JPS63197115A - Optical transmitter - Google Patents

Abstract

PURPOSE:To use a small sized variable resistor by utilizing a change in the internal resistor of a transistor (TR) for the adjustment of a drive current of a light emitting element so as to reduce the power consumption of a variable resistor in use. CONSTITUTION:A 1st TR 5 is connected in parallel with the light emitting element 4 and a 2nd TR 3 is connected in series with the parallel circuit and a power voltage is supplied from a power input terminal 1. The change in the internal resistance of the 2nd TR 3 is used to adjust the drive current of the light emitting element. On the other hand, the digital signal fed to a signal input terminal 7 intermits the base current of the 1st TR 5 through a drive circuit 6. The DC bias voltage fed to the base of the 2nd TR 3 is obtained by using the variable resistor 2 to divide the power voltage. Thus, the power consumption of the variable resistor and the size is made small.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an optical transmitter used in optical fiber communication,
In particular, it relates to optical transmitters for digital signal transmission.

[Conventional technology]

Conventionally, this type of optical transmitter is as shown in the second example.

In order to switch on and off the drive current of the light emitting element 4 in response to an input digital signal, a drive circuit 6 was used in which transistors 5 were connected in parallel and the base current was switched on and off. Here, in order to vary the current flowing through one light emitting element 4 and adjust the output optical power, a variable resistor 2 was inserted in series.

[Problem that the invention seeks to solve]

The above-described conventional optical transmitter has the disadvantage that the driving current of the light emitting element also flows through the variable resistor, which increases the power consumption of the variable resistor. Furthermore, for example, to allow power consumption of about 300 mW.

A variable resistor with a rated power of about 0.5 W must be used, and a variable resistor with a large external dimension is required, which is an obstacle to downsizing the optical transmitter.

The present invention is an attempt to solve these problems with the prior art, and aims to provide an optical transmitter that can reduce the power consumption of a variable resistor and can be made smaller.

[Failure to solve the problem]

The optical transmitter of the present invention includes a light emitting element, a first transistor connected in parallel to the light emitting element, a drive circuit that connects and connects the pace current of the first transistor in accordance with an input digital signal, and the first transistor connected in parallel to the light emitting element. The second transistor is connected in series to a parallel circuit of the transistor and the light emitting element, and a variable resistor that adjusts the DC bias voltage applied to the second transistor.

〔Example〕

Next, one embodiment of the present invention will be explained with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment according to the present invention. In this figure, a first transistor 5 and a light emitting element 4 are connected in parallel, and a second transistor 3 is connected in series to this parallel circuit.

A power supply voltage is supplied from a power supply input terminal 1. This change in the internal resistance of the second transistor 3 is used to adjust the drive current of the light emitting element. On the other hand, the digital signal applied to the signal input terminal 7 cuts the base current of the first transistor 5 via the drive circuit 6. The DC bias voltage applied to the second transistor 3 is obtained by adjusting the partial voltage of the stain source voltage using the variable resistor 2.

Here, as an example, 2SC2954 is used for transistors 3 and 5, a normal TTL IC 7404 is used for drive circuit 6, the power supply voltage is set to DC + 5 V, and a 0.8 μm band light emitting diode is used for 1 light emitting element 4. 1. The drive current of the light emitting diode was varied in the range of 50 to 100 mA.

To vary the output optical power by approximately 3 dB, transistor 3
Since the DC current amplification factor of is 30 or more, the base current is 1
, 7 to 3.3 mA is required. If a variable resistor of IkΩ is used, the power consumption here will be about 50 mW.

〔Effect of the invention〕

As is clear from the above description, the present invention utilizes changes in the internal resistance of a transistor to adjust the drive current of a light emitting element, thereby reducing the power consumption of the variable resistor to several times that of the conventional one. It is possible to reduce the resistance to about 1, and it is also possible to use a smaller variable resistor, which is a great effect.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of an optical transmitter according to the present invention, and FIG. 2 is a circuit diagram showing an example of a conventional optical transmitter. In the figure, 1 is the power input terminal. 2 is a variable resistor, 3 and 5 are transistors, 4 is a light emitting element, 6 is a drive circuit, and 7 is a signal input terminal.

Claims (1)

[Claims] 1. a light-emitting element, a first transistor connected in parallel to the light-emitting element, a drive circuit that connects and connects the base current of the first transistor in response to an input digital signal, the first transistor and the light-emitting element; An optical transmitter comprising: a second transistor connected in series in a parallel circuit with an element; and a variable resistor that adjusts a DC bias voltage applied to the base of the second transistor.