JP2959485B2 - Light emitting element drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting element driving circuit in an optical communication device applied to a high-speed optical communication system.

[0002]

2. Description of the Related Art As a conventional driving circuit for driving a light emitting element such as an LD, a differential pair transistor circuit 3 is provided in an output stage circuit for supplying a pulse current to an LD 41 as shown in FIG.
1 and 32 are applied. The LD 41 functions as one load of a transistor forming a differential pair,
The LD can be turned on and off by providing a complementary input to the differential pair.

[0003]

However, in such a conventional configuration, the charge and discharge of the charge accumulated in the parasitic capacitance of the light emitting element causes the rise and fall of the optical output pulse signal as shown in FIG. However, there is a problem that the waveform response characteristic is degraded due to the parasitic capacitance, the rising of the drive pulse is shifted from the original position, and the jitter is increased. For this reason,
Even after the driving pulse of the light emitting element becomes “0” level, there is a problem that the influence of the previous pulse remains until the rise of the next pulse, and the light is not completely extinguished.

An object of the present invention is to provide a drive circuit for a light emitting element which can eliminate such a conventional drawback and can obtain an optical output waveform having a sharp rise / fall.

[0005]

In order to solve the above problems, a light emitting element driving circuit according to the present invention operates at an output terminal of the driving circuit when an input signal rises / falls.
A pull-up circuit is connected to a pull-up circuit or a capacitive element serving as a feed forward from an input terminal.

According to the above configuration, the driving force of the driving circuit is temporarily improved by the feed-forward from the input terminal by the pull-up circuit or the capacitive element when the input signal rises, and by the pull-down circuit when the input signal falls Operates, and the driving force of the driving circuit is temporarily improved, so that it is possible to quickly respond to the input signal waveform and obtain a steep rising / falling optical output waveform.

[0007]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a block diagram illustrating the principle of the present invention. In FIG. 1, a drive circuit of the present invention is provided with a drive circuit 200 for driving a light emitting element by obtaining a complementary input signal of positive / negative phase, and is connected to an output terminal of the drive circuit. A pull-up circuit 300 that temporarily has a driving force, and a pull-down circuit 4 that temporarily has a driving force at the time of rising of a reverse phase signal of the input signal.
00.

FIG. 2 is a circuit diagram showing an embodiment of the present invention. In the figure, the driving circuit of the present invention includes power supply terminals 1 and 2, input terminals 11 and 12, output terminals 21 and 22, transistors 31, 32, 33, 34, 35 and 36, a light emitting element 41, and resistance elements 51 and 52. , 53, 54, capacitive elements 61, 62, and offset voltage sources 101, 102. A signal having a phase opposite to that of the input terminal 11 is input to the input terminal 12, and as a result, the output terminal 22 is connected to the output terminal 2.
1 is output.

The potential of the base of the transistor 35, which is the input of the pull-up circuit, and the potential of the base of the transistor 36, which is the input of the pull-down circuit, are fixed by the offset voltage sources 101 and 102 to potentials that do not turn on in a steady state. I have. However, input terminal 1
1 and the base of the transistor 35 are connected via the capacitor 62, and the input terminal 12 and the base of the transistor 36 are connected via the capacitor 61, respectively.
When a waveform as shown in FIG. 4A is input to FIG. 1, the potential of the base of the transistor 35 rises temporarily at the time of rising, and the signal of the opposite phase rises at the time of falling. The electric potential rises temporarily by being entangled. In this way, the signal entering the base of the transistor 35 is as shown in FIG. As a result, the pull-up circuit is temporarily turned on when the signal rises, and the pull-down circuit is temporarily turned on when the signal falls, thereby temporarily increasing the driving force of the drive circuit.

FIG. 3 is a circuit diagram showing another embodiment of the present invention. In FIG. 3, the driving circuit of the present invention includes power supply terminals 1 and 2, input terminals 11 and 12, output terminals 21 and 22, transistors 31, 32, 33, 34 and 36, and a light emitting element 4.
1, resistance elements 51, 52, 54, capacitance elements 61, 62,
And an offset voltage source 102. Input terminal 12
, A signal having a phase opposite to that of the input terminal 11 is input, and as a result, a signal having a phase opposite to that of the output terminal 21 is output to the output terminal 22.

When a signal input to the input terminal 11 rises, a capacitive element 62 connected between the input terminal 11 and the collector terminal of the transistor 36 which is a pull-down circuit.
Functions as a pull-up circuit, and temporarily pulls up the potential of the collector terminal of the transistor 36. At this time, the potential of the base of the transistor 36, which is the input of the pull-down circuit, is fixed to a potential at which the transistor 36 does not turn on in a steady state, and the signal input to the input terminal 12 falls, so that it does not operate. Conversely, when the signal input to the input terminal 12 rises, the potential of the base of the transistor 36, which is the input of the pull-down circuit, is input to the input terminal 12 because it is connected to the input terminal 12 via the capacitor 61. When the signal rises, the potential rises temporarily, and the pull-down circuit is turned on. As a result, the driving force for pulling down is temporarily improved.

[0012]

As described above, according to the present invention, since the driving force can be temporarily increased when the input signal changes, it is possible to obtain an optical output waveform having a sharp rise and fall. is there.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating the principle of the present invention.

FIG. 2 is a circuit diagram illustrating one embodiment of the present invention.

FIG. 3 is a circuit diagram showing another embodiment of the present invention.

FIG. 4 is an operation waveform diagram according to the embodiment of the present invention.

FIG. 5 is a circuit diagram showing a conventional light emitting element drive circuit.

FIG. 6 is an operation waveform diagram of a conventional light emitting element drive circuit.

[Explanation of symbols]

 1, 2 Power supply terminal 11, 12 Input terminal 21, 22 Output terminal of drive circuit 31, 32, 33, 34, 35, 36 Transistor 41 Light emitting element 51, 52, 53, 54 Resistance element 61, 62 Capacitance element 101, 102 Offset voltage source

Claims (4)

(57) [Claims] 1. A light-emitting element driving circuit, comprising: an active pull-up circuit for inputting a signal having the same phase as the output via a capacitor to an output terminal connected to the light-emitting element; An active pull-down circuit input through an element is connected, and the respective input terminals of the active pull-up circuit and the active pull-down circuit are turned on by an input from a capacitive element in a normally-off state. A light-emitting element driving circuit to which an offset voltage source for giving such a potential is connected. 2. An active pull-up circuit according to claim 1,
, A first transistor, and a resistive element connected to the collector terminal of the first transistor. The base of the first transistor is used as an input of the active pull-up circuit, An emitter of the active pull-up circuit as an output terminal of the active pull-up circuit;
A second transistor; and a resistor connected to an emitter terminal of the second transistor. The base of the second transistor is used as an input of the active pull-down circuit, and the collector of the second transistor is connected to the second transistor. 2. The light emitting element drive circuit according to claim 1, wherein the output terminal is an output terminal of an active pull-down circuit. 3. A light emitting element driving circuit, wherein an output terminal connected to the light emitting element, an input terminal to which a signal in phase with the output is input, a capacitive element to which one terminal is connected, and a signal in phase opposite to the output. Is connected to an active pull-down circuit that is input through a capacitive element, and an input terminal of the active pull-down circuit is provided with an offset voltage source that gives a potential that turns on by an input from the capacitive element in a normally-off state. A light-emitting element driving circuit, which is connected. 4. An active pull-down circuit according to claim 2, wherein
And a resistor connected to the transistor and the emitter terminal of the transistor.The base of the transistor is an input of the active pull-down circuit, and the collector of the transistor is an output terminal of the active pull-down circuit. The light emitting element drive circuit according to claim 3, wherein: