JPH10321935A - Light-emitting element drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide light-emitting element drive circuit at low cost which can stabilize the peak light output of an light-emitting element without complex adjustments. SOLUTION: This circuit is provided with an environmental temperature detecting circuit constituted of a linear temperature resistor Rs, a variable resistor VR1 for bias adjustment and a voltage amplifier 4, and a drive current outputting circuit constituted of driving current generators 1, 2, 3 and a drive current adding circuit. In this case, the drive current generators 1, 2, 3 output drive currents which change linearly with respect to the change in environmental temperature, on the basis of a correction coefficient which has been previously set so as to make the light output of a semiconductor laser diode LD almost constant. Respective drive currents Io1, Io2, Io3 from the drive current generators 1, 2, 3 are summed by the drive current adding circuit, and the summed drive current Io is outputted to the semiconductor laser diode LD.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting device driving circuit for driving a light emitting device such as a semiconductor laser diode and a light emitting diode.

[0002]

2. Description of the Related Art Conventionally, as a light emitting element driving circuit,
There is one shown in FIG. 9 (Japanese Unexamined Patent Publication No. 7-107042).
Publication). This light emitting element driving circuit includes a light emitting element 401
A monitor signal detector 402 for receiving the light output of the light emitting element 401, a driving amplifier 403 for driving the light emitting element 401, and a peak value holding circuit for holding the peak value of the output of the monitor signal detector 402 404
A pseudo monitor signal shaping circuit 405 for generating a pseudo monitor signal from the data signal; a pseudo monitor peak value hold circuit 406 receiving the output from the pseudo monitor signal shaping circuit 405 and outputting the pseudo monitor signal; ,
A differential amplifier 407 for detecting a difference between the monitor signal from the peak value hold circuit 404 and the pseudo monitor signal from the pseudo monitor peak value hold circuit 406 and outputting a feedback signal to the driving amplifier 403; .

In the light emitting element driving circuit having the above configuration, even if the input data signal is a burst signal, the time constant of the peak value hold circuit 404 for the monitor signal and the pseudo monitor peak value hold circuit 406 for the pseudo monitor signal is obtained. Is optimized, it is possible to stabilize the peak light output other than the pulse of the first bit.

As another light emitting element driving circuit, there is one as shown in FIG. 10 (JP-A-2-129).
983). This light emitting element drive circuit includes a mark ratio detection circuit 501 for detecting a mark ratio of a data signal, a low-pass filter 502 for adjusting a cutoff frequency according to an output of a monitor signal, and a mark ratio detection circuit 501. A voltage-current converter 503 is provided that receives the output detection signal and the voltage signal output from the low-pass filter 502 and converts the voltage signal into a current signal. Further, the light emitting element driving circuit includes a light emitting element 511 and a monitoring light receiving element 512 for monitoring light of the light emitting element 511. The power supply + VB is connected to the cathode of the monitoring light receiving element 512, and the amplifier OP is connected to the anode of the monitoring light receiving element 512.
11 input terminals are connected. The output of the monitor light receiving element 512 is supplied to a differential amplifier OP via an integrating circuit including an amplifier OP11, a capacitor C1, and a resistor R12.
12 to the non-inverting input terminal of the differential amplifier OP1.
The detection signal of the mark ratio detection circuit 501 is input to the inverting input terminal of the second. The output signal of the differential amplifier OP12 is input to the low-pass filter 502. Further, a transistor Q11 in which the data signal is input to the base via the gate circuit 500,
And a transistor Q12 whose polarity is inverted is input to the base of the transistor Q12. The emitters of the transistors Q11 and Q12 are connected to each other, and both emitters are connected to the power supply -VEE via the resistor R11. The above transistor Q
12 is connected to one input terminal of the adder 504, and the other input terminal of the adder 504 is connected to the voltage-current converter 5
03 is connected, and the cathode of the light emitting element 511 is connected to the output terminal of the adder 504.

In the light emitting element driving circuit having the above configuration, the cut-off frequency of the low-pass filter 502 is controlled so as to be substantially inversely proportional to the mark ratio of the data signal. The frequency hardly depends on the mark rate of the data signal for driving the semiconductor laser 503,
Changes in response speed when adjusting the optical output can be reduced, and even when the input data signal is a burst signal, the peak optical output other than the first few bits can be stabilized.

[0006]

In the light emitting element driving circuit using the pseudo monitor signal, the time constants of the peak value hold circuit 404 for the monitor signal and the pseudo monitor peak value hold circuit 406 for the pseudo monitor signal are set. Even if the optimization is performed, if the input data signal is a burst signal, the pulse of the first bit of the burst signal has a disadvantage that the peak light output cannot be stabilized. This is due to the fact that the light emitting element drive circuit is constituted by a feedback circuit having a finite time constant, so that an unadjusted light emitting time is indispensable. Further, the light emitting element drive circuit is a useful means when it is not required to stabilize the peak light output of the first few bits of the pulse of the burst signal. However, since the light emitting element drive circuit includes at least two hold circuits, There is a problem that the cost increases because the circuit scale becomes large and the adjustment of the time constant is complicated.

The light emitting element driving circuit using the mark ratio detecting circuit 501 adjusts the cutoff frequency of the low-pass filter 502 in accordance with the detected mark ratio and the monitor signal, thereby providing a feedback circuit. The time constant is independent of the mark rate of the input data signal, and as a result, the peak light output is stabilized.However, the peak light output of the first few bits of the burst signal is stabilized. I can't do it. This is the same as the light emitting element driving circuit using the pseudo monitor signal, as in the case of the mark ratio detecting circuit 50.
This is because the light-emitting element driving circuit using No. 1 is composed of a feedback circuit having a finite time constant, and thus the light-emitting time without adjustment is indispensable. Further, the light emitting element driving circuit is a useful means when it is not required to stabilize the peak light output of the pulse of the first few bits of the burst signal, but it is a complicated feedback circuit incorporating a low-pass filter. , There is a problem that the circuit scale is large and the cost is high. Further, even if the adjustment range of the time constant is wide, the mark rate is 0% or 100%.
In the case of (1), there is also a problem that the error of the peak light output becomes large.

An object of the present invention is to provide a low-cost light-emitting element driving circuit that can stabilize the peak light output of the light-emitting element without complicated adjustment.

[0009]

To achieve the above object, a light emitting element driving circuit according to a first aspect of the present invention includes an ambient temperature detecting circuit for detecting an ambient temperature, and an ambient temperature detecting circuit for detecting an ambient temperature detected by the ambient temperature detecting circuit. A driving current output circuit that outputs a driving current to the light emitting element so that the light output of the light emitting element becomes substantially constant based on the correction coefficient determined in advance.

The light emitting element includes a semiconductor laser diode and a light emitting diode. In these light emitting elements, the relationship between the ambient temperature and the driving current when the light output is constant is represented by a predetermined characteristic curve. Therefore, the correction coefficient of the drive current output circuit is determined in advance so that the drive current is output according to the ambient temperature based on the characteristic curve, and the drive current output circuit is controlled so that the optical output is always substantially constant. The driving current is output to the light emitting element. Therefore, a low-cost light-emitting element driving circuit that can stabilize the peak light output of the light-emitting element without complicated adjustment can be realized.

According to a second aspect of the present invention, there is provided a light emitting element driving circuit according to the first aspect, wherein the driving current output circuit linearly changes with the ambient temperature based on a preset correction coefficient. A plurality of drive current generators that output drive currents so as to change in the form of a current, and a drive that adds the respective drive currents from the plurality of drive current generators and outputs the added drive current to the light emitting element And a current adding circuit.

According to the light emitting element drive circuit of the second aspect, the drive current output from each of the drive current generators is:
Each changes linearly with respect to the ambient temperature. The sum of the drive currents output from the drive current generators is
The correction coefficient of each drive current generator is set in advance so as to approximate the characteristic curve of the drive current with respect to the ambient temperature when the light output is constant. By doing so, when the drive currents output from the plurality of drive current generators that generate the drive currents according to the correction coefficients are added to the drive current addition circuit and then output to the light emitting elements, the change in the ambient temperature causes Regardless, the light output of the light emitting element becomes substantially constant. As described above, the fluctuation of the peak light output of the light emitting element with respect to the ambient temperature can be suppressed at low cost without requiring complicated adjustment and a large-scale circuit. Further, since the light emitting element driving circuit has a configuration having no time constant without referencing an input signal sequence or monitoring an optical output, it does not depend on an input signal,
The peak light output of the burst signal can also be kept stable.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a light emitting element driving circuit according to the present invention will be described in detail with reference to the illustrated embodiments.

In general, the drive current required to obtain the same light output from a semiconductor laser diode is not a linear characteristic with respect to the ambient temperature, but a characteristic represented by a curve as shown in FIG. ing.

Therefore, in order to always obtain a constant light output with respect to the ambient temperature without monitoring the light output emitted from the semiconductor laser diode, the relationship between the ambient temperature and the drive current is shown in FIG. It is necessary to adjust so as to satisfy the following. Here, the slope of the characteristic curve shown in FIG.
It is known that the (coefficient) does not change significantly depending on the production variation of the semiconductor laser diode, but changes only only in its absolute value. Based on this fact, as shown in FIG. 1, the present applicant has made a drive current generation method capable of obtaining a desired drive current in consideration of temperature characteristics by performing current adjustment at one place at a normal temperature of 25 ° C. A light emitting element driving circuit was realized.

Hereinafter, the temperature dependence of the drive current for obtaining the same light output is 0.1 mA / ° C. at 25 ° C. or less, and 25 ° C. to 6 ° C.
A light emitting element driving circuit used to drive a semiconductor laser diode having 0.2 mA / ° C. at 0 ° C. and 0.8 mA / ° C. at 60 ° C. or more will be described.

FIG. 1 is a circuit diagram of a light emitting element driving circuit according to one embodiment of the present invention. In this light emitting element driving circuit, one end of a positive coefficient linear temperature resistor Rs is connected to ground, and the other end is connected. It is connected to one end of a bias adjusting variable resistor VR1. The other end of the bias adjusting variable resistor VR1 is connected to the power supply voltage + V. The connection point between the linear temperature resistor Rs and the bias adjusting variable resistor VR1 is connected to the non-inverting input terminal of the differential amplifier OP1. The output terminal and the inverting input terminal of the differential amplifier OP1 are connected through a resistor R1, and the inverting input terminal of the differential amplifier OP1 is connected through a resistor R2. The voltage amplifier 4 is constituted by the differential amplifier OP1, the resistor R1, and the resistor R2.

The output terminal of the differential amplifier OP1 is
It is connected to the base of the NPN transistor Q1, and the emitter of the NPN transistor Q1 is connected to the ground via the current adjusting resistor Ro1. The collector of the NPN transistor Q1 is connected to the cathode of the semiconductor laser diode LD via the switch SW. The power supply + V is connected to the anode of the semiconductor laser diode LD. The drive current generator 1 is composed of the NPN transistor Q1 and the current adjusting resistor Ro1.

The output terminal of the differential amplifier OP1 is connected to the non-inverting input terminal of the differential amplifier OP2 via a resistor R4, and the non-inverting input terminal of the differential amplifier OP2 and the ground are connected via a resistor R5. Connected. The above differential amplifier O
The negative side of the reference voltage source E1 whose positive side is connected to the ground is connected to the inverting input terminal of P2 via a resistor R3. The output terminal and the inverting input terminal of the differential amplifier OP2 are connected via a resistor R6. The output terminal of the differential amplifier OP2 is connected to the base of the NPN transistor Q2, and the emitter of the NPN transistor Q2 is connected to the ground via the current adjusting resistor Ro2. The collector of the NPN transistor Q2 is connected to the collector of the NPN transistor Q1. The above resistors R3 to R
6, the differential amplifier OP2, the reference voltage source E1, the NPN transistor Q2 and the current adjusting resistor Ro2 constitute the drive current generator 2.

Further, the output terminal of the differential amplifier OP1 is connected to the non-inverting input terminal of the differential amplifier OP3 via a resistor R8, and the non-inverting input terminal of the differential amplifier OP3 and the ground are connected via a resistor R9. Connected. The negative side of the reference voltage source E2 whose positive side is connected to the ground is connected to the inverting input terminal of the differential amplifier OP3 via a resistor R7. The output terminal and the inverting input terminal of the differential amplifier OP3 are connected via a resistor R10. The output terminal of the differential amplifier OP3 is connected to the base of the NPN transistor Q3, and the emitter of the NPN transistor Q4 is connected to the ground via the current adjusting resistor Ro3.
The collector of the NPN transistor Q3 is connected to the collector of the NPN transistor Q1. The above resistor R7
, R10, a differential amplifier OP3, a reference voltage source E1, an NPN transistor Q3, and a current adjusting resistor Ro3.

The drive current generators 1, 2, 3 and a drive current adder for connecting one end of the switch SW and the collector of each of the NPN transistors Q1, Q2, Q3 of the drive current generators 1, 2, 3 respectively. A drive current output circuit is constituted by a current path as a circuit.

In the light-emitting element driving circuit having the above-described configuration, the voltage determined by the voltage dividing ratio of the positive coefficient linear temperature resistor Rs and the bias adjusting variable resistor VR1 is amplified by the voltage amplifier 4. The voltage VS1 is output. As shown in FIG. 3, the voltage VS1 has a temperature dependence, and the absolute value of the voltage VS1 is substantially proportional to the ambient temperature by adjusting the bias adjusting variable resistor VR1. .

Further, the drive current generator 1 operates at a voltage VS
1 and the drive current Io1 determined by the current adjustment resistor Ro1.
From the power supply + VB to the semiconductor laser diode LD, the switch SW, the NPN transistor Q1, and the current adjusting resistor R.
Flows to ground via o1. The current adjustment resistor Ro
1 is ΔIo1 = ΔVS1 / ΔRo1 = 0.1 mA / ° C. ΔIo1: Current change of the drive current Io1 per 1 ° C. ΔVS1: Voltage change of the voltage VS1 per 1 ° C. ΔRo1: 1 ° C. of the resistance Ro1 Resistance change per contact Io1 = ID1 + △ Io1 · t ID1: Drive current at 0 ° C. t: Ambient temperature As a result, the drive current Io1
Has a temperature dependence shown in FIG. The vertical axis in FIG. 4 is an arbitrary scale.

The driving current generator 2 amplifies the voltage difference between the voltage VS1 and the reference voltage VS2 by the differential amplifier OP2, and generates the driving current Io determined by the current adjusting resistor Ro2.
2 is a semiconductor laser diode L from a power source (not shown).
D, flows to ground via NPN transistor Q2 and current adjusting resistor Ro2. The current adjusting resistor Ro2
ΔIo2 = Δ (VS1 · VS2) /ΔRo2=0.1 mA / ° C. ΔIo2: Current change of the drive current Io2 per 1 ° C. Δ (VS1 · VS2): Voltage of the voltages VS1, VS2 per 1 ° C. Change ΔRo2: The resistance Ro2 is set to change in resistance per 1 ° C. The reference voltage VS2 of the reference voltage source E1 is equal to the voltage VS at 25 ° C. in FIG.
It is set to be equal to 1. As a result, the characteristic of the drive current Io2 with respect to the ambient temperature has a temperature dependence shown in FIG. The vertical axis in FIG. 5 is an arbitrary scale.

The drive current generator 3 amplifies the voltage difference between the voltage VS1 and the reference voltage VS3 by the differential amplifier OP3, and the current determined by the current adjusting resistor Ro3 is supplied from the power supply + VB to the semiconductor laser diode LD3. , Switch S
It flows to the ground via the W, NPN transistor Q3 and the current adjusting resistor Ro3. The current adjusting resistor Ro3
ΔIo3 = Δ (VS1 · VS3) /ΔRo3=0.6 mA / ° C. ΔIo3: Current change of the drive current Io2 per 1 ° C. Δ (VS1 · VS3): Voltage of the voltages VS1, VS3 per 1 ° C. Change ΔRo3: The resistance Ro2 is set to change in resistance per 1 ° C. The reference voltage source E2
Is the reference voltage VS1 at 60 ° C. in FIG.
Is set to be equal to As a result, the characteristic of the drive current Io3 with respect to the ambient temperature has a temperature dependence shown in FIG. The vertical axis in FIG. 6 is an arbitrary scale.

Then, with the switch SW turned on, the bias adjusting variable resistor VR1 is adjusted so that a predetermined driving current is obtained at 25 ° C. Then,
The respective drive currents Io1, Io, of the three drive current generators 1, 2, 3
The drive current Io obtained by adding Io2 and Io3 has characteristics with respect to the ambient temperature shown in FIG. That is, the temperature dependency of the drive current Io is 0.1 mA / ° C at 25 ° C or less, and 25 ° C to 6 ° C.
It becomes 0.2 mA / ° C at 0 ° C and 0.8 mA / ° C at 60 ° C or more, and satisfies the relationship between the driving current and the ambient temperature required to obtain the same light output from the semiconductor laser diode LD. . As a result, as shown in FIG. 8, the light output of the semiconductor laser diode LD keeps the fluctuation within a few% with respect to the light output of 25 ° C. in a wide temperature range (−40 to 80 ° C.).

As described above, the light emitting element driving circuit comprises the linear temperature resistor Rs, the bias adjusting variable resistor VR
1 and a voltage amplifier 4, and a drive current output circuit including drive current generators 1, 2, and 3 and a drive current addition circuit, thereby providing The fluctuation of the peak light output of the laser diode LD is suppressed. Further, for example, at a normal temperature of 25 ° C., the light output characteristics can be adjusted by one bias adjusting variable resistor VR1, so that the adjustment in the production line becomes very easy. Therefore, without complicated adjustments,
By adjusting the variable resistor VR1 for bias adjustment, it is possible to realize a low-cost light emitting element drive circuit that can stabilize the optical output of the semiconductor laser diode LD.

Further, the three drive current generators 1, 2, 3 of the drive current output circuit and the drive current addition circuit for adding the drive currents Io1, Io2, Io3 of the drive current generators 1, 2, 3 include: The fluctuation of the peak light output of the light emitting element with respect to the ambient temperature can be suppressed without requiring complicated adjustment and a large-scale circuit. Further, since the light emitting element driving circuit does not have a time constant without referring to an input signal sequence or monitoring an optical output, it does not depend on an input signal, and thus does not depend on an input signal. Light output can also be kept stable.

In the above embodiment, the drive circuit of the semiconductor laser diode LD has been described. However, the light emitting element is not limited to the semiconductor laser diode, but may be a light emitting element such as a light emitting diode.

In the above embodiment, the drive current output circuit includes the three drive current generators 1, 2, and 3. However, the number of drive current generators of the drive current output circuit is not limited to this.
An appropriate number may be set according to the characteristics of the light emitting element. The drive current output circuit may not include a plurality of drive current generators and a drive current addition circuit, and may include a drive current output circuit based on a correction coefficient predetermined according to an ambient temperature detected by an ambient temperature detection circuit. So that the light output is almost constant
Any device that outputs a drive current to the light emitting element may be used.

[0031]

As apparent from the above description, the light emitting element driving circuit according to the first aspect of the present invention comprises an ambient temperature detecting circuit for detecting an ambient temperature, and an ambient temperature detecting circuit which detects the ambient temperature in advance according to the ambient temperature detected by the ambient temperature detecting circuit. The driving current output circuit outputs a driving current to the light emitting element based on the determined correction coefficient so that the light output of the light emitting element becomes substantially constant.

Therefore, according to the light emitting device driving circuit of the first aspect of the present invention, in the light emitting device such as a semiconductor laser diode or a light emitting diode as the light emitting device, the relationship between the ambient temperature and the driving current when the light output is constant. Based on a predetermined characteristic curve representing the relationship, a correction coefficient of the drive current output circuit is determined in advance so as to output a drive current according to an ambient temperature, and the drive current output circuit determines a light emitting element based on the correction coefficient. , And the light output of the light emitting element is always substantially constant. Therefore, a low-cost light-emitting element driving circuit that can stabilize the peak light output of the light-emitting element without complicated adjustment can be realized.

According to a second aspect of the present invention, in the light emitting element driving circuit according to the first aspect, the plurality of driving current generators of the driving current output circuit are configured based on a preset correction coefficient. A driving current is output so that the driving current changes linearly with respect to a change in the ambient temperature, and the driving currents are added by a driving current adding circuit to each of the driving currents from the plurality of driving current generators. Is output to

Therefore, according to the light emitting element drive circuit of the second aspect of the present invention, the sum of the drive currents output from the respective drive current generators is equal to the drive current with respect to the ambient temperature when the light output is constant. To approximate the characteristic curve of
By setting a correction coefficient of each drive current generator in advance, each drive current output from a plurality of drive current generators is added by a drive current addition circuit according to the correction coefficient,
The added drive current is output to the light emitting element to make the light output of the light emitting element substantially constant. Therefore, the fluctuation of the peak light output of the light emitting element with respect to the ambient temperature can be suppressed without requiring a complicated adjustment or a large-scale circuit. Further, since the light emitting element driving circuit does not have a time constant without referring to an input signal sequence or monitoring an optical output, it does not depend on an input signal, and thus does not depend on an input signal. Light output can also be kept stable.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a light emitting element drive circuit according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating characteristics of a driving current required to obtain the same light output of a semiconductor laser diode of the light emitting element driving circuit with respect to an ambient temperature.

FIG. 3 is a diagram showing characteristics of a voltage VS1 with respect to an ambient temperature of the light emitting element drive circuit.

FIG. 4 is a diagram showing characteristics of a drive current Io1 with respect to an ambient temperature of the light emitting element drive circuit.

FIG. 5 is a diagram showing characteristics of a driving current Io2 with respect to an ambient temperature of the light emitting element driving circuit.

FIG. 6 is a diagram showing characteristics of a driving current Io3 with respect to an ambient temperature of the light emitting element driving circuit.

FIG. 7 is a diagram showing characteristics of a drive current Io with respect to an ambient temperature of the light emitting element drive circuit.

FIG. 8 is a diagram showing a change in light output with respect to an ambient temperature of a semiconductor laser diode driven by the light emitting element drive circuit.

FIG. 9 is a circuit diagram of a light emitting element driving circuit using a conventional peak hold circuit.

FIG. 10 is a circuit diagram of a light emitting element drive circuit using a conventional mark ratio detection circuit.

[Explanation of symbols]

1, 2, 3 ... drive current generator, 4 ... voltage amplifier, Rs ... linear temperature resistor, VR1 ... variable resistor for bias adjustment,
OP1, OP2, OP3: Differential amplifier, E1, E2: Reference voltage source, Q1, Q2, Q3: NPN transistor, Ro1, Ro
2, Ro3: current adjusting resistor, LD: semiconductor laser diode, SW: switch.

Claims (2)

[Claims] An optical output of a light emitting element becomes substantially constant based on an ambient temperature detecting circuit for detecting an ambient temperature, and a correction coefficient predetermined according to the ambient temperature detected by the ambient temperature detecting circuit. A driving current output circuit that outputs a driving current to the light emitting element. 2. The light emitting element drive circuit according to claim 1, wherein the drive current output circuit is configured to change the drive current linearly with respect to a change in ambient temperature based on a preset correction coefficient. And a drive current addition circuit that adds the respective drive currents from the plurality of drive current generators and outputs the added drive current to the light emitting element. A light emitting element driving circuit characterized by the above-mentioned.