JPS63250229A - Light receiving circuit - Google Patents

Abstract

PURPOSE:To prevent a malfunction by deciding a signal as an error with an level deciding circuit and preventing the signal from being sent to the circuit of rear steps when the output of a first voltage comparator is '1' and the output of a second voltage comparator is '0'. CONSTITUTION:A received light signal (a) is, after converted into an electric signal (b) with a photodetector 1, amplified with an amplifying circuit 2 and goes to a voltage signal (c) and this signal (c) is inputted into the voltage comparator 3 and a voltage comparator 4 for peak detection. When the received light signal (c) is at an insufficient level and at the boundary of the detecting level of the voltage comparator 3, since the detecting level of the voltage comparator 4 for peak detection is not satisfied, a peak detecting signal (e) always goes to '0'. In this case, a level deciding circuit 5, since an output signal (d) is in a '1' condition and the peak detecting signal (e) goes to '0', decides it as an error, outputs an error detecting signal (f), activates an error detecting signal generating circuit 6 and blocks a signal at an insufficient light level. Thus, the malfunction of the circuit of rear steps can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention (Industrial Application Field) The present invention relates to an optical receiving circuit used for optical fiber communication.

(Prior Art) Generally, in optical fiber communication, particularly when transmitting digital binary signals, an optical receiving circuit as shown in FIG. 3 is used for receiving optical signals.

In this circuit, a received optical signal a is converted into an electrical signal by a light receiving element 1, amplified by an amplifier circuit 2 to produce a voltage signal C with sufficient amplitude, and then converted to the original binary signal by a voltage comparator 3. The configuration is such that the signal d is restored.

In such optical receiving circuits, there is a permissible range of optical signal levels that can be operated depending on the circuit configuration of each element used.
The optical fiber transmission line, optical transmitter output, etc. are designed so that the received optical signal falls within this permissible range.

(Problem to be solved by the invention) However, if a situation such as deterioration or failure of the transmission line or optical transmitter occurs, the received optical signal level may fall outside the above-mentioned allowable range, and even if operation is not possible. If it is just at the limit, the level of LLOJT"1"' cannot be detected correctly, and an abnormal signal will be output as the output signal d. That is, when a packet consisting of a series of bit strings is received (B), if the same I
Even though I 1 gg, LL
Identified as OII.

The packet will be identified as u I 11, and a bit string different from the original packet will be output.

If the received signal is sufficiently lower than the operational limit over the entire packet, nothing will appear as the output signal d, so there is actually less of a problem, but an abnormal signal in the case of such an operation limit.

There is a problem in that this causes malfunction of the transmission circuit connected after the optical receiving circuit, resulting in serious abnormal phenomena. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an optical receiving circuit in which subsequent circuits do not malfunction even when receiving light at a level outside the permissible range.

[Structure of the Invention] (Means for Solving the Problems) For this reason, the present invention provides a second signal comparator whose setting level is higher than that of the first signal comparator that shapes the waveform of an electrical signal converted from an optical signal. and the output of the first signal comparator is '1''
Check whether the output of the second signal comparator is 111'g when It consists of a determination circuit and a circuit that blocks signals with insufficient light levels when the level determination circuit determines that there is an error.

(Function) With the above configuration, when light of a level outside the permissible range is received, that is, the output of the first voltage comparator is
When the output of the voltage comparator is 0'', the level determination circuit determines that there is an error and prevents the signal from being sent to the subsequent circuit, thereby making it possible to prevent malfunctions.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a block configuration diagram of an optical receiving circuit according to an embodiment of the present invention.The optical receiving circuit includes a light receiving element 1 that converts an optical signal a into an electrical signal, Amplifying circuit 2) Amplifying the voltage signal C to a sufficient amplitude and outputting the voltage signal C 2) A voltage comparator 3 which restores the voltage signal C to a binary signal and outputs an output signal d; A peak detection voltage comparator 4 whose detection level is set higher than that of the detector 3 and outputs a peak detection signal e, determines the level of the received signal from the output signal d and the peak detection signal e, and outputs an error detection signal f and a switching signal. A level determination circuit 5 which outputs the signal a, an error signal generation circuit 6 which is activated by the error detection signal f and generates a pseudo reception signal that is determined to be an error in the subsequent circuit.It is controlled by the switching signal %g and outputs the output signal d and the pseudo and a selector 7° which switches the received signal and outputs the receiving circuit output signal i.

With the above configuration, the received optical signal a is converted into an electrical signal by the light receiving element 1, and then amplified by the amplifier circuit 2 to become a voltage signal C. This signal C is passed through two voltage comparators,
That is, they are input to the voltage comparator 3 and the peak detection voltage comparator 4, but when the received optical signal level is within the operable range, the output signal d is rr 1 u and the peak detection signal e is 1'''. This situation is shown in Figure 2 (a).
Shown below. In Figure 1, ■ is the detection level of voltage comparator 3,
(2) is the detection level of the voltage comparator 4 for peak detection. Voltage comparators f13 and f4 both output '1' when there is an input of this level or higher.

In this state, the level determination circuit 5 determines that it is normal, turns off the error detection signal f, and sets the switching signal g so that the selector 7 selects the output signal d as the receiving circuit output signal i. That is, when the received optical signal level is within the operable range, the output of the W1 pressure comparator 3 directly becomes the optical receiving circuit output i, similar to a general optical receiving circuit.

On the other hand, if the received optical signal is at an insufficient level and is just below the detection level of the voltage comparator 3, then
), the peak detection signal e is always 1701 because it no longer satisfies the detection level of the peak detection voltage comparator 4.
It becomes 1. In this case, the level determination circuit 5 determines that there is an error since the peak detection signal e becomes 't On while the output signal d is 111 B, outputs the error detection signal f, and activates the error signal generation circuit 6.

The received signal after m' outputted by the error signal generation circuit 6 is a signal that is definitely determined as an error by the subsequent circuit, and is 1.
For example, it is assumed that the signal simulates a packet reception signal with an abnormal CRC code. The switching signal g is switched so that the selector 7 selects this pseudo reception signal as the receiving circuit output signal i as the error is detected, so that the subsequent circuit receives the pseudo reception signal as the optical receiving circuit output i, This means that it can be detected and processed as an error.

If the received optical signal is below the detection level of the voltage comparator 3, as shown in FIG. 2(c), both voltage comparators do not operate and no reception is performed.

In this case, the setting of the detection level ■ of the voltage comparator 4 for peak detection is to maximize the sensitivity by setting it close to the detection level ■ so that peak detection can be performed at the minimum signal level at which the voltage comparator 3 can operate normally. It is possible to raise it.

As described above, the optical receiving circuit of this embodiment operates in the same way as a general optical receiving circuit when the received optical signal level is within the operable range, but when the received optical signal level is insufficient, There is no possibility of outputting abnormal signals that may cause malfunction of subsequent circuits. Therefore, no matter what level of optical signal is received, the stability of operation will be compromised.

Note that in the above embodiment, an error signal generation circuit is provided,
Although an example has been shown in which a pseudo signal is output to make the subsequent circuit recognize an error, a configuration in which no error signal generation circuit is provided is also possible. In this case, in the error state, the receiving circuit output signal 1 is 110! 6 [Effects of the Invention] As described above, according to the present invention, optical transmission is stolen.

Even if performance deterioration, failure, etc. occur in the optical transmitter system, it is possible to prevent an abnormal signal from being output from the optical receiver circuit. Therefore, abnormal operation of the subsequent transmission circuit can be reliably avoided, which greatly contributes to improving the reliability of the optical fiber communication system. Furthermore, by using the optical receiving circuit of the present invention, there is no need to take abnormal signal output from the optical transmission circuit into consideration when designing the subsequent transmission circuit itself, which greatly contributes to simplification and efficiency of design. be.

[Brief explanation of the drawing]

FIG. 1 is a block configuration diagram of an optical receiving circuit according to an embodiment of the present invention, and FIGS. 2(a) to 2(e) are explanatory diagrams of the operation of the voltage comparator in FIG. 1 according to the level of a received optical signal. FIG. 3 is a block diagram of a conventional optical receiving circuit. 4... Voltage comparator for peak detection, 5... Level judgment circuit, 6... Error signal generation circuit, 7... Select. Bow figure 2

Claims (2)

[Claims] (1) After amplifying the electrical signal converted from the optical signal via the light receiving element through the amplifier, it is input to the first signal comparator and compared with a preset detection level, and a binary value is generated depending on the magnitude. An optical receiver circuit that extracts a digital signal and outputs it to a subsequent circuit has a detection level set higher than that of the first signal comparator, and has a detection level set higher than the first signal comparator,
a second signal comparator that converts the signal into a value; a level judgment circuit that inputs the outputs of these two signal comparators and judges whether the signal levels match or do not match; An optical receiving circuit characterized in that a blocking circuit is provided for blocking output from the first signal comparator to a subsequent circuit when the signals do not match. (2) In claim 1, the blocking circuit includes an error signal generating circuit that generates an error signal that causes a subsequent circuit to detect an error when the signal levels do not match, and the first signal comparison circuit. An optical receiving circuit comprising a selector that switches the output of the device to this error signal and outputs it to a subsequent circuit.