JPH0254977A - Semiconductor laser drive circuit - Google Patents

Abstract

PURPOSE:To change capacity between resistor terminals between an FET drain and a laser diode by connecting an FET in parallel to a resistance between an FET drain electrode and a laser diode and controlling gate voltage. CONSTITUTION:When a pulse signal enters a gate electrode G of a FET1, drive pulse signal corresponding to an input pulse signal is obtained. When the current is implanted into a semiconductor laser diode 5, the diode 5 oscillates. A drive pulse current waveform is speeded up and overshoot is provided to the first-bit pulse by capacity between the drain and source of an FET7 connected in parallel to a resistor 4 or capacity between the gate and source and between the gate and drain and the resistor 4. By controlling gate voltage of the FET7, capacity between the resistor terminals between the drain of the FET7 and a laser diode 5 can be changed continuously.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a semiconductor laser drive circuit.

In particular, the present invention relates to a circuit that drives a semiconductor laser using a field effect transistor used in a transmitting section of a high-speed digital transmission exceeding GHz.

(Conventional technology) An example of a conventional semiconductor laser drive circuit is shown in the tXz diagram.

Conventionally, this type of semiconductor laser drive circuit connects a capacitor 3 between a field effect transistor 10 source electrode S and a reference potential 9, a resistor 2 between the source electrode S and a power supply 7, and connects a field effect transistor 10 to a reference potential 9. A series circuit of a resistor 4 and a semiconductor laser 5 is connected between the drain electrode and the reference potential.

A capacitor 8 is connected in parallel to the resistor 4, and a DC bias supply circuit 6 is further connected to the cathode of the semiconductor laser 5 to form a structure.

(An open problem to be solved by the invention) This conventional semiconductor laser drive circuit uses a resistor 4 to compensate for pattern effects caused by excavation delay of the semiconductor laser 5, etc.
A speed-up capacitor 8 is connected in parallel to 1, but as the frequency becomes higher, the influence of mounting and the variation of the semiconductor laser become larger, so it is necessary to change the value of the optical waveform compensation capacitor 8 to obtain the best optical waveform. There is.

However, since the conventional circuit has a configuration as shown in Fig. 2, the capacitor 8 must be replaced to compensate for the pattern effect of the optical waveform, and the disadvantage is that the compensation capacitance cannot be continuously varied. There is.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks and to provide a semiconductor laser drive circuit that can continuously change the capacitance between the resistor between the drain of a field effect transistor and a laser diode.

Friendly Means for Solving Problem C11) To achieve the above object, the semiconductor laser drive circuit according to the present invention connects a first capacitor between the source electrode of the field effect transistor and a reference potential, and connects the first capacitor between the source electrode and the reference potential. A first resistor is connected between the field effect transistor and a power source, a second resistor and a laser diode are connected in series between the drain electrode of the field effect transistor and a reference potential, and the second resistor and the laser diode are connected in series. A DC bias supply circuit is connected to a common connection point of the diodes, and a second capacitor is connected in parallel with the second resistor, and a pulse current is supplied to the gate of the field effect transistor. In the semiconductor laser drive circuit for excavating the laser diode, a second field effect transistor is connected in parallel to the $2 resistor instead of the second capacitor, and the second field effect transistor is connected in parallel to the $2 resistor. In order to control the gate voltage of the second resistor, the four-pronged capacitance fI
The kt is configured so that it can be changed continuously.

(Example> Hereinafter, the present invention will be explained in more detail with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of a semiconductor laser drive circuit according to the present invention.

In the figure, 1.7 is a field effect transistor (hereinafter P
It will be abbreviated as ET. ), 2.4 is a resistor.

3 is a capacitor, and 5 is a semiconductor laser diode.

6 is a DC bias supply circuit.

When a pulse signal is input to the gate electrode G of FET1,
Nine driving pulse currents are obtained according to the input pulse signal. When the drive pulse current is injected into the semiconductor laser diode 5, the semiconductor laser diode 5 oscillates. However, in the semiconductor laser diode 5, there is an excavation delay with respect to the first bit pulse, which delays one light emission, and a pattern effect occurs, deteriorating the optical waveform.

In order to compensate for this, the present invention connects the second FET 7t and the resistor 4ζ in parallel. Therefore, the drain-source capacitance of FBT7 is the gate-source capacitance and gate-drain capacitance.

Resistor 4 increases the speed of the drive pulse current waveform and has an overshoot on the 1st bit pulse.
It's set.

In general, in the high frequency region, the influence of mounting and variations in the semiconductor laser diode 5 are large, so the amount of deterioration of the optical waveform due to pattern effects is not uniform.

Therefore, it becomes necessary to vary the capacitance for compensation, and the higher the frequency, the smaller the capacitance value becomes, making it difficult to realize it with ordinary discrete components.

In the present invention, this optical waveform compensation capacitor is connected to the 20th FET7.
drain-source capacitance or.

This is realized by the gate-source capacitance and gate-drain capacitance. These capacitances are a function of current and can be changed continuously by controlling the gate voltage of FI3T7.

(Effects of the Invention) As explained above, the present invention provides a second field effect transistor in place of the speed-up capacitor connected in parallel to the resistor between the drain electrode of the field effect transistor and the laser diode. By connecting and controlling the drain-source capacitance, gate-source capacitance, and gate-drain capacitance of the second field effect transistor with the gate voltage, it becomes possible to continuously change the capacitance t', and the voltage This has the effect of easily compensating and optimizing the optical waveform simply by changing the .

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of a semiconductor laser drive circuit according to the present invention, and FIG. 2 is a diagram showing an example of a conventional semiconductor laser drive circuit. 1.7... Field effect transistor 2.4... Resistor 3.8... Capacitor 5...
・Semiconductor laser diode 6... [R bias supply circuit patent applicant NEC Corporation representative Patent attorney Ii) Ro Hisashi 2 diagram

Claims (1)

[Claims] A first capacitor is connected between the source electrode of the field effect transistor and a reference potential, a first resistor is connected between the source electrode and a power supply, and the drain electrode of the field effect transistor is connected to the reference potential. In between, a series circuit of a second resistor and a laser diode is connected, a DC bias supply circuit is connected to a common connection point of the second resistor and the laser diode, and a second resistor is connected in parallel with the second resistor. In a semiconductor laser drive circuit that connects a capacitor and oscillates the laser diode by supplying a pulse current to the gate of the field effect transistor, the circuit is connected in parallel to the second resistor instead of the second capacitor. Second
By connecting a field effect transistor of and controlling the gate voltage of the second field effect transistor,
A semiconductor laser drive circuit characterized in that a capacitance applied between terminals of the second resistor is continuously changed.