optical transmitting circuit - Google Patents

Abstract

PURPOSE:To convert a transmitting side to a low power, and to lengthen a transmission distance by converting a signal pulse to a signal of a narrow width once without converting the signal pulse to an optical signal of a waveform of that state, executing an optical transmission, and thereafter, demodulating it to its original output signal, in case of converting the signal of a transmitting side to the optical signal. CONSTITUTION:An FF9 leads in a difference code and a signal of a high frequency,and outputs a signal delayed a phase of a difference signal by a one pulse portion of this signal. An exclusive OR gate (Ex-OR)3 leads in a difference code and a signal brought to this difference code to phase shift a little, and outputs a signal of a narrow pulse width in a part where the polarities of both signals are different. This pulse signal is positioned just in the center of a pulse width of an input signal. When this pulse signal is received, an optical transmitter 17 drives a light emitting element 23. That is to say, the light emitting element 23 emits a light in only an extremely short period. An optical signal is irradiated to a photodetector 25 being in a separated position through an optical fiber cable 27. In response to this light, the photodetector 25 outputs a minute signal, and this signal is amplified by an optical receiver 19.

Description

[Detailed Description of the Invention] A. ``Object of the Invention'' [Industrial Application Field] The present invention relates to improvement of power consumption on the transmitting side of start-stop type NRZ serial data transmission using optical fiber, and improvement of transmission distance. It is something.

[Conventional technology]

Optical fibers are widely used as transmission media for digital data transmission. Optical fiber has features such as noise resistance, broadband performance, low loss, and light weight, and is widely used for long-distance, high-speed transmission, including public lines.

On the other hand, it can also be used for applications that do not require high speed but require noise resistance, such as transmission inside a pill, indoors, or inside a device.
The usefulness of optical fibers is attracting attention.

[Problems to be solved by the invention] However, the start-stop type NRZ using the above-mentioned optical fibers
Serial data transmission has the following problems.

(1) In start-stop type NRZ serial data transmission, the signal level is set to the Hr level when no signal is transmitted. Further, even during transmission, the H level period of the signal pulse is long. Therefore, if you try to transmit start-stop serial data by changing the brightness m (whether it emits light or not) as it is on the transmitting side, when the communication line is not in operation, the light emitting element (for example, LED) will be continuously charged with current. , and in the transmitting state, the ffi stream frequently flows, resulting in increased power consumption, which is undesirable.

(If plastic optical fibers and LEDs are used, the transmission distance is 10 m to 30 m, which means that it can only be used for relatively short distances.

The present invention solves these problems.The purpose of the present invention is to reduce the power on the transmitting side in start-stop serial data transmission, to extend the transmission distance compared to the conventional method, and to achieve this with a simple configuration. It provides a structure for managing

``Structure of the Invention'' [Means for Solving the Problems] In order to solve the above problems, the present invention provides that, when converting a signal pulse on the transmitting side into an optical signal, the signal pulse is converted into an optical signal in its original waveform. Instead of converting the signal into an optical signal, the signal pulse is first converted into a signal with a narrow pulse width for optical transmission, and then demodulated into a previous input signal.

(Actual! IP4) An embodiment embodying the present invention will be described below.

FIG. 1 is a diagram showing an embodiment of the present invention.

In the same figure, 1 to 5 are exclusive OR gates (hereinafter Ex
-OR), and 7 to 15 are flip-flop circuits (hereinafter referred to as FF). Reference numeral 17 denotes an optical transmitter, which is a circuit that causes a current to flow to a light emitting element connected to an output terminal based on an introduced signal.

Reference numeral 19 denotes an optical receiver, which amplifies the minute current introduced from the light receiving element and outputs a level-converted signal. Reference numeral 21 denotes a clock extraction circuit, which reproduces a lock signal similar to the clock on the transmitting side from the introduced signal. 23 is a light emitting element, such as an LED or a laser light emitting element.

25 is a light receiving element, for example, a PIN photodiode or the like. 27 is an optical fiber cable, which may be a quartz optical fiber, a plastic optical fiber, or the like. However, when an LED is used as the light emitting element 23, a plastic optical fiber with a thick fiber cross section is preferable.

Further, in FIG. 1, the signal lines are designated with symbols .about.O as shown in the figure for explanation. Input signal (transmission signal) ■ is E
It is added to x-ORI and introduced into FF7 via this. Further, a lock signal (hereinafter referred to as CLK) (2) is applied to FF7, and the 01 output of FF7 is fed back to ExORl.

This Ex-ORI and FF7 constitute a differential code conversion circuit. The differential code ■ which is the output of FF7 is introduced into FF9. Furthermore, a signal ■ having a frequency that is 128 times CLK■ is also added to the FF9.

This FF9 output signal ■ and the difference sign ■ are Ex-OR
3 and then to the optical transmitter 11 via this. A light emitting element 23 is connected to the output terminal of the optical transmitter 17. The light from the light emitting element 23 is irradiated onto the light receiving element 25 via the optical fiber cable 27. The signal from the light receiving element 25 is level-converted by the optical receiver 19 and introduced into the FF 11. The output signal (2) of the FF 11 is input to the next stage FF 13 and the output extraction circuit 21 and the ExOR5.

The output signal ■ of the clock extraction circuit 21 is the FF1
3 and FF15. The output Q4 of FF13 is E
x Introduced into OR5. Introducing the output 0 of ExOR5 and the signal ■, the FF15 outputs the I[key signal ■.

In the configuration shown in FIG. 1, the portion above the optical fiber cable 27 is the transmitting side (encoder side), and the portion below is the receiving side (decoder side).

The operation of the apparatus shown in FIG. 1 constructed as described above is as follows. FIG. 2 is a time chart showing the relationship between signals 0 to 0, and the operation of FIG. 1 will be explained with reference to this diagram.

The input signal (2) is an asynchronous serial data signal, and is at HI level when the signal is not being transmitted.

Assume that a pulse with a waveform as shown in FIG. 2 is added. CLK■ as shown in FIG. 2 is added to FF7. Ex-.

R1 and FF7 constitute a differential code conversion circuit, which outputs a differential code ■ as shown in FIG.

Specifically, FF7 detects that the input signal ■ immediately before the rising edge of CLK■ and the difference sign ■ have the same polarity (H
I-HI or Lo-LO) (In the case of 71), the next differential code ■ is set to Hl.

The FF 9 introduces the differential code ■ and a high-frequency signal ■ as shown in FIG. 2, and outputs a signal ■ with the phase of the signal ■ delayed by one pulse of the signal ■.

Ex-OR3 introduces a differential code ■ and a signal ■ whose phase is slightly shifted from this differential code, and generates a signal ■ with a narrow pulse width as shown in FIG.
Output. This pulse signal (2) is located exactly at the center of the pulse width of the input signal (2).

Moreover, at the center of the pulse where the input signal ■ becomes the LO level, and at the center of the pulse where the input signal becomes the HI level, the signal ■ becomes
Does not occur. In other words, the data of the input signal ■ is designed to convey information in the form of pulses that are at the LO level, so
In the present invention, this wide pulse width LO level signal ■ is
It was converted into a signal ■ with an extremely narrow pulse width.

In response to this pulse signal (2), the optical transmitter 17 drives the light emitting element 23. That is, the light emitting element 23 emits light for only an extremely short period of time.

The optical signal is irradiated via an optical fiber cable 27 to a light receiving element 25 located at a remote location. In response to this light, the light receiving element 25 outputs a minute signal, and this signal is amplified by the optical receiver 19. Generally, the frequency response of the optical receiver 19 is poorer than that of the light emitting element 23 and the light receiving element 25, so the pulse width of the output signal (2) is slightly expanded as shown in FIG.

This signal (2) is introduced into the FF 11 and becomes a signal (2). Since this signal (2) is similar to the above-mentioned differential code (2), it will hereinafter be referred to as a differential code. Difference code■Beam Otsuk extraction circuit 21
2, and a signal (2) similar to CLK (2) is reproduced as shown in FIG. This O-k extraction circuit 21 is a known technology, and its operation will be briefly described later.

By introducing this extraction clock ■ and the difference code ■, FF1
3 outputs a signal as shown in FIG.

However, the waveform of signal 0 shown in FIG. 2 is that of Q4, and since the signal transferred to the next stage is from Q4, the phase is inverted from the waveform of FIG. 2. The FF 13 operates so as to output the state of the signal (2) immediately before the rising edge of the extracted clock (2) as a signal [share]. Signal ■ and Shin@[stock] are introduced into Ex-OR5, and signal [F
] is obtained. Further, the signal (2) passes through the FF 15 and becomes the demodulated signal (2).

This demodulated signal 0 is delayed by one clock compared to the input signal ■.

An example of the operation of the clock extraction circuit 21 is to detect the rising edge of the differential code ■ as shown in FIG. 3, and use this edge as a trigger to oscillate and output a clock for one frame. is possible.

Incidentally, since the oscillation frequency (clock frequency) is a known frequency in the transmission circuit system, as long as the rising edge of the differential code (2) is detected, the clock signal (2) can be automatically output.

Note that since FIG. 2 depicts the middle of the operation, it is depicted as if the clock (2) is operating even before the rising edge of the differential code (2). This is the clock in the previous frame.

In addition, in the above explanation, the operation was explained using a specific example using ExORs 1 to 3, FFs 7 to 9, 17 optical transmitters, and 23 light emitting elements.
The invention is not limited to the configuration shown in the figure.

In addition, in Fig. 1, the circuit that generates a signal with a minute pulse width at the center of the pulse of the input signal (■) is explained, but the generation position of the signal with a minute pulse width is not necessarily the position of the pulse of the signal (■). It is not necessary to correspond to the center.

C. "Effects of the Present Invention" As described above, according to the present invention, the following effects can be obtained.

(1) Since information can be transmitted using extremely thin pulses, the time ratio (duty) during which the light emitting element emits light is low. Therefore, even if the peak current is large, the average current is extremely low, making it possible to perform low-power optical transmission of start-stop NRZ signals.

(2) LEDs are common as light emitting elements, but L
As a characteristic of the ED, the maximum allowable forward peak current tends to be inversely proportional to the duty ratio. When LEDs are used with extremely low duty as in the present invention, the peak current can be made considerably large, thereby extending the transmission distance. In addition, by lowering the duty ratio, the life of the LED is extended.
Reliability is also improved.

(3) Since DC coupling is not required inside the optical receiver, the circuit configuration is simplified.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the configuration of an optical transmission circuit according to the present invention,
FIG. 2 is a time chart of signals of each part of the circuit of FIG. 1, and FIG. 3 is a diagram for explaining an example of clock extraction operation. 1~5...EX-OR17~15...FF117・
... Optical transmitter, 19... Optical receiver, 21.
...Clock extraction circuit, 23...Light emitting element, 25...
- Light receiving element, 27... optical fiber cable. Atsushi 1 Part 3 Prisoner Illustration

Claims (1)

[Claims] In a system that converts a signal in the start-stop NRZ serial data transmission format into an optical signal and transmits it to a receiving side via an optical fiber cable, the pulse of the input signal ([1]) is and a light emitting means for emitting light based on the signal, and the light from the light emitting means is transferred to the receiving side via the optical fiber cable. Optical transmission circuit.