JPS62210747A - Light transmission equipment - Google Patents

Abstract

PURPOSE:To reduce fluctuation in the phase of a clock to be extracted, by setting a signal transmitted by a LED as the signal on which the inverted polarity of a CMI (Code Mark Inversion) coding signal is attached, and taking a phase lock with the leading edge of the pulse of an inverted signal at a reception part. CONSTITUTION:An NRZ signal (a) is converted at an encoder 1, and is changed to a CMI signal (b), and furthermore, it is changed to a signal (c) whose polarity is inverted at an inversion gate 30. Since the LED has a sharp rising characteristic, the fluctuation of the phase in the leading edge of a signal (f) obtained by identifying the output signal (e) of an amplifier 5 with the identification level H of a gate 10, is very small. Therefore, the change of the phase of a clock (g) extracted by performing the phase comparison at the rising of the pulse of the signal (f), is very small. As a result, a judgment error accompanied by the identification of a code at a decoder 6 is reduced. Also, since the fluctuation of the phase of a reproduced signal (b) is reduced, the quantity of the fluctuation accumulated in a relay time, is also reduced, thereby it is possible to increase the number of stages to relay.

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial field of application The present invention is directed to CMI (Code Mark Inverg.
ion) relates to an optical transmission device for encoded signals.

2. Description of the Related Art In a conventional optical transmission device, as shown in FIG.
ED) 31 converts it into an optical signal and sends it out to the optical fiber 3. The waveforms of each part at this time are shown in FIGS. 5a, b, and d. As shown in FIG. '' even if the same sign continues, the trailing edge of the pulse always occurs once every three bits, so loss of timing information can be avoided. Furthermore, since the interval between the falling edges of the pulse is an integral multiple of the basic period T, a clock synchronized with the CMI signal can be drawn by performing phase synchronization every falling edge. On the receiving side, a light receiving element 4 converts the optical signal into an electrical signal, and an amplifier 5 obtains a signal θ' with a constant amplitude. After that, the identification level H of the gate 11 is used to determine whether it is 0 or 1,
Obtain an inverted signal f'.

However, in an LED, the pulse has a steep rise but a slow fall, which causes interference between adjacent codes, causing the phase (position) of the fall to shift.
The discrimination level H also has a certain discrimination uncertainty range, and furthermore, the level changes due to fluctuations in ambient temperature, power supply voltage, and element irregularities.

As a result, the phase of the rising edge of the inverted signal I', which identifies the output waveform e' of the amplifier at level H, is shown in Fig. 5 f'.
It will fluctuate greatly like this. Therefore, the signal f
' is input to the timing extraction circuit 32, and the phase of the extracted clock q' is phase synchronized at every rising edge of the pulse.The phase of the extracted clock q' fluctuates as shown in FIG. 6, q'. The same applies to the reproduced waveform h' of the decoder 6.

Problems to be Solved by the Invention In such conventional methods, attention is paid to the fact that the characteristics of the rise and fall of the pulse (in an LED) are different, and the fall is more gradual than the rise. do not have.

Therefore, when phase synchronization is performed at the rising edge of the signal CMI, which is inverted after reception, the phase of the clock fluctuates greatly, making it easy to make judgment errors when identifying codes. Also, the phase of the reproduced signal Since the clock also fluctuates with the clock, and this is accumulated during relaying, there is a problem that it is not suitable for multi-stage relaying.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an optical transmission device that has a simple circuit configuration, reduces code judgment errors, and is still suitable for multi-stage relay.

- Means for Solving the Problems In order to solve the above problems, the present invention provides a digital optical transmission system with a transmitter that inverts the polarity of a CMI signal to generate a CMI signal and drives an LED with the CMI signal; Said CMI
It is formed by a receiving section of a timing extraction circuit which receives a signal and establishes phase synchronization at the rising edge of the pulse of the CMI signal.

Effects According to the above-described method, the present invention uses the CMI signal as the signal transmitted by the LED, and achieves phase synchronization at the rising edge of the CMI signal pulse in the receiving section, thereby making it possible to reduce fluctuations in the phase of the extracted clock. Therefore, code judgment errors can be reduced and multi-stage relay can be performed.

Embodiment An embodiment of the present invention is shown in FIG. In the figure, 30 is an inversion gate. Components that are the same as those in FIG. 4 are given the same numbers, and details of their operations will be omitted.

The operation will be explained below using FIG. 2 showing operation waveforms. First, the NRZ signal d is converted by the encoder 1 into a CMI signal, and further converted into a CMI signal C by the inverting gate 3o.

In the CMI signal C, the interval between pulse rises is the basic period T.
Therefore, the rise of the output waveform d of the LED, which is converted into an optical signal, is also an integral multiple of the fundamental period T.

On the other hand, LEDs have a characteristic of having a steep rise.

Therefore, the rising edge of the signal f obtained by identifying the output signal e of the amplifier 5 using the discrimination level H of the gate 1° has an interval of an integer of the fundamental period, and the phase fluctuation is extremely small. Therefore, the change in the phase of the clock q extracted by phase comparison at the rising edge of the pulse of the signal f is extremely small. As a result, errors in judgment when identifying codes by the decoder 6 are reduced. Furthermore, since the phase fluctuation of the reproduced signal is also reduced, the amount of phase fluctuation accumulated during relaying is also reduced, and the number of relay stages can be increased.

FIG. 3 shows another embodiment of the present invention, in which the encoder 1
By constructing the output stage of a D-type flip-flop having an inverting output terminal, the inverting gate 30 shown in FIG. 1 becomes unnecessary and the circuit can be simplified.

Effects of the Invention As described above, according to the present invention, in a CMI encoding system, it is possible to extract a lock having extremely small phase fluctuation with a simple configuration, and it is extremely useful in practice.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an optical transmission system in one embodiment of the present invention, FIG. 2 is a waveform diagram of its main parts, FIG. 3 is a block diagram of an optical transmission system in another embodiment of the invention, and FIG. The figure is a block diagram showing a conventional optical transmission system, and FIG. 6 is a waveform diagram of its essential parts. 30...Inversion gate, 31...LED
, 32...PLL circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person N
2 Figure a) Castle mound

Claims (1)

[Claims] The polarity of a CMI (Code Mark Inversion) encoded signal is inverted to produce a CMI signal, and the CMI
A transmitter that drives a light emitting diode with different characteristics at the rising and falling edges of the pulse, and a timing extraction circuit that receives the @CMI@ signal and performs phase synchronization at the rising edge of the @CMI@ signal. An optical transmission device comprising: