JP4733944B2 - Optical transmitter - Google Patents

Description

  The present invention relates to an optical transmitter, and more particularly, to an optical transmitter with improved optical output adjustment range, stability of optical output operation, and deterioration detection accuracy of a light emitting element included in the optical transmitter. is there.

  The optical transmitter is provided in a front end of an optical communication system or the like, and plays a role of converting an electrical signal into an optical signal. Usually, to stabilize an optical communication system, it is desirable that the output intensity of an optical signal emitted from an optical transmitter is always a constant value regardless of the environmental temperature or the passage of time, and the optical output is automatically constant. In general, an APC (Automatic Power Control) method of controlling to a value is often used.

  Conventionally, as a document related to this type of APC-based optical transmitter, there is a disclosure example in Patent Document 1 below. This document shows the circuit configuration of an optical output monitor circuit in the APC system, and also shows the simplest circuit configuration as a conventional example of the document.

  In this conventional optical output monitor circuit, a variable resistor is disposed between the anode terminal of the light receiving element and the ground so as to convert a current generated in the light receiving element into a voltage. Also, in order to take into account individual variations in the light output of the light emitting element and the current conversion efficiency of the light receiving element, the resistance value can be made variable and the current / voltage conversion magnification can be changed to expand the applicable dynamic range. Yes.

JP-A-8-298337

  However, in the optical transmitter shown in Patent Document 1, the variable resistance is set to a small value for the one with high conversion efficiency between the light output of the light emitting element and the current of the light receiving element, and conversely, the conversion efficiency is low. In other words, the optical output of the optical transmitter is adjusted by increasing the variable resistance. In this case, a relational expression is established in which the product of the current of the light receiving element and the resistance value is a constant value. That is, the current of the light receiving element and the resistance value are in an inversely proportional relationship. Therefore, when the conversion efficiency between the light output of the light emitting element and the current of the light receiving element is large, the change of the light output becomes very sensitive to the error of the resistance value, and the dynamic range that can be adjusted by itself is limited. was there.

  In addition, in the optical transmitter according to this prior art, when the optical output of the light emitting element decreases due to aging during APC operation, the optical output of the optical transmitter is increased by increasing the drive current of the light emitting element driving circuit. Operates to keep a constant value. However, when the degree of aging is large and the driving capability of the light emitting element driving circuit is exceeded, a desired driving current cannot be supplied to the light emitting element, and the light output is reduced. In this case, since the current of the light receiving element is insufficient with respect to the desired value, the product of the current of the light receiving element and the resistance value becomes smaller than the initial value, and there is a problem that the APC loop becomes unstable.

  The present invention has been made in view of the above problems, and provides an optical transmitter that ensures a wide dynamic range characteristic of light output adjustment and stability of operation, and improves deterioration detection accuracy of a light emitting element. The purpose is to do.

In order to solve the above-described problems and achieve the object, an optical transmitter according to the present invention receives a light emitting element and a light output of the light emitting element, and generates a current proportional to the intensity of the received light output. A current / voltage converter for converting a current generated by the light receiving element into a voltage, a voltage signal output by the current / voltage converter, and a reference; A comparison amplifier that compares and amplifies the voltage signal output from the voltage source, a light emitting element drive circuit that varies the drive current based on the voltage signal output from the comparison amplifier, and a current connected in parallel to the light receiving element comprising an automatic optical output control loop stabilization circuit having a source, wherein the automatic optical power control loop stabilization circuitry, operates as the light receiving element to compensate for the shortage of the current supplied to the current / voltage converter Features to do To.

According to the present invention, the automatic light output control loop stabilization circuit has a current source connected in parallel to the light receiving element, and this current source is a current source that the light receiving element supplies to the current / voltage converter. Since it operates to compensate for the shortage, the output voltage of the current / voltage converter is maintained at the output voltage of the reference voltage source.

According to the optical transmitter of the present invention, the shortage of the current supplied to the current / voltage converter by the light receiving element is compensated by the current source provided in the automatic light output control loop stabilization circuit. There is an effect that the stability of the light output control loop can be improved.

  Embodiments of an optical transmitter according to the present invention will be described below in detail with reference to the drawings. In addition, this invention is not limited by this embodiment. The circuit configuration shown below shows an example, and various modifications can be made without departing from the technical significance of the present invention.

Embodiment 1 FIG.
FIG. 1 is a block diagram showing a configuration of the optical transmitter according to the first exemplary embodiment of the present invention. The optical transmitter shown in the figure includes a light emitting element 1 as a light emitting device, a light receiving element 2 as a light receiving device that receives a light output of the light emitting element 1 and generates a current proportional to the received light intensity, and a light receiving device. A current / voltage converter 3 that converts a current generated in the element 2 into a voltage, and a comparison amplifier 5 that compares and amplifies the voltage signal output from the current / voltage converter 3 and the voltage signal output from the reference voltage source 4. And a light emitting element driving circuit 6 that varies an output current based on a voltage signal output from the comparison amplifier 5 and an automatic light output control loop stabilization circuit 7 connected in parallel to the light receiving element 2. Has been. The current / voltage converter 3 includes a pull-down resistor 31 and a sink current source 32 that variably controls the current value. The pull-down resistor 31 and the sink current source 32 are connected in parallel. Has been. On the other hand, the automatic light output control loop stabilization circuit 7 includes a current source 71.

  Next, the connection relationship of the components constituting the optical transmitter shown in FIG. 1 will be described. In the figure, the light emitting element 1 has an anode terminal connected to a power source and a cathode terminal connected to a light emitting element driving circuit 6. The light receiving element 2 has a cathode terminal connected to a power supply and an anode terminal connected to an input end of the current / voltage converter 3 (one end of a connection point between the pull-down resistor 31 and the suction current source 32). The current source 71 of the automatic light output control loop stabilization circuit 7 is connected in parallel to both ends of the light receiving element 2.

  Next, the operation of the optical transmitter shown in FIG. 1 will be described. However, in the following description, the operation when the automatic light output control loop stabilization circuit 7 does not exist will be described first, and then the operation when the automatic light output control loop stabilization circuit 7 is included will be described.

(Operation when there is no automatic light output control loop stabilization circuit 7)
In FIG. 1, the light emitting element 1 emits light upon receiving a drive current from the light emitting element driving circuit 6. The light receiving element 2 receives the back light of the light emitting element 1 and converts it into a current corresponding to the amount of light received. At this time, the current generated in the light receiving element 2 is proportional to the light output intensity of the light emitting element 1. The current / voltage converter 3 converts the current generated in the light receiving element 2 into a voltage and outputs the converted voltage signal to the comparison amplifier 5. The comparison amplifier 5 compares the voltage signal output from the current / voltage converter 3 with the output voltage of the reference voltage source 4, and the optical output of the optical transmitter converges to a predetermined set value based on the comparison result. Thus, a control signal for controlling the drive current of the light emitting element driving circuit 6 is output to the light emitting element driving circuit 6. This control technique is called automatic light output control (APC), and the light output is automatic so that the voltage signal output from the current / voltage converter 3 becomes substantially equal to the output voltage of the reference voltage source 4. Control is performed.

  Here, the principle of optical output setting for the optical transmitter will be described. Generally, the conversion efficiency between the light output of the light-emitting element 1 and the current of the light-receiving element 2 has a variation of about 10 times. Therefore, in order to obtain a desired light output as an optical transmitter, individual optical transmission Individual adjustments are required for the vessel. On the other hand, the current / voltage converter 3 provided in the optical transmitter of this embodiment is configured such that the output voltage of the current / voltage converter 3 and the reference voltage source 4 are in a state where the automatic optical output control is converged. It is equal to the output voltage. Therefore, a fixed current obtained by dividing the reference voltage value by the resistance value flows through the pull-down resistor 31 of the current / voltage converter 3. Further, the sum of the current value flowing through the pull-down resistor 31 and the sink current value of the current source 32 is the current value of the light receiving element 2, and the current value of the light receiving element 2 and the light output of the light emitting element 1 are in a proportional relationship. Therefore, the optical output of the optical transmitter can be set by adjusting the sink current value of the current source 32.

  Such automatic control of the light output is executed, for example, when the light output of the light emitting element 1 is lowered due to aging. In such a case, control in the direction of increasing the drive current of the light emitting element drive circuit 6 is performed, and the optical output of the optical transmitter is held at a constant value.

  As described in the background art section, in the optical transmitter disclosed in Patent Document 1 described above, the current / voltage converter is composed of only a variable resistor, and the set resistance value of the variable resistor and the optical transmitter Therefore, when the conversion efficiency of the light output of the light-emitting element 1 and the current of the light-receiving element 2 is large and the set resistance value needs to be small, an error in the set resistance value However, the change of the light output becomes very sensitive, and there is a problem that the adjustable dynamic range is limited.

  On the other hand, in the optical transmitter according to this embodiment, since the set current value of the current source 32 and the optical output of the optical transmitter are in a proportional relationship, the conversion efficiency of the light output of the light emitting element 1 and the current of the light receiving element 2 is improved. Regardless of the variation, the change in the light output with respect to the error in the set current value can always be maintained constant, and the dynamic range characteristics of the light output adjustment can be improved.

(Operation when automatic light output control loop stabilization circuit 7 exists)
Next, the operation when the automatic light output control loop stabilization circuit 7 exists will be described. Now, let us consider a case where the light-emitting element 1 has a large degree of deterioration over time and the drive current required for the light-emitting element drive circuit 6 exceeds the drive capability of the light-emitting element drive circuit 6. In this case, the light emitting element driving circuit 6 cannot output a desired driving current to the light emitting element 1, and the optical output of the optical transmitter is reduced. At this time, since the current of the light receiving element 2 that receives the light output of the light emitting element 1 is insufficient as compared with a desired value, the output voltage of the current / voltage converter 3 cannot reach the output voltage of the reference voltage source 4. The automatic light output control loop may not be converged and may become unstable.

  On the other hand, in the optical transmitter of this embodiment, when the automatic light output control does not converge, the automatic light output control loop stabilization circuit 7 operates to compensate the current shortage of the light receiving element 2. Is supplied to the current / voltage converter 3, it is possible to prevent the automatic light output control from falling into a state where it does not converge and becomes unstable. Therefore, the stability of the automatic light output control loop can be improved even when the light output of the light emitting element 1 decreases due to aging or the like and a driving current exceeding the driving capability of the light emitting element driving circuit 6 is required. Wide dynamic range characteristics of light output adjustment and operational stability can be ensured.

  On the other hand, in the optical transmitter of this embodiment, when the automatic light output control does not converge, the automatic light output control loop stabilization circuit 7 operates to compensate the current shortage of the light receiving element 2. Can be supplied to the current / voltage converter 3. Therefore, the stability of the automatic light output control loop can be improved even when the light output of the light emitting element 1 decreases due to aging or the like and a driving current exceeding the driving capability of the light emitting element driving circuit 6 is required. Wide dynamic range characteristics of light output adjustment and operational stability can be ensured.

  The automatic light output control loop stabilization circuit 7 of this embodiment is operated so as to compensate for the shortage of the current supplied from the light receiving element 2 to the current / voltage converter 3 as described above. On the other hand, when the current generated in the light receiving element 2 is insufficient and the output voltage of the current / voltage converter 3 does not reach the output voltage of the reference voltage source 4, that is, automatic light output control ( The operation may be performed only when (APC) does not converge and the control loop becomes unstable. By performing such control, energy consumption efficiency can be improved.

  As described above, according to the optical transmitter of this embodiment, the current source of the automatic optical output control loop stabilizer compensates for the shortage of the current supplied to the current / voltage converter by the light receiving element. Therefore, the stability of the automatic light output control loop can be improved, and the wide dynamic range characteristic of the light output adjustment and the stability of the operation can be ensured.

Embodiment 2. FIG.
FIG. 2 is a block diagram showing the configuration of the optical transmitter according to the second embodiment of the present invention. In the figure, the same parts as those in FIG. 1 are denoted by the same reference numerals. In FIG. 2, the automatic light output control loop stabilization circuit 7 includes a current source 71 and a resistor 72 connected in series. In addition, a light emitting element deterioration detection circuit 8 including a reference voltage source 81 and a comparator 82 is provided, and an input terminal of the light emitting element deterioration detection circuit 8 is a current source 71 constituting the automatic light output control loop stabilization circuit 7. And a resistor 72 are connected to a connection point.

  Next, the operation of the optical transmitter shown in FIG. 3 will be described. In the figure, the light emitting element deterioration detection circuit 8 compares the input voltage with the output voltage of the reference voltage source 81 and outputs an alarm signal of “High” or “Low” based on the comparison result. The input voltage to the light emitting element deterioration detection circuit 8 is maintained at the output voltage of the reference voltage source 4 when the automatic light output control is operating normally. On the other hand, when the light output of the light-emitting element 1 decreases due to aging or the like, the automatic light output control loop stabilization circuit 7 operates, and a voltage drop occurs in the resistor 72 due to the current supplied by the current source 71. The voltage at the connection point between the source 71 and the resistor 72 is larger than the output voltage of the reference voltage source 4. Therefore, by setting the output voltage of the reference voltage source 81 to a value higher than the output voltage of the reference voltage source 4, it is possible to detect a decrease in the light output of the light emitting element 1. For example, the output voltage of the reference voltage source 81 can be set to a value about 10% higher than the output voltage of the reference voltage source 4.

  Thus, according to the optical transmitter of this embodiment, since the input end of the light emitting element deterioration detection circuit is connected to the connection point between the variable current source and the resistor, Embodiment 1 In addition to the above effect, it is possible to detect the deterioration of the light emitting element without impairing the stability of the automatic light output control loop.

Embodiment 3 FIG.
FIG. 3 is a block diagram showing a configuration of the optical transmitter according to the third embodiment of the present invention. In the figure, the same parts as those in FIG. 1 are denoted by the same reference numerals. In FIG. 3, the automatic light output control loop stabilization circuit 7 includes a current source 71. In addition, a light emitting element deterioration detecting circuit 8 including a reference voltage source 81 and a comparator 82 is provided, and an input terminal of the light emitting element deterioration detecting circuit 8 is connected to an anode terminal of the light receiving element 2 through a resistor 9. Yes.

  Next, the operation of the optical transmitter shown in FIG. 4 will be described. The input voltage to the light emitting element deterioration detection circuit 8 is maintained at the output voltage of the reference voltage source 4 when the automatic light output control is operating normally. On the other hand, when the light output of the light emitting element 1 decreases due to aging or the like, the automatic light output control loop stabilization circuit 7 operates, and a voltage drop occurs in the resistor 9 due to the current supplied by the current source 71. The voltage at the connection point between the current / voltage converter 3 connected to the element deterioration detection circuit 8 and the resistor 72 is smaller than the output voltage of the reference voltage source 4. Therefore, by setting the output voltage of the reference voltage source 81 to a value lower than the output voltage of the reference voltage source 4, it is possible to detect a decrease in the light output of the light emitting element 1. For example, the output voltage of the reference voltage source 81 can be set to a value about 10% lower than the output voltage of the reference voltage source 4.

  Here, differences in functions of the light emitting element deterioration detection circuits of the second embodiment and the third embodiment will be described.

  In the optical transmitter according to the second embodiment shown in FIG. 2, when the automatic light output control loop stabilization circuit 7 starts to operate due to deterioration of the light emitting element, the voltage difference generated between both ends of the resistor 72 is detected as the light emitting element deterioration detecting circuit 8. Is detected and an alarm indicating the deterioration of the light emitting element is issued.

  When the current source 71 is configured with an actual circuit, the current source 71 does not operate normally unless the voltage between the terminals of the current source 71 can be secured, for example, 0.5 V or more. As described above, when the deterioration of the light emitting element is detected, the voltage between the terminals of the current source 71 constituting the automatic light output control loop stabilization circuit 7 becomes small. The resistance value of the configuring resistor 72 cannot be increased too much.

  On the other hand, in the optical transmitter according to the third embodiment shown in FIG. 3, when the automatic light output control loop stabilization circuit 7 starts to operate due to the deterioration of the light emitting element, the voltage difference generated between both ends of the resistor 9 is detected. The circuit 8 detects and an alarm indicating the deterioration of the light emitting element is issued. In this case, unlike the operation of the second embodiment, the voltage between the terminals of the current source 71 constituting the automatic light output control loop stabilization circuit 7 does not change, so the value of the resistor 9 affects the operation of the current source 71. do not do.

  On the other hand, when the resistance value of the resistor 9 is increased, the voltage between the terminals of the current source 32 constituting the current / voltage converter 3 is reduced, so that it is necessary to examine the operation on the actual circuit. When configuring the current source 32, as described above, it is necessary to secure a voltage of, for example, 0.5 V or more as the voltage between the terminals of the current source 32. If this voltage cannot be secured, the current source 32 will not operate normally. . However, even if the current source 32 cannot operate normally and no current flows through the current source 32, the input voltage of the comparison amplifier 5 and the output voltage of the reference voltage source 4 are maintained equal, and the automatic light output control loop. The stable operation is maintained.

  With the above-described operation, in the configuration of the second embodiment, the resistance value of the resistor 72 cannot be increased too much from the viewpoint of normal operation of the automatic light output control loop stabilization circuit 7. On the other hand, in the configuration of the third embodiment, there is no restriction on the selection of the resistance value of the resistor 9, and the contrast can be increased by increasing the resistance value of the resistor 9, so that the degree of deterioration of the light emitting element can be accurately detected. It becomes possible.

  As described above, according to the optical transmitter of this embodiment, since the input end of the light emitting element deterioration detection circuit is connected to the connection point between the resistor and the current / voltage converter, In addition to the effect of the first embodiment, it is possible to detect deterioration of the light emitting element with high accuracy without impairing the stability of the automatic light output control loop.

  As described above, the optical transmitter according to the present invention is useful as an APC optical transmitter.

It is a block diagram which shows the structure of the optical transmitter concerning Embodiment 1 of this invention. It is a block diagram which shows the structure of the optical transmitter concerning Embodiment 2 of this invention. It is a block diagram which shows the structure of the optical transmitter concerning Embodiment 3 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light emitting element 2 Light receiving element 3 Voltage converter 4 Reference voltage source 5 Comparison amplifier 6 Light emitting element drive circuit 7 Automatic light output control loop stabilization circuit 8 Light emitting element deterioration detection circuit 9, 72 Resistor 31 Pull-down resistor 32, 71 Current source 81 Reference voltage source 82 Comparator

Claims (4)

A light emitting element;
A light receiving element that receives the light output of the light emitting element and generates a current proportional to the intensity of the received light output;
A current / voltage converter having a first resistor and a variable current source connected in parallel, and converting a current generated in the light receiving element into a voltage;
A comparison amplifier that compares and amplifies the voltage signal output from the current / voltage converter and the voltage signal output from the reference voltage source;
A light emitting element driving circuit that varies a driving current based on a voltage signal output from the comparison amplifier;
One end is connected to the cathode end of the light receiving element, and the other end is connected to the anode end of the light receiving element, and a shortage of current supplied from the light receiving element to the current / voltage converter is reduced. An automatic light output control loop stabilization circuit that stabilizes the operation of an automatic light output control loop including the light emitting element, the light receiving element, the comparison amplifier, and the light emitting element driving circuit by performing an operation compensated by the current source When,
Optical transmitter characterized by comprising a. A second resistor having one end connected to the other end of the current source and the other end connected to the anode end of the light receiving element;
Have a comparator and a reference voltage source, a light emitting element deterioration detection circuit for detecting the deterioration of the light emitting element based on the potential of the connection end between the second resistor and the current source,
Optical transmitter according to claim 1, characterized in that with a. A second resistor inserted between the anode end of the light receiving element and the current / voltage converter;
A comparator and a reference voltage source, have a, a light emitting element deterioration detection circuit, wherein the detecting the deterioration of the light emitting element based on the potential of the connection end between the current / voltage converter and said second resistor,
The optical transmitter according to claim 1, further comprising: The optical transmitter according to any one of claims 1 to 3, wherein the automatic optical output control loop stabilization circuit operates only when a current generated in the light receiving element is insufficient.

Images