JPH0380378B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to speeding up an optical transmitter.

[Conventional technology]

Figure 3 is an example of the Institute of Electronics and Communication Engineers technical research report.
It is a diagram showing the circuit configuration of the conventional optical transmitter shown in QE82-96, in which 1 is a signal input terminal;
2 is FET, 3 is bias resistor for this FET, 4
is the bias power supply terminal, 5 is the FET source terminal,
6 is a semiconductor light emitting device; 7 is a semiconductor light emitting device;
A resistor is connected between the drains of the FET, 8 is a capacitor connected in parallel to this resistor, and 9 is a coaxial short-circuited reflection line. FIG. 4 is a diagram showing signal waveforms at each part in FIG. 3.

The conventional optical transmitter is configured as described above, and when a binary signal as shown in FIG. ”, FET2 is suddenly disconnected, so the drain voltage of FET2 is as shown in Figure 4b.
become that way. In addition, a coaxial short-circuited reflection line 9 is connected to the drain of the FET 2, and if the delay time for the pulse to go back and forth on the coaxial shorted reflection line 9 is set to the same time as the pulse width of the signal waveform to be transmitted,
The drain voltage of FET2 changes from “Low” to “High”
As shown in Figure 4c, when FET2 changes to
A pulse of opposite polarity to the drain voltage of is applied to the drain of FET2. Therefore, the drain voltage of FET2 changes as shown in FIG. 4d.
The voltage waveform shown in FIG. 4d is applied to the light emitting element 6 through a differentiator circuit composed of a resistor 7 and a capacitor 8. Therefore, the drive impedance at the waveform change point becomes small, and in the steady state, the resistance 7
The value is . As a result, the driving current of the light emitting element 6 exhibits peaking, and its waveform becomes as shown in FIG. 4e. Therefore, the rise and fall times of the optical output waveform of the light emitting element 6 become faster.

[Problem that the invention seeks to solve]

The conventional optical transmitter is configured as described above.
By applying a reverse bias pulse at the falling edge of the signal waveform using the coaxial short-circuited reflection line 9, the fall time of the optical output waveform is made faster, so that when the pulse width of the transmitted signal changes, the coaxial short-circuited reflection line 9
The disadvantage was that the delay time of the delay time had to be changed.

The present invention was made to solve these drawbacks, and aims to provide a high-speed optical transmitter that operates with signals of arbitrary pulse widths.

[Means for solving problems]

The optical transmitter according to the present invention uses two current switching switches, and a capacitor is connected between a semiconductor light emitting element connected to each current switching switch and a resistor.

[Effect]

In this invention, since the two current changeover switches are coupled by a capacitor, it is possible to drive a high-speed signal with an arbitrary pulse width.

〔Example〕

FIG. 1 is a diagram showing the circuit configuration of an embodiment of the present invention, in which 1 is a signal input terminal, 6 is a semiconductor light emitting device, 10 is a gate circuit, 11 is a first current selection switch, and 12 and 13 are first and second current selector switches. 1 is a transistor constituting the current changeover switch, 14 is a second current changeover switch, 15 and 16 are transistors constituting the second current changeover switch, 17 is a capacitor, 18
is a resistor, 19 and 20 are constant current sources, and 21 is a bias voltage application terminal. FIG. 2 is a diagram showing signal waveforms at various parts of the circuit shown in FIG. 1.

In the optical transmitter configured as described above, a binary signal as shown in FIG. 2a is transmitted to the signal input terminal 1.
is applied to the first one through the gate circuit 10.
and the second current switching switches 11 and 14, and when the signal is "High", the transistors 12,
14 becomes conductive, and currents having the current values of constant current sources 19 and 20 flow, respectively, and transistors 13 and 16 are turned off. When the signal is "Low", transistors 12 and 14 are turned off, and transistors 13 and 14 are turned off.
16 is conductive. Therefore, transistor 1
The collector voltage of 2 corresponds to the input signal as shown in Fig. 2b.
It will look like this. Therefore, if the value of the resistor 18 is made larger than the internal resistance of the semiconductor light emitting element 6, the variation in the collector voltage of the transistor 14 can be reduced as shown in FIG.
The voltage is applied to the semiconductor light emitting device 6 through the capacitor 17 as shown in FIG. Therefore, the semiconductor light emitting device 6
As shown in FIG. 2d, the current flowing through the current has a waveform with peaking at its rise and fall, and as a result, the rise and fall times of the optical output waveform become faster.

〔Effect of the invention〕

As explained above, this invention applies peaking by coupling two current selection switches with a capacitor to speed up the rise and fall times of the optical output waveform, so it can drive signals with arbitrary pulse widths. effective.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the circuit configuration of an embodiment of the present invention, Fig. 2 is a diagram showing signal waveforms of each part of the circuit configuration shown in Fig. 1, and Fig. 3 is the circuit configuration of a conventional optical transmitter. FIG. 4 is a diagram showing signal waveforms at various parts of the circuit configuration shown in FIG. 3. In the figure, 1 is a signal input terminal, 2 is a FET,
3 is a bias resistor, 4 is a bias power supply terminal,
5 is the source terminal of the FET, 6 is the semiconductor light emitting element,
7 is a resistor, 8 is a capacitor, 9 is a coaxial short-circuited reflection line, 10 is a gate circuit, 11 is a first current selection switch, 12 and 13 are transistors, and 14 is a second
current selection switch, 15 and 16 are transistors, 17 is a capacitor, 18 is a resistor, 19 and 20
is a constant current source, and 21 is a bias voltage application terminal. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] 1. The capacitor is connected to first and second current changeover switches that switch current paths in the same phase in response to binary data, and a capacitor connected between the terminals of the first and second current changeover switches. a semiconductor light emitting element connected to a terminal of the second current changeover switch, and a resistor connected to a terminal of the first current changeover switch connected to the capacitor. transmitter.