JPH04252529A - Agc circuit in optical duplex communication - Google Patents

Abstract

PURPOSE:To realize the stable AGC circuit operation by selecting a capacitor or a DC power supply. CONSTITUTION:A gain of a gain variable element 3 is changed by a voltage Vc of a capacitor 12 or a battery voltage Vb. The capacitor 12 is charged by a signal level detected by a level detection circuit 10. A switch 11 is operated by a control signal from a control circuit 5 and thrown to the position B at transmission and thrown A at reception. The voltage Vb is a constant DC voltage generated by a DC power supply such as a battery and reduces the gain of the gain variable element 3 sufficiently. At the reception of an optical input, a control voltage in response to the detection level is stored in the capacitor 12 and held even for a transmission period. Furthermore, the voltage Vb is selected by the switch 11 at the transmission and the transmission signal is outputted from the gain variable element 3 subject to AGC with a low gain. On the other hand, the reception signal is made constant by the AGC.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to light emitting diodes (LEDs).
AGC (
(automatic gain control) circuit.

0002

[Prior Art] In a time-division direction control method (so-called ping-pong transmission method) in which a light-emitting diode (LED) or a semiconductor laser (LD) is used as both a light-emitting element and a light-receiving element, a high-level signal when the LED or LD emits light is received. This may affect the circuit and deteriorate reception characteristics in light reception 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, and 19
20 is a level detection circuit that detects the level of the received output obtained at the output of the AGC amplifier 9;
AGC feedback circuit for controlling the amplification degree of the GC amplifier 9, 21
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 LED 21 emits transmission light that is controlled on and off in accordance with the transmission data. In the reception mode, a reception signal corresponding to the reception light is obtained from the LED 21 and taken out as a reception output via the amplifiers 8 and 9. In this first conventional example, the transmission mode is detected by the transmission mode detection circuit 23, and when the transmission mode is detected, the switch 24 is turned OFF (open) to prevent the transmission signal from being applied to the AGC amplifier 9 and stabilize the transmission mode. Na A
Operates to ensure GC operation.

Furthermore, in a second conventional example shown in FIG. 5, a preamplifier 8 extracts the output signal of the LED 21 in the transmission mode, and a suppression signal generating circuit 25 generates a waveform that should have been transmitted. and the signal using an adder circuit 26,
By canceling, the input to the AGC amplifier 9 is cut off during the transmission mode.

Furthermore, in the third conventional example shown in FIG. 6, a mode control device 29 controls a switch (SW1) 27 and a switch (SW2) 28. When transmitting, both switches 27 and 28 are turned OFF (open), and when receiving, they are both turned ON (closed). This results in a circuit in which the signal from the semiconductor laser 6 is not input to the receiving circuit during reception.

[0006]

[Problem to be solved by the invention] These conventional circuits have the following problems:
Since the received signal itself is turned on and off by a switch, there is a drawback that it is affected by the electrical characteristics of the SW, ie, voltage spikes during transitions when ON and OFF, offset fluctuations during transitions, etc. In addition, in the case of Fig. 5, A
In order to timely block the input to the GC,
The preamplifier output and the suppression signal must match not only in voltage level (opposite signs) but also in time. When a time lag occurs, the deviated time portion is output from the adder circuit 26, a voltage spike is input to the AGC amplifier 9, and the blocking effect is lost. Therefore, this circuit requires precise adjustment and is not economical.

An object of the present invention is to provide an AGC in two-way communication that can economically achieve stable reception in a time-division control system that performs two-way communication using a single optical element.
The purpose is to provide circuits.

[0008]

[Means for Solving the Problem] In order to achieve this object, the AGC circuit in bidirectional communication according to the present invention has two modes: 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. In an AGC circuit disposed on the receiving side of a system that performs two-way optical communication by time-division direction control, a variable gain element disposed on the output side of the single optical element, and a variable gain element disposed on the output side of the single optical element; A level detection circuit that detects the level of the received output obtained on the output side, a capacitor that accumulates and holds a voltage corresponding to the level of the received output detected by the level detection circuit, and means for setting a constant DC voltage value. In the receiving mode, the gain of the variable gain element is controlled by the voltage accumulated and held in the capacitor, and in the transmitting mode, the variable gain element is controlled to have a low gain by the constant DC voltage of the DC power supply. The present invention has a configuration characterized in that it includes a switching control circuit that switches between the capacitor and the DC power source so that the following is true.

The present invention will be explained in detail below with reference to the drawings. FIG. 1 shows a diagram of the principle of the present invention. 1 is an optical element, LD
, LED, etc. 2 is a drive circuit for driving the optical element 1, 3 is a variable gain element, and 4 is a memory that generates a burst signal. Reference numeral 5 denotes a control circuit that outputs a control signal for switching between the transmission mode and the reception mode, and this control signal controls the memory 4 to cause the optical element 1 to emit light in a burst pattern. 10 is a level detection circuit for extracting an output corresponding to the level of the received output obtained from the output of the variable gain element 3; 11 is a switch (SW); and 12 is a capacitor (C). From the connections in the figure, the gain of the variable gain element 3 changes depending on the voltage Vc of the capacitor 12 or the battery voltage Vb. A capacitor 12 is charged with the signal level detected by a level detection circuit 10. The switch 11 is operated by a control signal from the control circuit 5, and is set to the B side when transmitting and to the A side when receiving. The voltage Vb is a constant DC voltage created by a DC power source such as a battery, and is a constant DC voltage generated by a DC power source such as a battery.
This is a value that makes the gain sufficiently low. When receiving optical input, a control voltage corresponding to the detection level is stored in the capacitor 12 and is maintained during the transmission period. Further, during transmission, the voltage is forcibly set to Vb by the switch 11, and the transmission signal is outputted from the variable gain element 3 which performs AGC operation at a very low value. On the other hand, the received signal becomes a substantially constant value due to the AGC operation. If the received signal is larger than the transmitted signal to some extent, the AG
By inputting the output of the C circuit to a comparator circuit, it is possible to extract only the received signal. This allows the received signal itself to be turned ON/OFF with a switch.
Since no F is applied, there is little influence from the electrical characteristics of the SW.
This has the advantage that no adjustment is required.

0010

Embodiment FIG. 2 shows an example of a circuit configuration as an implementation means. The output from the preamplifier 8 is A as a variable gain element.
Enters GC amplifier 9. In this example, the gain adjustment terminal g of the AGC amplifier 9 is set to a low gain with Vb=0. For example, in the case of a commercially available AGC amplifier (Com Linear), if the terminal voltage of terminal g is 0.4 volts or less, the input voltage is 500 mV.
However, the output will be less than 20mV. The terminal voltage of terminal g is 1
．． At 5 volts, the input is 10 mV and the output is 200 mV.

FIG. 3 shows another example of a circuit configuration as an implementation means. In this example, the slice amplifier 18 is installed in front of the AGC amplifier 9, and is configured to prevent inputs above (below) a certain level from being applied to the AGC. The other operations are the first
This is similar to the embodiment.

0012

[Effects of the Invention] According to the present invention, stable AGC circuit operation can be realized in which a high level transmission signal does not affect the receiving circuit in a time-division direction control bidirectional communication system using a single optical element. It is possible. Furthermore, the present invention can be realized with simple circuit elements as shown in the embodiments, and therefore can be constructed economically.

[Brief explanation of the drawing]

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

[Figure 2]

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

[Figure 4]

[Figure 5]

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

[Explanation 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 Adder circuit 27 Switch (SW1) 28 Switch (SW2) 29 Mode control device 30 Receiving amplifier

Claims (1)

[Claims] [Claim 1] A transmitting mode in which a single optical element emits light and a receiving mode in which the single optical element receives light are time-divisionally controlled and arranged on the receiving side of a system that performs optical bidirectional communication. In the AGC circuit, a variable gain element disposed on the output side of the single optical element, a level detection circuit that detects the level of the received output obtained on the output side of the variable gain element, and detection by the level detection circuit. a capacitor for storing and holding a voltage corresponding to the level of the received output, a means for setting a constant DC voltage value, and a gain of the variable gain element using the voltage stored and held in the capacitor during the reception mode. A switching control circuit that performs variable control and switches between the capacitor and the DC power source so that the variable gain element has a low gain due to a constant DC voltage of the DC power source when in the transmission mode. AGC circuit for optical two-way communication.