JPS6089987A - Drive circuit of light-sensitive and light emitting element - Google Patents

Abstract

PURPOSE:To obtain an inexpensive and preferable drive circuit for bidirectional communication with one optical fiber using a light-sensitive and light emitting element by suitably controlling the switching of a switching circuit and the control of a control circuit. CONSTITUTION:A switching circuit 21 is connected between a high potential source +V and the collector C of a light-sensitive and light emitting element 20. A load resistor RL is connected between the emitter and the earth of the element 20. When the circuit 21 is closed, the voltage of the potential source +V is applied to the collector C of the element 20, which operates as a phototransistor to flow a light-sensitive current to the resistor RL when receiving a light (b), and a reception signal RS is led from an output terminal 34. A control circuit 22 is connected between the collector C of the element 20 and the low potential source -V. When the circuit 21 is opened and the voltage of -V is applied to the collector C of the element 20 by the circuit 22, a current I is flowed in the order of diode D, base B, collector C, the circuit 22, and V, the element 20 emits a light (a). In other words, it operates as a light emitting diode.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of the Invention (1) The present invention relates to a drive circuit for a light-receiving and light-emitting element used in fields such as optical communications.

(b) Prior art and its problems In general, in optical communications, bidirectional communications using optical fibers are often performed. Conventional two-way communication using optical fibers uses separate light-emitting elements and light-receiving elements, so it is normal to use two optical fibers, and in some cases, a splitter is used to connect one optical fiber. Two-way communication is carried out. However, it is uneconomical to use two optical fibers, and even if one optical fiber is used, if a splitter is used, the splitter is expensive and is a relatively large component, so it increases the cost of the transmission equipment as a whole. However, it had the disadvantage of being large in size.

In order to overcome this drawback and enable bidirectional communication with a single optical fiber without using a splitter, the inventors of this application passed a forward current through the p-n junction. When the semiconductor emits light, a three-layer phototransistor is formed: a collector layer, a base layer, and an emitter layer.
We have created a semiconductor light-receiving and light-emitting device in which (2) a part of the emitter layer has a region of a conductivity type opposite to that of the emitter layer, that is, a device in which the light-receiving part and the light-emitting part are integrally formed, and we have already filed a patent application for this device. Gansho 57-
No. 69270).

(c) Purpose of the Invention The purpose of the present invention is to use the light-receiving and light-emitting device of the above-mentioned earlier application.
An object of the present invention is to provide a driving circuit for a light receiving/emitting element that is inexpensive and suitable for performing bidirectional communication using a single optical fiber.

(d) Structure and effect of the invention In order to achieve the above object, the drive circuit for the light receiving/emitting element of the present invention uses a semiconductor that emits light when a forward current is passed through the p-n junction to form a collector layer, a base layer , a three-layer phototransistor having an emitter layer is formed, and a semiconductor light-receiving/emitting element having a region of a conductivity type opposite to that of the emitter layer is formed in a part of the emitter layer, a high potential source, and a high potential source. a switching circuit for opening and closing the connection of the source to the collector layer; and a switching circuit connected between the emitter layer and a reference potential;
a light reception signal output circuit for deriving a light reception signal; a Hosmi flow injection circuit connected between the base layer and the reference potential; a low potential source; and a connection between the low potential source and the collector layer. and a control circuit that controls the current flowing from the heat source layer through the collector layer to the low potential source. A current is passed through the collector layer, base layer, and emitter layer of the element, and the light reception signal is derived from the light reception signal output circuit. When emitting light, the switching circuit is turned off, and the base layer of the light reception and light emitting element is controlled by the input signal of the control circuit. , the collector layer, the control circuit, and the low-potential source to control the light-emitting current that flows.

According to the drive circuit for the light-receiving and light-emitting element of the present invention, by properly opening and closing the switching circuit and controlling the control circuit, it is possible to reliably switch between light reception and light emission, and the circuit configuration is simple. If this is used in a transmission device, the entire device can be made small and inexpensive.

(E) Description of Examples (4) The present invention will be explained in more detail below with reference to Examples.

FIG. 1 is a cross-sectional view of a light-receiving and light-emitting element used in carrying out the present invention. In the same figure, a light receiving/emitting device 1 is formed of an n-type Ga0,6A7!0.
4 A s layer 3, p-type layer a A s layer 4, n-type layer a
0.6 A j! 0.4 As layers 5 are formed by sequentially stacking them. These n-type layer 3, p-type layer 4, and n-type layer 5 are the collector layer of the phototransistor, respectively.
Functions as base layer and anode layer. In addition, p-type Ga
The As layer 4 also functions as an active layer of the light emitting diode.

Furthermore, in the center of the n-type Ga016Aβ0.4As layer 5, a p-type layer 6 whose conductivity type is opposite to that of the surrounding layer is formed. Note that 7 is a 5i02 layer, 8 is between collector C, 9 is a base electrode, and 10 is an emitter electrode. A hole 11 through which light exits is bored in the center of the base electrode 9.

This light-receiving and light-emitting element 1 is constructed by connecting the electrode 8 to the plus (+) side of the power source and the electrode 10 to the minus (-) side of the power source.
It functions as a phototransistor, receives light (5) from the fiber 12, and a light receiving current flows. Further, when the electrode 9 is connected to the positive side of the power source and the electrode 8 is connected to the negative side of the power source, a p-n junction is formed between the layers 4 and 3, and a forward current flows to emit light and operate as a light emitting diode. Since this light-receiving/emitting element 1 is described in detail in the aforementioned prior application, further explanation of the element itself will be omitted.

FIG. 2 is a connection diagram of a drive circuit for a light-receiving and light-emitting element showing one embodiment of the present invention. In the figure, numeral 20 represents the light-receiving and light-emitting element shown in FIG. 1 with the symbol of a phototransistor. Reference numeral 21 denotes a switching circuit, which is connected between the high potential source 10 V and the collector C of the light receiving/emitting element 20. A load resistor RL is connected between the emitter E of the light receiving/emitting element 20 and the ground (reference potential). When the switching circuit 21 is turned on, a voltage of a high potential source +■ is applied to the collector C of the light receiving/emitting element 20, and the light receiving/emitting element 20 operates as a phototransistor. The load resistance RT
, and a reception signal R3 is derived from the output terminal (6) 24.

Further, a control circuit 22 is connected between the collector C of the light receiving/emitting element 20 and the low potential source -■.

A diode D for injecting current is connected between the heath of the light receiving and emitting device 20 and the ground.

The switching circuit 21 is turned off, and the control circuit 22 applies the voltage of the low potential source -■ to the collector C of the light receiving/emitting element 20.
That is, when a voltage lower than zero potential is applied, diode D + base B - collector C → control circuit 22 → low potential source -
A current 1 s flows in the order of V, and the light receiving/emitting element 20 emits light.
emits light a.

In other words, it operates as a light emitting diode.

In this case, the control circuit 22 can change the current Is by the transmission signal Ts input to the input terminal 23,
With this, the light a can be changed and an optical signal can be sent.

FIG. 3 is a circuit connection diagram showing the embodiment circuit of FIG. 2 in more detail. As shown in the figure, the switching circuit 21 is composed of a PNP type transistor Q1, the emitter of this transistor is connected to (7) a high potential source 10 V, and the collector is connected to the light receiving/emitting element 20.
A signal 11 is inputted from an input terminal 25 to the base via a resistor R1.

The control circuit 22 is also composed of a PNP type l-randisk Q2, the collector of which is connected to the low potential source -■, the emitter connected to the collector C of the light-receiving/emitting element 20, and a resistor R2 between the base and the emitter. is connected.

In this circuit, a low level 1 is applied to the input terminal 25 during reception.
1 signal is applied. As a result, the transistor Q1 is turned on, and a voltage of 10 V from the high voltage source is applied to the collector C of the light receiving/emitting element 20. Further, during transmission, a high level signal 11 is applied to the input terminal, the l transistor Ql is turned off, and the collector C of the light receiving/emitting element 20 is separated from the high potential source +V. When a negative level transmission signal Ts is applied to the input terminal 23 in this state, a current Is flows. Then, the light-receiving and light-emitting element 20 emits light. The current IS is the transmission signal Ts
The larger the negative voltage of (8), the stronger the light emitting power of the light-receiving and light-emitting element 20 becomes. In other words,
The light emission power can be changed depending on the level of the transmission signal Ts.

If a negative potential is applied to the bases of transistors Ql and Q2 at the same time to turn them on, a large current may flow through both transistors Ql and Q2 and cause them to be damaged.
It is desirable that signals of opposite polarity be input to the input terminals 23 and 25. For example, when the light-receiving and light-emitting element 20 is used as a light-receiving element, that is, at the time of reception, the input terminal 23 is forcibly set high by a reception command signal, etc., and conversely, when the light-receiving and light-emitting element 1 is used as a light-emitting element, that is, at the time of transmission, Input terminal 25 for sending command signals, etc.
All you have to do is force it to high.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a light-receiving and light-emitting device used to carry out the present invention, FIG. 2 is a connection diagram of a drive circuit for a light-receiving and light-emitting device showing one embodiment of the present invention, and FIG. 3 is a drive circuit of the same embodiment. It is a circuit connection diagram showing more specifically. (9) 1; Light-receiving and light-emitting element, 21 Varnish notching circuit, 22:
Control circuit, V: high potential source, -V: low potential source, RL: load resistance, D: diode]' Patent applicant: Tateishi Electric Co., Ltd. agent, patent attorney Shigeru Nakamura (10) No. 1 2 Figure ÷V Small "-65-21 3rd and above +V

Claims (1)

[Claims] (1) The semiconductor that emits light when a forward current is passed through the p-n junction makes the three layers of the collector layer, base layer, and emitter layer
a semiconductor light-receiving/emitting element having a region of a conductivity type opposite to that of the emitter layer in a part of the emitter layer, a high potential source, and the collector layer of the high potential source. a switching circuit that opens and closes the connection to the emitter layer, a light reception signal output circuit that is connected between the emitter layer and the reference potential and that derives the light reception signal, a base current injection circuit that is connected between the base layer and the reference potential; A drive circuit for a light-receiving and light-emitting element, comprising a potential source and a control circuit connected between the low potential source and the collector layer to control a current flowing from the base layer through the collector layer to the low potential source.