JP2860715B2 - AGC circuit in optical bidirectional communication - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting diode (LE).
A) AGC in a time-division directional control system for performing bidirectional communication using a single optical element such as D) or a semiconductor laser (LD)
(Automatic gain control) circuit.

[0002]

2. Description of the Related Art In a time-division directional control system (a so-called ping-pong transmission system) in which a light-emitting diode (LED) or a semiconductor laser (LD) is used as a light-emitting element and a light-receiving element, a high-level signal when an LED or LD emits light is received. It may affect the circuit and degrade the reception characteristics in the light receiving mode. For this reason, techniques as shown in FIGS. 4, 5, and 6 have been conventionally proposed.

In the first conventional example shown in FIG. 4, 7 is a transistor, 8 is a preamplifier, 9 is an AGC amplifier, 19
Is a level detection circuit for detecting the level of the reception output obtained from the output of the AGC amplifier 9;
AGC feedback circuit for controlling the degree of amplification of GC amplifier 9, 21
Is an LED used as a light emitting element, 22 is a buffer circuit for applying transmission data to the base of the transistor 7, 23 is a transmission mode detection circuit, and 24 is a switch. In the transmission mode, the transmission light that is on / off controlled according to the transmission data is emitted from the LED 21. In the reception mode, a reception signal corresponding to the reception light is obtained from the LED 21 and is taken out as a reception output via the amplifiers 8 and 9. In the first conventional example, the transmission mode is detected by the transmission mode detection circuit 23, and in the detected transmission mode, the switch 24 is turned off (open) to prevent the transmission signal from being applied to the AGC amplifier 9 so that the AGC amplifier 9 is stabilized. It operates so as to secure a proper AGC operation.

In the second conventional example shown in FIG. 5, a signal obtained by extracting the output signal of the LED 21 in the transmission mode by the preamplifier 8 and a waveform to be transmitted are generated by the suppression signal generation circuit 25. The signal and the signal are added using an addition circuit 26,
By canceling each other, the input to the AGC amplifier 9 in the transmission mode is cut off.

Further, in a third conventional example shown in FIG. 6, a mode control device 29 controls a switch (SW ₁ ) 27 and a switch (SW ₂ ) 28. When transmitting, switch 2
7 and 28 are both OFF (open), and both are ON when receiving
(Closed). Thereby, at the time of reception, the semiconductor laser 6
Is not input to the receiving circuit.

[0006]

These conventional circuits are:
Since the received signal itself is turned on / off by the switch, there is a drawback that the electrical characteristics of the SW, that is, a voltage spike at the time of transition at the time of ON or OFF, an offset variation at the time of transition, and the like are affected. In the case of FIG. 5, A
In order to cut off the input to GC in a timely manner,
It is necessary that the output of the preamplifier and the suppression signal exactly coincide not only with the voltage level (the opposite sign) but also with time.
When a time shift occurs, a time portion that is shifted is output from the adder circuit 26, a voltage spike is input to the AGC amplifier 9, and the cutoff effect is lost. Therefore, this circuit requires precise adjustment and is not economical.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an AGC in bidirectional communication capable of economically achieving stable reception in a time division control system in which bidirectional communication is performed using a single optical element.
It is to provide a circuit.

[0008]

In order to achieve this object, an AGC circuit in bidirectional communication according to the present invention comprises a transmission mode in which a single optical element emits light and a reception mode in which the single optical element receives light. In the AGC circuit arranged on the receiving side of the system that performs time-division direction control and performs optical bidirectional communication, a gain variable element arranged on the output side of the single optical element; A level detection circuit for detecting the level of the reception output obtained on the output side, a capacitor for storing and holding a voltage corresponding to the level of the reception output detected by the level detection circuit, and a means for setting a constant DC voltage value Controlling the variable gain of the variable gain element by the voltage stored and held in the capacitor during the reception mode, and setting the constant DC voltage of the DC power supply during the transmission mode. The variable gain element has a structure which is characterized in that a switching control circuit for switching said DC power supply and the capacitor to have a low gain Ri.

Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a principle diagram of the present invention. 1 is an optical element, L
D, LED and the like. 2 is a drive circuit for driving the optical element 1, 3 is a variable gain element, and 4 is a memory for generating a burst signal. Reference numeral 5 denotes a control circuit for outputting a control signal for controlling the switching between the transmission mode and the reception mode. The control signal controls the memory 4 to control the optical element 1 in a burst.
To emit light. Reference numeral 10 denotes a level detection circuit for extracting an output corresponding to the level of the reception output obtained from the output of the variable gain element 3, reference numeral 11 denotes a switch (SW), and reference numeral 12 denotes a capacitor (C). From the connection of FIG., The variable gain element 3 is the gain is changed by voltage V _c or the battery voltage V _b of the capacitor 12. The capacitor 12 is charged at the signal level detected by the level detection circuit 10. The switch 11 operates according to a control signal from the control circuit 5, and is set to the B side during transmission and to the A side during reception. The voltage _Vb is a constant DC voltage generated by a DC power supply such as a battery, and is a value that sufficiently lowers the gain of the variable gain element 3. At the time of receiving an optical input, a control voltage corresponding to the detection level is accumulated in the capacitor 12, and is held during the transmission section. Further, at the time of transmission, the voltage _Vb is forcibly set by the switch 11, and the transmission signal is output from the gain variable element 3 which performs AGC operation at a very low value. On the other hand, the received signal has a substantially constant value due to the AGC operation. If the received signal is larger than the transmitted signal to some extent, the output of the AGC circuit is input to the comparator (comparator) circuit,
It is possible to extract only the received signal. As a result, since the received signal itself is not turned ON / OFF by the switch, there are advantages that the influence of the electrical characteristics of the SW is small and that no adjustment is required.

[0010]

FIG. 2 shows an example of a circuit configuration as a realizing means. The output from the preamplifier 8 is A as a variable gain element.
Enter the GC amplifier 9. In this example, the gain adjustment terminal g of the AGC amplifier 9 is set to a low gain at V _b = 0. For example, in the case of a commercially available AGC amplifier (Comlinear Corporation), if the terminal voltage of the terminal g is 0.4 volt or less, the output will be 20 mV or less even if the input is 500 mV. When the terminal voltage of the terminal g is 1.5 volts, the input is 10 mV and the output is 200 mV.

FIG. 3 shows another example of the circuit configuration as the realizing means. In this example, the slice amplifier 18 is provided before the AGC amplifier 9 so that an input of a certain level or higher (or lower) is not applied to the AGC. Other actions are the first
This is the same as the embodiment.

[0012]

According to the present invention, it is possible to realize a stable AGC circuit operation in which a high-level transmission signal does not affect a receiving circuit in a time-division directional control bidirectional communication system using a single optical element. It is possible. Further, the present invention can be realized economically because it can be realized by simple circuit elements as shown in the embodiments.

[Brief description of the drawings]

FIG. 1 is a block diagram for explaining the principle of the present invention.

FIG. 2

FIG. 3 is a block diagram showing an embodiment of the present invention.

FIG. 4

FIG. 5

FIG. 6 is a block diagram illustrating an example of a conventional AGC circuit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Optical element 2 Drive circuit 3 Variable gain element 4 Memory 5 Transmission / reception control circuit 6 Semiconductor laser (LD) 7 Transistor 8 Preamplifier 9 AGC amplifier 10 Level detection circuit 11 Switch 12 Capacitor 13 Buffer circuit 18 Slice amplifier 19 Level detection Circuit 20 AGC feedback circuit 21 Light-emitting diode (LED) 22 Buffer circuit 23 Transmission mode detection circuit 24 Switch 25 Suppression signal generation circuit 26 Addition circuit 27 Switch (SW ₁ ) 28 Switch (SW ₂ ) 29 Mode control device 30 Receiving amplifier

Continued on the front page (51) Int.Cl. ⁶ Identification code FI H04L 5/14

Claims (1)

(57) [Claims] 1. A receiving side of a system that performs time-division directional control between a transmission mode in which a single optical element emits light and a reception mode in which light is received by the single optical element to perform optical bidirectional communication. A
In the GC circuit, a gain variable element disposed on the output side of the single optical element, a level detection circuit for detecting a level of a reception output obtained on the output side of the gain variable element, and a level detection circuit A capacitor for storing and holding a voltage corresponding to the level of the received output, and a means for setting a constant DC voltage value; and a gain of the variable gain element according to the voltage stored and held in the capacitor in the reception mode. A switching control circuit that performs variable control and switches between the capacitor and the DC power supply so that the gain variable element has a low gain by a constant DC voltage of the DC power supply in the transmission mode. AGC circuit in optical two-way communication.