JPH0832517A - Optical transmission and reception circuit - Google Patents

Abstract

PURPOSE:To improve the transmission efficiency by separating a semiconductor laser and an amplifier circuit at transmission so as to eliminate the need for a switch connected at reception thereby eliminating deterioration in a minimum light reception level caused by switch noise and parasitic capacitance. CONSTITUTION:A switch 11 is closed and a switch 26 is open when a transmission signal is at a high level in the case of transmission. In this case, a semiconductor laser 12 is driven by a drive circuit 13 and stimulated to charge a parasitic capacitance C1 being a low frequency term. When the level of the transmission signal is low, the switch 11 is open and the switch 26 is closed, In this case, the semiconductor laser 12 is reversely biased by a reference voltage Vref applied via the switch 26 and the charge stored in a parasitic capacitance C1 is discharged. The resistance of a feedback resistor of a preamplifier 22 is several tens of kohms and the parasitic resistance of the semiconductor laser 12 is several Mohms, then the feedback resistor of the preamplifier 22 does not give effect on a time constant. Thus, the deterioration in the minimum light receiving level is eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transceiver circuit for transmitting and receiving an optical signal in a terminal of an optical communication system. In particular, the present invention relates to an optical transmitter / receiver circuit that uses a semiconductor laser as a light emitting element and a light receiving element to transmit and receive an optical signal with one element.

[0002]

2. Description of the Related Art Conventionally, an optical transmission circuit and an optical reception circuit were separately configured, but an optical transmission / reception circuit in which one element is switched between transmission and reception for cost reduction has been proposed. Such an optical transmission / reception circuit can be easily configured by using a semiconductor laser that functions as a light emitting element and a light receiving element.

FIG. 5 shows the configuration of a conventional optical transmitter / receiver circuit using a semiconductor laser. In the figure, a power source (V _DD ) terminal 10 is connected to a switch 11, a semiconductor laser 12, and a drive circuit 1.
An optical transmission circuit unit is configured by connecting 3 in series. Also,
A switch 21, a preamplifier 22, a gain control amplifier (GCA) 23, an anode of the semiconductor laser 12,
The comparison circuit 24 and the level conversion circuit 25 are connected to each other, and the cathode of the semiconductor laser 12 is connected to the reference voltage (Vref) terminal 27 via the switch 26 to form a light receiving circuit section. The switching control circuit 31a outputs to the switch 11 a transmission / reception switching signal (hereinafter referred to as “S / R signal”) which becomes high level at the time of transmission (S) and becomes low level at the time of reception (R), and causes the inverting circuit 32 to operate. The inverted S / R signal generated via the output is output to the switches 21 and 26.

At the time of transmission (S), the switch 11 is turned on and the switches 21 and 26 are turned off. Drive circuit 13
Drives the semiconductor laser 12 according to the transmission signal, and the semiconductor laser 12 outputs an optical signal according to the transmission signal.

At reception (R), the switch 11 is turned off and the switches 21 and 26 are turned on. The semiconductor laser 12 receives the reference voltage Vref via the switch 26 and functions as a light receiving element. The detection current corresponding to the optical signal is current-voltage linearly amplified by the preamplifier 22 via the switch 21. Furthermore, gain control amplifier 2
At 3, the signal becomes a signal of a constant voltage that does not depend on the input optical signal level, the comparison circuit 24 performs duty adjustment and voltage amplification, and the level conversion circuit 25 converts it to a predetermined level and outputs it.

With such a configuration, the semiconductor laser 12 can be made to function as a light emitting element or a light receiving element by switching between the transmission mode and the reception mode by the S / R signal.

[0007]

By the way, the equivalent circuit of the semiconductor laser 12 has a low frequency term consisting of a series circuit of a parasitic resistance R ₁ and a parasitic capacitance C ₁ as shown in FIG. 6, a parasitic resistance R ₂ and a parasitic resistance R _2. It has a high frequency term consisting of a parallel circuit of a capacitance C ₂ . Among them, the parasitic resistance R ₁ and the parasitic capacitance C of the low frequency term
_The time constant due to ₁ is as large as tens of microseconds to hundreds of microseconds. Therefore, when the parasitic capacitance C ₁ is sufficiently charged during transmission,
When switching from the transmission mode to the reception mode, the discharge time of the unnecessary charges becomes long. The discharge is performed via the feedback resistor Rf of the preamplifier 22. FIG. 7 shows S /
The output waveform of the preamplifier 22 when the transmission mode is switched to the reception mode according to the R signal is shown, but it can be seen that it takes time for the reception characteristics to stabilize depending on the time constant. Therefore, it is necessary to take a long protection time when switching between transmission and reception.

Further, the conventional optical transmission / reception circuit has a problem that the minimum light receiving level is deteriorated due to noise of the switch 21 inserted in the preceding stage of the preamplifier 22 and the characteristic is deteriorated due to switch parasitic capacitance.

According to the present invention, in a structure in which one semiconductor laser functions as a light emitting element and a light receiving element, deterioration of the minimum light receiving level caused by noise and parasitic capacitance of a switch for switching between transmission and reception is eliminated, and when switching between transmission and reception. It is an object of the present invention to provide an optical transmitter / receiver circuit capable of improving the transmission efficiency by reducing the protection time.

[0010]

The optical transmitter / receiver circuit of the present invention comprises a first switch connected between a first terminal of a semiconductor laser and a power supply terminal, a second terminal of the semiconductor laser, and a reference voltage. A second switch connected to the terminal, a gate circuit connected to the output stage of the amplifier circuit, the gate circuit is closed at the time of transmission, and the first switch is turned on at the high level of the transmission signal to turn on the second switch. A switching signal that turns off the switch, turns off the first switch and turns on the second switch at a low level of the transmission signal, turns off the first switch when receiving, turns on the second switch, and opens the gate circuit. And a switching control circuit for sending out.

Further, in a structure in which a voltage follower circuit for making the potential difference therebetween is zero is connected between the first terminal and the second terminal of the semiconductor laser, the first terminal and the power supply terminal of the semiconductor laser are connected. A second switch connected between the second terminal of the semiconductor laser and the reference voltage terminal, a third switch connected in series with the voltage follower circuit, and an amplifier The gate circuit connected to the output stage of the circuit and the gate circuit are closed at the time of transmission, the third switch is turned off, the first switch is turned on and the second switch is turned off at the high level of the transmission signal, and the transmission signal is transmitted. At a low level, the first switch is turned off and the second switch is turned on. At reception, the first switch and the second switch are turned off, the third switch is turned on, and the gate circuit is opened. Delivering and a switching control circuit.

[0012]

In the optical transmitter / receiver circuit of the present invention, the semiconductor laser and the amplifier circuit are directly connected, and the output thereof is taken out through the gate circuit. The gate circuit cuts off the output of the amplifier circuit at the time of transmission, and validates the output of the amplifier circuit at the time of reception. As a result, the semiconductor laser and the amplifier circuit are separated at the time of transmission, and the switch connected at the time of reception becomes unnecessary, and the deterioration of the minimum light receiving level due to noise and parasitic capacitance of this switch can be eliminated.

Further, by alternately applying the power source and the reference voltage to the semiconductor laser in accordance with the high level and the low level of the transmission signal at the time of transmission, the electric charge charged in the parasitic capacitance of the semiconductor laser is transmitted for each bit of the transmission signal. Can be discharged to. Therefore, the accumulated charge when switching from the transmission mode to the reception mode is small, and the protection time when switching between transmission and reception can be greatly shortened.

Further, at the time of reception, by connecting a voltage follower circuit that makes the potential difference between both terminals of the semiconductor laser to be zero, the semiconductor laser can be made non-biased and the influence of dark current can be suppressed.

[0015]

FIG. 1 shows the configuration of a first embodiment of the present invention.
In the figure, a power supply (V _DD ) terminal 10 is connected to a switch 11,
The semiconductor laser 12 and the drive circuit 13 are connected in series to form an optical transmission circuit section. In addition, the preamplifier 22, the gain control amplifier (GCA) 23, the comparison circuit 24, the gate circuit 41, and the level conversion circuit 25 are connected to the anode of the semiconductor laser 12, and the reference voltage ( Vref) terminal 27 is connected to form a light receiving circuit section.

The switching control circuit 31b includes an inverting circuit 32 which inverts the S / R signal and gives it to the gate circuit 41, an AND circuit 33 which inputs the S / R signal and the transmission signal, and an S / R signal and the transmission signal. And a delay circuit 35a, 35b for applying a predetermined delay τ to the outputs of the AND circuit 33 and the NAND circuit 34. The output of the delay circuit 35a is given to the switch 11, and the output of the delay circuit 35b is given to the switch 26. The delay circuits 35 a and 35 b are provided with the drive timing of the semiconductor laser 12 due to the propagation delay in the drive circuit 13 and the switch 1.
It is provided to adjust the switching timing of 1 and 26.

The first feature of this embodiment is that the semiconductor laser 1
The preamplifier 22 is directly connected to the anode of 2 and the comparison circuit 24
Between the level conversion circuit 25 and the level conversion circuit 25 is provided with a gate circuit 41 that performs a gate operation according to the inverted S / R signal.
The gate circuit 41 cuts off the output of the comparison circuit 24 at the time of transmission, and transfers the output of the comparison circuit 24 to the level conversion circuit 25 at the time of reception.

The second characteristic of this embodiment is that the AND circuit 33 is provided.
AND the NAND circuit 34 is used to obtain the logical product of the S / R signal and the transmission signal, and at the time of transmission (S / R signal is at a high level), the switch 11 is turned on / off according to the transmission signal, and the inverted transmission signal is obtained. Accordingly, the switch 26 is turned on / off.

The transmission / reception operation will be described below with reference to the timing chart shown in FIG. At the time of transmission, the switch 11 is turned on when the transmission signal is at the high level,
The switch 26 is turned off. At this time, the semiconductor laser 1
2 is driven by the drive circuit 13 to emit light, and charges the parasitic capacitance C ₁ of the low frequency term. Next, when the transmission signal is low level, the switch 11 is turned off and the switch 26 is turned on. At this time, the semiconductor laser 12 is reverse-biased by the reference voltage Vref applied via the switch 26 and discharges the electric charge accumulated in the parasitic capacitance C ₁ . This discharge is performed via the feedback resistor Rf of the preamplifier 22, but the value of the feedback resistor Rf is generally several tens of kilohms.
On the other hand, since the parasitic resistance R ₁ of the semiconductor laser 12 is several megaΩ, the feedback resistance Rf of the preamplifier 22 does not affect the time constant.

At this time, the output of the comparison circuit 24 is cut off by the gate circuit 41, so that the preamplifier 2
Even if the output voltage level of 2 fluctuates, the output of the level conversion circuit 25 can be fixed at a low level. This operation does not affect the characteristics, unlike the on / off operation of the switch (21).

During reception, the switch 11 is turned off,
The switch 26 is turned on. The semiconductor laser 12 receives the reference voltage Vref via the switch 26 and functions as a light receiving element. The detection current corresponding to the optical signal is processed by the preamplifier 22, the gain control amplifier 23, and the comparison circuit 24 in the same manner as in the conventional case, and the output signal thereof is input to the level conversion circuit 25 via the gate circuit 41 and a predetermined value is obtained. Converted to a level and output.

FIG. 8 shows an output waveform of the preamplifier 22 in this embodiment when the transmission mode is switched to the reception mode according to the S / R signal. In the configuration of this embodiment, the semiconductor laser 1 is used every time the transmission signal becomes low level during transmission.
Since 2 is reverse biased to discharge the accumulated charge, the accumulated charge is small when the transmission mode is switched to the reception mode, and the protection time at the time of transmission / reception switching can be greatly shortened.

FIG. 3 shows the configuration of the second embodiment of the present invention. The feature of this embodiment is that, in addition to the structure of the first embodiment, a voltage follower circuit 42 and a switch 43 are connected between the cathode and the anode of the semiconductor laser 12.

The switching control circuit 31c includes an inverting circuit 32 which inverts the S / R signal and gives it to the gate circuit 41 and the switch 43, an AND circuit 33 which inputs the S / R signal and the transmission signal, and an S / R signal. AND circuit 36 for inputting the inverted transmission signal and AND circuit 33 and AND circuit 3
Delay circuits 35a, 35 for giving a predetermined delay τ to the output of 6
and b. The output of the delay circuit 35a is given to the switch 11, and the output of the delay circuit 35b is given to the switch 2.
6 given. The delay circuits 35a and 35b are provided to adjust the drive timing of the semiconductor laser 12 due to the propagation delay in the drive circuit 13 and the switching timing of the switches 11 and 26.

The operation at the time of transmission is the same as that of the first embodiment except that the switch 43 is turned off. During reception, the switches 11 and 26 are turned off and the switch 43 is turned on.
The semiconductor laser 12 is put into a non-biased state by the voltage follower circuit 42, and the influence of dark current is suppressed. As a result, the deterioration of the minimum light receiving level due to the dark current can be improved. The operation of the other parts is the same as in the first embodiment.

[0026]

As described above, in the optical transmitter / receiver circuit of the present invention, the semiconductor laser and the amplifier circuit are separated at the time of transmission, and the switch connected at the time of reception is unnecessary. As a result, deterioration of the minimum light receiving level due to noise and parasitic capacitance of the switch is eliminated, and good characteristics can be obtained.

Further, during transmission, since the electric charge charged in the parasitic capacitance of the semiconductor laser is discharged for each bit of the transmission signal, the accumulated electric charge is small when the transmission mode is switched to the reception mode, and when the transmission / reception is switched. The protection time can be greatly reduced. Thereby, the transmission efficiency can be improved.

Further, by connecting the voltage follower circuit between both terminals of the semiconductor laser at the time of reception, the influence of the dark current of the semiconductor laser can be suppressed and the characteristics can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a first embodiment of the present invention.

FIG. 2 is a timing chart of the first embodiment.

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

FIG. 4 is a timing chart of the second embodiment.

FIG. 5 is a block diagram showing a configuration of a conventional optical transmission / reception circuit using a semiconductor laser.

FIG. 6 is a diagram showing an equivalent circuit of a semiconductor laser.

FIG. 7 is a diagram showing an output waveform of a preamplifier 22 in a conventional configuration.

FIG. 8 is a diagram showing an output waveform of the preamplifier 22 in the first embodiment.

[Explanation of symbols]

10 power supply (V _DD ) terminal 11, 21, 26, 43 switch 12 semiconductor laser 13 drive circuit 22 preamplifier 23 gain control amplifier (GCA) 24 comparison circuit 25 level conversion circuit 27 reference voltage (Vref) terminal 31 switching control circuit 32 inversion Circuit 33, 36 AND circuit 34 NAND circuit 35 Delay circuit (τ) 41 Gate circuit 42 Voltage follower circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H04B 10/26 10/14 10/04 10/06

Claims (4)

[Claims] 1. A power supply terminal is connected to a first terminal of a semiconductor laser, a drive circuit for driving a semiconductor laser by a transmission signal is connected to a second terminal, and an optical signal according to the transmission signal is output from the semiconductor laser. And an optical transmission circuit unit, an amplifier circuit is connected to the first terminal of the semiconductor laser, and a reference voltage terminal for applying a reference voltage to the second terminal,
In an optical transmitter / receiver circuit including an optical receiver circuit section that outputs an electric signal corresponding to an optical signal received by the semiconductor laser from an amplifier circuit, the optical transmitter / receiver circuit is connected between a first terminal of the semiconductor laser and the power supply terminal. A first switch, a second switch connected between the second terminal of the semiconductor laser and the reference voltage terminal, a gate circuit connected to the output stage of the amplifier circuit, and The gate circuit is closed, the first switch is turned on and the second switch is turned off when the transmission signal is at a high level, and the first switch is turned off and the second switch is turned on when the transmission signal is at a low level. And a switching control circuit for turning off the first switch and turning on the second switch at the time of reception to send a switching signal for opening the gate circuit. Receiver circuit. 2. The optical transmission / reception circuit according to claim 1, wherein the switching control circuit ANDs a logical product of a transmission / reception switching signal that is high level during transmission and low level during reception and a transmission signal, and the transmission / reception switching circuit. A NAND circuit that performs a NAND operation of a signal and a transmission signal, a first delay circuit that gives a predetermined delay to the output signal of the AND circuit and gives the first switch, and a predetermined delay to the output signal of the NAND circuit An optical transmission / reception circuit comprising: a second delay circuit for applying the signal to a second switch and an inverting circuit for inverting the transmission / reception switching signal and applying the inverted signal to a gate circuit. 3. A power supply terminal is connected to a first terminal of the semiconductor laser, a drive circuit for driving the semiconductor laser by a transmission signal is connected to the second terminal, and an optical signal corresponding to the transmission signal is output from the semiconductor laser. And an amplifier circuit connected to the first terminal of the semiconductor laser, and a voltage follower circuit for setting a potential difference between the first terminal and the second terminal to zero. An optical transmitter / receiver circuit including an optical receiver circuit section for outputting an electric signal corresponding to an optical signal received by a semiconductor laser from an amplifier circuit, the optical transmitter / receiver circuit being connected between a first terminal of the semiconductor laser and the power supply terminal. A first switch; a second switch connected between a second terminal of the semiconductor laser and a reference voltage terminal; a third switch inserted in series with the voltage follower circuit; and an amplifier circuit. Output stage The gate circuit to be connected, the gate circuit is closed at the time of transmission, the third switch is turned off, the first switch is turned on and the second switch is turned off at a high level of the transmission signal, and the transmission signal is transmitted. At a low level, the first switch is turned off, the second switch is turned on, the first switch and the second switch are turned off at the time of reception, the third switch is turned on, and the gate circuit is turned on. And a switching control circuit for sending a switching signal for opening the optical transmission / reception circuit. 4. The optical transmitter / receiver circuit according to claim 2, wherein the switching control circuit ANDs a transmission / reception switch signal that is at a high level during transmission and is at a low level during reception and a transmission signal. A second AND circuit that takes a logical product of the transmission / reception switching signal and the inverted transmission signal; and a first delay circuit that gives a predetermined delay to the output signal of the first AND circuit to give it to the first switch, A second delay circuit for giving a predetermined delay to the output signal of the second AND circuit and giving it to the second switch; and an inverting circuit for inverting the transmission / reception switching signal and giving it to the gate circuit and the third switch. An optical transmitter / receiver circuit characterized by being provided.