JPH0340540A - Optical signal input disconnection detector for optical signal receiver - Google Patents

Abstract

PURPOSE:To correctly detect the disconnection of an optical signal input by monitoring a change in a control signal for controlling a phase difference in a phase synchronizing loop circuit and detecting the disconnection of the optical signal input. CONSTITUTION:When an optical signal input is disconnected, the contents of an output from a clock extraction circuit 3 are made completely indistinct and the indistinct contents are inputted to a phase synchronizing loop circuit 2, so that a phase difference control signal is changed to a voltage shifted from a fixed voltage obtained when the optical input exists. The DC phase difference control signal is compared with a previously set reference value by an optical input disconnection deciding circuit 4 to decide the disconnection of the optical signal input. Thus, the disconnection of the optical signal input can correctly be detected.

Description

[Detailed Description of the Invention] [Summary] An object of the present invention is to provide an optical signal input disconnection detection device for an optical signal receiver that can correctly detect an optical signal input disconnection. A photoelectric conversion circuit that converts a signal into an electrical signal and outputs it, a clock extraction circuit that extracts a timing component from the output signal of the photoelectric conversion circuit and outputs a clock signal, and inputs the clock signal output from the clock extraction circuit. and a phase-locked loop circuit that generates a clock signal having a certain phase difference from the clock signal by feedback control, and a DC signal that controls the output signal phase of the phase-locked loop circuit is compared with a preset reference value. By doing so, the optical input disconnection determination circuit is provided to determine whether or not the optical signal input is disconnected.

[Industrial application field]

The present invention relates to an optical signal input disconnection detection device for an optical signal receiver.

Optical communication systems require various failure detection functions in order to discover whether the system is operating normally or not and to discover failure points in the event of an abnormality. Among them,
The function of detecting whether an optical signal is being received or not, that is, whether the input of an optical signal is disconnected, is an indispensable function of an optical receiver, and must operate normally in order to discover failure points.

[Conventional technology]

A conventional optical signal input disconnection detection device for an optical signal receiver is equipped with a photoelectric conversion circuit that inputs a digital optical signal, converts it into an electrical signal, equalizes and amplifies the electrical signal using automatic gain control, and outputs it. , the timing component extracted from the output signal of the photoelectric conversion circuit is amplified, the peak value of the timing component is detected, and the peak value is compared with a predetermined threshold to detect the "disconnection" of the optical signal input. ” was detected.

[Problems to be Solved by the Invention] However, the timing component naturally decreases as the mark rate of the optical input signal decreases. Therefore, if you increase the gain of the timing component amplification so that the peak value does not decrease,
When the optical signal input is cut off, the amplifier circuit oscillates and the peak value does not drop, resulting in a problem where it is mistakenly determined that the optical signal input is not cut off.

In addition, noise components are likely to be added to the charging conversion circuit, and it is not easy to detect the peak value of the amplitude of a signal mixed with noise components, resulting in an incorrect determination.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical signal input disconnection detection device that can eliminate such conventional drawbacks and correctly detect optical signal input disconnection.

[Means to solve the problem]

In order to achieve the above object, an optical signal input disconnection detection device for an optical signal receiver according to the present invention includes a photoelectric conversion circuit l that converts an optical input signal into an electrical signal and outputs the electrical signal, as shown in FIG. , a clock extraction circuit 3 that extracts a timing component from the output signal of the photoelectric conversion circuit 1 and outputs a clock signal; and a clock signal outputted from the clock extraction circuit 3 is inputted, and A phase-locked loop circuit 2 that generates a clock signal having a phase difference by feedback control and a DC signal that controls the output signal phase of the phase-locked loop circuit 2 are compared with a preset reference value to determine the optical signal input. It is characterized by having an optical input disconnection determination circuit 4 that determines whether the optical input is disconnected.

[Effect]

When an optical signal is input, a clock signal is input from the clock extraction circuit 3 to the phase-locked loop circuit 2, and a clock signal having a constant phase difference is generated by feedback control. Therefore, the DC control signal (DC voltage) that controls the phase difference becomes a constant voltage.

When the optical signal input is cut off, the output of the clock extraction circuit 3 becomes a completely unknown output, which is input to the phase locked loop circuit 2. Therefore, the phase difference control signal is a constant voltage when optical input is present. The voltage changes to a value that deviates from the voltage. Then, by comparing this DC phase difference control signal with a reference value set in advance in the optical input disconnection determination circuit 4, it is determined whether the optical signal input has been interrupted.

〔Example〕

Examples will be described with reference to the drawings.

FIG. 2 is a circuit block diagram of the embodiment. In the figure, ti is an avalanche photodiode (APD) that inputs an RZ-modulated digital optical signal and converts it into an electric signal, and this RZ electric signal output is input to the equalization amplifier circuit 12 and equalized and amplified. .

The equalization amplifier circuit 12 detects the peak of the equalized waveform to control the gain, and also feeds back a control signal for controlling the multiplication factor of the APD to the APD bias control circuit 13. This provides automatic gain control. The output signal of the equalization amplifier circuit 12 is output to the clock extraction circuit 3 and the identification circuit 5.

31, 32, and 33 are a timing extraction circuit, a timing amplification circuit, and a limiter amplification circuit forming the clock extraction circuit 3. Here, the timing extraction circuit 31 first extracts a narrow band timing component from the output data of the equalization amplifier circuit 12, and the timing component is amplified by the timing amplifier circuit 32. Further, the limiter amplifier circuit 33 extracts the timing component of a narrow band from the output data of the equalization amplifier circuit 12. is formed.

Then, the clock pulse output from the limiter amplifier circuit 33 is input to the identification circuit 5, and the identification circuit 5 identifies rN or rQJ with respect to the data signal input from the equalization amplifier circuit 12 at the timing of the clock. is performed and the result is output along with the clock.

Further, the clock signal output from the clock extraction circuit 3 is input to the phase locked loop (PLL) circuit 2. P
In the LL circuit 2, a clock signal is input to the first input terminal of the phase comparison circuit 21, and the difference signal (DC control signal) output from the phase comparison circuit 21 is sent to the internal oscillator (O8C) 2.
2, and based on that signal, a clock signal having a certain phase difference with the original clock signal is output from 08C22, and this clock signal is input to the second phase comparator circuit 21.
Feedback control is performed by inputting it to the input terminal of.

Note that the phase difference within the PLL circuit 2 only needs to be a constant phase difference (for example, 90 degrees), and the phase difference may be zero.

The DC control signal that controls the phase difference in the PLL circuit 2 is branched and input to the optical input disconnection determination circuit 4, where the reference value (
reference voltage). By comparing them, it is determined whether or not there is an optical signal input, that is, it is detected that the optical signal input is "off".

Specifically, when there is an optical signal input, the PLL circuit 2
The control voltage of is always constant. However, when the optical signal input is cut off, the output from the clock extraction circuit 3 becomes a completely unknown output and is input to the PLL circuit 2, so the control signal (DC voltage) of the PLL circuit 2 However, the voltage changes from the constant voltage when an optical signal is input. When the interruption of the optical signal input is detected in this way, the alarm circuit 9 issues an alarm by sound or light based on the output signal from the optical input interruption determination circuit 4.

〔Effect of the invention〕

According to the optical signal input disconnection detection device for an optical signal receiver of the present invention, optical signal input disconnection can be detected by monitoring changes in the control signal that controls the phase difference within the phase-locked loop circuit. Therefore, it is possible to always accurately detect optical signal input disconnection, regardless of the noise of the photoelectric conversion circuit or the gain of the timing component amplification of the clock extraction circuit.Moreover, since the phase difference control signal is DC, its voltage Since it is only necessary to detect a change, it is extremely easy to detect interruption of optical signal input.

[Brief explanation of drawings]

Figure 1 is a diagram of the principle of the present invention. FIG. 2 is a circuit block diagram of the embodiment. In the figure, ■...Photoelectric conversion circuit, 2...phase-locked loop circuit, 3...clock extraction circuit, 4... Optical input disconnection determination circuit.

Claims (1)

[Claims] A photoelectric conversion circuit (1) that converts an optical input signal into an electrical signal and outputs it; and a clock extraction circuit that extracts a timing component from the output signal of the photoelectric conversion circuit (1) and outputs a clock signal. circuit(
3); and a phase-locked loop circuit (2) that receives the clock signal output from the clock extraction circuit (3) and generates a clock signal having a certain phase difference with the clock signal by feedback control; an optical input disconnection determination circuit (4) that determines whether the optical signal input is "interrupted" by comparing a DC signal that controls the output signal phase of the phase-locked loop circuit (2) with a preset reference value; An optical signal input disconnection detection device for an optical signal receiver, comprising: