JPH02192190A - Semiconductor laser drive circuit - Google Patents

Abstract

PURPOSE:To supply a pulse current stable in a wide range to a semiconductor laser element by a method wherein the collectors, the bases, and the emitters of transistors are connected with each other through optional wiring materials so as to enable the transistors to operate under such a condition that the transition times of the transistors are made maximum when currents branch off from a current source. CONSTITUTION:The current of a current source 22 is set so as to obtain a pulse current supplied to an required semiconductor laser element. And, when currents branch off from the current source 22 and are supplied to transistors 10, 12, 14, 16, 18, and 20 which constitute a differential type open collector output circuit, the electrodes of these transistors are connected with each other through optional wiring materials 40-45 so as to make transition times fT of the transistors maximum. The number of transistors to which currents branched off from the current source 22 are supplied is determined depending on the current set in the current source 22. By this setup, a stable pulse current in a wide range can be supplied to a semiconductor laser element by changing the wiring materials 40-45.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser drive circuit, and more particularly to a semiconductor laser drive circuit configured with a differential open collector output circuit of a bipolar semiconductor integrated circuit.

[Conventional technology]

A conventional semiconductor laser drive circuit of this type is comprised of a differential open collector output circuit, as shown in FIG. 2, and its output section is comprised of a single transistor.

[Problem to be solved by the invention]

As mentioned above, in conventional semiconductor laser drive circuits, the output section of the differential open collector output circuit is composed of a single transistor. The transition time f of the transistor changes with the variable amount of current that drives the semiconductor laser element by the output circuit.

For example, if the transition time f of a transistor constituting a differential open collector output circuit is maximum when its collector current Ic is lQmA, then the collector current Ic
When the current is 50 mA, the transition time f is in a high current region, so it decreases. Due to this, the operating time of the transistor,
In other words, the rise time and fall time of the drive waveform tend to be longer. Furthermore, if a differential open collector output circuit is configured using a transistor whose transition time fT is maximum when the collector current Ic is 50 mA, then the transition time fT is the maximum when the collector current Ic is 10 mA.
, decreases.

In this way, when a differential open collector output circuit is configured with a single transistor, the applicable range of pulse current values supplied to the semiconductor laser device becomes narrow, and therefore, there is a problem that it can only be used for a specific semiconductor laser device. .

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a semiconductor laser drive circuit that can be used with various semiconductor laser devices.

[Means to solve the problem]

In order to achieve the above object, the present invention connects the emitters of a pair of transistors in common, connects the emitters to a current source, and connects a plurality of transistors in parallel to the pair of transistors. In the semiconductor laser drive circuit that constitutes the dynamic open collector output circuit, when current is shunted from the current source to each transistor, each collector of each transistor is operated under conditions that maximize the transition time of each transistor. The device is characterized in that the bases, the bases, and the emitters are connected using any wiring material.

According to the present invention, by changing the wiring material that connects the collectors, bases, and emitters of the transistors constituting the differential open collector output circuit, a stable pulse current over a wide range can be applied to the semiconductor laser element. can be supplied to

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of an embodiment of a semiconductor laser drive circuit according to the present invention. In the figure, the semiconductor laser drive circuit includes transistors 10, 12, 14, 16, 18, 20, . . . that constitute a differential open collector output circuit.
It is composed of a current source 22 and a power source 24. Also,
32.33 is the input terminal to the base of each transistor, 3
0.31 is the output terminal of the semiconductor laser drive circuit, 40.4
Reference numeral 1 indicates an arbitrary wiring material that connects between the collectors of the transistors, 42.43 between the bases of the transistors, and 44.45 between the emitters of the transistors.

Here, the current value of the current source 22 is set to obtain a pulse current value supplied to a desired semiconductor laser element.

Furthermore, at the current value set in the current source 22, each transistor 1 constituting the differential open collector output circuit
0.12.14.16.18.20 These transistors can be connected using any wiring material 40.41.42.43.44.45 so that the transition time f1 of each transistor is maximized when current is shunted to 0.12.14.16.18.20. The respective electrodes are connected.

The number of transistors that divide the current from the current source 22 is determined according to the current value set for the current source 22.

In the above-described configuration, when a pulse signal is input from the input terminal 32.33 to each transistor 10.12.14.16.18.20, each transistor 10.1
2.14.16.18.20 operates so that the transition time f is maximized, and the current from the current source 22 is shunted, and a predetermined pulse current is supplied from the output terminal 30.31 to the semiconductor laser element. Ru.

〔Effect of the invention〕

As explained above, in the present invention, each transistor operates under conditions where the transition time of each transistor is maximized when current is shunted from a current source to each transistor constituting a differential open collector output circuit. Since the collectors, the bases, and the emitters are connected using any wiring material, according to the present invention, a wide range of stable pulse current can be supplied to the semiconductor laser element. That is, it is possible to realize a semiconductor laser drive circuit that is compatible with various semiconductor laser devices.

Furthermore, according to the present invention, each transistor constituting the differential open collector output circuit is configured to operate under conditions where its transition time is maximized according to the current value set by the current source. , deterioration in the rise time and fall time of the pulse current supplied to the semiconductor laser element can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the structure of an embodiment of a semiconductor laser drive circuit according to the present invention, and FIG. 2 is a circuit diagram showing the structure of a conventional semiconductor laser drive circuit. 10, 12, 14, 16, 18,
20... Transistor, 22...
...Current source, 24...Power supply, 30.31...Output terminal, 32.33...Input terminal, 40.41.42.43.44.45. ...Wiring material.

Claims (1)

[Claims] A semiconductor laser drive circuit that configures a differential open collector output circuit in which the emitters of a pair of transistors are commonly connected, the emitters are connected to a current source, and a plurality of transistors are connected in parallel to the pair of transistors. In this case, when current is shunted from the current source to each transistor, arbitrary wiring is established between each collector, between each base, and between each emitter of each transistor so that the transition time of each transistor is maximized. A semiconductor laser drive circuit characterized by being connected using a material.