JPH0260331A - Light emitting element drive circuit - Google Patents

Abstract

PURPOSE:To effectively compensate the pulse width distortion of an output light signal and to prevent the distortion generation of a light output waveform by driving a light emitting element by a driving signal generated as the OR of input data and the delay signal of the input data. CONSTITUTION:Since inversion input data SD are inputted through an amplifier IC1 to an inverter IC2 and an output signal is delayed for the input signal only for the delay time of a gate, for the output of IC2, the signal equal to the delay signal of the input data SD is outputted. Continuously, the delay signal and the data SD are inputted to an OR/NOR circuit IC3 and as the OR of both, the signal with the wide pulse width is generated and made into the driving signal of the light emitting element. Consequently, by setting the delay time of IC2 so as to be coincident with the rising delay time of a laser diode LD, the light signal emitted by a diode LD driven by the driving signal with the wide pulse width maintains a 50% duty. Thus, the pulse width distortion is effectively compensated and the generation of the distortion in the light output waveform can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a light emitting device driving circuit. More specifically,
The present invention can be advantageously used as an optical transmitter in an optical communication system, etc., and is superior to the prior art. Fig. 4 shows a typical configuration of a light emitting element drive circuit conventionally used in an optical transmitter. FIG.

As shown in the figure, this drive circuit includes input terminals SD and SD into which digital electrical signals to be transmitted are input;
It includes a pair of transistors Q1 and Q2 whose bases are coupled to these input terminals, and a laser diode LD connected in series with the collector of one transistor Q1 for performing electro-optical conversion of signals. Transistor Q1, Q
The two emitters are commonly connected to a current source IO. A pair of complementary digital signals applied to the input terminals SD and SD cause one of the transistors Ql and Q2 to become conductive, and the other to become non-conductive. That is, when the transistor Q1 becomes conductive, the laser diode LD emits light.

Problems to be Solved by the Invention Incidentally, it generally takes some time for a laser diode LD to generate light of a predetermined power after a current starts being applied.

FIGS. 5(a) and 5(a) are diagrams showing typical current/voltage characteristics of the laser diode LD, and the input signal waveform and output signal waveform to the laser diode LD.

That is, as shown in FIGS. 5(a) and 5(b), it takes time for the laser diode LD to actually generate optical output after a voltage is applied by a drive pulse and current begins to flow. Therefore, as shown in FIG. 5(b),
Light emission is delayed by time τ, which causes waveform distortion of the optical output signal.

Therefore, in a conventional circuit as shown in FIG. 4 using a light emitting element having the above characteristics, no matter how fast the other elements operate, the output optical signal is
Duty changes occur due to distortion of the rising waveform.

In this way, when using the conventional light emitting element drive circuit,
Input data SD and its inverted signal, input data S
Even if D is a signal with a duty of 50%, the delay in the rise characteristics of the light emitting element causes the difference in Fig. 5 (b
), the output optical signal has a duty of 50
It will be smaller than %.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art described above and to provide a novel light emitting element drive circuit that does not cause distortion in the optical output waveform.

Means for Solving the Problems According to the present invention, a light-emitting element and a drive circuit supplying a drive current modulated in accordance with an input signal to the light-emitting element are provided, and input data in the form of an electric signal is input. In the light emitting element driving circuit configured to output an optical signal corresponding to the input data, the driving circuit drives the light emitting element with a signal obtained by superimposing the input data and a delayed signal of the input data. Provided is a light emitting element drive circuit characterized by the following configuration.

Further, according to one embodiment of the present invention, the drive circuit includes:
a non-inverting input and an inverting input, a pair of parallel transistors whose bases are connected to the pair of inputs, and a light emitting element connected between the collector of one transistor of the pair of transistors and a power supply terminal; A light emitting element driving circuit comprising:

A light emitting element driving circuit according to the present invention drives a light emitting element with a drive signal generated as a logical sum of a delayed signal generated by delay processing an input signal and an original input signal. Its main feature is that it is configured to compensate for the rise delay.

In other words, the signal generated as the logical sum of the delayed signal generated from the input signal through some delay processing and the original input signal has a pulse that is shorter than the original input signal by the delay of the delayed signal, as will be described later. This results in a wide signal. Therefore, by making this delay amount correspond to the light emission delay of the light emitting element, it is possible to compensate for the delay in the rise characteristics of the light emitting element, and thus the distortion of the output optical signal caused by the delay in the rise characteristics of the light emitting element can be reduced. Can be canceled out.

According to a preferred embodiment of the present invention, the delay signal generation circuit and the superimposition processing circuit for the generated delay signal and input signal are both formed using ○R/NOR elements (circuits), as will be specifically described later. By using and configuring the circuit, the circuit according to the present invention can be realized easily and inexpensively using a general-purpose integrated circuit.

The present invention will be described in more detail below with reference to the drawings, but the following disclosure is only one embodiment of the present invention and does not limit the technical scope of the present invention in any way.

Embodiment FIG. 1 is a circuit diagram showing a configuration example of a light emitting element driving circuit according to the present invention.

This circuit is added to the conventional light emitting element drive circuit shown in FIG.
The circuit is constructed by inserting the circuit surrounded by the dotted line in the figure.

That is, an amplifier ICI which is provided with a non-inverting input and an inverting input and receives data from the outside, and this input amplifier ICI.
NOR element IC2 connected to the inverted output of amplifier I
An OR element IC3 receives the non-inverted output of CI and the inverted output of NOR element IC2, and further includes transistors Ql and 0.
2 and current source ■. It consists of a laser diode L
A circuit that supplies drive current to D.

Note that the NOR circuit IC2 in this circuit uses only one input thereof, and actually functions as an inverter. Further, the OR element IC3 has a non-inverted output and an inverted output, and operates as an OR/NOR element.

The circuit according to this embodiment configured as described above operates as follows.

FIGS. 2(a) to 2(d) are waveform diagrams illustrating the operation of the above-mentioned circuit.

FIG. 2(a) shows the waveforms of data SD and SD input to this circuit. In the circuit shown in FIG. 1, the inverted input data SD of these signals is input to the inverter IC2. Here, since the output signal is delayed with respect to the input signal by the delay time of the gate, a signal equivalent to the delayed signal of the input data SD is output from the output of IC2, as shown in FIG. 2(b). be done.

Subsequently, this delayed signal and the input data SD are OR/
The signal is input to the NOR circuit C3, and the logical sum of the two is generated as shown in FIG. 2(C). This OR signal is the second
As can be seen from the diagram (C), the signal has a wider pulse width by the delay in IC2, and this wider signal becomes the drive signal for the light emitting element.

Therefore, the delay time t of IC2 is
By setting the rise delay time τ to match the rise delay time τ, the optical signal generated by the laser diode LD driven by the drive signal with a wide pulse width is as shown in Fig. 2 (d
), 50% duty is maintained despite the delay in the rise characteristics.

That is, in this light emitting element drive circuit, the light emitting element is driven by a drive signal having a wider pulse width than the input signal, so that pulse width distortion caused by the rising characteristics of the light emitting element is effectively compensated for.

FIG. 3 is a diagram showing the configuration of an apparatus for checking the operation of the circuit according to the present invention as described above.

That is, this device includes the light emitting element drive circuit 3 shown in FIG.
an 0/E converter 32 that monitors the output optical signal of the circuit 30; and an oscilloscope 33 that visualizes the intensity of the optical signal monitored by the 0/E converter 32. It can be ensured that the pulse width distortion of the optical signal output from this circuit is effectively compensated.

Effects of the Invention As detailed above, the light emitting element drive circuit according to the present invention has an extremely simple configuration, but has the function of effectively canceling out the distortion of the output optical signal caused by the delay in the rise and fall characteristics of the light emitting element. have. Therefore, generated input data can be faithfully transmitted as an optical signal without considering the characteristics of the light emitting element.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a configuration example of a light emitting element driving circuit constructed according to the present invention, and FIG. 2(a) to (d)
1 is a waveform diagram illustrating the operation of the circuit shown in FIG. 1 and a conventional light emitting element driving circuit, and FIG. FIG. 4 is a circuit diagram showing a typical configuration of a conventional light-emitting element drive circuit, and FIGS. 5(a) and (b) show the current-voltage characteristics of the light-emitting element, FIG. 3 is a diagram showing an input signal waveform and an output signal waveform for a light emitting element. [Main reference numbers and reference symbols] 30... Light emitting element drive circuit, 31... 32... 33... ICI, IC2, IC3, R1 to 6 Ql, 2 LD... SD... SD ・ ・ ・Pulse pattern generator, ・○/E converter, ・Onroscope, ・Amplifier, ・○R element, ・OR/NOR element, ・Resistor, ・Transistor, ・Laser diode, ・Non-inverting input, ・Inverting Input patent applicant Sumitomo Electric Industries, Ltd.

Claims (1)

[Scope of Claims] A light-emitting element and a drive circuit that supplies a drive current modulated in accordance with an input signal to the light-emitting element, and outputs an optical signal corresponding to the input signal input as an electrical signal. In the light emitting element driving circuit configured as above, the driving circuit is configured to drive the light emitting element with a driving signal generated as a logical sum of input data and a delayed signal of the input data. Features a light emitting element drive circuit.