JP2536178B2 - Optical transceiver - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical transmitter / receiver of an optical communication device that converts the strength of an electric signal into the strength of an optical signal to perform optical communication through an optical fiber cable.

[Conventional technology]

Generally, in an optical transmitter / receiver that uses an optical fiber cable as a transmission path, when an electric pulse signal is directly converted into an optical signal and transmitted through the fiber cable, attenuation of light by a connecting portion such as a connector and attenuation during propagation of the fiber cable Diffusion causes a drop in light level and pulse rounding.

The receiver must have the function of faithfully reproducing the input pulse electric signal on the transmission side (that is, reproducing the pulse having the same width as the transmission pulse width) against the attenuation and rounding of the optical reception level. When reproducing, it is especially important that the pulse width distortion is small.

An automatic discriminator equipped with an AGC (Automatic Gain Control) circuit and an ATC (Automatic Threshold Contnol) circuit has become widespread as a circuit that has a small pulse width distortion and can cope with fluctuations in the reception level.

When the AGC circuit is a burst signal, the AGC function stops at the data stop part and normal operation cannot be maintained.

 An optical receiver equipped with an ATC circuit is shown in FIG.

In FIG. 4, (1) is a light receiving diode for converting an optical pulse into a current signal, (2) is an amplifier for amplifying a current signal converted by the light receiving diode and converting it into a voltage signal, (3)
Is a feedback resistor that determines the amplification of the amplifier (2),
(4) to (9) are resistors, (10) is a capacitor that determines the response speed of the ATC circuit, and (11) is a voltage signal depending on the size of the two inputs of positive input (+) and negative input (-). FIG. 5 is a diagram showing a pulse width output operation of the identification reproduction operation of the optical receiver shown in FIG.

VC1 is a received voltage signal applied to the positive input (+) of the discriminator (11), VC2 is a received voltage signal applied to the negative input (-) of the discriminator (11), and VC3 is the discriminator ( The pulse voltage signal identified in 11) is shown.

The optical pulse transmitted through the optical fiber is converted into a current corresponding to the level of the optical pulse by the light receiving diode (1), and the voltage signal shown by the following equation is obtained by the amplifier (2) and the resistor (3) connected to its input and output. Converted to (Vo).

Vo = SPR (V) (1) Vo (received voltage signal), S (photoelectric conversion sensitivity of light emitting diode A / W) P (received level W), R (resistance value Ω of resistor (3)) The received voltage signal Vo is applied as VC1 to the positive input (+) of the discriminator (11) through the resistor (5).

At the same time, VC2 is applied to the negative input (-) of the discriminator (11) through the resistor (6).

To the negative input (-) of the discriminator (11), + 5V of the DC voltage becomes a DC voltage divided by the resistors (8) and (9) and is applied through the resistor (7).

Since the DC voltage is applied to the negative input (-) of the discriminator (11) before the reception voltage signal (Vo) is applied, the discriminator output signal VC3 is held at OV.

Even if the optical pulse transmitted by the transmitter is a normal pulse signal with a duty of 50%, attenuation and rounding occurs during optical fiber transmission, and the optical pulse input to the receiver has a waveform as shown in FIG. This becomes the photoelectrically converted reception voltage signal Vo.

The received voltage signal VC2 is a capacitor (10) and a resistor (6)
It rises with a delay from the received voltage signal VC1 by the integration operation determined by and its level follows VC1.

The discriminator (11) sets the output signal VC3 to high (1) when the positive input (+) VC1 is larger than the negative input (−) VC2. In this way, the discriminator (11) performs an operation (ATC) of discriminating and reproducing while following a small level fluctuation of the electric pulse signal.

When the fluctuation of the optical level and the rounding of the optical waveform are large, the output pulse voltage signal Vc3 has large pulse width distortion (narrow pulse width) because the reception voltage signal Vc1 becomes larger than Vc2 as shown in FIG. Voltage output.

[Problems to be Solved by the Invention]

The discriminator of the conventional optical receiver can suppress the pulse width distortion to some extent by the tracking effect of the threshold, but when the fluctuation of the optical level and the rounding of the optical waveform are large, it goes out of the tracking range of the threshold and the pulse distortion becomes large. If the pulse width distortion of the pulse voltage signal output by the optical receiver is reduced and the pulse voltage signal having almost the same pulse width as the transmitted electric pulse signal cannot be identified and reproduced, the problem that the regular clock cannot be extracted occurs. There was a problem that the problem could not be solved only by the threshold tracking action.

The present invention has been made to solve the above problems, and an object thereof is to obtain an optical receiver that controls the transmission optical pulse width corresponding to the distortion in order to minimize the reception electric pulse width distortion. .

[Means for solving the problem]

The optical transmitter of the optical transmitter / receiver according to the present invention comprises a pulse width control circuit capable of spreading the pulse width of the input pulse voltage signal, and the optical receiver comprises a discriminator for reproducing and outputting a pulse voltage signal from the received voltage signal, and a discriminator. The pulse width comparator for comparing the pulse widths of both the pulse voltage signal and the input pulse voltage signal, and the pulse width discriminating circuit for discriminating the sign of the difference between the pulse widths.

[Action]

The optical transceiver according to the present invention compares the pulse width of the received pulse voltage signal with the pulse width of the input pulse voltage signal, outputs a negative (-) sign when the pulse width of the received pulse voltage signal is narrow, and then outputs a negative (-) sign. Receiving the code, the pulse width of the input pulse voltage signal is expanded by the pulse width control circuit, this expanded signal is received and reproduced, and the received pulse voltage signal is compared again with the pulse width of the input pulse voltage signal. The function of expanding or contracting the width is performed.

〔Example〕

 An embodiment of the present invention will be described below with reference to FIGS.

In FIG. 1, (12) is a pulse width adjusting circuit capable of enlarging or reducing the pulse width of an input pulse voltage signal, and (13) is a driver for turning on or off a light emitting diode corresponding to the pulse voltage signal. A circuit, (14) is a light emitting diode for turning on or off light by the driver circuit (13), and (15) is an optical fiber cable for transmitting the light emitted from the light emitting diode to an optical receiver.

When the input pulse voltage signal is applied to the transmitter after the optical transmitter and the optical receiver are installed via the fiber cable (15), the pulse width adjustment circuit (12) initially adjusts the pulse width without adjusting the pulse width. Driver circuits to keep (13)
Send a signal to When the transmission light pulse signal converted by the light emitting diode (14) arrives at the receiver through the optical fiber cable (15), it is caused by the connecting portion such as a connector as shown in the waveform of the reception side light pulse signal in FIG. Attenuation of light and attenuation and diffusion during propagation through the fiber cable result in a decrease in light level and rounding of pulses. The light pulse signal is converted into a current corresponding to the presence or absence of a light pulse by the light emitting diode (1) of the receiver, and is expressed by the above equation (1) by the amplifier (2) and the resistor (3) connected to its input and output. Converted to received voltage signal (Vo).

The received voltage signal (Vo) is applied as Vc1 to the positive input (+) of the discriminator (11) through the resistor (5). At the same time, through the resistor (6) to the negative input (-) of the discriminator (11)
Applied as Vc2. To the negative input (-) of the discriminator (11), + 5V of the DC voltage becomes a DC voltage divided by the resistors (8) and (9) and is applied through the resistor (7). Since the DC voltage is applied to the negative input (-) of the discriminator (11) before the reception voltage signal (Vo) is applied, the discriminator output signal Vc3 is held at OV.

The received voltage signal Vc2 is a capacitor (10) and a resistor (6)
It rises with a delay from the received voltage signal Vc1 by the integration operation determined by and its level follows Vc1.

This is shown by the discriminator input voltage in FIG. As shown in FIG. 3, when the optical level is lowered and rounded, the discriminator output pulse voltage signal Vc3 becomes an output signal with a narrow pulse width, which causes a problem that the clock cannot be accurately extracted by the clock extraction circuit that follows.

In order to eliminate this problem, the pulse width of the output pulse voltage signal Vc3 is measured beforehand as shown in FIG. 3, and the pulse width adjustment circuit (1
In 2), the pulse width of the input pulse voltage signal is widened.

The one shown in Fig. 2 shows that the optical pulse signal transmitted by the local station returns to the receiving section of the local station (16) is a pulse width control circuit that can expand or contract the input pulse voltage signal,
(17) is an optical star coupler that is connected to a transmitter / receiver via a number of optical fiber cables (15) and equally distributes the transmitted optical pulse signal, and (18) is a pulse that is discriminated and regenerated from the discriminator (11) in the receiving section. The pulse width comparators (18) and (19) that compare the magnitude of the pulse width of the voltage signal and the input pulse voltage signal output the sign depending on the magnitude of the pulse width. The pulse width difference determination circuit outputs a negative (-) when the pulse width is smaller than the pulse width and a positive (+) when the pulse width is larger than the pulse width.

When the pulse width of the pulse voltage signal narrower than that of the input pulse voltage signal is compared by comparing the pulse width of the pulse voltage signal regenerated by the discriminator (11) of the optical receiver and the input pulse voltage signal with the pulse width comparator (18). Is output from the pulse width difference determination circuit (19) to the pulse width control circuit (16) with a negative (-) sign.
The pulse width control circuit (16) receives a negative (-) sign and performs control for expanding the pulse width of the input pulse voltage signal.

This control is repeated to equalize the pulse widths of the input pulse voltage signal and the received pulse voltage signal.

〔The invention's effect〕

As described above, according to the present invention, the pulse width of the pulse voltage signal discriminated and reproduced by the receiver is visually judged or automatically judged by the measuring device, and the pulse width of the transmitter is expanded or reduced to increase or decrease the pulse width of the input pulse voltage signal. It is possible to obtain a received pulse voltage signal that is almost equal to, and it is possible to easily extract a clock from the received pulse voltage signal, and to provide an accurate optical transceiver.

[Brief description of drawings]

1 and 2 are diagrams showing an optical transceiver according to an embodiment of the present invention, and FIG. 3 is a diagram showing waveforms of the optical transceiver of the present invention.
FIG. 4 is a diagram showing an optical transmitter / receiver of a conventional example, and FIG. 5 is a diagram showing output waveforms of the conventional optical transmitter / receiver. (1) is a light receiving diode, (2) is an amplifier, (3)-
(9) is a resistor, (10) is a capacitor, (11) is a discriminator, (12) is a pulse width adjusting circuit, (13) is a driver circuit, (14) is a light emitting diode, and (15) is an optical fiber cable. , (16) is a pulse width control circuit, (17) is a star coupler, (18) is a pulse width comparator, and (19) is a pulse width difference determination circuit. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

(57) [Claims] 1. An optical transmitter for converting an input pulse voltage signal into an optical pulse signal by optical intensity modulation, an optical fiber for transmitting the optical pulse signal, and an optical star connected to the optical fiber for distributing light to a plurality of optical fibers. In a plurality of optical transceivers having a coupler and a receiver for demodulating the optical pulse signal into a pulse voltage signal and outputting the pulse voltage signal, the input pulse voltage signal is a plurality of optical transceivers connected in a star shape around the star coupler. A pulse width control circuit capable of expanding the pulse width of the light emitting element, a light emitting element for converting the pulse signal into an optical pulse, an optical transmitting section including a drive circuit for driving the light emitting element in response to the pulse signal, A light receiving element that converts the optical pulse distributed by the star coupler into a current signal, an amplifier that amplifies this current signal, and a pulse signal from the voltage signal output from this amplifier. A discriminator to reproduce and output a voltage signal,
A pulse width comparator that compares the pulse widths of the pulse voltage signal from the discriminator and the input pulse voltage signal, and a pulse width difference determination circuit that outputs the sign of the difference between the pulse widths of the two to the pulse width control circuit An optical transmitter / receiver comprising an optical receiver.