JPH04283978A - Laser diode drive circuit - Google Patents

Abstract

PURPOSE:To achieve a laser diode drive circuit with a low power consumption and a high-speed operation. CONSTITUTION:A title item is provided with a pulse bias generation means 20 which is turned on by an input signal and a drive current generation means 30 which is turned on by the input signal where a drive current of a laser diode 10 is equal to a sum of a pulsive bias current which is generated by the pulse bias generation means 20 and a pulsive drive current which is generated by the above drive current generation means 30.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for driving a laser diode. In recent years, with the development of optical communications, the optical signals used there have also become higher output and faster. On the other hand, in order to make devices more economical, there is a demand for smaller size and lower power consumption, and each circuit that constitutes the device also needs to be smaller.

[0002] Laser diode drive circuits used in such optical communications are also required to be capable of high-speed operation with low power consumption.

0003

2. Description of the Related Art FIG. 7 shows a diagram illustrating a conventional example. In the figure, 10 is a laser diode, 21 and 32 are transistors, and R1 and R2 are resistors.

The current-light output characteristic of the laser diode 10 is such that when the driving current is below a certain constant, almost no optical output is generated, and when the driving current exceeds the threshold current Ith, an optical output proportional to the driving current is obtained.

Therefore, in FIG. 7, a bias power source is applied to the transistor 21, and a bias current Ib equivalent to the threshold current Ith is constantly caused to flow through the laser diode 10.

When there is an input signal, the drive current Id is caused to flow by turning on the transistor 32 according to the input signal, and the bias current I flowing through the transistor 21 is
The laser diode 10 is driven by a current that is the sum of the driving current Id flowing through the transistor 32 and the driving current Id flowing through the transistor 32, thereby emitting light.

[0007]

FIG. 8 shows a diagram illustrating drive current in a conventional example. In the figure, the horizontal axis shows the current I, and the vertical axis shows the optical output L. In FIG. 8, a current equal to the threshold current Ith is constantly caused to flow as a bias current Ib (shown by shading) through the transistor 21 and resistor R1 of the circuit in FIG. The current becomes the sum of the bias current Ib flowing through the transistor 21 and the drive current Id flowing through the transistor 32, and light is emitted. However, in this circuit, the threshold current Ith is always used as the bias current Ib.
Since a current equal to , is flowing, the power consumption increases.

The present invention attempts to realize a laser diode drive circuit that can operate at high speed with low power consumption.

[0009]

Means for Solving the Problems FIG. 1 is a block diagram illustrating the principle of the present invention. 10 in the figure is a laser diode, 20 is a pulse bias generation means that is turned on by an input signal, 30 is a drive current generation means that is turned on by an input signal, and the laser diode 1
The drive current of 0 is defined as the sum of the pulsed bias current generated by the pulse bias generation means 20 and the pulsed drive current generated by the drive current generation means 30.

Further, by turning on the drive current generating means 30 by the output of the delay circuit 31 which delays the input signal by a predetermined time, the driving current generating means 30 is turned on.
A bias current is caused to flow a predetermined period of time prior to the timing when .

[0011]

[Operation] The current flowing through the laser diode 10 is the sum of the pulsed bias current generated by the pulse bias generation means 20 and the drive current generated by the drive current generation means 30.

Since the bias current flows only when the input signal is "high", power consumption can be reduced. Further, the drive current generating means 30 is turned on with an output obtained by delaying the input signal by a predetermined time by the delay circuit 31. Since the pulse bias generating means 20 receives an input signal that is not delayed, the pulse bias current has the same timing as the input signal.

[0013] Therefore, the bias current is turned on a predetermined period of time prior to the timing at which the drive current flows through the laser diode 10, making it possible to perform high-speed operation with low power consumption.

[0014]

Embodiment FIG. 2 is a diagram illustrating an embodiment of the present invention. This is an example in which the pulse bias generating means 20 described in the principle diagram of FIG.

FIG. 3 is a diagram illustrating the driving current in the embodiment of the present invention. The shaded area is the threshold current It
As for the bias current Ib corresponding to h, the bias current flows only while the input signal is "high", making it possible to reduce power consumption.

FIG. 4 is a diagram illustrating another embodiment of the present invention. The configuration shown in the figure is based on the embodiment explained in FIG.
1 has been added.

In FIG. 3, since the current flowing through the laser diode 10 rises instantaneously from "0" to "Ib+Id", the optical output of the laser diode 10 cannot follow it and the high-speed characteristics deteriorate. The circuit shown in FIG. 4 improves this problem.

FIG. 5 is a time chart of another embodiment of the present invention, in which ``■'' to ``■'' indicate waveforms at points ``■'' to ``■'' in FIG. The operation of the circuit shown in FIG. 4 will be explained with reference to the time chart shown in FIG.

■ Indicates an input signal. ■ This is a signal obtained by delaying the input signal ■ by Δt. ■ This is the output of the OR circuit 22 which inputs the signals of ■ and ■.

The transistor 21 for generating a bias current is driven by the signal (2), turns "on" at the same time as the input signal becomes "high", and causes a bias current Ib to flow through the laser diode 10. On the other hand, the input signal delayed by the delay circuit 31 is applied to the transistor 32, and the driving current Id is caused to flow through the laser diode 10.

Therefore, since the drive current Id of the laser diode 10 flows Δt after the bias current Ib flows, the optical output can follow the drive current Id, and high-speed operation is possible.

FIG. 6 is a diagram illustrating the drive current of another embodiment of the present invention. The shaded part is the bias current Ib corresponding to the threshold current Ith, but the bias current Ib flows from the time Δt before the input signal becomes "high" until the delayed input signal becomes "low". The power consumption is low and high-speed operation is possible.

[0023]

[Effects of the Invention] According to the present invention, power consumption can be reduced by making the bias current flowing through the laser diode a pulsed current, and the bias current is caused to flow before the input signal becomes "high". This makes it possible to realize a laser diode drive circuit that can operate at high speed with low power consumption.

[Brief explanation of the drawing]

[Figure 1] Block diagram explaining the principle of the present invention

[Figure 2
] Diagram explaining an embodiment of the present invention

[Fig. 3] Diagram explaining the drive current of the embodiment of the present invention

FIG. 4 Diagram explaining other embodiments of the present invention

[Figure 5] Time chart of other embodiments of the present invention

[Fig. 6] A diagram illustrating the drive current of another embodiment of the present invention.

[Figure 7] Diagram explaining a conventional example

[Figure 8] Diagram explaining drive current in conventional example

[Explanation of symbols] 10 Laser diode 20 Pulse bias generation means 21, 32 Transistor 22 OR circuit 30 Drive current generation means 31 Delay circuit R1, R2 Resistor

Claims (2)

[Claims] 1. A circuit for driving a laser diode (10), comprising pulse bias generation means (20) that is turned on by an input signal, and drive current generation means (30) that is turned on by an input signal. The drive current of the laser diode (10) is the sum of the pulsed bias current generated by the pulse bias generation means (20) and the pulsed drive current generated by the drive current generation means (30). A laser diode drive circuit characterized by a current. 2. A delay circuit (31) for delaying an input signal for a predetermined time is provided, and the drive current generating means (30) is turned on by the output of the delay circuit (31). 2. The laser diode drive circuit according to claim 1, wherein the bias current is turned on a predetermined time prior to the timing at which the generating means (30) is turned on.