JPH01307325A - Optical transmission and reception circuit - Google Patents

Abstract

PURPOSE:To make the circuit operation stable at the time of turning on a power supply by sending a reset pulse signal to a 2-branch coupler just after application of power and utilizing the reflection of the signal at the 2-branch coupler so as to reset a reception circuit. CONSTITUTION:A pulse signal is generated from a reset signal generating circuit 1 at application of power, the pulse signal is sent from a transmission circuit 4 to a light emitting element 5, from which the resulting signal is sent to a 2-branch coupler 6 as an optical pulse signal. Part of the optical pulse signal is reflected in the 2-branch coupler 6, the result is given to a photodetector 8, and the reflected pulse light detected by the photodetector 8 is inputted to a reception circuit 7, which is reset. Thus, the operation at the time of turning on the power supply is made stable.

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to an optical transmitter/receiver circuit for bidirectional optical communication that uses a two-branch coupler to communicate over a single optical fiber. [Prior art 1] Conventionally, in order to eliminate instability in the operation of an optical transmitter/receiver circuit when the power is turned on, an identification/reproduction unit for digitizing the received signal in a receiving circuit for demodulating the optical signal is provided with a method as shown in FIG. Various reset circuits were used. That is, in the identification and reproduction section, the input signal from the light receiving element is input to the input terminal 21. A part of the 1λ signal inputted to the input terminal 21 is directly inputted to the negative input terminal of the comparison circuit 23. Also, a portion of the input signal is transmitted through the resistor 22. The signal is inputted to the positive input terminal of the comparator circuit 23 via an integrating circuit constituted by a capacitor 24. Furthermore, the comparison circuit 2
A feedback resistor 2525 is connected between the output terminal 21 of No. 3 and the capacitor 24 of the integrating circuit, and the output terminal 21 of the comparator circuit 23 is pulled up to the power supply by a resistor 26. The collector of a transistor 30 for reset operation is connected to the capacitor 24 of the integrating circuit.The emitter of the transistor 30 is grounded, and the base has a capacitor 28 connected to the power supply and a resistor connected to the ground. 29 is connected to form a differentiating circuit. In a conventional reset circuit constituted by this transistor 30, the base of the transistor 30 is at the power supply potential immediately after power is turned on, so the transistor 30 is in a conductive state. Therefore, the potential at the positive input terminal of the comparison circuit 23 becomes approximately OV, and the potential at the output terminal 27 of the comparison circuit 23 remains at a low level until a signal is input from the input terminal 21. This eliminates the instability of operation immediately after the power is turned on. [Problem M to be solved by the invention] However, with such conventional reset circuits, noise is generated in the power supply line. If the transistor 30 is turned on by the noise, the receiving circuit may be reset, resulting in a lack of reliability.Furthermore, if the reset transistor 30 is not used, the above-mentioned However, when the power is turned on, the potential state of the positive and negative re-input terminals of the comparator circuit 23 is unstable, and the operation of the comparator circuit 23 is unstable. The purpose is to provide a highly reliable optical transmitter/receiver circuit that operates stably when the power is turned on and is not reset due to power supply noise. .

[Means to solve the problem]

The optical transmitter/receiver circuit of the present invention inputs pulsed light to a two-branch coupler immediately after turning on the power, and resets the receiver circuit 1 by the pulsed light reflected by the two-branch coupler. That is, the optical transmitting/receiving circuit of the present invention includes a transmitting circuit that modulates a transmitted signal, a light emitting element that generates an optical signal according to an output signal of the transmitting circuit, and transmitting the optical signal generated by the light emitting element to an optical fiber. an optical transmitter/receiver circuit comprising: a two-branch coupler; a light-receiving element that receives an optical signal output from the two-branch coupler; and a receiving circuit that demodulates the optical signal received by the light-receiving element. The present invention is characterized in that a reset signal generating circuit is provided for inputting a pulse signal reflected by a coupler and resetting the receiving circuit to the transmitting circuit when the power is turned on. Further, the receiving circuit of the present invention includes, for example, an integrating circuit that integrates a part of the input signal from the light receiving element, and an output of the integrating circuit that is inputted to one input terminal, and a part of the input signal from the light receiving element. The identification and reproducing section includes a comparison circuit for directly inputting the signal to the other input terminal. [Operation 1] In the optical transmitter/receiver circuit of the present invention, a pulse signal is generated from the reset signal generation circuit when the power is turned on. The pulse signal is sent from the transmitting circuit to the light emitting element, and the light emitting element sends it as an optical pulse signal to the two-branch coupler. A portion of this optical pulse signal is reflected by the two-branch coupler and input to the light receiving element. The reflected pulsed light detected by the light receiving element is input to the receiving circuit to reset the receiving circuit. The receiving circuit operates as follows, for example. That is, a part of the input pulse signal from the light-receiving element is input to the integrating circuit, and is delayed by the integrating circuit for a certain period of time. This delayed input pulse signal is input to one input terminal of the comparison circuit. A part of the input pulse signal from the light receiving element is directly input to the other input terminal of the comparison circuit. Thus, when a pulse signal generated by the reflected pulsed light is incident on the comparison circuit, the pulse signal is divided into two signals having different rise times and input to the respective input terminals of the comparison circuit. Therefore, the comparison circuit is always dominated by the component that rises earlier, and the output terminal potential is reset to a constant level. [Example] Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG. 2 is a circuit diagram showing a specific example of the configuration of the reset signal generating circuit of the embodiment of FIG. 1. FIG. 3 is a circuit diagram showing a specific example of the configuration of the identification and reproducing section of the receiving circuit of the embodiment shown in FIG. 1, and FIG. 4 is a time chart showing the operation of the circuit shown in FIG. 3. In FIG. 1, l is a reset signal generation circuit that generates a reset signal, and the output signal of the reset signal generation circuit is input to one input terminal of the adder 3. The adder 3 is composed of, for example, an OR gate, and the transmitted signal is inputted from the input terminal 2 to the other input terminal. The output signal of the adder 3 is input to a transmitter circuit 4 that modulates the transmitted signal. The output signal of the transmitting circuit 4 is input to a light emitting element 5 made of a light emitting diode or the like. The signal light emitted from the light emitting element 5 is transmitted to the optical fiber via the two-branch line combiner 6. Further, the optical signal output from the two-branch line combiner 6 is input to the light receiving element 7. The output signal of the light receiving element 7 is transmitted to a receiving f which demodulates the output signal.
It is input to the engineering circuit 8. The output signal of the receiving circuit 8 is outputted from an output terminal 9. In the second section, the resistor 11 has one end connected to the power supply and the other end connected to the capacitor 12. The other end of the capacitor 12 is grounded and together with the resistor 11 forms an integrating circuit. A buffer amplifier 13 is connected to the capacitor 12, and the output signal of the buffer amplifier 13 is 1. Ridriger One Shot Multi-Vibe Break (hereinafter abbreviated as Ridriger One Shot)
14. The output signal of the redrigger one-shot 14 is outputted to the adder 3 from the output terminal 15 of the reset signal generating circuit 1. In the third factor, the input terminal 21 of the single identification reproducing circuit is connected to the negative input terminal of the comparison port n23. The comparison circuit 2
A resistor 23 is connected between the negative input terminal and the positive input terminal of No. 3. A capacitor 24 is grounded from the positive input terminal, and together with the resistor 23 forms an integrating circuit. Furthermore, a resistor 25 for determining the feedback voltage and a resistor 26 for determining the DC potential are connected to the output terminal 21 of the comparison circuit 23. Next, the operation of this embodiment will be explained with reference to FIGS. 1 to 4. First, when the 'a source is turned on, a charge is charged to the capacitor 12 via the resistor 11, and when the potential of the capacitor 12 reaches a predetermined input voltage of the buffer amplifier 13, the potential of the output terminal of the buffer amplifier 13 increases. High potential ratio changes. When the output level of the buffer amplifier 13 changes to a high potential, the Q output terminal of the ridger one-shot 14 becomes high level for a predetermined period of time, and a single pulse signal is output from the output terminal 15 to the adder 3. The pulse signal is input from the adder 3 to the transmitting circuit 4,
After being modulated by the transmitter circuit 4, it is input to the light emitting element 5. When the light emitting element 5 is turned on for a predetermined period of time by this pulse signal, this optical signal is inputted to the optical fiber via the two-branch line combiner 6. In the two-branch line combiner 6, a part of the input light fA is reflected and enters the light receiving element 7 as crosstalk. The reflected light is converted into an electrical signal by the light receiving element 7 and input to the receiving circuit 8. A portion of the reflected pulse signal input to the input terminal 21 of the receiving circuit 8 is directly input to the negative input terminal of the comparison circuit 23. Further, a part of the pulse signal is transmitted through the resistor 22. The signal is integrated by an integrating circuit consisting of a capacitor 24 and is input to the positive input terminal of the comparator circuit 23 with a time delay. Therefore, even if the potentials of the positive and negative input terminals of the comparison circuit 23 are initially unstable, immediately after the power is turned on, the comparison port i'i
The potential of the input terminal 23 is controlled by the potential of the reset pulse signal, and as shown in the first rising state of the upper graph in FIG. Since the potential is higher than that on the terminal side, the specific soft circuit 1523 is reset by the reset pulse signal. Thus, the receiving circuit 8 is reset and the signal modulated by the circuit is outputted from the output terminal 9. Note that the operation of the identification reproducing circuit is as shown in 4L84.
Utilizing the difference in the rise time of the voltage waveforms input to the positive input terminal side and the negative input terminal side of the comparator circuit 23, when the potential on the positive input terminal side becomes higher than the potential on the negative input terminal side, the As shown in the graph on the F side, the output of the comparison circuit 23 has a high potential and is converted into a digital signal. [Effects of the Invention] The optical transmitting/receiving circuit according to the present invention sends a reset pulse signal to a two-branch coupler immediately after power is turned on, and resets the receiving circuit by utilizing reflection at the two-branch coupler. Therefore, the circuit operation is stable when the power is turned on, and the reliability is high because it is not reset due to power supply noise.

[Brief explanation of the drawing]

The first Uji is a block diagram showing one embodiment of the present invention, and the second Uji is a block diagram showing an embodiment of the present invention.
1 is a circuit diagram showing a specific example of the configuration of the reset signal generation circuit of the embodiment shown in FIG. 1; FIG. FIG. 4 is a time chart showing the operating state of the circuit in FIG.
1 is a circuit diagram showing an example of a conventional reset circuit. 1... Reset signal generation circuit 3... Adder 4... Transmission circuit 5°/light emitting element 6... Two-branch coupler 7... Light receiving element 8... Receiving circuit 13... Buffer amplifier 14... Ridriger one-sit 23... Comparison circuit inventor Oka 1) Hiroshi Kaimae Ken Fuji Keiji Mikihiro patent applicant Mitsubishi Rayon Co., Ltd.

Claims (2)

[Claims] (1) a transmitting circuit that modulates a transmitted signal, a light emitting element that generates an optical signal according to the output signal of the transmitting circuit, and a two-branch coupler that transmits the optical signal generated by the light emitting element to an optical fiber; In an optical transmitter/receiver circuit comprising a light receiving element that receives an optical signal output from the two-branch coupler and a receiving circuit that demodulates the optical signal received by the light-receiver, the optical signal is reflected by the two-branch coupler and An optical transmitting/receiving circuit comprising: a reset signal generating circuit that inputs a pulse signal for resetting the receiving circuit to the transmitting circuit when power is turned on. (2) The receiving circuit includes an integrating circuit that integrates a part of the input signal from the light receiving element, the output of the integrating circuit is input to one input terminal, and a part of the input signal from the light receiving element is input to the other input terminal. 2. The optical transmitter/receiver circuit according to claim 1, further comprising a comparator circuit for direct input to the input terminal.