JP2002335017A - Light emitting element driving circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a drive circuit of a three-terminal light emitting element wherein speed is high, quenching characteristic is high, and application to high speed optical transmission is enabled. SOLUTION: Driving of the three-terminal light emitting element of high speed and high quenching characteristic is realized with a light emitting element driving circuit 3 provided with a modulation part 4 and a control part 5. The modulation part 4 performs intensity modulation of the three-terminal light emitting element 1 by changing the amount of current to an emitter terminal according to an input signal 2 to the element 1, in the common base three- terminal light emitting element 1. The control circuit 5 performs gate switching control of the intensity modulated light of the element by changing a voltage applied to a collector terminal according to the input signal 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving circuit for driving a semiconductor transistor having a light emitting region.

[0002]

2. Description of the Related Art Light-emitting diodes are widely used as one of light-emitting elements for medium- and high-speed baseband digital optical communication having a transmission speed of 1 Gbps or less. Light-emitting diodes promise excellent transmission quality and long-term reliability as light-emitting elements for short-distance transmission using multimode fibers due to features such as thresholdless current and low coherence. Also, from the viewpoint of eye safety in spatial transmission, the incoherence of emitted light is useful. On the other hand, in a normal light emitting diode, since the band characteristic and the light emission output have a trade-off relationship, the cutoff frequency is practically limited to about 100 MHz. It is possible to improve the band characteristics by driving the light emitting diode with a low extinction ratio or a low modulation factor, but the practicability in ordinary baseband digital optical transmission requiring high extinction characteristics is possible. Is low.

As a conventional technique for solving such a restriction on the modulation speed, a light emitting element and a driving circuit using a three-terminal structure similar to a transistor element are disclosed in Japanese Patent Application No. 2000-2018.
No. 98 discloses this. Pnp disclosed here
In the type three-terminal light-emitting device, a light-emitting operation can be obtained by injecting carriers into the pn connection between the emitter and the base, and the accumulated carriers in the light-emitting region can be controlled via the collector terminal.

FIG. 2 shows a driving circuit of the conventional three-terminal light emitting device. As shown in FIG.
1 is grounded to the base, a constant current is injected from the emitter terminal from the constant current controller 102, and a signal is input from the collector terminal by the control means 103 to modulate the emission intensity of the three-terminal element. Due to the direct control of the accumulated carriers, the pulse fall response is improved during pulse modulation. FIG. 3 shows an operation state of the driving circuit according to the prior art.

[0005]

However, the drive circuit for the three-terminal light emitting element according to the prior art described above has insufficient rise response and extinction characteristics in pulse response, and is therefore applicable to practical high-speed optical transmission. Was difficult.

[0006]

In order to solve the above-mentioned problems, a light emitting element driving circuit according to the present invention is a driving circuit for driving a semiconductor transistor element having a light emitting region. A modulating unit that modulates the intensity of the element by increasing or decreasing the amount of current injected into either the first terminal of the emitter or the collector of the element,
A control unit is provided for controlling gate opening / closing of intensity-modulated light of the element by changing a voltage applied to the other second terminal of the element according to an input signal.

Further, a light emitting element driving circuit according to the present invention is a driving circuit for driving a semiconductor transistor element having a light emitting region, wherein a base terminal of the element is grounded and an emitter or a collector of the element is turned on in response to an input signal. A modulator for increasing or decreasing the amount of current injected into any one of the first terminals to modulate the intensity of the element; and opening the other second terminal of the element and applying a signal to the second terminal according to an input signal. It has a control unit that applies a predetermined potential and controls opening and closing of the gate.

A light emitting element driving circuit according to the present invention is a driving circuit for driving a semiconductor transistor element having a light emitting region, wherein a base terminal of the element is grounded and either an emitter or a collector of the element is turned on in response to an input signal. A modulator for increasing or decreasing the amount of current injected into one of the first terminals to modulate the intensity of the element, and opening the other second terminal of the element and applying a predetermined amount to the second terminal according to an input signal. It has a control unit for applying potential and controlling the opening and closing of the gate.

A light-emitting element driving circuit according to the present invention is a driving circuit for driving a semiconductor transistor element having a light-emitting region, wherein a base terminal of the element is grounded and any one of an emitter and a collector of the element according to an input signal. A modulator for increasing or decreasing the amount of current injected into one of the first terminals to intensity-modulate the element, and connected to the other second terminal of the element in response to an input signal; A first phase of a signal output from the modulation unit and a second phase of a signal output from the control unit.
Are in-phase (or opposite phases), the second phase is a leading phase (or lagging phase) with respect to the first phase, and the first phase and the second phase The phase difference between the phases is shorter (or longer) than one time slot of the input signal.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A semiconductor transistor device having a light emitting region according to the present invention has a third terminal in addition to two current injection terminals, and performs a light emitting operation by two current injection terminals and a third operation. This is a light-emitting element that can perform a light-emitting state control operation by the terminal of (1). In the present specification, the three terminals are hereinafter referred to as a base terminal, an emitter terminal, and a collector terminal in the same manner as a normal bipolar transistor. According to this name, the semiconductor transistor device according to the present invention is provided with a light emitting operation by current injection between a base terminal and an emitter terminal (or a base terminal and a collector terminal) and a control of a light emitting state of the device by a remaining collector terminal (or an emitter terminal). It shall be expressed as a three-terminal light emitting element capable of obtaining an operation.

Hereinafter, the present invention will be described in detail.

(Embodiment 1) FIG. 1 shows a configuration of a drive circuit according to the present embodiment. In FIG. 1, reference numeral 1 denotes a three-terminal light-emitting element which is a pnp type semiconductor transistor element having a light-emitting region, 2 denotes an input signal, 4 denotes a modulator, 5 denotes a controller,
Reference numeral 3 denotes a drive circuit including the modulation unit 4 and the control unit 5. In this embodiment, of the three terminals of the three-terminal light-emitting element, the base terminal is a ground terminal, the first terminal of either the emitter or the collector is the emitter terminal, and the other terminal is the collector terminal. I have.

The input signal 2 input to the drive circuit 3 is input to a modulation unit 4 and a control unit 5 constituting the drive circuit 3, respectively. In response to the input signal, the modulator 4 increases or decreases the amount of current injected into the emitter terminal, and similarly, the controller 5 controls the voltage applied to the collector terminal. Here, by increasing / decreasing the injection current according to the input signal to the emitter terminal, in other words, by injecting the current modulation signal, the three-terminal light emitting element 1 is intensity-modulated, and an output signal light proportional to the current modulation signal is generated. Is output. Further, in the transistor element according to the present invention, by applying a predetermined voltage to the collector terminal, the amount of light emission due to current injection from the emitter terminal can be suppressed. Therefore, the control unit 5 applies a predetermined voltage signal to the collector terminal according to the input signal, whereby a substantial gate opening / closing control operation for the output light of the element can be obtained.

Here, when a voltage signal is applied to the collector terminal, the response speed when the gate is open shows a relatively slow response governed by the recombination time constant of the light emitting region. It has been clarified by our research that the amount of suppression of light emission and the response speed are governed by the depth of the potential of the voltage applied to the collector terminal, and exhibit a faster response than when the gate is open. Therefore, according to the input signal,
By injecting a current modulation signal into the emitter terminal and applying a control signal voltage to the collector terminal of the three-terminal light emitting device according to the present invention, a response characteristic of light emission suppression when the gate is closed,
A high-speed signal response that achieves both the response characteristics to the injection of the current modulation signal into the emitter terminal can be realized. Further, even when the extinction ratio of the intensity-modulated light is low, an output signal light having high extinction characteristics can be obtained by the light emission suppressing operation when the gate is closed.

Further, in the present embodiment, the modulating unit 4
Has, for example, a differentiating circuit having a circuit time constant that is a product of R and C connected in parallel with a resistor having a resistance value R and having a capacitance value of C, and outputting a differential current signal with respect to an input signal. By having, since the frequency characteristics of the light emitting element can be compensated, it is possible to obtain a high-speed response intensity modulated light at a frequency equal to or higher than the frequency band of the light emitting element.
By combining the gate closing operation and the intensity modulation operation by the differential current modulation signal to the emitter terminal, a higher extinction characteristic and a faster waveform response can be easily realized.

By selecting the time constant of the differentiating circuit approximately equal to the recombination time constant of the light emitting region, the frequency characteristics of the light emitting device can be almost ideally compensated. The maximum realizable high-speed response characteristics can be easily obtained.

FIG. 4 shows an operation state of the drive circuit according to the above-described embodiment. In this embodiment, the three-terminal light-emitting element is driven at a higher speed and with a higher extinction ratio compared to the related art by the modulation of the current signal to the emitter by the modulator for differentiating the input signal and the gate opening / closing control by the controller. I have.

In the light emitting element driving circuit shown in the first embodiment, the potential relationship between the potential V1 applied to the collector terminal during the gate opening operation and the potential V2 generated at the collector terminal when the collector terminal is opened is expressed by When | V1 |> | V2 |, current is injected from the collector terminal to the base terminal, which may damage the light emitting element. Therefore, the potential relationship between V1 and V2 is | V1 | ≦ | V
By setting 2 |, shortage situations can be avoided beforehand.

Note that the potential relationship between the potential V1 and the potential V2 is |
By setting V1 | ≒ | V2 |, in the three-terminal light emitting device according to the present invention, the light emission suppressing function is stopped, that is, the gate is completely opened, so that it depends only on the amount of current injected from the emitter terminal. A light emission output is obtained, and in the case of this potential relationship, it is needless to say that the light emitting element is not damaged and the extinction characteristics are further improved.

As described above, according to the present driving circuit, the injection of the current modulation signal to the emitter terminal and the application of the control signal voltage to the collector terminal of the three-terminal light emitting element according to the present invention are performed in accordance with the input signal. By doing so, a high-speed signal response that achieves both a response characteristic of light emission suppression when the gate is closed and a response characteristic to injection of a current modulation signal into the emitter terminal can be realized. Furthermore, even when the extinction ratio of the intensity-modulated light is low, an output signal light with high extinction characteristics can be obtained by the light emission suppression operation when the gate is closed, and a light emitting element driving circuit applicable to practical high-speed optical transmission is provided. realizable.

(Embodiment 2) In the light emitting element drive circuit shown in Embodiment 1, the potential V1 applied to the collector terminal when the gate is opened and the potential V2 generated at the collector terminal when the collector terminal is opened are determined. | V1 |｜|
By setting V2 |, the light-emitting element is not damaged and the extinction characteristic can be improved. However, in practice, the potential relationship between the potential V1 and the potential V2 fluctuates depending on the temperature characteristic of the element and the temperature characteristic of the circuit. Therefore, its realization is not easy.

FIG. 5 shows the configuration of the drive circuit according to the present embodiment. In FIG. 5, reference numeral 1 denotes a three-terminal light-emitting element which is a pnp type semiconductor transistor element having a light-emitting region, 2 denotes an input signal, 4 denotes a modulator, 6 denotes a controller, 7 denotes a modulator 4 and a controller 6. Drive circuit. In the present embodiment, of the three terminals of the three-terminal light emitting element, the base terminal is a ground terminal, the first terminal of either the emitter or the collector is the emitter terminal, and the other terminal is the collector terminal. I have.

The input signal 2 input to the drive circuit 3 is input to a modulation unit 4 and a control unit 6 constituting the drive circuit 3, respectively. In response to the input signal, the modulator 4 increases or decreases the amount of current injected into the emitter terminal, and similarly, the controller 6 controls the state of the collector terminal. Here, for the emitter terminal,
By increasing or decreasing the injection current according to the input signal, in other words, by injecting the current modulation signal, the intensity of the three-terminal light emitting element 1 is modulated, and an output signal light proportional to the current modulation signal is output. Further, in the transistor element according to the present invention, by applying a predetermined voltage to the collector terminal, the amount of light emission due to current injection from the emitter terminal can be suppressed. Therefore, the control unit changes to an electrically open state with the collector terminal and an applied state of the predetermined potential to the collector terminal in response to the input signal, thereby substantially controlling the gate opening / closing operation for the output light of the element. can get.

Here, the control unit 6 according to the present embodiment
Can be composed of, for example, one stage of a common-collector pnp-type control transistor. The control transistor is turned on / off depending on whether or not a current is supplied from the three-terminal light-emitting element according to the present invention, so that the control transistor responds to an input signal. In addition, it is possible to realize an electrical open state with the collector terminal and a change in the applied state of the predetermined potential to the collector terminal. More specifically,
The potential relationship between the potential V1 applied to the collector terminal when the gate of the three-terminal light emitting element is closed, that is, the potential V2 generated at the collector terminal when the collector terminal is opened, is | V1 | <| V2.
In the case of |, the control transistor operates as a voltage follower for an input signal supplied with current from the three-terminal element. In other words, during this period, a potential corresponding to the input signal can be applied to the collector terminal. On the other hand, since the current supply from the three-terminal element decreases as the gate changes from the closed state to the open state, the control transistor shifts to the off state, and is completely turned off when the current supply is completely cut off. At this time, since the control transistor and the collector terminal when the three-terminal light emitting element is open are in an electrically open state, the collector terminal generates the potential V2. In other words, during this period,
The collector terminal is electrically open regardless of the input signal.

Therefore, by setting the potential relationship between the potential V1 and the potential V2 to | V1 | ≒ | V2 | by the above operation, the light emission suppressing function is stopped in the three-terminal light emitting element according to the present invention, ie, Since the gate is completely opened, a light emission output depending only on the amount of current injected from the emitter terminal can be obtained, and this potential relationship can be stably realized over a wide temperature range, and high extinction characteristics are realized. Can do things. Therefore, by injecting a current modulation signal to the emitter terminal and applying a control signal voltage to the collector terminal of the three-terminal light emitting element according to the present invention in response to an input signal, the response characteristic of light emission suppression when the gate is closed is performed. And a high-speed signal response that achieves both the response characteristics to the injection of the current modulation signal into the emitter terminal. Further, even when the extinction ratio of the intensity-modulated light is low, an output signal light having high extinction characteristics can be obtained by the light emission suppressing operation when the gate is closed.

As described above, according to the present invention, the current modulation of the emitter terminal and the gate opening / closing control of the light emission output by controlling the voltage of the collector terminal are simultaneously performed for the three-terminal light emitting element, thereby realizing a high speed by the current modulation of the emitter terminal. Not only can simultaneously use the rising response and the high-speed falling response by the gate opening / closing control, but also can operate stably over a wide temperature range and realize high extinction characteristics. It can be applied to high-speed optical transmission.

(Embodiment 3) The above-described Embodiments 1 and 2 provide a good high-speed response operation when the signal phases of the control section and the modulation section are aligned, but are practical. In some cases, the light emission output signal may be distorted with respect to the input signal due to a signal phase shift caused by a difference in signal waveform between the control unit and the modulation unit. Management is not easy.

FIG. 6 shows the configuration of the drive circuit according to the present embodiment. In FIG. 6, reference numeral 1 denotes a three-terminal light emitting element which is a pnp type semiconductor transistor element having a light emitting region, 2 denotes an input signal, 4 denotes a modulation section, 5 denotes a control section, 8 denotes a delay section for delaying an input signal, and 9 denotes a delay section. Modulation unit 4, control unit 5, and delay unit 8
Is a driving circuit composed of

In this embodiment, of the three terminals of the three-terminal light emitting device, the base terminal is a ground terminal, the first terminal of either the emitter or the collector is the emitter terminal, and the other terminal is the other terminal. Used as collector terminal. Note that, in the present embodiment, the first signal phase output from the modulation section 4 and the second signal phase output from the control section 5 have an in-phase relationship.

The input signal 2 input to the drive circuit 9 is input to each of the delay unit 8 and the control unit 5 constituting the drive circuit 9. In the delay unit 8, the input signal delayed by a delay amount equal to or less than one time slot of the input signal is input to the modulation unit 4, and the modulation unit 4 increases or decreases the current injection amount to the emitter terminal according to this signal. . On the other hand, the control unit 5 controls the voltage applied to the collector terminal according to the input signal.

Here, the delay generated by the delay unit 8
Compared with the phase of the current modulation signal of the modulation section 4, the phase of the output voltage signal of the control section 5 is the advanced phase. During the period in which the input signal is switched from space to mark due to this phase difference, first, the control unit 5 causes the light emitting state of the three-terminal light emitting element 1 to transition from the gate closed state to the gate open state. Increases according to the input signal. Therefore, the response speed of the rising edge of the optical output waveform in this period is determined only by the response speed to the injection current from the modulator 4 to the emitter terminal.

During the period when the input signal is switched from the mark to the space due to the delay generated by the delay unit 8, first, the control unit 5 changes the light emitting state of the three-terminal light emitting element 1 from the gate open state to the gate closed state. Thereafter, the amount of current injected from the modulating unit 4 to the emitter terminal decreases according to the input signal. Accordingly, a high-speed response is obtained in which the response speed of the fall of the light output waveform in this period is determined only by the above-described transition speed from the gate open state to the gate closed state.

FIG. 7 shows an operation state of the drive circuit according to the above-described embodiment.

With the above operation, the light emitting element driving circuit according to the present invention applies current modulation of the emitter terminal and gate opening / closing control of the light emission output by controlling the voltage of the collector terminal to the three terminal light emitting element, and modulates the current of the modulation section. Compared to the signal phase, the output voltage signal of the control unit has the advanced phase, so that the accuracy of practical signal phase control is achieved, and the fast rise response by current modulation of the emitter terminal and the gate opening / closing control High-speed falling response can be easily used. Furthermore, high extinction characteristics can be realized, and therefore, it can be applied to high-speed optical transmission.

[0035]

As described above, the light emitting element driving circuit of the present invention is a driving circuit for driving a semiconductor transistor element having a light emitting region. The base terminal of the element is grounded, and the element is driven in accordance with an input signal. A modulator for increasing / decreasing the amount of current injected into one of the first terminals of the emitter or collector to modulate the intensity of the element,
With a configuration that is connected to the other second terminal of the element and that includes a control unit that controls gate opening and closing of the intensity-modulated light of the element, a rising response and a quenching characteristic in a pulse response are improved, and practical A light emitting element drive circuit applicable to high-speed optical transmission can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a drive circuit according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a driving circuit according to a conventional technique.

FIG. 3 is a diagram showing an operation state of a drive circuit according to the related art.

FIG. 4 is a diagram showing an operation state of the drive circuit according to the first embodiment of the present invention.

FIG. 5 is a diagram showing a configuration of a drive circuit according to a second embodiment of the present invention.

FIG. 6 is a diagram showing a configuration of a drive circuit according to a third embodiment of the present invention.

FIG. 7 is a diagram showing an operation state of a drive circuit according to a third embodiment of the present invention.

[Explanation of symbols]

Reference Signs List 1 semiconductor transistor element having light emitting region (three terminal light emitting element) 2 input signal 3, 7, 9 drive circuit 4 modulation part 5, 6 control part 8 delay part 101 three terminal light emitting element 102 constant current control device 103 control means

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04B 10/28

Claims (9)

[Claims] 1. A driving circuit for driving a semiconductor transistor element having a light emitting region, wherein a base terminal of the element is grounded and a first terminal of one of an emitter and a collector of the element is connected to an input signal according to an input signal. A modulator for increasing or decreasing the current injection amount of the element and modulating the intensity of the element, according to an input signal,
A light-emitting element drive circuit, comprising: a control unit that controls opening and closing of the intensity-modulated light of the element by changing a voltage applied to the other second terminal of the element. 2. A driving circuit for driving a semiconductor transistor element having a light emitting region, wherein a base terminal of the element is grounded and a first terminal of one of an emitter and a collector of the element is connected to an input signal according to an input signal. A modulator for increasing or decreasing the current injection amount of the element and modulating the intensity of the element, according to an input signal,
A light-emitting element driving circuit, comprising: a control unit that opens and closes a gate by controlling opening and closing of a gate by opening a second terminal of the element and applying a predetermined potential to the second terminal. 3. The modulator according to claim 1, wherein the modulator has a function of differentiating the input signal by a predetermined differential amount.
The light emitting element drive circuit according to any one of the preceding claims. 4. The light emitting element drive circuit according to claim 3, wherein the differential amount is substantially equal to a recombination time constant of the element. 5. The potential difference Vb1 between the base terminal and the first terminal of the element and the potential difference Vb2 between the base terminal and the second terminal when the gate is closed satisfy a relationship of | Vb1 | × | Vb2 | ≦ 0. The light emitting element drive circuit according to claim 1 or 2, wherein: 6. A potential V1 applied to a second terminal and a potential V2 generated at the second terminal when the second terminal is opened.
2. The light emitting element drive circuit according to claim 1, wherein the potential relationship of | V1 | ≦ | V2 |. 7. A driving circuit for driving a semiconductor transistor element having a light emitting region, wherein a base terminal of the element is grounded and a first terminal of one of an emitter and a collector of the element is connected to an input signal according to an input signal. A modulator for increasing or decreasing the current injection amount of the element and modulating the intensity of the element, according to an input signal,
A control unit connected to the other second terminal of the element and controlling gate opening and closing of the intensity-modulated light of the element; a first phase of a signal output from the modulation unit and output from the control unit; A second phase of the signal is in phase (or out of phase), the second phase is a leading phase (or lagging phase) with respect to the first phase, and the first phase is A light-emitting element driving circuit, wherein a phase difference between the second phases is shorter (or longer) than one time slot of an input signal. 8. The method according to claim 1, wherein the period of the large amount of current injection is longer than the period of the input signal corresponding to the state of the large amount of current injection when increasing or decreasing the amount of current injection to the first terminal. A light emitting element drive circuit according to claim 7. 9. The light emitting element driving circuit according to claim 7, wherein the gate open period of the control unit is longer than the period of the input signal corresponding to the open state of the gate.