JPH09284222A - Optical input interruption detection method and circuit for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect optical input interruption at a high speed. SOLUTION: When a reception signal 11 is interrupted, a timing extract circuit 2 cannot extract a reception clock signal 13 based on received data signal and conducts self-running and the output of the timing extract circuit 2 deviates from a substantial frequency. As a result, a phase difference is caused between the output of the timing extract circuit 2 and a reference clock 14. The phase difference is detected by a phase comparator circuit 3 and decides it to be input interruption when the phase difference reaches a prescribed value or over and outputs an interruption detection signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical signal inputting optical signal for optical communication, converting the optical signal into an electric signal and outputting the electric signal as a received data signal, for detecting disconnection of an optical signal input. The present invention relates to an input loss detection method and a circuit for implementing the method.

[0002]

2. Description of the Related Art Conventionally, an optical input break detection circuit has been used in order to reliably detect an optical input break in optical communication. For example, Japanese Patent Application Laid-Open No. 2-104153 describes a method of detecting an input disconnection based on the level of a received clock signal output from a timing extraction circuit after passing through a bandpass filter.

FIG. 3 is a block diagram of a light input break detection circuit described in the publication. First, the optical input signal a is
After being converted into an electric signal by the electric conversion unit 21, the data signal b is amplified by the equalization amplification unit 22 to an amplitude optimum for identification, and then sent to the identification unit 24 as a data signal c.

The timing extraction unit 23 extracts a clock signal (sine wave) d from the data signal c. Limiter unit 25
Outputs the clock signal (sine wave) d extracted by the timing extraction section 23 to a rectangular wave and outputs it to the identification section 24 as a clock signal (rectangular wave) e. The identification unit 24 identifies the logic level of the data signal c in synchronization with the clock signal e and sends it as a data signal output f. The identification unit 2
The signal g output from 4 is a clock signal output.

Next, the clock signal (sine wave) d from the timing extracting section 23 is amplified by the amplifying section 26 and then input to the bandpass filter 28 of the disconnection detecting section 27. Here, noise components corresponding to bit rates other than data are removed, and only signal components are input to the input disconnection detection circuit 29 in the next stage. The input break detection circuit 29 inputs the output of the bandpass filter 28, compares the input signal with a reference signal,
When the input signal becomes lower than the reference signal, the optical input disconnection alarm signal h is output. The bandpass filter 28
The input disconnection detection circuit 29 constitutes a disconnection detection unit 27.

[0006]

In the above-described conventional optical input break detection circuit, the optical input break detection is carried out by using the reception clock output from the timing extraction section. However, the timing extraction unit outputs a clock signal that is out of phase by running for a while even after the reception signal is cut off,
After that, noise is output. Therefore, even if the output of the timing extractor is filtered by a bandpass filter, a clock component having a phase shift is output from the bandpass filter for a while after the optical input is cut off, and the cutoff cannot be detected during that time.
As a result, there is a problem that it takes a long time to detect the light input break and the light input break cannot be accurately detected.

It is an object of the present invention to provide a light input break detection method and apparatus capable of detecting a light input break at high speed.

[0008]

In order to solve the above problems, an optical input disconnection detecting method of the present invention inputs an optical signal, converts the optical signal into an electric signal, and outputs it as a reception data signal. A method for detecting an optical input break in an opto-electric conversion circuit for generating a reception clock signal by extracting a clock signal from a reception data signal, the reception clock signal and a reference clock signal having the same frequency as the reception clock signal. The phase difference between and is detected, and when the phase difference exceeds a predetermined value, it is determined that the optical input is disconnected.

As described above, when an optical input interruption occurs, the optical input interruption is determined by the change in the phase difference between the reception clock signal and the reference clock signal caused by the frequency change of the reception clock signal. It is possible to detect the optical input disconnection before the generation of the reception clock signal is stopped due to the input disconnection. Therefore, the light input break can be detected at high speed.

The light input break detection circuit of the present invention is a circuit for implementing the above-mentioned light input break detection method. This circuit is an optical input disconnection detection circuit that detects disconnection of an optical signal input in an optical-electrical conversion circuit that inputs an optical signal of optical communication, converts the optical signal into an electric signal, and outputs the electric signal as a reception data signal. A timing extraction circuit for extracting a clock signal from the received data signal and outputting the received clock signal, an output of the timing detection circuit, and a reference clock signal having the same frequency as the received clock signal, and timing extraction It has a phase comparison circuit that detects the phase difference between the output of the circuit and the reference clock signal and determines that the optical input is disconnected when the phase difference exceeds a predetermined value.

When the input of the optical signal is cut off, the received data signal is not output, but the timing extraction circuit is self-propelled and outputs a clock signal whose frequency is shifted. As a result, the phase difference between the output of the timing extraction circuit and the reference clock signal changes. When the phase difference becomes equal to or larger than a predetermined value, the phase comparison circuit performs input disconnection processing.

[0012]

Next, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram of an optical input break detection circuit for carrying out the optical input break detection method of the present invention, and FIG. 2 is a timing diagram of the optical input break detection circuit of FIG.

In FIG. 1, the optical input break detection circuit is an opto-electric conversion circuit 1, a timing extraction circuit 2, and a phase comparison circuit 3.
It has. The photoelectric conversion circuit 1 converts the received signal (optical signal) 11 into an electric signal and outputs it as a received data signal 12. The timing extraction circuit 2 receives the received data signal 12
Then, the clock signal is extracted from and output as the reception clock signal 13. The phase comparison circuit 3 compares the phase difference between the reference clock signal 14 having the same frequency as the reception clock signal 13 and the timing extraction circuit 2 and outputs the disconnection detection signal 15 when the phase difference changes.

Next, the operation of the circuit shown in FIG. 1 will be described with reference to FIG. Normally, when the optical signal is normally input, the reception data signal 1 extracted by the timing extraction circuit 2 by the reception data signal 12 of the electro-optical conversion circuit 1
3 is extracted as a reception clock signal 13 having a certain period. By frequency-synchronizing the reference clock signal 14 with the reception clock signal 13, the phase relationship between the reference signal 14 and the reception clock signal 13 is maintained at a certain phase relationship. FIG. 2 shows a state in which the optical signal is normally input during the time between time T0 and time T1, and the reception clock signal 13 and the reference clock signal 14 are kept at a constant phase difference. There is.

When the reception signal 11 is cut off, the reception data signal 12 is not generated. Therefore, the timing extraction circuit 2 cannot extract the reception clock signal 13 from the reception data signal 12, but the timing extraction circuit 2 runs by itself. The clock frequency output from the timing extraction circuit 2 deviates from the original frequency. As a result, there is a phase shift between the reference clock signal 14 and the clock signal generated by free running. In FIG. 2, the timing extraction circuit 2
The deviation of the clock frequency output from is expressed as starting at time T1.

This phase shift is detected by the phase comparison circuit 3, and when the phase shift exceeds a predetermined value, the disconnection detection signal 15
Is output. In FIG. 2, at time T2, the phase difference between the clock signal generated by the free running of the timing extraction circuit 2 and the reference clock signal becomes 180 degrees, and the clock signal generated by the free running falls and the reference clock signal is generated. Rises and the disconnection detection signal 15 is output at this time.

[0017]

As described above, according to the present invention, the phase of the received clock signal extracted from the received signal is compared with the phase of the reference clock signal, and the disconnection detection process is performed when the phase difference exceeds a predetermined value. By doing so, it is possible to detect disconnection of the received signal at high speed.

[Brief description of drawings]

FIG. 1 is a block diagram of a high-speed light input break detection circuit of the present invention.

FIG. 2 is a timing diagram of the high-speed light input break detection circuit of FIG.

FIG. 3 is a block diagram of a conventional example of a light input break detection circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical-electrical conversion circuit 2 Timing extraction circuit 3 Phase comparison circuit 11 Received signal 12 Received data signal 13 Received clock signal 14 Reference clock signal 15 Break detection signal 21 Optical-electrical conversion unit 22 Equalization amplification unit 23 Timing extraction unit 24 Identification Section 25 limiter section 26 amplifying section 27 disconnection detection section 28 bandpass filter 39 input disconnection detection circuit

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display area H04B 10/06

Claims (2)

[Claims] 1. An optical input disconnection detecting method in an optical-electrical conversion circuit, which receives an optical signal, converts the optical signal into an electric signal and outputs the electric signal as a received data signal, wherein a clock signal is extracted from the received data signal. To generate a reception clock signal and detect a phase difference between the reception clock signal and a reference clock signal having the same frequency as the reception clock signal. When the phase difference exceeds a predetermined value, it is determined that the optical input is disconnected. An optical input disconnection detection method in optical communication, comprising: 2. An optical input disconnection detection circuit for detecting disconnection of an optical signal input in an optical-electrical conversion circuit for inputting an optical signal for optical communication, converting the optical signal into an electric signal and outputting it as a reception data signal. A timing extraction circuit that extracts a clock signal from the received data signal and outputs the received clock signal; an output of the timing extraction circuit and a reference clock signal are input, and an output of the timing extraction circuit is the same as the received clock signal An optical input disconnection detection circuit in optical communication, comprising a phase comparison circuit that detects a phase difference from a reference clock signal having a frequency and determines that the optical input is disconnected when the phase difference becomes a predetermined value or more. .