JPH09214053A - Light output control circuit - Google Patents

Abstract

A logical sum circuit that logically sums input data and a control signal that specifies a period during which intermittent control is performed,
A light emitting element that generates a light output, a current switch that opens and closes a current supplied to the light emitting element by the output of the OR circuit, a current source that determines a current supplied to the light emitting element, and an output light of the light emitting element. Circuit for electrically converting a part of the output voltage to generate a monitor voltage proportional to the output light, an error amplifier for generating an output according to the difference between the monitor voltage and a predetermined reference voltage, and a control signal for conducting. , An analog switch whose non-conduction is controlled, and detects the DC output of the error amplifier while the analog switch is conducting, and holds the detected DC output when the analog switch is non-conducting A direct current holding circuit, and the current of the current source is controlled by the output of the direct current holding circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an intermittent control optical output control circuit that can be realized at a low cost, and a stable optical output is provided in the optical output control circuit that controls the envelope of the optical output. The present invention relates to a light output control circuit for intermittently controlling the light output.

Optical technology is now applied not only to optical communication, but also to an extremely wide field such as OA equipment such as printers and disk storage devices used for computers and AV equipment. Further, in the field of optical communication, it is applied to a device for testing an optical-electrical conversion device as well as an electric-optical conversion device that provides a communication function. Therefore, the function of the light output control circuit for controlling the light output of the light emitting element such as a laser diode has various functions.

For example, in a printer, intermittent light output control is performed in which the light output is controlled by using the time between the end of printing one line and the line feed. The tendency for personal use of various OA equipment and improvement of the quality of equipment for personal use is the same for printers, and there is a strong demand for lowering the cost of the optical output control circuit used for intermittent optical output control. Has been done.

Further, in the optical communication system, when the vibration applied from the outside of the device is applied to the optical connector section or the optical fiber is bent with a small radius of curvature, the light level suddenly changes. For this reason, the optical-electrical conversion device is required to have resistance to a sudden change in light level, and a test device having a function of controlling the envelope of the optical output has been put to practical use in order to test the resistance to this sudden change in light. . Generally, it cannot be said that the use environment of the test apparatus is always managed in a preferable state, but it is required to realize a test apparatus that operates stably in such a use environment. Furthermore, it is also extremely important to reduce the cost of the test equipment. Therefore, it is necessary to stabilize and reduce the cost of the optical output control circuit that controls the envelope of the optical output.

[0005]

2. Description of the Related Art FIG. 8 shows a conventional optical output control circuit for performing intermittent control. In FIG. 8, 1 is a logical sum circuit that takes the logical sum of input data and a control signal, 2 is a current switch that is on / off controlled by the output of the logical sum circuit, 3
Is a current source that determines a current supplied to a laser diode described later through the current switch, 4 is a laser diode that supplies output light, and 5 is a laser diode that receives back light of the laser diode. A photo diode for monitoring the light output, 6 is a resistor for converting the current of the photo diode into a voltage, 7 is a reference voltage source for generating a reference voltage to be supplied to a comparator described later, 13 is a pulse generator, and 14 is An AND circuit for supplying the output signal of the pulse generator to the counter described later only when the control signal designating the period for performing the optical output control is "1", and 15 is the control signal and a comparator described later. AND circuit that calculates the logical product of the signals and outputs a signal designating the counting direction to a counter, which will be described later.
A counter 6 counts the output of the logical product circuit 14 whose count direction is controlled by the output of the logical product circuit 15 in addition to whether the count is controlled by the control signal.
Reference numeral 7 is a digital-analog converter for converting the count value of the counter to analog, and 18 is a comparator for outputting "0" or "1" according to the magnitude of the output of the reference voltage source and the terminal voltage of the resistor 6. Is.

FIG. 9 is a time chart of the configuration of FIG. The operation of the configuration shown in FIG. 8 will be described below with reference to FIGS. 8 and 9. As described above, the control signal is a signal that designates a period during which intermittent light output control is performed, and the control signal is "1".
The control signal is supplied to the input terminal of the current switch and the enable terminal of the counter because the light output is controlled by closing the loop only during the period. Then, the input data is supplied while the control signal is "0". The current switch 2 is fixed to ON when the control signal is "1", and it is necessary to repeat ON and OFF depending on the input data. Therefore, it is necessary to supply the logical sum of the control signal and the input data to the input terminal of the current switch.

First, when the control signal is "1", the counter 19 becomes countable, and at the same time, the output of the pulse generator is supplied to the counter, and at the same time, the current switch is turned on and the laser diode 4 is turned on. When a current is supplied, the laser diode 4 outputs light. Part of the output light (called pack light) is incident on the photodiode 5,
The photodiode 5 passes a current according to the intensity of the incident light. This current supplies the voltage generated in the resistor 6 to the inverting input terminal of the comparator 18 and compares it with the reference voltage supplied to the non-inverting input terminal of the comparator 18. The comparator 18 outputs "1" when the terminal voltage of the resistor 6 is lower than the reference voltage. Since the control signal is now "1", the output "1" of the comparator 18 is supplied to the up / down control terminal of the counter 16 and advances the count of the counter 16. The count value of the counter 16 is digital-
It is supplied to the analog converter 17 for analog conversion, and the output of the digital-analog converter 17 is supplied to the control terminal of the current source 3. Therefore, the current of the current source 3 increases in accordance with the increment of the count value of the counter 16. The monitor voltage of the optical output generated in the resistor 6 rises corresponding to this increased current. In this way, when the monitor voltage rises and exceeds the reference voltage, the comparator 16 outputs "0". This time,
Since the AND circuit 15 outputs "0", the counter 16
Decrements the count value. As a result, the output of the digital-analog converter 17 is reduced and the laser diode 4
Current also decreases, and the monitor voltage also decreases. If the lowered monitor voltage is lower than the reference voltage, the comparator is again "1".
Is output, and the counter increments the count by this "1". That is, when the monitor voltage becomes a voltage close to the reference voltage, the counter 16 repeats stepping and backward counting, and the output of the digital-analog converter 17 also stabilizes at a substantially constant value. The above is the control state when the monitor voltage starts from the state lower than the reference voltage, but the control when the monitor voltage starts from the state higher than the reference voltage is only in the opposite direction to the digital- It is the same that the output voltage of the analog converter 17 settles down to a substantially constant value. Since it is easy to set the error of the output voltage of the digital-analog converter 17 at this time to the minimum step of the digital-analog converter 17, the error voltage can be ignored. And in FIG.
In, the area in which the broken vertical line is drawn on the output of the comparator shows the above-mentioned situation.

Next, when the control signal becomes "0", the counter 16 cannot count, so the count value is fixed. Therefore, the output voltage of the digital-analog converter 17 is also fixed, and the current of the current source 3 is fixed. Since the input data is supplied to the current switch 2 in this state, the current switch 2 turns on and off the current of the current source 3 to drive the laser diode 4. Therefore, when the input data is "1", a current equal to the current determined while the control signal is "1" flows through the laser diode, and the optical output corresponding to the input data "1" is also kept constant. Be done. By the way, during this period, when the input data is "0", the comparator 21 outputs "1", and when the input data is "1", the comparator outputs it just before the control signal changes to "0". The logic level is output from the digital-analog converter. However, no matter what logic level the comparator outputs, it is blocked by the control signal in the AND circuit 15 and the counter 16 cannot count. The output of 17 has no effect. In that sense, the output of the comparator 18 when the control signal is "0" is represented by "0" for convenience.

Incidentally, FIG. 10 shows the details of the circuit around the laser diode in FIG. In FIG. 10, 2-1 and 2-2 are transistors, 2-3 is a negative circuit, and 2-1 to 2-3 form a current switch. 3-1 is a transistor, 3-2 is a resistor, 3-
A current source is constituted by 1 and 3-2. 4, 5 and 6 are the same as in FIG. Although FIG. 10 will not be described further, it will be easier to understand the above description with reference to FIG.

FIG. 11 shows a conventional optical output control circuit (No. 1) for controlling the envelope of optical output. FIG. 11A shows the configuration and FIG. 11B shows the optical output. Figure 11 (a)
In the figure, 20 is a pulse generator, 21 is an electro-optical converter that converts an electric signal into an optical signal, and 22 is, for example, a lithium
An external modulator using niobate, 23 is a signal generator for controlling the envelope of the optical output, and is, for example, a triangular wave generator.

The output of the pulse generator 20 is supplied to the electro-optical converter 21 and modulates the output light of the light-emitting element forming the electro-optical converter 21. That is, the electro-optical converter 21 outputs an optical signal whose envelope has a constant level, which is turned on and off by the output of the pulse generator 20, and supplies the optical signal to the input terminal of the external modulator 22. The input signal of the external modulator 22 is
Since the signal supplied to the control signal terminal of the external modulator 22 is modulated by the amplitude of the signal to be output, when the signal supplied to the control signal terminal is a triangular wave, the phase of the input signal corresponding to the triangular wave is used. The envelope changes into a triangular wave,
An optical signal having an envelope as shown in 1 (b) is output. Therefore, the optical level can be suddenly changed by the triangular wave supplied to the control signal terminal of the external modulator 22.

However, the configuration of FIG. 11 has some problems. In particular, when the external modulator is composed of lithium niobate, a remarkable problem is the influence of the drift characteristic shown in FIG. The optical output of the external modulator using lithium niobate can be approximated by the sinusoidal function of the control voltage supplied to the control signal terminal. Now, when the triangular wave input is applied when the relationship between the control voltage and the optical output is in the state of the broken line,
The triangular wave output (approximated by) of the broken line drawn to the right of the curve of the optical output characteristic is obtained. However, there is a non-negligible drift in the light output characteristics. As a result of the drift, when the relationship between the control voltage and the light output becomes as shown by the solid line, the light output with respect to the control voltage of the triangular wave becomes the output of the solid wave triangular wave (approximated by) drawn on the right of the curve of the light output characteristic. . Therefore,
As a result of the drift, non-negligible fluctuations occur in the light output. In this case, it cannot be used as a test device for testing the proof stress of the opto-electrical conversion device against sudden changes in light level. Further, in the external modulator using lithium niobate, it is necessary to fix the polarization of the incident light to the external modulator, and there is also a problem that the cost of the external modulator is high.

Therefore, what has been developed is a conventional optical output control circuit (part 2) for controlling the envelope of the optical output shown in FIG.
It is. In FIG. 13, 2 is a current switch, 3 is a current source, 4 is a laser diode, 5 is a photo diode, 6 is a resistor, 7 is a reference voltage source for supplying a reference voltage to an error amplifier described later, and 8 is the reference. An error amplifier that outputs a voltage corresponding to the difference between the voltage and the output voltage of an average value holding circuit described later, 12 is an adder circuit that adds the output of the error amplifier and the output of a triangular wave generator described later, and 19 is a triangular wave generator ,
An average value holding circuit 25 holds the average value of the voltage generated in the resistor 6.

In the configuration of FIG. 13, the photo diode 5 generates a current proportional to the optical output of the laser diode 4, and the resistor 6 converts the current into a monitor voltage. The average value holding circuit 24 holds the average value of the monitor voltage and supplies it to the inverting input terminal of the error amplifier 8. The error amplifier 8 outputs a voltage according to the difference between the output voltage of the average value holding circuit 24 and the reference voltage, and the summing amplifier 1
Feed to 2. The summing amplifier 12 controls the current source 3 by generating a voltage obtained by adding the output of the error amplifier 8 and the output of the triangular wave generator 19. In this way, feedback control is performed so that the output voltage of the average value holding circuit 24 becomes equal to the reference voltage, and the output of the laser diode 4 becomes constant at the point where the output voltage of the average value holding circuit 24 becomes equal to the reference voltage. .
At this time, it is necessary to make the discharge time constant of the average value holding circuit 24 much longer than the duration of the triangular wave.

According to the configuration of FIG. 13, it is possible to solve all the problems of drift, polarization fixing, and cost, which have been problems in the configuration of FIG.

[0016]

In the configuration of FIG. 8, a pulse generator, a counter and a digital / analog converter are used for intermittently controlling the light output. Since these are relatively expensive elements, there arises a problem that the price of the optical output control circuit for performing intermittent control increases.

Therefore, an object of the present invention is to provide an optical output control circuit which is intermittently controlled at a low price. In the configuration of FIG. 13, when the triangular wave has a long duration and cannot be ignored with respect to the discharge time constant of the average value holding circuit, the held average value is affected by the triangular wave. There is an error in the level of the flat part of the envelope.

Therefore, an object of the present invention is to provide an optical output control circuit for controlling the envelope of optical output, in which the level of the flat portion of the envelope of optical output is not affected by the triangular wave.

[0019]

FIG. 1 shows an embodiment of a light output control circuit for intermittently controlling the present invention. In FIG. 1, reference numeral 1 is a logical sum circuit for taking a logical sum of a control signal designating feedback for performing optical output control and input data, 2 is a current switch whose on / off control is performed by the output of the logical sum circuit, Reference numeral 3 is a current source for determining a current supplied to a laser diode described later through the current switch, 4 is a laser diode for generating output light, and 5 is a photo diode for electrically converting back light of the laser diode. , 6 is a resistor for converting the current of the photodiode into a monitor voltage, 7 is a reference voltage source for supplying a reference voltage, and 8 is an output corresponding to the difference between the output of the peak value holding circuit and the reference voltage. Error amplifier for generating a 9 control signal is "1"
An analog switch (indicated as SW in the figure) that conducts only during the period 10 is a peak value that holds the peak value of the output of the error amplifier and is a voltage for controlling the current of the current source 3. It is a holding circuit.

For details of the circuit around the laser diode, refer to FIG. FIG. 2 is a time chart of the configuration of FIG. Hereinafter, the operation of the configuration of FIG. 1 will be described with reference to FIGS.

The control signal is a signal for designating a period for performing intermittent light output control. Since the light output control is performed by closing the loop only while the control signal is "1", the analog switch 9 is opened / closed by the control signal. To do. Then, the input data is supplied while the control signal is "0". Current switch 2
Is fixed to ON when the control signal is "1", and it is necessary to repeat ON and OFF depending on the input data. Therefore, it is necessary to supply the logical sum of the control signal and the input data to the input terminal of the current switch 2.

First, when the control signal is "1", the current switch 2 is turned on to supply current to the laser diode 4, and the laser diode 4 outputs light. A part of the output light is incident on the photo diode 5, and the photo diode 5 supplies a current according to the intensity of the incident light. The voltage generated by this current in the resistor 6 is the monitor voltage. The monitor voltage is supplied to the inverting input terminal of the error amplifier 8. Further, the reference voltage is supplied to the non-inverting input terminal of the error amplifier, and the error amplifier 8 generates a voltage corresponding to the difference from the monitor voltage. Now, considering that the control voltage is "1", the analog switch 9 is conducting. Therefore, the output of the error amplifier 8 is supplied to the peak value holding circuit 10 and the peak value is detected. The detected peak value is supplied to the current source 3 and controls the current of the current source 3. In this way, feedback is applied so that the monitor voltage becomes equal to the reference voltage, and finally the output of the laser diode 4 becomes the desired output at the point where the monitor voltage becomes equal to the reference voltage. The output voltage of the holding circuit 10 also becomes constant.

Next, when the control signal becomes "0", the analog switch 9 becomes non-conductive, so that the peak value holding circuit 10
Is disconnected from the error amplifier 8 and continues to hold the output voltage which has become constant. At this time, the input data is supplied to the current switch 2, the current switch 2 does not supply the current to the laser diode 4 when the input data is “0”, and the current switch 2 when the input data is “1”. Supplies current to the laser diode 4. Since this current is determined by the voltage held by the peak value holding circuit 10, the laser diode 4 when the input data is "1".
The optical output of the optical signal is equal to the expected output set while the control signal is "1".

After this, when the control signal becomes "1" again,
The light output control loop is closed and the light output control is restarted. Ideally, since the peak value holding circuit 10 supplies the desired voltage to the current source 3 at this time, no change occurs due to the loop being closed. However, since the actual discharge time constant of the peak value holding circuit is not infinite, the holding voltage of the peak value holding circuit 10 is slightly decreased, and the output of the laser diode 4 is also decreased accordingly. . Therefore, when the control signal becomes "1" again, the control is performed only to correct the decrease in the holding voltage of the peak value holding circuit 10.

As described above, the configuration of FIG. 1 realizes an optical output control circuit for performing intermittent control by using only the elements and circuits used in a normal optical output control circuit, a pulse generator and a counter. Device, digital / analog converter is not required. Therefore, the light output control circuit for intermittently controlling the configuration of FIG. 1 can be realized at a lower cost than the conventional light output control circuit for intermittently controlling.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Although not shown in FIG. 1, the impedance of the peak value holding circuit 10 in consideration of the current source 3 from the output terminal of the peak value holding circuit 10 is set to be sufficiently high so that the peak value holding circuit 10 can be controlled. It is necessary to keep the discharge time constant large during the period when the control signal is "0".

Further, although the example of using the peak value holding circuit is shown in FIG. 1, the present invention is not limited to the peak value holding circuit, and an analog signal is provided while the control signal is "0". Since the output of the error amplifier 8 is cut off by the switch 9, an average value holding circuit may be used. That is, the "DC holding circuit" may be used at the position of the peak value holding circuit in FIG. This also applies to the embodiments described below.

FIG. 3 shows a second embodiment of the light output control circuit for intermittently controlling the present invention. In FIG. 3, 1
Is a logical sum circuit for taking a logical sum of a control signal designating feedback for performing optical output control and input data, 2 is a current switch whose on / off is controlled by the output of the logical sum circuit,
Reference numeral 3 is a current source for determining a current supplied to a laser diode described later through the current switch, 4 is a laser diode for generating output light, and 5 is a photo diode for electrically converting back light of the laser diode. , 6 is a resistor for converting the current of the photodiode into a monitor voltage, 7 is a reference voltage source for supplying a reference voltage, and 8 is an output corresponding to the difference between the output of the peak value holding circuit and the reference voltage. An analog amplifier (denoted as SW in the figure) which conducts only while the control signal is "1", and a peak which holds the peak value of the output of the error amplifier. A value holding circuit, 11 is a comparator that outputs “0” or “1” according to the magnitude of the input data and the voltage of a threshold voltage source described later, and 12 is the addition of the input data and the output of the peak value holding circuit 10. Adder circuit, 4 is a threshold voltage source for generating a threshold voltage for determining whether the level of the input data is a significant level.

For details of the circuit around the laser diode, refer to FIG. The configuration of FIG. 3 is characterized in that the light output control can be intermittently performed even when the input data is multi-valued data (multi-gradation data).

FIG. 4 is a time chart of the configuration of FIG. The operation of the configuration of FIG. 3 will be described below with reference to FIGS. 3 and 4. The control signal is a signal designating a period for performing intermittent light output control. Since the control signal closes the loop to perform light output control, the analog switch 9 is opened / closed by the control signal. Then, the input data is supplied while the control signal is "0". The current switch 2 is controlled by a control signal and input data. When the input data is multi-valued data, it is converted into binary by comparing with a threshold voltage in a comparator, and the input data converted into the binary is used. The logical sum with the control signal is supplied to the current switch 2. The current switch 2 is fixed to ON when the control signal is "1", and repeats ON and OFF according to the binarized input data.

First, when the control signal is "1", the current switch 2 is turned on to supply a current to the laser diode 4, and the laser diode 4 outputs light. A part of the output light is incident on the photo diode 5, and the photo diode 5 supplies a current according to the intensity of the incident light. The voltage generated by this current in the resistor 6 is the monitor voltage. The monitor voltage is supplied to the inverting input terminal of the error amplifier 8. Further, the reference voltage is supplied to the non-inverting input terminal of the error amplifier, and the error amplifier 8 generates a voltage corresponding to the difference from the monitor voltage. Now, considering that the control voltage is "1", the analog switch 9 is conducting. Therefore, the output of the error amplifier 8 is supplied to the peak value holding circuit 10 and the peak value is detected. The detected peak value is supplied to the adder circuit 12 and added with the input data to control the current of the current source 3. At this time, since the input data continues to be "0", it is the output of the peak value holding circuit 10 that controls the current of the current source 3. Feedback is applied so that the monitor voltage becomes equal to the reference voltage, and finally the output of the laser diode 4 becomes the desired output at the point where the monitor voltage becomes equal to the reference voltage, and the peak value holding circuit 10 is reached. The output voltage of is also constant.

Next, when the control signal becomes "0", the analog switch 9 becomes non-conductive, so the peak value holding circuit 10
Is disconnected from the error amplifier 8 and continues to hold the output voltage which has become constant. At this time, the current switch 2 is supplied with the binarized input data, and when the binarized input data is “0”, the current switch 2 does not supply the current to the laser diode 4 and The current switch 2 supplies a current to the laser diode 4 when the digitized input data is "1". Since this current is determined by the output voltage of the adder circuit 12, when the input data is not "0", the laser diode 4 outputs light having an intensity corresponding to the amplitude of the input data. At this time, analog
Since the switch 9 is non-conductive, the monitor voltage changes according to the amplitude of the input data, but the change does not affect the peak value holding circuit 10.

After this, when the control signal becomes "1" again,
The light output control loop is closed and the light output control is restarted. Ideally, the peak value holding circuit 10 holds the desired voltage at this time, so that there is no change due to the loop being closed. However, since the actual discharge time constant of the peak value holding circuit is not infinite, the peak value holding circuit 10
The holding voltage of the
The output of is decreasing accordingly. Therefore, when the control signal becomes "1" again, the control is performed only to correct the decrease in the holding voltage of the peak value holding circuit 10.

In this way, with the configuration of FIG. 3, it is possible to realize a light output control circuit which simply controls even if input data is multi-valued data. FIG. 5 shows details of the adder circuit in FIG.

In FIG. 5, reference numeral 12-1 is an operational amplifier forming a voltage follower, 12-2 is an operational amplifier for performing addition, and 12-3 to 12-5 are resistors. The operational amplifier 12-1 is used to increase the load impedance of the peak value holding circuit 10 so that the electric charge corresponding to the peak value voltage detected by the peak value holding circuit 10 is not discharged. Therefore, while the control signal is "0" and the analog switch 9 is non-conducting, the peak value voltage detected by the peak value holding circuit 10 is the input side of the peak value holding circuit 10. It is held without being discharged to the output side.

FIG. 6 shows an embodiment of the optical output control circuit for controlling the envelope of the optical output of the present invention. In FIG.
Reference numeral 2 is a current switch that opens and closes according to input data to control a current of a laser diode described later. Reference numeral 3 is a current source that determines a current supplied to the laser diode through the current switch. Reference numeral 4 is a laser that outputs light. Diode, 5
Is a photo diode for converting the back light of the laser diode into a current, 6 is a resistor for converting the current of the photo diode into a monitor voltage, and 7 is a reference voltage for supplying a reference voltage to an error amplifier described later. Source, 8 is an error amplifier that outputs a voltage according to the difference between the monitor voltage and the reference voltage,
Reference numeral 9 is an analog switch whose conduction and non-conduction are controlled by a control signal. Reference numeral 10 is a peak value holding circuit which holds the peak value by receiving the output of the error amplifier when the analog switch 9 is conductive. An adder circuit for adding an output of the peak value holding circuit and an output of a triangular wave generator described later, and 19 is a triangular wave generator for generating a triangular wave which is a signal for controlling the envelope curve in synchronization with the control signal.

FIG. 7 is a time chart of the configuration of FIG. The operation of the configuration of FIG. 5 will be described below with reference to FIGS. 6 and 7. The output of the triangular wave generator is a waveform in which the amplitude is reduced like a triangular wave with a part of the DC voltage as shown in the "triangular wave" in FIG. 7, and the triangular wave portion is repeated in synchronization with the control signal.

On the other hand, the input data is applied to the current switch 2, and when the level is "0", the laser diode 4
When the level is "1", the current of the current source 3 is supplied to the laser diode 4.

When a current is supplied to the laser diode 4, the laser diode 4 outputs light, and the back light is incident on the photo diode 5. The photodiode 5 converts the packed light into a current and causes it to flow through the resistor 6.
A current-voltage conversion is performed in the resistor 6, and a monitor voltage proportional to the light output of the laser diode 4 is obtained.

The error amplifier 8 outputs a voltage according to the difference between the monitor voltage and the reference voltage. Since the analog switch 9 is conducting while the control signal is "1", the output voltage of the error amplifier 8 is supplied to the peak value holding circuit 10 to detect the peak value. The detected peak value and the triangular wave output of the triangular wave generator are guided to an adding circuit and added. The current of the current source 3 is controlled by the added voltage, and the monitor voltage corresponding to the controlled current is supplied to the inverting input terminal of the error amplifier. While the control signal is "1", the output of the error amplifier is supplied to the peak value holding circuit 10, the voltage detected by the peak value holding circuit is changed, and the current source 3 is turned on again.
To control the current. In this way, the control signal is "1".
During this period, feedback is applied so that the voltages at the two input terminals of the error amplifier become equal, and the voltage detected by the peak value holding circuit 10 becomes a predetermined value.

When the control signal becomes "0" in this state, the analog switch 9 becomes non-conductive, so that the held charges are not discharged to the input side of the peak value holding circuit 10. If the impedance of the input terminal on the peak value holding circuit 10 side of the adder circuit is very high, the peak value holding circuit 1
The charge held by 0 is not discharged to the output side, and the output voltage of the peak value holding circuit 10 is kept constant. Therefore, the voltage held by the peak value holding circuit 10 and the voltage obtained by adding the triangular wave are kept constant when the control signal becomes "0". The details of the adder circuit will be described later.

In this state, when the output of the triangular wave generator changes its amplitude in a triangular wave shape, the output of the adder circuit changes its amplitude in a triangular wave shape at that portion. Therefore, the current source 3
Current drops in a triangular waveform, and the optical output also drops in a triangular waveform. The monitor voltage also changes in response to this change in optical output,
Although it reaches the inverting input terminal of the error amplifier 8, since the sample or pulse is "0" and the analog switch 9 is non-conductive, the influence of the change of the monitor voltage is influenced by the peak value holding circuit 10.
I can't tell you. Therefore, the envelope of the optical output is reduced to a triangular wave shape only at the triangular wave portion, and the amplitude of the envelope curve for the portion where the output of the triangular wave generator is constant does not change.

After this, when the control signal becomes "1" again,
The light output control loop is closed again and the light output control is restarted. Ideally, the peak value holding circuit 10 holds the desired voltage at this time, so that there is no change due to the loop being closed. However, in the actual peak value holding circuit, the holding voltage is slightly lowered, and the output of the laser diode 4 is also lowered accordingly. Therefore, when the control signal becomes "1" again, the peak value holding circuit 10
Therefore, control is performed only to correct the decrease in the holding voltage of.

With the configuration of FIG. 6, the problems of the configuration of FIG. 10, such as drift, fixed polarization, and the price of the element used, are affected by the triangular wave portion, and the level of the flat portion of the envelope changes. The problem of the configuration of FIG. 13 is solved.

The configuration of FIG. 5 can also be used as the adder circuit of FIG. That is, the peak value holding circuit 1 of FIG.
Connect the output terminal of 0 to the input terminal of the operational amplifier 12-1, connect the output terminal of the triangular wave generator of FIG. 6 to the resistor 12-3, and connect the output terminal of the operational amplifier 12-2 to the current source 3. Good.

[0046]

As described above in detail, according to the present invention, it is possible to reduce the cost of the optical output control circuit for performing intermittent control and to improve the stability and cost of the optical output control circuit for controlling the envelope of the optical output. Can be realized.

Since the optical technique is widely applied and it is considered that the tendency will be further advanced in the future, the present invention can contribute to the industrial development in a wide field.

[Brief description of drawings]

FIG. 1 is an embodiment of an optical output control circuit for intermittently controlling the present invention.

FIG. 2 is a time chart of the configuration of FIG.

FIG. 3 is a second embodiment of an optical output control circuit for intermittently controlling the present invention.

FIG. 4 is a time chart of the configuration of FIG.

FIG. 5 shows details of the adder circuit in FIG.

FIG. 6 is an embodiment of an optical output control circuit for controlling an envelope of the present invention.

7 is a time chart of the configuration of FIG.

FIG. 8 is a conventional light output control circuit for intermittently controlling.

9 is a time chart of the configuration of FIG.

10 is a detailed circuit diagram around the laser diode in FIG.

FIG. 11 is a conventional optical output control circuit for controlling an envelope (No. 1).

FIG. 12 is a problem with the configuration of FIG.

FIG. 13 is a conventional optical output control circuit for controlling an envelope (Part 2).

[Explanation of symbols]

 1 OR circuit 2 Current switch 3 Current source 4 Laser diode 5 Photo diode 6 Resistance 7 Reference voltage source 8 Error amplifier 9 Analog switch 10 Peak value holding circuit

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H04B 10/14 10/04 10/06

Claims (3)

[Claims] 1. A logical sum circuit for taking a logical sum of input data and a control signal designating a period during which intermittent control is performed, a light emitting element for generating a light output, and the light emission by the output of the logical sum circuit. A current switch that opens and closes the current supplied to the element, a current source that determines the current supplied to the light emitting element, and a part of the output light of the light emitting element is electrically converted to generate a monitor voltage proportional to the output light. Monitor circuit, an error amplifier that generates an output according to the difference between the monitor voltage and a predetermined reference voltage, an analog switch whose conduction and non-conduction are controlled by the control signal, and the analog switch that is conductive. And a DC holding circuit that holds the detected DC output when the analog switch is non-conducting, and the DC output of the error amplifier is detected by the output of the DC holding circuit. Light output control circuit and controlling the current. 2. The optical output control circuit according to claim 1, further comprising a comparator for comparing input data with a predetermined threshold voltage and binarizing the input data, and the ORing circuit for binarizing the binarized input. An adder circuit for controlling the opening and closing of the current switch by taking the logical sum of the data and the control signal and for adding the output voltage of the DC holding circuit and the input data in an analog manner is provided. A light output control circuit, wherein the current of the current source is controlled by the following. 3. The optical output control circuit according to claim 1, wherein a waveform generator intermittently generates a predetermined waveform at a timing different from the control signal, an output voltage of the waveform generator, and the DC holding circuit. And an adder circuit for analogically adding the output of the current source, and controlling the current of the current source by the output of the adder circuit.