JPH03244166A - Light-emitting element driving circuit - Google Patents

Abstract

PURPOSE:To enhance the degree of freedom of setting of functions by a method wherein an adjustment of the gain of an output stabilizing circuit, which is necessitated because of variations in the characteristics of a light-emitting element and a photodetector, is automatically made and at the same time, functions, such as the stabilization of an optical signal achieved taking temperature change into consideration, the stop drive at the time of cut-off of input, the sending-out of a bias current abnormality increase alarm and the like, are added. CONSTITUTION:One part of a light output signal 11a from a light-emitting element 3a is given to a photodetector 3b for monitor use as an optical signal 16b for monitor use, a monitor current 12c converted from the signal 11a is detected in a current detecting part 5a as a monitor current value 14a and the current value 14a is outputted to an output stabilizing circuit 2. A current modulating part 4a and a bias part 4b respectively receive a modulation current signal 13a and a bias current control signal 13b from the circuit 2 and the amplitudes of a modulated current 12a and a biased current 12b are respectively controlled at prescribed values. A modulation current control signal 17a and a bias current signal 17b are found in a microcomputer 9 builted in the circuit 2 on the basis of these signal values so that the magnitude of the optical signal 11a has a desired value and these signals are outputted to a light-emitting element drive circuit 1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a light emitting element drive circuit, and particularly to a light emitting element drive circuit suitable for use in stabilizing the output of a light emitting element.

[Prior Art] As a conventional technology related to a light emitting element drive circuit, the technology described in "Optical Fiber Application Technology Collection" (Published by Nikkei Gijutsu Tosho Co., Ltd., p. 374) is known.

Hereinafter, an example of a light emitting element driving circuit according to the prior art will be explained with reference to the drawings.

FIG. 4 is a circuit diagram showing an example of the prior art.

In FIG. 4, 41 is a light emitting element, 42 is a light receiving element, 4
3 is a voltage comparator, 44 is a bias current drive circuit, and 45 is a pulse current drive circuit.

In the prior art shown in Fig. 4, a laser diode (L
D) The light emitting element 41 such as a light emitting diode (LED) is
It is driven by a current, +hb, which is the sum of the output current (2) of the pulse current drive circuit 45 which receives input pulses and controls the drive of the light emitting element using the pulses, and the output current Ib of the bias current drive circuit 44. Emits light.

This light emission output is received by a light receiving element 42 such as a pinPD, and a current flowing through this light receiving element 42 is detected.

This detected current is applied to a voltage comparator 4 that performs analog differential amplification.
3 and a reference voltage, and the bias current drive circuit 44 is controlled by the comparison output of the output stabilizing circuit made up of the voltage comparator 43. As a result, the output current of the bias current drive circuit 44 is controlled, and the light output of the light emitting element 41 is stabilized.

[Problems to be Solved by the Invention] The above-mentioned prior art does not take into account the need for adjustment due to variations in the characteristics of the light emitting element and the light receiving element, On the other hand, it has a problem in that it has at least one adjustment part and requires manual adjustment.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art described above, to automatically perform gain adjustment for stabilizing the level of output light of a light emitting element, and to provide a method for controlling and monitoring a light emitting element driving circuit. It is an object of the present invention to provide a light emitting element driving circuit in which functions can be added using only a small number of circuit elements.

[Means for Solving the Problems] According to the present invention, the object is to integrate the output stabilization circuit into a microcomputer, ROM, DA converter, comparator, or AD
This is achieved by using a converter and an analog signal selector, and using software installed in a microcomputer to automatically detect the adjustment point for stabilizing the output of the light emitting element.

[Function] The output stabilization circuit imports the monitor current value and ambient temperature detection current value generated by the light-receiving element paired with the light-emitting element into the microcomputer, processes them with software, and adjusts them to the desired magnitude. The drive current for the light emitting element is controlled so that a light output of 1 is obtained.

During adjustment, internal constants corresponding to variations in the characteristics of the light emitting element and light receiving element can be automatically determined by manually inputting a switching signal to the microcomputer from the outside and operating the adjustment software.

[Example] Hereinafter, an example of a light emitting element driving circuit according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention, and FIG. 2 is a block diagram showing the functions of an adjustment system.

In Figures 1 and 2, 1 is a light emitting element drive section, 2 is an output stabilization circuit, 3a is a light emitting element, 3b is a monitoring light receiving element, 4a is a current modulation section, 4b is a bias section, and 5a is a current detection section. 6a, 6b, 6C are DA converters, 7a is ROM
, 7b is a comparator, 8 is an IO port, 9 is a microcomputer, 21 is a drive circuit, 22 is an optical fiber, 23 is an optical-electrical converter, and 24 is a level determiner.

As shown in FIG. 1, an embodiment of the light emitting element driving circuit according to the present invention includes a light emitting element driving section that includes a light emitting element 3a, a monitoring light receiving element 3b, a current modulating section 4a, a bias section 4b, and a current detecting section 5a. 1 and DA converters 6a, 6b, 6c
, a ROM 7a, a comparator 7b, a board 8, and an output stabilizing circuit 2 consisting of a microcomputer 9.

In the light emitting element driving section 1, the light emitting element 3a is driven by a bias current 12b supplied from a bias section 4b and a modulation current 12b modulated and outputted by a human power signal IO in a current modulation section 4a, and also by intensity modulation. The resulting optical output signal 11a is output to the outside. A part of the optical output signal 11a outputted from the light emitting element 3a is given to the monitoring light receiving element 3b as a monitoring optical signal 11b.

The monitor current 12c converted corresponding to the optical signal 11b received by the monitor light-receiving element 3b is sent to the current detection unit 5.
a, it is detected as a monitor current value 14a and output to the output stabilization circuit 2.

Further, the current modulation section 4a and the bias section 4b receive a modulation current control signal 13a and a bias current control signal 13b, respectively, from the output stabilization circuit 2, and control the amplitudes of the modulation current 12a and bias current 12b to predetermined values. do.

In the output stabilization circuit 2, the digital comparison value 15 output from the microcomputer 9 via the board is converted into an analog value 14b by the DA converter 6C, and then manually inputted from the light emitting element drive section 1. It is compared with the monitor current value 14a by the comparator 7b. The microcomputer 9 changes the aforementioned comparison value 15 while monitoring the comparison result of the comparator 7b, and reads the value of the monitor current value 14a.

Based on this value, the microcomputer 9 determines and outputs a digital modulation current control signal 17a and bias current control signal 17b so that the magnitude of the optical signal 11a becomes a desired value. These control signals 1
The signals 7a and 17b are converted into a modulation current control signal 13a and a bias current control signal 13b of analog values by the DA converters 6a and 6b, respectively, and outputted to the light emitting element driving section 1.

One embodiment of the present invention performs the output stabilization operation as described above, but this operation is performed when the operation mode manual power 20a is "1", and the operation mode manual power 20a is II Q II.
In this case, an adjustment operation is performed.

Further, in the embodiment of the present invention described above, the ROM write voltage input 19 and the adjustment power 20b are used only during the adjustment operation. All of the above-mentioned signal transmission and reception in the microcomputer 9 is performed via the IO boat 8, and signal processing operations are performed by executing instructions read from the ROM 7a via the bus 18.

According to the embodiment of the present invention described above, the light emitting element 3a due to variations in the characteristics of the light emitting element 3a and the light receiving element 3b
It is possible to automatically adjust the output stabilizing circuit 2, which stabilizes the output.

The adjustment method will be explained below with reference to FIG.

The adjustment system shown in FIG. 2 includes the light emitting element drive circuit 21 explained in FIG. 23, and an optical fiber 22 that transmits the optical signal 11a.

As described above, the light emitting element drive circuit 21 executes the adjustment operation by setting the operation mode manual power 20a to O''. At this time, the light emitting element drive circuit 21 receives the input signal 10
and outputs the optical output signal 11a, and outputs the optical output signal 11a.
a is provided to an optical-to-electrical converter 23 via an optical fiber 22. The optical-to-electrical converter 23 converts the optical output signal 11a into an optical conversion signal 25, and then supplies this signal 25 to a level determiner 24, which determines the difference between the level of this signal and a desired level. Determine the size relationship.

The light emitting element drive circuit 21 adjusts the above-mentioned judgment result by human power 2.
0b is input into the microcomputer 9, and the microcomputer 9 adjusts the optical output signal 1.1a to the desired magnitude based on this adjustment manual 20b.
Adjust the internal constants of the output stabilization circuit 2. Optical output signal 1
When a desired value for the magnitude of 1a is obtained, the internal constant at that time is written into the ROM 7a by applying the ROM write voltage input 19.

As described above, the adjustment operation is completed, and thereafter, the light emitting element drive circuit 21 performs R during the output stabilization operation for the light emitting element 3a.
Based on the aforementioned internal constants stored in OMVa, modulation current control signal 17a and bias current control signal 17b
is determined, and the driving of the light emitting element 3a is controlled.

FIG. 3 is a circuit diagram showing the configuration of another embodiment of the present invention. In FIG. 3, 5b is a temperature detection section, 5c is a current detection section, and 7c is an analog signal selector, and other symbols are the same as in FIG. 1.

Another embodiment of the present invention shown in FIG. 3 is one in which another function is added to the embodiment of the present invention explained in FIG.
Since its basic operation is exactly the same as that of the embodiment shown in FIG. 1, only the added elements and functions will be explained below.

Another embodiment of the present invention illustrated in FIG.
It is composed of a light emitting element driving section 1 to which a current detecting section 5C for detecting the current of b is added, and an output stabilizing circuit 2 to which an analog signal selector 7C is added.

In the light emitting element driving section (2), the current detection section 5C detects the bias current 12b, and the temperature detection section 5b detects the ambient temperature. Further, in the output stabilization circuit 2, the analog signal selector 7C receives the monitor current value 1.4a from the current detection section 5a, which is input from the light emitting element drive section 1,
Temperature detection value from temperature detection unit 5a], 4b and bias current detection value 14c from current detection unit 5c are sequentially selected by selection signal 17c given from microcomputer 9, and outputted in a time-divisional manner as signal 14e. .

The microcomputer 9 receives these values and the input signal 1.
0 and internally processes it to output a modulated current control signal 17a and a bias current control signal], 7b that also take into account ambient temperature changes, and detects that the bias current value has increased, The bias abnormality increase alarm signal can be outputted to the outside, and control can also be performed to stop the operation of the entire circuit when the input signal is cut off.

According to such another embodiment of the present invention, the output stabilizing circuit 2 can be configured by simply adding the analog signal selector 7C even when the above-mentioned functions are added to the embodiment of FIG. It can be realized.

In the embodiments of the present invention shown in FIGS. 1 and 3 described above, the DA converter 6c and the comparator 7b may be composed of one DA converter.

Further, in another embodiment of the present invention shown in FIG.
Optical conversion signal 25 output from optical-to-electrical converter 23 in the figure
is applied to the input end of the analog signal selector 7c], 4f to selectively output it, and the comparator 7b compares it with the adjustment value previously set in the rafts 1' and 4a.
The comparison result can be used instead of the adjustment human power 2ob.

In this case, the level determiner 24 in the adjustment system shown in FIG. 2 becomes unnecessary.

[Effects of the Invention] As explained above, according to the spring invention, the gain adjustment of the output stabilizing circuit, which is necessary due to variations in the characteristics of the light emitting element and the light receiving element in the light emitting element drive circuit, can be automatically performed. Therefore, it is possible to simplify the adjustment work and shorten the adjustment work time, thereby making it possible to make the entire circuit more economical.

Further, according to the present invention, it is possible to add functions such as stabilizing the optical signal output in consideration of temperature changes, stopping the drive when human power is cut off, and sending out an abnormal bias current increase alarm, with a small number of powerful circuit elements. This makes it possible to simplify the entire light emitting element drive circuit, improve economic efficiency, and increase the degree of freedom in setting functions.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the configuration of one embodiment of the present invention, FIG. 2 is a block diagram showing the function of the adjustment system, FIG. 3 is a circuit diagram showing the configuration of another embodiment of the present invention, and FIG. The figure is a circuit diagram showing an example of the prior art.

Claims (1)

[Scope of Claims] 1. In a drive circuit that controls light emission of a light emitting element, a modulation section that modulates the intensity of a light output signal of the light emitting element according to an input signal, and a bias section that causes a constant current to flow through the light emitting element; The light-emitting device includes a light detection section that detects a part of the output light of the light-emitting element, a temperature detection section, a memory section, and a microcomputer, and the microcomputer adjusts the light output signal of the light-emitting element to a predetermined level. Upon receiving the adjustment signal, the adjustment signal is stored in the memory section as adjustment data, and the modulation section and the bias 1. A light emitting element driving circuit characterized by controlling a light emitting element driving circuit. 2. The microcomputer further includes a bias current detection section and an analog signal selector, and the microcomputer controls the photodetection section, the temperature detection section, and the temperature detection section via the analog signal selector.
The output signal value of the bias current detection section is taken in in a time-division manner, and the data stored in the memory section and the photodetection section are
2. The light emitting element drive circuit according to claim 1, wherein the modulation section and the bias section are controlled according to output values of the temperature detection section and the bias current detection section.