JPH05268272A - Signal identification system - Google Patents

Abstract

PURPOSE:To suppress the error of identification and to improve reliability by detecting the peaks of the levels '1' and '0' of an equalization wave-form inputted to an identification circuit and superimposing their average value to a constant identification level. CONSTITUTION:Peak detection circuits 12 and 13 respectively detect the peak levels in the signal levels '0b and '1', a first adding circuit 14 adds the peak levels in the signal levels '1' and '0', and a dividing circuit 15 divides the output value of the circuit 14 into two. Both of the circuits 14 and 15 obtains the average level of the peak level in the signal levels '0' and '1'. A second adding circuit 16 adds the constant identification level and the average value of the peak levels to control the identification level of the identification circuit 9. As the output of the circuit 15 is the instant value of the average value of the levels '1' and '0', the identification level is always the intermediate value between '0' and '1' even in the case of the code of which mark rate in not 1/2. Thus, data output generating few errors even to the signal with an optional mark rate is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discrimination level control method. Information handled by communication systems in recent years is related to many aspects of society, and it is often the case that a slight error in signal transmission causes a serious social impact, not to mention transmission interruption. For this reason, there is a demand to introduce a system configuration that prevents in advance the cause that may occur during operation of the communication system. When performing work such as maintenance of the spare panel during operation of the communication system, when the optical fiber of the working line is mechanically impacted, the equalized waveform is momentarily deteriorated and the signal error rate becomes sharp. Therefore, there is a demand for a measure that does not cause the deterioration of the equalized waveform.

[0002]

2. Description of the Related Art FIG. 5 shows a configuration example of a conventional optical receiving circuit. In the figure, 1 is a light receiving element, which converts an optical signal into an electric signal, 2 and 3 are amplifiers, which amplify the electric signal to a predetermined level, 4 is a branching part, which is an electric signal having a constant level That is distributed to each part for the following processing,
Reference numerals 5 and 6 are peak detection circuits for detecting peak levels in the signal levels of "0" and "1", respectively.
Reference numeral 7 is a DC converter, which adjusts the bias of the light receiving element 1, 8 is a timing extraction unit, which extracts a timing signal from an electric signal, and 9 is an identification circuit, which is "1" of the electric signal.
Is a terminal for setting an identification level, b is a data output terminal, and c is a clock output terminal.

In this configuration, FullA for changing M of the light receiving element 1 (APD) in order to keep the level on the "1" side constant.
Similarly, the output amplitude is made constant by three loops of GC, EAGC that changes the gain of the electric stage (that is, amplifier) to make the level of "1" side constant, and DCFB that makes the level of "0" side constant. There is. On the other hand, the loop time constants of the loops are gradually changed so that the loop constants do not interfere with each other and the loop operation becomes unstable. For example, the time constant is gradually increased in the order of EAGC, DCFB, and FullAGC.

In this case, when the optical input level fluctuates as shown in FIG. 6, there are the following three cases from the relationship between the fluctuation time and the loop time constant. In the first case, the fluctuation time is sufficiently longer than the time constant of each loop, and each loop responds sufficiently, so that the equalized waveform deterioration does not occur as shown in the equalized waveform A. In the second case, the variation time is sufficiently shorter than each loop time constant, and each loop does not respond, so that symmetrical degradation from the "1" side and the "0" side occurs as shown in the equalized waveform B. , A, an error is more likely to occur. Third
In the case of, when the fluctuation time is full AGC does not respond and DCFB responds, only DCFB operates and the eye deterioration on the "0" side decreases, but the eye deterioration from the "1" side increases and an error occurs. It is larger than when the occurrence is B.

[0005]

Therefore, there is a problem that the tracking of the AGC is not appropriate depending on the variation time and the error occurrence becomes large. An object of the present invention is to reduce the frequency of such error occurrence.

[0006]

FIG. 1 illustrates the principle of the present invention. In the figure, 1 is a light receiving element for converting an optical signal into an electric signal, 20 is an amplifying section for amplifying the electric signal to a predetermined level, 8 is a timing extracting section for extracting a timing signal from the electric signal 5 is a discrimination circuit for discriminating between "1" level and "0" level of an electric signal, and 20 is an amplifying section, which is 2, 3, 4, 5, in FIG.
Including the functions of 6 and 7, 30 is a discrimination level control unit,
A circuit for controlling the discrimination level of the discrimination circuit 9, a is a terminal for setting the discrimination level, b is a data output terminal, and c is a clock output terminal. Since the output of the discrimination level control unit 30 is a value obtained by superimposing the average value of the instantaneous value of the level "1" and the instantaneous value of the level "0" on the constant discrimination level, the discrimination levels are always "1" and "0". The intermediate value of “” can be taken, and the data output with less error can be obtained.

[0007]

In the present invention, as shown in FIG. 1, the average value of the output of the amplifying section 20 is detected, and the discrimination level is increased or decreased centering on a constant discrimination level. For example, as shown in FIG. 4, when the level of "1" changes as X and the level of "0" changes as Y, the identification level changes between X and Y like Z, so "1" The distinction between "level" and "0" level became clear,
It is possible to suppress the occurrence of signal errors.

[0008]

FIG. 2 shows a first embodiment of the present invention. In the figure,
1 is a light receiving element, 2 and 3 is an amplifier, 4 is a branching section, 5 and 6 are peak detecting circuits, 7 is a DC converter, 8 is a timing extracting section, 9 is an identification circuit, 10 is an average value detection circuit, and identification is performed. Detecting the average value of the equalized waveform input to the circuit, 1
Reference numeral 1 denotes an adder circuit, which adds the average value detection circuit output to a fixed discrimination level, and is one example of the constitution of the discrimination level control unit in FIG. B is a terminal for setting a discrimination level, B is a data output terminal, and C is a clock output terminal.

In the case of the present embodiment, the average value detection circuit 10
Since the output of is the average value of the equalized waveform input to the discrimination circuit (9), the discrimination level is always "1" as shown in FIG.
By taking an intermediate value (Z) between (X) and "0" (Y), data output with less error occurrence can be obtained. FIG. 3 shows a second embodiment of the present invention. In the figure, 12 and 13 are both peak detection circuits for detecting the peak levels in the signal levels of "0" and "1", respectively, and 14 is a first addition circuit for the "0" and "1". Addition of peak levels in the signal level, 15 is a division circuit that reduces the output value of the first addition circuit to 1/2, and signal levels of "0" and "1" by both 14 and 15. The second addition circuit 16 obtains the average value of the peak level of the inside, and adds a constant identification level and the average value of the peak levels among the signal levels of "0" and "1" to identify It controls the discrimination level of the circuit 9. Other symbols are the same as those described above.

In the case of this embodiment, the output of the "1" peak detection circuit (13) is an instantaneous value of the level "1",
The output of the "0" peak detection circuit (12) is an instantaneous value of the level of "0", and the output of the division circuit (15) is "1".
And the average value of the levels of "0", the discrimination level always takes an intermediate value between "1" and "0" even in the case of a code whose mark ratio is not 1/2. For this reason,
Data output with few errors can be obtained even for an arbitrary signal of the mark ratio.

[0011]

As described above, according to the present invention, even if the signal level suddenly changes due to an unexpected mechanical shock or the like given by work while operating the communication system, the discrimination circuit The identification level is instantaneously adjusted to the optimum value, which has the effect of suppressing identification errors and contributes greatly to the improvement of the reliability of the optical communication line.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is a configuration diagram of a first embodiment of the present invention.

FIG. 3 is a configuration diagram of a second embodiment of the present invention.

FIG. 4 is a diagram illustrating the operation of the identification circuit.

FIG. 5 is a conventional configuration example.

FIG. 6 is a response example of an equalized waveform.

[Explanation of symbols]

 1 Photodiode 2, 3 Amplifier 4 Branching section 5, 13 “1” peak detection circuit 6, 12 “0” peak detection circuit 7 DC converter 8 Timing extraction section 9 Discrimination circuit 10 Average value detection circuit 11, 14, 16 Adder circuit 15 Divider circuit 20 Amplification unit 30 Discrimination level control unit a Terminal for setting the discrimination level b Data output terminal Ha clock output terminal

Claims (2)

[Claims] 1. An equalization waveform output of an amplification section of an optical receiver and a timing extraction section output are inputted to a discrimination circuit, and whether the equalization waveform is 1 level or 0 level based on a given constant discrimination level. In the signal identification method for determining the above and outputting data, the average value of the equalized waveform is superimposed on the constant identification level. 2. The average value of the 1-level peak and the 0-level peak is detected by detecting the 1-level peak and the 0-level peak of the equalized waveform input to the discrimination circuit. Discrimination method characterized by superimposing a signal on a certain discrimination level