JPH0785535B2 - Current switching type drive circuit - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current switching type drive circuit that can be used in a drive circuit for a semiconductor laser or a light emitting diode.

2. Description of the Related Art Semiconductor lasers are used as light sources for optical communication, optical discs, compact discs, laser beam printers, and the like. Conventionally, as a pulse modulation circuit of a semiconductor laser,
A current switching type drive circuit using a pair of silicon transistors in a differential configuration has been often used. However, in order to drive the semiconductor laser, it is necessary to switch a large pulse current at high speed, and silicon transistors are limited in their high-speed response. Therefore, gallium arsenide Schottky junction field effect transistors (hereinafter referred to as Ga
A current switching type drive circuit using a differential pair configuration (As MESFET) has come to be used.

FIG. 3 shows the configuration of a current switching type drive circuit using a GaAs MESFET. In the figure, T ₁ and T ₂ are a pair of GaAs MESFETs, J ₁ that form a current changeover switch.
Is a constant current source (circuit), LD is a semiconductor laser, V _DD is a positive power supply terminal, V _SS is a negative power supply terminal, and OUT is an output terminal. The semiconductor laser LD is connected between the positive power supply terminal V _DD and the output terminal OUT. In addition, φ is a complementary input signal input to each gate of GaAs MESFET T ₁ , T ₂ , S is GaAs MESFET T ₁ ,
The source of T ₂ is shown.

In the current switching type drive circuit composed of the GaAs MESFET as described above, the pulse current flowing through the semiconductor laser LD is controlled by the constant current source J ₁ . Input signal corresponding to the gate potential of the GaAs MESFET T ₁ φ is is higher than the complementary (inverted) input signal corresponding to the gate potential of the _{GaAs MESFET T 2, GaAs MESFET T} 1 is turned on, the semiconductor laser L
A current flows through D, and the semiconductor laser LD emits light. On the other hand, GaA
When the gate potential of the s MESFET T ₁ is lower than the gate potential of the _{GaAs MESFET T 2, GaAs MESFET T} 1 is turned off,
No current flows through the semiconductor laser LD.

Problems to be Solved by the Invention However, in the current switching type drive circuit composed of GaAs MESFETs shown in FIG. 3, the input signals φ corresponding to the gate potentials of GaAs MESFETs T ₁ and T ₂ are complementary to each other. Therefore, the potential of the source S of the GaAs MESFETs T ₁ and T ₂ is kept constant. In such a case, the GaAs MESFET T ₁ is turned on, current flows through the semiconductor laser LD, and the output terminal OU
When the potential of T decreases, the drain-source voltage of the GaAs MESFET T ₁ becomes smaller, the GaAs MESFET T ₁ can not be used in the saturation region. In such a state, the semiconductor laser
There was a phenomenon in which the rise and fall of the pulse current flowing through the LD became as shown in Fig. 4.

Means for Solving the Problems According to the present invention, when the GaAs MESFET T ₁ is turned on and a current flows through the semiconductor laser LD to lower the potential of the output terminal OUT, the potential of the source S is lowered and the GaAs MESFET is reduced. drain-source voltage of T ₁ is kept sufficiently large, the but it is intended to provide a current switching type driving circuit as GaAs MESFET T ₁ is always used in the saturation region.

That is, the current switching type drive circuit of the present invention has a pair of Ga
A differential configuration current changeover switch consisting of As MESFET,
In the preceding stage, the high level of one of the complementary signals input to each gate of the pair of GaAs MESFETs is made lower than the high level of the other signal, and the low level of the one signal is changed to the other level. And an input signal conversion circuit for making the voltage higher than the low level.

Function With this configuration, the GaAs MESFET on the output side is turned on, and even if a current flows through the semiconductor laser and the potential at the output terminal drops, the drain-source voltage of the GaAs MESFET on the output side is kept sufficiently large. Therefore, this output side GaAs M
The ESFET can always be used in the saturation region. As a result, the pulse current flowing through the semiconductor laser exhibits steep rise and fall characteristics.

Embodiment One embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing a configuration of a current switching type drive circuit of the present invention.

In FIG. 1, T _{1 to} T ₁₄ are GaAs MESFETs, and D _{1 to} D ₇ are GaAs.
Schottky diode, R ₁ and R ₂ are resistors, J ₁ is a constant current source (circuit), LD is a semiconductor laser, V _DD is a positive power supply terminal, V _SS1 ,
V _SS2 is negative power supply terminal, GND is ground terminal, V _IN is input terminal, OU
T is an output terminal, and φ is a complementary input signal input to each gate of a pair of GaAs MESFETs T ₁ and T ₂ that composes a current changeover switch. Semiconductor laser LD is a positive power supply terminal V _DD
Connected to the output terminal OUT.

The operation of the circuit configured as described above will be described below.

The signal input to the input terminal V _IN is GaAs MESFET T ₃ ,
The level shift circuit composed of T ₄ and GaAs Schottky junction type diodes D ₁ , D ₂ and D ₃ is voltage-shifted to the switching level of the inverter circuit composed of GaAs MESFETs T ₅ and T ₆ . The output of the inverter circuit composed of GaAs MESFETs T ₅ and T ₆ passes through the level shift circuit composed of GaAs MESFETs T ₁₃ and T ₁₄ and GaAs Schottky junction type diode D ₇ to form one of the current switching switches. GaAs
It becomes the input signal of MESFET T ₂ . GaAs MESFET T ₅ , T ₆
The output of the inverter circuit composed of is also GaAs MESFE
GaAs MESFET T ₉ , T ₁₀ by a level shift circuit composed of TT ₇ , T ₈ and GaAs Schottky diodes D ₄ , D ₅ , D _6.
The voltage is shifted to the switching level of the inverter circuit configured by. The output of the inverter circuit composed of GaAs MESFETs T ₉ and T ₁₀ is divided by resistors R ₁ and R ₂ ,
s MESFET T ₁₁ , T ₁₂ through the buffer circuit, the other GaAs MES which constitutes the current changeover switch
It becomes the input signal of FET T ₁ .

By the above operation, input signal and input to the gates of GaAs MESFETs T ₁ and T ₂ that make up the current selection switch 2
The relationship between the two input signals φ, is as shown in FIG.
That is, the two input signals phi, includes an input terminal V _IN
When the input signal to is high level, it is in state A, and when it is low level, it is in state B. In each state, one side of GaAs MESFETs T ₁ and T ₂ is in the on state. However, in the A state, the potentials of the sources S of the GaAs MESFETs T ₁ and T ₂ are lowered by ΔV lower in the high level and the low level than in the B state.
Therefore, even if the input signal φ becomes high level and one of the GaAs MESFETs T ₁ forming the current changeover switch is turned on, current flows through the semiconductor laser LD and the potential at the output terminal OUT drops, the GaAs MESFET Drain of T ₁
Since the potential difference between the sources is kept large enough, GaAs MES
FET T ₁ can always be used in the saturation region. Therefore, the rise and fall of the pulse current flowing through the conductor laser LD becomes steep.

The main elements of the circuit shown in Fig. 1 are GaAs MESFETs, G
It is an aAs Schottky diode and a resistor, and it is extremely easy to make this circuit integrally in a single GaAs substrate to form an integrated circuit.

As described above, according to the current switching type drive circuit of the present invention, it is possible to supply a pulse current having a steep rise and a fall to the conductor laser, and it is possible to perform the optical communication, the optical disc, the compact disc and the laser beam printer. It is suitable as a drive circuit for a semiconductor laser used as a light source.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a current switching type drive circuit according to the present invention, and FIG.
FIG. 3 is a diagram showing the relationship between the input signal of the current switching type drive circuit of the present invention and the gate inputs of a pair of GaAs MESFETs constituting the current switching switch. FIG. 3 is a circuit diagram of the current switching type drive circuit using GaAs MESFETs. FIG. 4 is a pulse current waveform diagram when a semiconductor laser is driven by the current switching type drive circuit having the configuration of FIG. T _{1 to} T ₁₄ …… GaAs MESFET, D _{1 to} D ₇ …… GaAs Schottky diode, R ₁ , R ₂ …… Resistor, J ₁ …… Constant current circuit, LD…
… Semiconductor laser, V _DD …… Positive power supply terminal, V _SS1 , V _SS2 …… Negative power supply terminal, GND …… Grounding terminal, V _IN …… Input terminal, OUT…
... Output terminal, φ, ... Signal input to the gates of GaAs MESFETs T ₁ and T ₂ .

Claims (1)

[Claims] 1. A current changeover switch having a differential structure composed of a pair of GaAs MESFETs, and the pair of GaAs MESFETs before the current changeover switch.
An input signal that makes the high level of one of the complementary signals input to the respective gates of the FETs lower than the high level of the other signal and makes the low level of the one signal higher than the other low level. A current switching type drive circuit characterized by comprising a conversion circuit.