JP2004088503A - Alarm circuit and optical transmitter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an alarm circuit concerned with the bias or modulation control of a driving circuit considering distortion in the characteristics of light emitting elements. <P>SOLUTION: Voltage obtained by adding offset to control voltage for controlling the bias of the driving circuit is set as threshold voltage for generating a bias alarm. The alarm circuit is provided with a buffer amplifier 25 for inputting control voltage, an alarm adjustment circuit 26 for adding voltage adjusted by an alarm adjusting terminal to output voltage from the buffer amplifier 25 and outputting the added voltage and an amplifier 27 for amplifying the output of the alarm adjustment circuit 26 by reference voltage to which a temperature characteristic is added and outputting voltage obtained by adding offset to the control voltage. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an alarm circuit and an optical transmitter, and more particularly, to an alarm circuit of a driving circuit that controls light output of a light emitting element and an optical transmitter including the same.
[0002]
[Prior art]
In recent years, optical transmission systems using an optical fiber as a transmission medium are not limited to trunk networks of public networks for long-distance, large-capacity transmission, subscriber systems of public networks, private area local area networks, private networks, and the like. It is used for various applications such as short-distance transmission and short-distance transmission as an alternative to electrical wiring between devices and packages. Further, miniaturization of optical devices and integrated circuits has been achieved, and for short-distance transmission and short-distance transmission, an optical module in which an optical transmitter and an optical receiver are integrally formed is used.
[0003]
In such an optical module, for example, an APC (Automatic Power Control) circuit that keeps the output of the light emitting element constant is mounted on the optical transmitter in order to realize a maintenance-free operation of an apparatus including the optical module. . In addition, a detection circuit for confirming that the APC circuit is operating properly is also provided.
[0004]
FIG. 1 shows a configuration of a conventional optical transmitter. The optical transmitter 10 includes a light emitting element 11, a driving circuit 12 for driving the light emitting element 11, and a light receiving element 13 for monitoring output light of the light emitting element 11. The drive circuit 12 includes a retiming circuit 14 that performs retiming by inputting data and a clock from a device on which the optical module is mounted; An APC circuit 16 that converts the output current of the light receiving element 13 into a voltage and controls the bias of the light emitting element 11
[0005]
In addition, the drive circuit 12 includes a disable terminal for forcibly extinguishing the light output of the light emitting element and a bias current of the light emitting element 11 or an output current of the light receiving element 13 for use in maintenance of the optical module. It has a comparator 17 for converting and outputting an alarm by comparing with the alarm adjustment terminal voltage.
[0006]
With such a configuration, the APC circuit 16 converts the output current of the light receiving element 13 into a voltage, compares the output current with a voltage set in advance, and controls the bias current and the modulation current of the light emitting element 11 to thereby control the light emitting element 13. The optical output 11 is kept constant. In this way, a decrease in the light output of the light emitting element 11 due to a change in the ambient temperature and a decrease in the light output due to aging of the light emitting element 11 are compensated.
[0007]
[Problems to be solved by the invention]
2. Description of the Related Art Conventionally, an optical transmitter has a bias adjustment terminal so that a bias current of a light emitting element can be adjusted to an appropriate value according to variation in characteristics of the light emitting element. Therefore, it is possible to compensate for the temperature characteristic and the decrease in output due to aging with the APC circuit, and also to compensate for the initial deviation of the characteristics of the light emitting element.
[0008]
On the other hand, the alarm adjustment terminal voltage, which is a threshold value at which an alarm is issued, is directly input to the comparator 17, so that it was not possible to take into account variations in the initial deviation, temperature characteristics, and aging of the light emitting element. Therefore, there is a problem that a malfunction of issuing an alarm occurs due to a variation in characteristics of individual light emitting elements.
[0009]
The present invention has been made in view of such a problem, and an object of the present invention is to provide an alarm circuit and an optical transmitter in which variations in characteristics of a light emitting element are considered.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, a bias and modulation of the light emitting element are controlled in accordance with an output current from a light receiving element for monitoring an optical output of the light emitting element. In an alarm circuit of an optical transmitter provided with a drive circuit, a voltage obtained by adding an offset to a control voltage for controlling a bias of the drive circuit is set as a threshold voltage for issuing a bias alarm.
[0011]
The invention according to claim 2 is an alarm circuit of an optical transmitter including a drive circuit that controls bias and modulation of the light emitting element according to an output current from a light receiving element that monitors an optical output of the light emitting element. A voltage obtained by adding an offset to a control voltage for controlling the modulation of the drive circuit is set as a threshold voltage for generating a modulation alarm.
[0012]
According to a third aspect of the present invention, in the alarm circuit according to the first or second aspect, a buffer amplifier for inputting the control voltage, a voltage adjusted by an alarm adjustment terminal, and an output voltage of the buffer amplifier are added. And an amplifier that amplifies the output of the alarm adjustment circuit with a reference voltage to which a temperature characteristic is added and outputs a voltage obtained by adding an offset to the control voltage. I do.
[0013]
According to a fourth aspect of the present invention, the alarm adjusting circuit according to the third aspect includes a variable resistor connected to an output of the buffer amplifier, and a product of an amplification degree of the amplifier and a resistance value of the variable resistor. The voltage value of the offset is set by the following.
[0014]
The invention according to claim 5 includes a light emitting element, a light receiving element for monitoring the light output of the light emitting element, and a drive circuit for controlling bias and modulation of the light emitting element according to the output current of the light receiving element. In an optical transmitter, an alarm circuit for outputting a voltage obtained by adding an offset to a control voltage for controlling the bias and modulation of the drive circuit, and a bias alarm and a modulation alarm for a voltage output from the alarm circuit as a threshold voltage. And an alarm issuing circuit for issuing an alarm.
[0015]
According to a sixth aspect of the present invention, in the alarm circuit according to the fifth aspect, the buffer circuit that inputs the control voltage, a voltage adjusted by an alarm adjustment terminal, and an output voltage of the buffer amplifier are added. And an amplifier that amplifies the output of the alarm adjustment circuit with a reference voltage to which a temperature characteristic is added and outputs a voltage obtained by adding an offset to the control voltage. .
[0016]
According to a seventh aspect of the present invention, the alarm adjustment circuit according to the sixth aspect includes a variable resistor connected to an output of the buffer amplifier, and a product of an amplification degree of the amplifier and a resistance value of the variable resistor. The voltage value of the offset is set by the following.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 2 shows a configuration of an APC circuit according to one embodiment of the present invention. The APC circuit 20 includes a buffer amplifier 21 that converts the output current of the light receiving element 13 into a voltage and inputs the voltage, an amplifier 22 that performs phase compensation and amplification, an amplifier 23 that adds a temperature characteristic, and control from a bias adjustment terminal. An amplifier 24 for applying a voltage is cascaded. Further, an alarm adjustment circuit 26 for inputting a control voltage from a bias adjustment terminal and a voltage set by an alarm adjustment terminal via a buffer amplifier 25 to adjust an alarm threshold voltage, and adding a temperature characteristic And an amplifier 27 for outputting to the alarm terminal.
[0018]
The temperature characteristic adding circuit 28 outputs a reference voltage having a predetermined temperature characteristic according to the control voltage from the temperature adjustment terminal, supplies the reference voltage to the amplifier 23, and supplies the reference voltage to the amplifier 27 via the buffer amplifier 29.
[0019]
With such a configuration, the APC circuit 20 converts the output current of the light receiving element 13 into a voltage, adds a temperature characteristic in the amplifier 23 by the reference voltage from the temperature characteristic adding circuit 28, and sets the voltage set by the bias adjustment terminal. Is added in the amplifier 24 to control the bias current of the light emitting element 11. The bias control terminal is output as a reference voltage of a differential amplifier for controlling a bias current, and keeps the output of the light emitting element 11 constant by adding a temperature characteristic to the reference voltage.
[0020]
In the present embodiment, an alarm of a circuit for controlling the bias current of the light emitting element 11 will be described. However, the present invention can also be applied to an alarm of a circuit for controlling the modulation current of the light emitting element 11.
[0021]
FIG. 3 shows a configuration of an alarm adjustment circuit according to one embodiment of the present invention. The alarm adjustment circuit 26 is configured by a current mirror circuit. The control voltage from the bias adjustment terminal, input via a buffer amplifier 25, and outputs a voltage corresponding to the resistance value of the current mirror current × R _ALM as an offset.
[0022]
Next, a method of adjusting the threshold voltage of the alarm will be described. The output voltage of the amplifier 22 is 1.1 V, and the reference voltage output from the temperature characteristic adding circuit 28 is +1.3 V ＠ + 0 ° C.
+1.1V＠+50°C
+0.9V＠+100℃
And Assuming that the amplifier 23 is an inverting amplifier having an amplification degree A = 1, the output becomes
+1.5V＠+0℃
+1.1V＠+50°C
+0.7V＠+100℃
It becomes. Assuming that the control voltage from the bias adjustment terminal is 1.1 V and the amplifier 24 is an inverting amplifier of A = 2.5, the output of the bias control terminal is
+0.1V＠+0℃
+1.1V＠+50°C
+2.1V＠+100°C
It becomes.
[0023]
The alarm adjusting circuit 26 adds a 0.1 V offset to the control voltage 1.1 V from the bias adjustment terminal and outputs the resultant. The reference voltage output from the temperature characteristic adding circuit 28
+1.5V＠+0℃
+1.1V＠+50°C
+0.7V＠+100℃
And If the amplifier 27 is an inverting amplifier of A = 2.5, the alarm terminal output is
+ 0.45V + 0 ° C
+ 1.45V + 50 ° C
+ 2.45V + 100 ° C
It becomes.
[0024]
That is, the voltage is obtained by adding an offset of 0.35 V to the output of the bias control terminal. As described above, the set value of the bias current is a set value in consideration of variations such as the initial deviation, temperature characteristics, and aging of the light emitting element. Therefore, since the offset is added based on the set value of the bias current, the alarm terminal voltage, which is a threshold value for issuing an alarm, is not affected by the variation of the light emitting elements.
[0025]
【The invention's effect】
As described above, according to the present invention, the voltage obtained by adding the offset to the control voltage of the drive circuit is used as the threshold voltage at which an alarm is issued. It becomes possible.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of a conventional optical transmitter.
FIG. 2 is a block diagram showing a configuration of an APC circuit according to one embodiment of the present invention.
FIG. 3 is a circuit diagram showing a configuration of an alarm adjustment circuit according to one embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Optical transmitter 11 Light emitting element 12 Drive circuit 13 Light receiving element 14 Retiming circuit 15 Amplifying circuits 16, 20 APC circuits 21, 25, 29 Buffer amplifiers 22, 23, 24, 27 Amplifier 26 Alarm adjustment circuit 28 Temperature characteristic addition circuit

Claims (7)

A control circuit for controlling a bias of the drive circuit in an alarm circuit of an optical transmitter including a drive circuit for controlling a bias and a modulation of the light-emitting element according to an output current from a light-receiving element for monitoring a light output of the light-emitting element. An alarm circuit, wherein a voltage obtained by adding an offset to a voltage is used as a threshold voltage for generating a bias alarm. A control circuit for controlling modulation of the drive circuit in an alarm circuit of an optical transmitter including a drive circuit for controlling bias and modulation of the light-emitting element according to an output current from a light-receiving element for monitoring a light output of the light-emitting element; An alarm circuit, wherein a voltage obtained by adding an offset to a voltage is used as a threshold voltage for issuing a modulation alarm. A buffer amplifier for inputting the control voltage,
An alarm adjustment circuit that adds and outputs the voltage adjusted by the alarm adjustment terminal and the output voltage of the buffer amplifier;
3. The amplifier according to claim 1, further comprising: an amplifier that amplifies an output of the alarm adjustment circuit by a reference voltage to which a temperature characteristic is added and outputs a voltage obtained by adding an offset to the control voltage. Alarm circuit. The alarm adjustment circuit includes a variable resistor connected to an output of the buffer amplifier,
4. The alarm circuit according to claim 3, wherein the voltage value of the offset is set by a product of an amplification degree of the amplifier and a resistance value of the variable resistor. A light-emitting element, a light-receiving element that monitors the light output of the light-emitting element, and an optical transmitter that includes a drive circuit that controls bias and modulation of the light-emitting element according to the output current of the light-receiving element;
An alarm circuit that outputs a voltage obtained by adding an offset to a control voltage that controls bias and modulation of the drive circuit,
An optical transmitter, comprising: an alarm issuing circuit that issues a bias alarm and a modulation alarm using a voltage output from the alarm circuit as a threshold voltage. The alarm circuit,
A buffer amplifier for inputting the control voltage,
An alarm adjustment circuit that adds and outputs the voltage adjusted by the alarm adjustment terminal and the output voltage of the buffer amplifier;
The optical transmitter according to claim 5, further comprising: an amplifier that amplifies an output of the alarm adjustment circuit by a reference voltage to which a temperature characteristic is added and outputs a voltage obtained by adding an offset to the control voltage. vessel. The alarm adjustment circuit includes a variable resistor connected to an output of the buffer amplifier,
The optical transmitter according to claim 6, wherein a voltage value of the offset is set by a product of an amplification degree of the amplifier and a resistance value of the variable resistor.

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