JPH10117032A - Laser diode-drive circuit and laser diode drive method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep an optical output peak power constant for holding the duty of an optical output signal in the ideal condition by respectively detecting a mean value of output voltage of data and a mean value of an output voltage depending on optical output and then giving a difference signal obtained by arithmetic calculation as a control signal of a duty variable circuit. SOLUTION: A laser diode drive circuit 1 is provided with a first arithmetic operational amplifier 10 for calculating a difference between an output voltage of a first peak value detecting circuit 9 and an output voltage of a second peak value detecting circuit 16. Moreover, a first and a second mean value detecting circuits 17, 18 are also provided for detecting each mean value of output voltages of the first and second differential amplifiers 7, 14. An output voltage of the first arithmetic operational amplifier 10 is converted into a current through a voltage-current converting circuit 11, to execute the negative feedback control to keep the peak powder of optical output constant. An output voltage of the second arithmetic operational amplifier 19 is given as the control signal of the duty variable circuit 4 to execute negative feedback control so as to keep the duty of the optical output to the ideal condition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a laser diode driving circuit and a laser diode driving method for keeping the peak power and duty of an optical output signal constant.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram for explaining a conventional laser diode driving circuit. That is, the laser diode drive circuit 1 'mainly includes a D-flip-flop 2 for retiming and outputting data based on a clock timing, a buffer 3, and a duty compensation circuit 4' for controlling a pulse width of data. And a current switch 5 for supplying a current based on the data to the laser diode 6.

An APC for obtaining a constant light output
As an (Automatic Power Control) circuit, a first differential amplifier 7 to which the voltage of data output from the buffer 3 and the voltage of the first reference voltage source 8 are input, and a peak value voltage of the output signal are detected. A first peak value detection circuit 9 and a photodiode 12 for monitoring an optical output signal of the laser diode 6 receive light,
A second differential amplifier 14 to which an output voltage obtained by converting the current by the current-voltage conversion amplifier 13 and a voltage of the second reference voltage source 15 are input, and a peak value voltage of the output signal is detected. The second peak value detection circuit 16 and the output voltage of the first peak value detection circuit 9 and the second peak value detection circuit 16
And a voltage-current conversion circuit 11 which converts an output signal from the operational amplifier 20 into a current and supplies the current to the current switch 5.

In this laser diode driving circuit 1 ',
The data input to the D-flip-flop 2 is retimed, and drives the current switch 5 via the buffer 3 and the duty compensation circuit 4 '. By driving the current switch 5, a current corresponding to the data is given to the laser diode 6 to obtain an optical output.

On the other hand, the first differential amplifier 7 includes a buffer 3
And the output of the first reference voltage source 8 are amplified and output. Here, the potential of the first reference voltage source 8 is
Is equal to the potential when the digital signal “0” is output. Then, the peak value voltage of the output signal of the first differential amplifier 7 is detected by the first peak value detection circuit 9,
It becomes a reference voltage for laser diode drive current control.

[0006] The optical output signal of the laser diode 6 is detected by the photodiode 12, converted into a voltage signal by the current-voltage conversion amplifier 13, and then input to the second differential amplifier 14. The second differential amplifier 14 amplifies the difference between this voltage signal and the voltage from the second reference voltage source 15. Here, the potential of the second reference voltage source 15 is equal to the output potential of the current-voltage conversion amplifier 13 when there is no input. Then, the peak value voltage of the output signal of the second differential amplifier 14 is detected by the second peak value detection circuit 16.

[0007] AP in light output of laser diode 6
To perform C, the peak value voltage of the first peak value detection circuit 9 detected as the reference voltage of the laser diode drive current control is applied to the positive input of the operational amplifier 20, and the peak value of the second peak value detection circuit 16 The value voltage is input to each of the negative inputs of the operational amplifier 20, and the difference is amplified. Then, the output voltage of the operational amplifier 20 is converted into a current by the voltage-current conversion circuit 11 and given as a drive current for the laser diode 6.

[0008] For example, the laser diode 6
When the optical output peak power of the operational amplifier 2 decreases, the voltage detected by the second peak value detection circuit 16 decreases.
0 output voltage rises. As a result, the drive current of the laser diode 6 is increased, and the negative feedback control is performed in a direction to increase the optical output peak power. Conversely, when the optical output peak power of the laser diode 6 increases, the voltage detected by the second peak value detection circuit 16 increases, and the output voltage of the operational amplifier 20 decreases. As a result, the drive current of the laser diode 6 is reduced, and the negative feedback control is performed in a direction to reduce the optical peak power.

The conventional laser diode drive circuit 1 'shown in FIG. 4 is called a zero-bias drive method in which a DC bias is not applied in advance. Instead of the extinction ratio of the optical output signal not deteriorating, the following ( The light emission delay time τd according to the expression (1) is generated, and the duty distortion of the optical output signal is generated.

Τd = τs · ln {Ip / (Ip−Ith)} (1)

In the equation (1), τs is the average lifetime of carriers in the laser diode, Ip is the modulation current for driving the laser diode, and Ith is the oscillation threshold current of the laser diode. Therefore, in the conventional laser diode driving circuit 1 'shown in FIG. 4, the duty distortion of the optical output signal is compensated by increasing the pulse width of the data signal input to the current switch 5 by the duty compensation circuit 4'. doing.

[0012]

However, the equation (1) includes a term such as Ip or Ith whose value changes depending on the temperature. Therefore, when the temperature changes, the light emission delay time changes, and the duty compensation of the optical output signal is distorted due to the shortage or excess of the duty compensation amount, which causes a problem that the transmission quality of the optical signal is deteriorated. is there. In addition, Idegradation due to the aging of the laser diode
p and Ith change from the initial values, causing similar problems.

In order to make the duty compensation amount follow the temperature fluctuation of the light emission delay time, a circuit for detecting the temperature and a circuit for generating and adjusting the temperature change of the compensation amount are required. Becomes complicated. Further, when adjusting the temperature change of the duty compensation amount, the temperature change amount of the drive current versus the light emission characteristic of the laser diode must be measured in advance, and a temperature test for confirming the appropriateness of the adjustment is required. Therefore, the manufacturing cost of the laser diode drive circuit becomes very large.

[0014]

SUMMARY OF THE INVENTION The present invention provides a laser diode driving circuit and a laser diode driving method which are provided to solve such problems. That is, the laser diode drive circuit according to the present invention includes a duty variable circuit that controls a pulse width of data by a control signal to adjust a pulse width of a current supplied to the laser diode, and a first circuit that detects an average value of an output voltage of data. Average value detection circuit, a second average value detection circuit for detecting the average value of the output voltage according to the light output of the laser diode, and an average value and a second average value detected by the first average value detection circuit And a calculation circuit for calculating a difference from the average value detected by the detection circuit and providing a difference signal resulting from the calculation as a control signal for the duty variable circuit.

Further, according to the laser diode driving method of the present invention, a step of detecting an average value of the output voltage of data to obtain a first average value, and a step of detecting the average value of the output voltage according to the optical output of the laser diode And obtaining a second average value, and calculating a difference between the first average value and the second average value, and controlling a pulse width of data by a difference signal obtained by the calculation.

In the laser diode driving circuit of the present invention,
The first average value detection circuit detects the average value of the output voltage of the data, and the second average value detection circuit detects the average value of the output voltage according to the light output of the laser diode. Calculates the difference between these two average values and inputs it as a control signal for the variable duty circuit. For this reason, if the control amount of the pulse width of the duty variable circuit is insufficient or exceeds, the difference in the arithmetic circuit increases or decreases, and negative feedback is performed in a direction to keep the duty constant. .

Further, in the laser diode driving method of the present invention, a difference between the average value of the output voltage of the data and the average value of the output voltage according to the optical output of the laser diode is obtained, and based on this, the pulse width of the data is obtained. Control the
The duty can be controlled to be constant with reference to the input data to the laser diode.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a laser diode driving circuit and a laser diode driving method according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram illustrating a laser diode driving circuit according to the present embodiment, and FIG. 2 is a flowchart illustrating a laser diode driving method according to the present embodiment.

First, a laser diode driving circuit according to the present embodiment will be described. As shown in FIG. 1, a laser diode drive circuit 1 of the present embodiment mainly controls a D-flip-flop 2 for retiming and outputting data based on a clock timing, a buffer 3, and a pulse width of data. And a current switch 5 for supplying a current based on data to a laser diode 6.
And

Further, as an APC circuit for the optical output of the laser diode 6, a first voltage input from the voltage of the data output from the buffer 3 and the voltage of the first reference voltage source 8 is used.
Differential amplifier 7, a first peak value detecting circuit 9 for detecting a peak value voltage of the output signal, and a laser diode 6
12 for monitoring the optical output signal of the
And a second differential amplifier 14 which receives as input the output voltage obtained by converting the current by the current-voltage conversion amplifier 13 and the voltage of the second reference voltage source 15, and the peak value of this output signal. A second peak value detection circuit 16 for detecting a voltage, a first operational amplifier 10 for calculating a difference between an output voltage of the first peak value detection circuit 9 and an output voltage of the second peak value detection circuit 16, And a voltage-current conversion circuit 11 which converts an output signal from the first operational amplifier 10 into a current and supplies the current to the current switch 5.

Further, as a characteristic part of the laser diode drive circuit 1 in the present embodiment, a first differential amplifier 7
A first average value detection circuit 17 for detecting the average value of the output voltage of the second differential amplifier 14, a second average value detection circuit 18 for detecting the average value of the output voltage of the second differential amplifier 14, and a first average value A second operational amplifier 19 is provided which receives the average value signal from the detection circuit 17 as a positive input, and receives the average value from the second average value detection circuit 18 as a negative input and supplies the operation result to the duty variable circuit 4. .

In the laser diode drive circuit 1 having such a circuit configuration, the output voltage from the first operational amplifier 10 is converted into a current through the voltage-current conversion circuit 11,
Negative feedback control for making the peak power of the optical output constant by giving it as the drive current of the laser diode 6 is performed, and the optical output is given by giving the output voltage from the second operational amplifier 19 as the control signal of the duty variable circuit 4. The negative feedback control which keeps the duty ideally is performed.

Next, a laser diode driving method according to this embodiment will be described. In the following, description will be given along the flowchart of FIG. 2, but reference numerals not shown in FIG. 2 refer to FIG. 1.

First, the input data is retimed by the D-flip-flop 2, output to the duty variable circuit 4 via the buffer 3, and the laser diode 6 is driven by the current output from the current switch 5. At this time, the peak value voltage from the first peak value detection circuit 9 and
The difference from the peak value voltage from the second peak value detection circuit 16 is calculated by the first operational amplifier 10, and the result is given to the current switch 5 via the voltage-current conversion circuit 11 to provide a light output peak. APC control is performed so that the power becomes constant.

The current output corresponding to the data shown in step S1 of FIG.
It is assumed that PC control is included. In the present embodiment, the duty is controlled in the following procedure together with the APC control.

First, as shown in step S3, a first average value is detected. The first average value is obtained by averaging the signals output from the first differential amplifier 7 by the first average value detection circuit 17. Since the first average value is obtained by averaging output signals from the first differential amplifier 7 which are good signals without duty distortion, the first average value is used as a reference in duty control.

Next, as shown in step S4, a process of detecting an optical output and converting it into a voltage is performed. That is, the light output of the laser diode 6 is detected by the photodiode 12, and the detected current is used as the current-voltage conversion amplifier 1
At 3 the voltage is converted.

Next, as shown in step S5, the second
As the detection of the average value, the output voltage from the current-voltage conversion amplifier 13 is input to the second average value detection circuit 18 via the second differential amplifier 14, and the average value is detected.

In the next step S6, the difference between the first average value output from the first average value detection circuit 17 and the second average value output from the second average value detection circuit 18 is calculated. This operation is performed by applying the first input to the positive input of the second operational amplifier 19.
The difference is obtained by inputting the average value and the second average value to the negative input.

After calculating the difference, it is determined whether or not the difference value is +, as shown in step S7. If the difference value is +, the process proceeds to step S8, and processing for increasing the data pulse width is performed. That is, when a positive difference value is output from the second operational amplifier 19,
The duty variable circuit 4 performs a process of increasing the data pulse width according to the positive difference value. Then, based on the data with the increased pulse width, an optical output is performed as shown in step S2.

If the difference value is not + in step S7, the process proceeds to step S9, and it is determined whether the difference value is-. If the difference value is-, the process proceeds to step S10, and processing for reducing the pulse width of data is performed. That is, when a negative difference value is output from the second operational amplifier 19, the duty variable circuit 4 performs a process of reducing the data pulse width according to the negative difference value. Then, the optical output shown in step S2 is performed based on the data with the reduced pulse width.

In step S9, it is determined that the difference value is not "-" when the difference value is "0". When the control proceeds to step S11 and the control is further continued, the pulse width control of the data is performed. Without returning to step S1, the above processing is repeated until the control is completed.

Here, an example of control according to the difference in duty will be described. FIG. 3 is an optical output waveform diagram according to the difference in duty. FIG.
(B) is a case where the duty control amount is insufficient, and (c) is a case where the duty control amount is excessive.

As shown in FIG. 3B, when the duty control amount is insufficient, the second average value detected by the second average value detection circuit 18 is a signal having an ideal duty. It is lower than the first average value from the first average value detection circuit 17 which is the average value of the reference waveform). In this case, the difference value in the second operational amplifier 19 is amplified, and the determination in step S7 shown in FIG. Then, the process shown in step S8, that is, this difference value is
To control so that the pulse width of data is amplified. As a result, the output pulse width is controlled to increase, and an ideal duty as shown in FIG. 3A can be obtained.

As shown in FIG. 3C, when the duty control amount is exceeded, the second average value detection circuit 1
The second average value detected at 8 is higher than the first average value from the first average value detection circuit 17 which is the average value of a signal (reference waveform) having an ideal duty. in this case,
The difference value in the second operational amplifier 19 decreases, and the determination in step S7 shown in FIG.
The determination is Yes. Then, the process shown in step S10, that is, the difference value is input to the duty variable circuit 4, and control is performed so that the pulse width of the data is reduced. As a result, the output pulse width is controlled to decrease, and an ideal duty as shown in FIG. 3A can be obtained.

In the present embodiment, since the duty is controlled in an ideal direction together with the APC control for the light output of the laser diode, a constant light output and a constant duty can be obtained even if there is a temperature fluctuation or the like. become able to.

[0037]

As described above, the laser diode driving circuit and the laser diode driving method of the present invention have the following effects. In other words, in addition to a negative feedback circuit that keeps the optical output peak power constant, a negative feedback circuit that ideally keeps the duty of the optical output signal is provided. It is possible to obtain a good light output without being affected. This makes it possible to drive the laser diode stably while maintaining the ideal duty. In addition, the manufacturing cost of the laser diode drive circuit can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a laser diode drive circuit according to an embodiment.

FIG. 2 is a flowchart illustrating a laser diode driving method according to the embodiment.

FIG. 3 is an optical output waveform diagram.

FIG. 4 is a block diagram illustrating a conventional laser diode drive circuit.

[Explanation of symbols]

1 Laser diode drive circuit 2 D-
Flip-flop 3 Buffer 4 Duty variable circuit 5 Current switch 6 Laser diode 7 First differential amplifier 9 First
Peak value detection circuit 10 first operational amplifier 12 photodiode 14 second differential amplifier 16 second peak value detection circuit 17 first average value detection circuit 18 second average value detection circuit 19 second operation amplifier

Claims (2)

[Claims] 1. A laser diode drive circuit for applying a current corresponding to a pulse width of predetermined data to a laser diode to emit light, wherein the pulse width of the data is controlled by a control signal to control the current supplied to the laser diode. A duty variable circuit that adjusts a pulse width; a first average value detection circuit that detects an average value of an output voltage of the data; and a second that detects an average value of an output voltage according to an optical output of the laser diode. An average value detection circuit; an average value detected by the first average value detection circuit;
Calculate the difference from the average value detected by the average value detection circuit of
A calculation circuit for providing a difference signal obtained by the calculation as a control signal of the duty variable circuit. 2. A method of driving a laser diode to emit a current by applying a current corresponding to a pulse width of predetermined data to a laser diode, wherein an average value of an output voltage of the data is detected to obtain a first average value. Detecting an average value of the output voltage according to the light output of the laser diode to obtain a second average value; and calculating a difference between the first average value and the second average value. Controlling the pulse width of the data by a difference signal obtained by the calculation.