JPS58146151A - Optical transmitter and receiver for digital signal transmission - Google Patents

Abstract

PURPOSE:To obtain an optical transmitter/receiver in which an AC amplifier is used as a reception amplifier, has high a S/N ratio and is stable to fluctuation of temperature and voltage, by transmitting and receiving a DC data signal on an optical signal after it is converted into an AC signal. CONSTITUTION:In the transmitter 1, an input signal (a) from a terminal 2 is converted into an AC signal (b) having a pulse train converted from a high level signal part at a pulse oscillator 11 to control a light emitting diode 4 with flickering. The optical signal from the diode 4 is transmitted to a receiver 6 via an optical fiber 5. The reception signal changed into an electric signal at a photodetector 7 is amplified at an AC amplifier 12, an output signal (c) is wave-shaped at a comparator 9, converted into an AC signal (d) consisting of a pulse train and applied to a monostable multivibrator 13. The returning time constant of the multivibrator 13 is made slightly larger than the pulse interval of the pulse train and is stable, then a reception data signal (e) is obtained at an output terminal 10.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for transmitting digital signals using an optical fiber transmission line.

Recently, digital signals have been widely used for data transmission between computers. Furthermore, optical fibers are often used as transmission lines, which have features such as excellent resistance to electrical noise, low loss, and light weight. An example of a conventional device like this is shown in Figure 1.

In Fig. 1, data No. 448 enters the input terminal (2) of the transmitter (1), and according to its high and low level states, the light emitting diode (+4J r A) is extinguished by the drive circuit (31). The light is transmitted to the receiver (61) through the fiber (5), converted into an electrical signal by the photodetector diode (7), amplified by the amplifier 6181, subjected to waveform shaping by comparison # (9), and sent to the transmitter (1 ) is output from the output terminal.

In such conventional equipment, it is possible to transmit arbitrary digital signals ranging from direct current, that is, constant level or low level signals, to signals at speeds of several Mb/S to 10 Mb/S. required. Therefore, as the amplifier (8), a DC amplifier with a width of 1.4 from DC to cylindrical frequency is used.

However, this has resulted in the following serious drawbacks.

(a) The output voltage of the mountain flow multiplier lTh1 drifts significantly depending on the vorticity and power supply voltage.

Therefore, is the fluctuation in the signal voltage at the input side of the comparator (9) due to a change in the signal itself?

It is difficult to distinguish whether this is due to the drift of the amplifier (8), leading to erroneous signal transmission.

(b) In order to amplify the @ current to high frequency, an amplifier (8
) is the range of input light levels within which the signal-to-noise ratio of the output is significantly degraded and correct signal transmission occurs (dynamic range)
becomes narrower.

The present invention has been made in order to improve the above-mentioned drawbacks and realize a stable optical transceiver for digital signal transmission.

FIG. 2 shows an embodiment of the apparatus of the present invention.

As shown in the figure, the transmitter (1) is a pulse oscillator αυ that generates a pulse train only when the input signal is at a high level.

Light emitting diode drive circuit (3) and light emitting diode (
4). The receiver (6) also includes a light receiving diode (7), an AC amplifier 04. It consists of a comparator (9) and a monostable multivibrator (131).

The operation of the apparatus of this invention will be explained with reference to FIGS. 2 and 3. Figure 3 (&) shows the input signal to the transmitter (1).For such an input signal, the pulse oscillator Qυ
A pulse train as shown in FIG. 3(b) is generated, and the light emitting diode (4) blinks in accordance with this pulse train. (Lights up when the pulse signal is high level, turns off when the pulse signal is low level) This optical signal is transmitted to the receiver (6) via an optical fiber, converted into an electrical signal by the photodetector diode (7), and then amplified by the amplifier □. As a result, the waveform shown in Fig. 3 (,) is obtained. This waveform.

The waveform shaped by the comparator (9) is shown in FIG. 3(d). The output of this ratio W (91) is input to the monostable multivibrator Q31, and the multivibrator α (to)
If the return time constant Δtm of the pulse train is selected to be slightly larger than the pulse interval Δtp of the pulse train, the output waveform of the multivibrator 0 becomes as shown in Fig. 3 (e), and the input waveform to the transmitter (1) and the You get something equal.

In this case, the pulse width in Fig. 3 (al and (,) is maximum △t
This causes a waveform distortion during transmission, but △tm is 10 for the shortest pulse width of the digital signal to be transmitted.
% or less, there is no practical problem.

The apparatus of this invention is as described above.

Since DC signals are also converted to AC signals and transmitted, there is no need to amplify the DC signals as an amplifier @.

It is extremely advantageous over conventional devices in that it is an AC amplifier and is extremely stable against fluctuations in temperature and power supply voltage, and that signal noise can be reduced by narrowing the amplification band.

In the above description, it is assumed that the transmitter generates a 747 sequence when the input signal is at a high level, but the same effect can be obtained even if the transmitter generates a pulse sequence only when the input signal is at a low level.

[Brief explanation of the drawing]

137', x is a block diagram of a conventional optical transmitting/receiving device for digital signal transmission, FIG. 2 is a diagram showing an embodiment of the receiving device for digital signal transmission of the present invention, and FIG. 3 is a detailed explanation of the present invention. FIG. In the figure, (1) is a transmitter, (2) is an input terminal, (3) is a drive circuit, (4) is a light emitting diode, and (5) is an optical fiber. (6) is a receiver, (7) is a photodetector diode, (8) is a DC amplifier, (9) is a comparator, (Iljl is an output terminal,
01) is a pulse oscillator, 02 is an AC amplifier, Cl31
is a monostable multivibrator. Note that the same or corresponding parts in the figures are indicated by the same reference numerals. Agent Makoto Kuzuno - Figure 1 6 Figure 2 - 11 trn ≠μ''〈-1!

Claims (1)

[Claims] In an optical transmitter/receiver for digital signal transmission that converts the transmission of digital signals having high-level and low-level states into light, a pulse train is used only when the transmitted signal is at either a high level or a low level. a transmitter that generates the pulse train, and a receiver that receives the pulse train and reproduces the digital signal. An optical transmitter/receiver for digital signal transmission comprising an optical fiber connecting the transmitter and the receiver.