JPS62257778A - Drive circuit for laser diode - Google Patents

Abstract

PURPOSE:To reduce power consumption by connecting a pulse/DC converter to a collector for a transistor on the side reverse to the laser-diode drive side and utilizing the DC currents of an output from the converter as the bias of a laser diode. CONSTITUTION:Transistors 1, 2 are arranged facing each other and emitters are coupled, a laser diode 3 is connected to a collector for the element 2, and a bias circuit A including a transformer 7 and a pulse/DC converter 10 is con nected to a collector for the element 1. When a signal RZ and an inversion signal (the inverse of RZ) RZ are applied simultaneously to bases for the elements 1, 2, the element 1 is turned ON when the element 2 is turned OFF, and pulse currents on the secondary side of the transformer 7 are half-wave rectified by a diode 8 and a capacitance 9 in the converter 10, and changed into DC. The diode 8 and the capacitance 9 are connected to an emitter for a transistor 6 and inductance to a collector, thus eliminating a high-frequency section. According to the constitution, power consumption is reduced.

Description

[Detailed Description of the Invention] [Summary] In a current switching type laser diode drive circuit, a DC current obtained by connecting a pulse/DC converter is used as a load on the collector of a transistor on the side opposite to the laser diode drive side. By using it as a bias, it is possible to make effective use of the power that would otherwise be wasted, and to reduce power consumption.

[Industrial application field]

The present invention relates to improvements in laser diode drive circuits used in light sources for optical communications.

The optical signal turns on and off depending on the input pulse signal on and off.
In optical communication that uses intensity modulation to turn off, there are many so-called current switching circuits that use two transistors facing each other and their emitters coupled together as a drive circuit for a light source such as a laser diode (hereinafter referred to as LD). used.

In this case, in the current switching circuit, an LD is connected to the collector of one of the transistors.

At this time, it is desirable that the current switching circuit be a circuit that can minimize wasteful power consumed other than power for driving the LD.

[Conventional technology]

FIG. 3 is a diagram of a conventional LD drive circuit.

FIG. 4 is a diagram illustrating the method of the LD drive circuit.

FIG. 5 is a characteristic diagram showing the relationship between the drive current and the output optical power of the LD in Example -. In the same figure, the horizontal axis is the drive current IL
D, the vertical axis indicates the output optical power Po.

In FIG. 3, transistor 1,
A case will be described in which, for example, an RZ pulse signal shown in FIG. 4 is inputted to the base of FIG.

The current switching circuit 5 has a property that a current flows through the collector of the transistor 1.2 which has a higher input voltage to the base of the two transistors 1.2 facing each other.

Therefore, the RZ signal with a mark rate of 1/2, which indicates the probability that the signal "1" will occur, and a duty of 50%, which indicates the ratio of the pulse width to the period T, shown in FIG. Also, at the same timing as the RZ signal 1δ, No. 18 RZ, which is an inverted version of the RZ signal, is input to the base of the first transistor l.

As a result, the second transistor 20 shown by diagonal lines in FIG.
When the RZ signal input to the base is l'', current flows through the LD connected to the collector of the second transistor 2, and the LD
emits light.

On the other hand, when the RZ signal input to the base of the first transistor 1 is l'', a current flows to the collector of the first transistor 1.

Although the transistor 4 applies a DC bias up to the threshold value 1th of the LD3 shown in FIG. 5, there may be variations in the threshold value rth or the LD
Since the threshold value 1th of transistor 3 may change, the control voltage Vc applied to the base of transistor 4 is automatically controlled.

In this way, the LD3 was driven.

[Problem that the invention seeks to solve]

However, in the above-mentioned LD drive circuit, for example, when manually operating RZ No. 13 with a mark rate of 1/2 and a duty of 50%, the power used to drive the LD is 2.
5%, and the remaining 75% was wasted.

[Means for solving problems]

The problem mentioned above is that a pulse IDC converter is connected as the collector load of the transistor on the opposite side to the LD driving side.
This problem is solved by the LD drive circuit of the present invention, which uses the output DC current as the LD bias current.

[Effect]

According to the present invention, when the signal input to the transistor on the opposite side to the LD driving side is "1", a current flows to the collector of that transistor. By using the resulting output DC current as the LD bias current, the power that would have been wasted can be effectively used.
It is possible to reduce power consumption.

〔Example〕

FIG. 1 is a diagram showing the principle of the present invention.

FIG. 2 is an LD drive circuit diagram of an embodiment of the present invention.

The present invention differs from the conventional example shown in FIG. 3 by removing the DC bias circuit including transistor 4 for driving the LD shown in FIG. In Figure 1, the area is shown surrounded by a dotted line.
The point is that the DC current output from the bias circuit A, which is formed by connecting the pulse IDC converter 10 through the transformer 7, is used as the bias current for the LD.

To explain in more detail, the signals RZ and 7 are applied to the bases of transistors 1 and 2 at the same timing as shown in FIG.
When the input signal of [ applied to the base of is “1”, the input voltage of RZ to the base of the other transistor (transistor 2) is “
0'', and a pulse current flows through the collector of the transistor l.

The same pulse current flows through the secondary side of the transformer 7 connected to this collector, but the pulse is half-wave rectified by the diode 8 and capacitor 9 in the pulse/DC converter 10 shown in FIG. The emitter of the transistor 6 is connected to the point where the diode 8 and the capacitor 9 are connected, and the L is connected to the collector of the transistor 6 through an inductance directly above the high frequency component.
Added to D3.

In this way, when no current flows through the transistor 2 on the LDa side, the current flowing through the transistor l on the opposite side can be effectively utilized, thereby reducing power consumption.

〔Effect of the invention〕

As explained above, in the LD drive circuit according to the present invention, a pulse/DC converter is connected as the collector load of the transistor on the opposite side to the LD drive side, and the output DC current is used as the LD bias. It is possible to reduce power consumption.

[Brief explanation of drawings]

Fig. 1 is a principle diagram of the present invention, Fig. 2 is an LD drive circuit diagram of an embodiment of the present invention, Fig. 3 is a conventional LD drive circuit diagram, and Fig. 4 is a diagram explaining the method of the LD drive circuit. , FIG. 5 is a characteristic diagram showing the relationship between the drive current and output optical power of an example LD. In the figure, ■ is the first transistor, 2 is the second transistor, and 3 is the LD. 4.6 is a bias control transistor, 5 is a current switching circuit, 7 is a transformer, 8 is a diode, 9 is a capacitor, 10 is a pulse/DC converter, and A is a bias circuit. single figure leather figure 2 figure

Claims (1)

[Claims] In a current switching type laser diode drive circuit in which two transistors are opposed, their emitters are coupled, and a laser diode is connected to the collector of one transistor, as a load on the collector of the transistor on the side opposite to the laser diode drive side, A laser diode drive circuit, characterized in that a pulse/DC converter is connected and its output is applied as a DC bias power source to the laser diode.