JPS5935226B2 - optical receiver circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention particularly relates to an optical receiving circuit that can perform information discrimination of optically transmitted optical signals with high reliability and accuracy.

Recently, optical information communication systems using optical data buses have been attracting wide attention. This type of optical communication system can be roughly divided into star networks and ring networks. The former star network in particular has a high degree of freedom when installing lines, and prevents system down of all lines due to failure of individual stations. Since it has advantages such as easy maintenance and inspection, it is thought that it will be further developed in the future. This star network is constructed by connecting N stations 1a|1b to 1n in a star shape via optical fibers 3a, 3b to 3n via a star coupler 2, as shown in FIG. N:N optical information communication is performed between each station. Further, each station 1a, 1b to 1n is configured to transmit an optical signal from its transmitting station Tx, and receive the communicated optical signal at its receiving station Rx. However, in such a system, the length of the optical transmission path consisting of the optical fibers 3a, 3b to 3n differs between stations depending on the installation location of each station 1a, 1b to 1n, and as a result, the signal Since the loss also varies, there is a problem that the reception level of the communication optical signal is not constant.

For this reason, there has been a desire for an optical receiving circuit that can always perform stable and accurate information discrimination even when the optical signal reception level changes. One method that satisfies this requirement is, for example, 1EEE
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There is a device configured as shown in FIG.

In this circuit, an optical signal received by a photodiode 4 is amplified to a required level by a preamplifier 5a and a postamplifier 5b, and then regenerated as DC by a DC regenerator 6, and then passed through a buffer amplifier T. Leads to comparator 8. The comparison reference voltage of this comparator 8 is given by dividing the peak value of the received signal detected by the peak detection circuit 9, and is given by the output of the delay detection circuit 10 to an initial value that allows the minimum light reception signal to be identified. is configured to be set. Further, the delay detection circuit 10 detects the END code inserted at the end of the data block of the received signal, and performs the above-mentioned set control. According to such a circuit configuration, the comparison reference voltage is set to follow the change in the peak level of the received signal, and therefore satisfies the above requirements well.
Since an END code generation and detection function is required in optical information communication, the circuit configuration becomes complicated and the control becomes complicated. Furthermore, it is difficult to set the circuit time constant for holding the peak detected value during the signal reception period to fully satisfy various specifications.If the time constant is made long, the reset action is delayed and the rising and falling edges are There was also concern that there might be false positives in the department. The present invention has been made in consideration of these circumstances, and its purpose is to easily and accurately transmit optical information signals communicated in various formats without requiring complicated control. It is an object of the present invention to provide a simple and highly practical optical receiving circuit that can perform discrimination detection with high reliability.

That is, in contrast to the conventional circuit configuration shown in FIG. 2, the present invention amplifies the optical signal received by the photodiode 4 through amplifiers 5a, 5b, and 7, as shown in FIG. Later, the objective is to realize an optical receiving circuit that can easily and accurately perform discrimination using the comparator 8.

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

FIG. 4 is a diagram showing the configuration of a comparator 8, which is a main part of an optical receiving circuit according to an embodiment of the present invention.

In the figure, reference numeral 11 denotes a comparison circuit that inputs the input signal In to the first terminal (4) and the comparison reference signal COMP to the second terminal (c), and compares and detects these two signals. Resistors 14 and 15 are connected in series between the first terminal of this comparison circuit 11 and the ground line. Therefore, a variable comparison voltage obtained by dividing the input signal In by a predetermined ratio (for example, 1/2) is generated at the connection point between these resistors 14 and 15. On the other hand, between the power supply line and the ground line, there is a resistor 12 that divides the power supply voltage (+) to generate a reference voltage.
13 are connected in series. These resistors 12 and 13
The connection point between the resistor 14 and the resistor 15 is
They are connected to the second terminal of the comparator circuit 11 via diodes 13 and 16 in the forward direction, respectively. Also, comparison circuit 1
A resistor 18 is connected between the second terminal of No. 1 and the ground line. Then, the resistor 18 is configured to always generate the voltage of the higher level of the reference voltage or the variable comparison voltage by the selective switching action of the two diodes 16 and 17 forming the OR circuit. It's summery. The selected larger voltage is introduced into the comparison circuit 11 as a comparison reference signal. Note that the resistor 1
The level of the reference voltage generated by dividing the power supply voltage by 2 and 13 is set to the minimum value that can reliably identify the signal input as no signal when the signal input is at the minimum level. According to the comparator 8 configured in this way, when the input signal In is at the minimum level (when no optical signal is received by the photodiode 4), it is compared to the level of the reference voltage generated by the resistors 12 and 13. Since the level of the variable comparison voltage generated by dividing the input signal Vln is low, diode 1
7 is forward biased and turns on, diode 16
is reverse biased and turns off. As a result, regardless of the level of the input signal In, only the above reference voltage is selected as a comparison reference voltage and applied to the comparison circuit 11, and the input signal In is discriminated based on this signal voltage. As explained earlier, the reference voltage is set at a level that allows accurate discrimination of the minimum signal input, so the comparator circuit 11 accurately discriminates the input signal In and outputs a 0'' level signal. On the other hand, when the input signal In includes an information signal and reaches a certain level, the level of the variable comparison lightning voltage, which is its divided voltage signal, becomes higher than the reference voltage.As a result, the diode 16 is forward biased and becomes conductive. ,
Although the diode 17 is reverse biased and becomes non-conductive, and a forward voltage drop occurs across the diode 16, the variable comparison voltage is selected as the comparison reference voltage.
will be applied to the terminal. As a result, the input signal Vin is distinguished from the variable comparison voltage set to one level as the comparison reference voltage, and information detection is performed here. According to the comparator 8 exhibiting such an effect, even if the optical reception signal level fluctuates due to station switching as shown in FIG. Since the comparison reference level is defined by the reference voltage until the level of the reference voltage changes or when there is no signal, the comparison circuit 11 always discriminates received signals at the optimum level.

As a result, information is reliably reproduced regardless of the received signal level.
It will be done accurately. Furthermore, since special control such as an END code is not required as in the past, the configuration can be greatly simplified, and the reference signal level can be quickly switched by the switching action of the diodes 16 and 17. You can expect stable operation. Therefore, the reliability is high and the operation is not influenced by the form of the optical communication signal, so it is convenient to be adopted in various optical communication systems and has high practicality. Further, by using such a comparator 8, there is an advantage that even if the preceding stage amplifiers 5a, 5b, and 7 are configured with DC-coupled amplifiers, the adverse effects caused by temperature drift can be significantly reduced. As shown in the above embodiments, according to the present invention, when there is no signal (60" signal) with respect to an optical reception signal, the signal is identified using a reference voltage that can reliably discriminate the received signal, and the signal is identified as a reference level. As for the signal, it is divided according to the input signal level and the signal is discriminated using a predetermined voltage.
Regardless of changes in the reception level of the optical signal, the signal can always be regenerated stably, reliably, and accurately.

Furthermore, since the comparison reference voltage level is optimized according to the level of the input signal, effects such as signal discrimination without causing signal pulse width fluctuations can be achieved. Therefore, even if it is incorporated into a system such as an optical communication system where the transmission path length or loss constantly changes, it has the tremendous effect of always being able to perform stable information reproduction. Moreover, according to the present invention, since the output voltage of the circuit that divides the optical signal is determined only by the constants of the elements constituting the circuit, it is easy to determine the constants of the elements. . Note that the present invention is not limited to the above embodiments. For example, by providing a delay circuit on one input terminal side of the comparator circuit 11 and slightly delaying the input of the input signal In or the setting of the comparison reference level, it is possible to prevent malfunctions due to jitter components at the rising and falling edges of the input signal. It may be configured to prevent this. Further, the voltage division conditions of the power supply voltage +V, etc. may be determined depending on the polarity of the input signal. Furthermore, it goes without saying that it can be widely adopted in various optical communication systems, such as not only star-shaped networks but also ring-shaped networks. In short, the present invention can be implemented with various modifications without departing from the gist thereof.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a star network showing an example of an optical communication system, FIG. 2 is a configuration diagram of an example of a conventional optical receiving circuit, and FIG. 3 is a basic configuration diagram of an optical receiving circuit according to the present invention. , FIG. 4 is a configuration diagram of a comparator showing one embodiment of the present invention, and FIG. 5 is a waveform diagram showing the signal discrimination action of the comparator shown in FIG. 4. 4...Photodiode, 8...Comparator, 11...Comparison circuit, 12, 13...
・Resistance (reference voltage), 14, 15... Resistor (auxiliary voltage), 16, 17... Diode, 18.
...Resistor, 25...Capacitor.

Claims (1)

[Claims] 1. In an optical receiving circuit that discriminately detects an optical signal that has reached a light receiver, a circuit that generates a reference voltage that defines a signal discrimination level at the time of minimum optical input, a circuit that divides the reception level of the optical signal, and the reference voltage An OR circuit in which the output of a circuit that generates a voltage and the output of a circuit that divides an optical signal are connected through diodes in a predetermined direction, and the diodes are caused to mutually switch, and this OR circuit selectively An optical receiving circuit comprising: a comparator that discriminates the optical signal using the extracted high-level voltage as a comparison reference voltage.