JPH03270331A - Signal interrupt detection system - Google Patents

Abstract

PURPOSE:To easily detect interruption of a reception signal by detecting a signal interruption due to increase in noise caused by the interrupt of the reception signal. CONSTITUTION:A reception amplifier reaches a maximum gain at interruption of a reception signal and lots of frequency components are included in a noise signal wave. In this case, only a clock frequency component of a transmission line goes to a 0 level and other frequency component signal remains, then the signal is outputted from a delay/adder means 110 as a signal amplitude. An output of the delay/adder means 110 is fed to a signal interruption detection means 130 to detect signal interruption as a difference between a 0 level at normal state and a noise component at interruption of the reception signal. Thus, the interruption of the reception signal is easily detected.

Description

[Detailed Description of the Invention] (Summary) Regarding a signal disconnection detection method in a receiving circuit for optical digital signal transmission, an object of the present invention is to provide a signal disconnection detection method that can easily detect disconnection of a received signal. In a receiving circuit that has a filter that extracts and outputs a transmission line clock frequency component after amplification and obtains a clock signal from the output of the filter, it is connected to the filter and the phase of the output of the filter and the output of the filter are halved. delay/addition means for adding signals with shifted periods;
A signal interruption detection means is connected to the addition means and is configured to detect a signal interruption due to an increase in noise caused by a political decision when the received signal is interrupted.

[Industrial application field]

The present invention relates to an improvement in a signal disconnection detection method in a receiving circuit for optical digital signal transmission.

The signal in the optical receiving circuit may be interrupted due to a failure of the laser diode on the transmitting side of the optical signal or a break in the optical fiber at the transmission line and 1-. In order to avoid adverse effects and reduce reliability, detection of a disconnection of a received signal is performed.At this time, there is a need for a signal disconnection detection method that can easily detect a disconnection of a received signal.

[Conventional technology]

FIG. 4 is a block diagram showing the configuration of an example optical signal receiving circuit.

FIG. 5 is a time chart showing the operation of the circuit shown in FIG. 4.

FIG. 6 is a block diagram showing the configuration of a conventional signal disconnection detection circuit.

FIG. 4 shows a receiving circuit for optical digital signals. In the figure, the optical signals received from the transmission line such as optical fiber are
For example, an avalanche photodiode C (hereinafter referred to as APD) IL: is converted into an electrical signal as shown in FIG.
and added to the SAW filter 3 (see Figure 5 ■ and ■) The AW filter 3 is a bandpass filter that passes the clock frequency component of the transmission path, and the SAW filter 3 as shown in
A sine wave signal of a predetermined frequency that has passed through the A-filter 3 is applied to a limiter amplifier 4.

The limiter amplifier 4 cuts the upper and lower parts of the input signal and outputs a clock signal of a predetermined frequency as shown in FIG. In the identification circuit 5, the limiter amplifier 4
According to the timing of the clock signal output from the amplifier 2, the output of the amplifier 2 is discriminated between "1" and "0" as described above, and a rectangular wave signal as shown in Figure 5 (■) is output. was.

Now, if the input signal to APD 1 is cut off, 1,
As shown in FIG. 6, peak detection is performed in the peak detection circuit 7 after passing through the linear amplifier 6 in the limiter amplifier 4.
The detected peak value is output to the comparator 8.

Comparator No. 8 compares the detected peak value with a preset reference value VreL, and detects the interruption of the received signal based on the difference between the normal signal amplitude level and the signal interruption.

[Problems to be Solved by the Invention] However, in the above circuits B and B, when the received signal is interrupted, APD 1 generates noise, while amplifier 2 is in the maximum gain state, so noise is generated. There is a problem in that it is not easy to detect the difference in signal level between the outputs of the SAW filters.

1- Therefore, it is an object of the present invention to provide a signal disconnection detection method that can easily detect disconnection of a received signal.

[Means for Solving the Problems] The above problems are solved by the circuit configuration shown in FIG.

That is, in FIG. 1, in a receiving circuit that has a filter 300 that amplifies a received signal and extracts and outputs a long frequency component on the post-transmission path, and obtains a clock signal from the output of the filter 300, 110 is a circuit that is connected to the filter 300. It is a delay/adding means that is connected to the filter 300 and adds the output of the filter 300 and a signal obtained by shifting the phase of the output of the filter 300 by 1/2 period.

Reference numeral 130 denotes signal interruption detection means that is connected to the delay/addition means 110 and detects a signal interruption when the received signal 8 is interrupted.

[Function] In FIG. 1, the phase of the output of the filter and the output of the filter 300 (this is the phase of a signal having a frequency equal to the clock frequency of the transmission line) is halved by the delay/addition means 110L. Addition of signal B whose period has been shifted is performed. As a result, under normal conditions, their phases cancel each other out, causing delay/
The output of the adding means 110 becomes "0" level.

On the other hand, when the received signal is interrupted, the receiving amplifier has the maximum gain, and the signal wave due to noise contains many frequency components. In this case, only the clock frequency component of the transmission path becomes 0'' level, but since signals of other frequency components remain, they are output from the delay/addition means 110 as signal amplitudes.

The output of this delay/addition stage 110 is detected by the signal disconnection detection means 13.
By adding it to 0, it becomes possible to detect a signal interruption as the difference between the normal "0" level and the noise component when the received signal is interrupted.

〔Example] FIG. 2 is a diagram showing the configuration of a circuit according to an embodiment of the present invention.

FIG. 3 is a diagram illustrating the operation of the embodiment.

The same reference numerals indicate the same objects throughout the figures.

In FIG. 2, a transistor (hereinafter referred to as Tr) 1
The output of the SA-filter 3 shown in FIG. 4 is added to the base of 0. T rlO is a so-called emitter follower type Tr circuit, and a matching resistor Ro (for example, 75Ω) is connected to the emitter output. One end of a delay line 11 made of, for example, a coaxial line (its characteristic impedance Zo is 75Ω, for example) with the other end open is connected to the other end of the resistor RO via a capacitor C0. Then, the delay amount of this delay line 11 is set to 1/4To. Here, TO is T□=l/fo, and fo is the clock frequency of the transmission line and is also the output frequency of the SA-filter 3.

The output of T rlo is branched at the input section of the delay line 11, one side is totally reflected at the delay line 11, and added to the original signal at the input section of the delay line 11. As a result, under normal conditions, the phase of the reflected wave is out of phase with the original signal by 1/2 period, so the synthetic liquid becomes at the "0" level as shown in FIG. 3(a).

On the other hand, when the received signal is interrupted, the gain of the amplifier 2 is maximum, and the APD 1 also generates noise, so the noise is also greater than in normal times. The signal wave due to this noise includes many frequency components. As shown in FIG. 3(b), in the synthetic liquid at the input part of the delay line 11, only the above-mentioned fO frequency component is at the "0" level, but other frequency components remain and appear as signal amplitude. By applying this output to the capacitor C3 connected to the emitter of T r12 and the comparison circuit 13 via T r12, the capacitor C
3 and a resistor (not shown) included in the comparison circuit 13, the peak is detected.

In the comparison circuit 13, by comparing this peak value with a preset reference value Vrefz, signal interruption is detected when the received signal is interrupted.

During normal operation, the synthetic liquid trapped in the delay line 11 is at the "0" level, so that it is easy to distinguish between normal operation and signal interruption.

In the figure 110 is a delay/addition means; 130 is a signal disconnection detection means shows.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to easily detect a disconnection of a received signal.

[Brief Description of the Drawings] Fig. 1 is a diagram showing the principle of the present invention, Fig. 2 is a diagram showing the circuit configuration of an embodiment of the present invention, Fig. 3 is a diagram explaining the operation of the embodiment, Fig. 4 is a block diagram showing the configuration of an example optical signal receiving circuit, FIG. 5 is a time chart showing the operation of the circuit shown in FIG. 4, and FIG. 6 is a block diagram showing the configuration of a conventional signal disconnection detection circuit. . The principles of the present invention are as follows: Figure 1: An illustration of the circuit of the embodiment of the present invention;
4 Figure 4 shows the structure of the conventional Pj0) Signal disconnection detection circuit. 6 Figure 2 shows the operation of the embodiment during normal operation (a) (b). ■ ■ Figure 4. Peeling of F

Claims (1)

[Claims] A receiving circuit that includes a filter (300) that extracts and outputs a transmission line clock frequency component after amplifying a received signal, and that obtains a clock signal from the output of the filter (300), 300) and the filter (300
) and the output of the filter (300) by 1/
Delay/addition means (11
0), and signal interruption detection means (130) connected to the delay/addition means (110) and detecting a signal interruption by an increase in noise due to the interruption when the reception signal is interrupted. Signal disconnection detection method.