JP2006269981A - Optical semiconductor light-emitting element driver circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To generate a bias current for driving an optical semiconductor light-emitting element following temperature characteristics of a threshold current of the optical semiconductor light-emitting element. <P>SOLUTION: An optical semiconductor light-emitting element driver circuit drives the optical semiconductor light-emitting element. The driver circuit has a temperature-coefficient signal generating circuit 101 generating a voltage or a current having a positive gradient or a negative gradient to an ambient temperature. The driver circuit further has a first amplifier circuit 102 to which the voltage or the current of the temperature-coefficient signal generating circuit is inputted, and which inverts the voltage or the current by a specified temperature gradient and outputs the voltage or the current; and a second amplifier circuit 103 to which the voltage or the current of the temperature-coefficient signal generating circuit is inputted, and which does not invert the voltage or the current by the specified temperature gradient and outputs the voltage or the current. The driver circuit further has output circuits (110 and 108) to which first and second output signals are inputted, and which select either a first or a second output signal and generate the bias current on the basis of the signal. The driver circuit generates the bias current following the temperature characteristics of the threshold current of the optical semiconductor light-emitting element. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical semiconductor light emitting element driving circuit.

  There are various driving methods for optical semiconductor light-emitting elements used for optical fiber communication and the like depending on the application. The application is, for example, when performing communication over a distance of several tens of meters at a high speed of 1 Gbps or more. When an optical semiconductor light emitting device is driven at a high speed of about gigabit, a laser diode is usually used as the optical semiconductor light emitting device. When performing communication, a modulated pulse current is supplied to the laser diode, and the communication is performed by turning light on or off.

  The laser diode has a threshold current Ith for starting oscillation in the drive current vs. optical output characteristics. Further, this threshold current has a temperature characteristic and changes depending on the ambient temperature used.

  In order to obtain good communication characteristics, modulation is usually performed by applying a bias current in the vicinity of the threshold current to the laser diode.

  Regarding the eye pattern when the bias current is extremely lower than the threshold current and when the bias current is near the threshold current, for example, page 9 of Honeywell's application sheet (Modulating VCSELs, 006703-1-EN) It is described in. The eye pattern is good when the bias current is near the threshold current. The document introduced describes the characteristics of a VCSEL called VCSEL.

  Therefore, in order to perform good communication, it is necessary that the bias current is set near the threshold current.

  However, as described above, the threshold current of the laser diode has temperature characteristics. For this reason, since the threshold current varies depending on the ambient temperature to be used, it is necessary to devise a method for detecting the temperature and setting the bias current near the threshold current.

  For example, Patent Literature 1 is cited as a conventional threshold current control method. According to the method proposed here, it is possible to accurately supply a DC bias current to the laser diode in the vicinity of the threshold current following the temperature change of the threshold current.

  However, conventional laser diodes have a temperature characteristic in which the threshold current increases as the temperature rises. The application sheet (Modulating VCSELs, 006703-1-EN) of US Honeywell previously introduced 3 As shown on the page, it has a parabolic temperature characteristic in which the current rises on the low temperature side below 25 ° C, and the current rises on the higher temperature side. Control of the threshold current (as introduced) has not been possible with the prior art. For this reason, since the bias current cannot be supplied near the threshold current particularly on the low temperature side, the eye pattern deteriorates and the communication characteristics deteriorate.

Also, depending on the laser diode, the threshold current may increase abruptly, particularly on the high temperature side, and the bias current cannot follow the temperature characteristics of the threshold current in the conventional control method.
JP 2003-131748 A (page 6-8, FIG. 1) Application sheet (Modulating VCSELs, 006703-1-EN), Honeywell, p. 3,9

  It is an object of the present invention to provide an optical semiconductor light emitting element driving circuit capable of generating a bias current for driving an optical semiconductor light emitting element that follows the temperature characteristics of the threshold current of the optical semiconductor light emitting element. .

According to one aspect of the present invention, a temperature coefficient signal generation circuit that generates a voltage or current having a positive slope or a negative slope with respect to the ambient temperature;
A first amplifier circuit that receives the voltage or current of the temperature coefficient signal generation circuit, inverts the voltage or current to a predetermined temperature gradient, and outputs the first output signal;
A second amplification circuit that receives the voltage or current of the temperature coefficient signal generation circuit and outputs the second output signal without inverting the voltage or current at a predetermined temperature gradient;
The first output signal and the second output signal are input, and either the first output signal or the second output signal is selected, and a bias current or a modulation current is selected based on the signal. An optical semiconductor light emitting element driving circuit having an output circuit to be generated is provided.

According to another aspect of the present invention, a temperature coefficient signal generation circuit that generates a voltage or current having a positive slope or a negative slope with respect to the ambient temperature;
A reference signal generation circuit that generates a reference signal having a substantially zero slope with respect to the ambient temperature;
An inverting amplifier circuit that receives the voltage or current of the temperature coefficient signal of the temperature coefficient signal generation circuit, inverts the voltage or current to a predetermined temperature gradient, and outputs the inverted signal as a first output signal;
A non-inverting amplifier circuit that receives the voltage or current of the temperature coefficient signal of the temperature coefficient signal generation circuit and outputs the second output signal without inverting the voltage or current at a predetermined temperature gradient;
The first output signal, the second output signal, and the reference signal are input, and one of the first output signal, the second output signal, and the reference signal is selected, and the signal is There is provided an optical semiconductor light emitting element driving circuit having an output circuit for generating a bias current or a modulation current based on the output circuit.

According to another aspect of the present invention, a temperature coefficient signal generation circuit that generates a voltage or current having a positive slope or a negative slope with respect to the ambient temperature;
A first amplifier circuit that receives the voltage or current of the temperature coefficient signal generation circuit, inverts the voltage or current to a predetermined temperature gradient, and outputs the first output signal;
A voltage or current of the temperature coefficient signal generation circuit is input, and at least two or more inverting amplification circuits are used to output the voltage or current as a second output signal without being inverted at a predetermined temperature gradient. An amplifier circuit;
A voltage or current of the temperature coefficient signal generation circuit is input, the voltage or current is inverted to a substantially zero temperature gradient, and a third output signal having a substantially zero gradient with respect to the ambient temperature is output. An amplifier circuit of
The first output signal, the second output signal, and the third output signal are input, and any one of the first output signal, the second output signal, and the third output signal is obtained. There is provided an optical semiconductor light emitting element driving circuit having an output circuit that selects and generates a bias current or a modulation current based on the signal.

  According to the present invention, it is possible to generate a bias current or a modulation current for driving an optical semiconductor light emitting element that follows the temperature characteristics of the threshold current of the optical semiconductor light emitting element.

Embodiments of the invention will be described with reference to the drawings.
Before explaining the optical semiconductor light emitting element driving circuit according to the first embodiment of the present invention with reference to FIG. 1, referring to FIG. 8 to FIG. 10, the entire configuration of the optical transmission module according to the present invention and the surface emitting laser used therefor The temperature characteristics of the diode will be described.

  FIG. 8 shows an overall view of the optical transmission module 100. The optical transmission module 100 includes a surface emitting laser diode LD1 such as a VCSEL (vertical surface emitting laser) as an optical semiconductor light emitting element, and a laser driver IC1 as an optical semiconductor light emitting element driving circuit 200.

  The laser driver IC1 includes a bias current generation circuit that generates a bias current Ibias for driving the laser diode that follows the temperature characteristic of the threshold current Ith of the surface emitting laser diode LD1, and a current signal (modulation current Im that is modulated at high speed). And a high-speed modulation circuit that applies the bias current Ibias supplied from the bias current generation circuit.

  Alternatively, the laser driver IC1 is a laser that follows the temperature characteristics of the bias current generation circuit that always generates a substantially constant current as the bias current Ibias without depending on the ambient temperature and the threshold current Ith of the surface emitting laser diode LD1. A high-speed modulation circuit that generates a high-speed modulation signal (modulation current Im) for driving a diode and applies the high-speed modulation signal (modulation current Im) to the bias current Ibias supplied from the bias current generation circuit. It may be configured. As the bias current Ibias, for example, a constant current corresponding to the threshold current Ith of the surface emitting laser diode LD1 at room temperature (25 ° C.) may be used.

  In addition to the power supply Vcc line and the ground GND line, the optical transmission module 100 is connected with data lines Data + and Data− for inputting data signals. The data lines Data + and Data− are data signals generated by an external data signal generation circuit (not shown) (pulse signals corresponding to digital signals of “1” and “0”) are modulated at the high speed in the laser driver IC1. A data supply line for supplying the circuit.

  Therefore, the laser diode LD1 is supplied with a drive current in which a modulated current signal (modulated current Im) is superimposed on the bias current Ibias, and optical power corresponding to the drive current is output.

  The light output emitted from the laser diode LD1 of the optical transmission module 100 is incident on one end of the optical fiber 120, travels a distance of several tens to several hundreds of meters through the optical fiber 120, and is received at the other end (not shown). Received by the module.

  FIG. 9 is a diagram showing the drive current versus optical output characteristics of a laser diode. The horizontal axis is the drive current, and the vertical axis is the optical power as the optical output.

  In FIG. 9, the laser diode emits little light with respect to the increase in drive current up to the threshold current Ith at which oscillation starts, and after reaching the threshold current Ith, the optical power increases linearly with a certain slope. Due to the characteristics of the laser diode, even if the threshold current Ith varies depending on the ambient temperature, it is necessary to set the bias current Ibias to the same value as the threshold current Ith in order to stably obtain optical power. is there. This is because if the bias current Ibias is much lower than the threshold current Ith, the light emission is delayed when the modulation current Im is applied, and the pulse width of the light output becomes narrower or the overshoot becomes larger. The eye pattern deteriorates. For this reason, it is necessary to set the bias current Ibias to the same value as the threshold current Ith. When the bias current Ibias is set to the same value as the threshold current Ith, optical power having a level of PHO0 to PHO1 shown in FIG. 8 is generated according to the modulation current Im. The extinction ratio represents the ratio between the optical power PHO0 and the optical power PHO1.

  FIG. 10 shows the temperature characteristics of the threshold current of the surface emitting laser diode. The horizontal axis is temperature, and the vertical axis is threshold current. The temperature characteristic of the threshold current of the surface emitting laser diode has a parabolic shape in which the threshold current increases on both the low temperature side and the high temperature side, for example, around 25 ° C. with respect to a change in ambient temperature. The temperature characteristics of the parabola shape vary depending on the type of the surface emitting laser diode or the manufacturing error, and the rate of decrease and increase in current differs between the low temperature side and the high temperature side. Symbols A, B, and C show examples of parabolic temperature characteristics.

From the above, as the bias current Ibias supplied to the surface emitting laser diode LD1, a bias current that follows the temperature characteristics of the threshold current as shown in FIG. 10 can be generated even if the ambient temperature fluctuates. Necessary. As described in FIG. 8, instead of the bias current Ibias supplied to the laser diode LD1, the bias current Ibias is a constant current having no temperature characteristics, and the temperature characteristics of the threshold current Ith of the surface emitting laser diode LD1. The modulation current Im may be generated following the above.
[Embodiment 1]

  FIG. 1 shows a configuration diagram of an optical semiconductor light emitting element driving circuit according to Embodiment 1 of the present invention. FIG. 1 shows a configuration of an optical transmission module 100 having an optical semiconductor light emitting element driving circuit 200 and a surface emitting laser diode LD1 driven thereby.

  In FIG. 1, an optical semiconductor light emitting element driving circuit 200 generates a bias current for generating a bias current Ibias for driving a laser diode following the temperature characteristic of a threshold current Ith of a surface emitting laser diode LD1 which is an optical semiconductor light emitting element. A circuit (101 to 109), and a high-speed modulation circuit 111 that generates a current signal (modulation current Im) modulated at high speed and applies it to the bias current Ibias supplied from the bias current generation circuit. Yes.

  The bias current generation circuit (101 to 109) is configured by a circuit using the temperature dependence of the transistor, and the temperature coefficient circuit 101 as a temperature coefficient signal generation circuit that generates a voltage having a positive temperature coefficient with respect to the temperature T. And a band gap reference type reference voltage circuit 109 that generates a stable voltage that does not depend on temperature, a voltage generated by the temperature coefficient circuit 101, and a voltage generated by the reference voltage circuit 109. Non-inversion as an inverting amplifier circuit 102 as a first amplifier circuit that generates a voltage of magnification and a second amplifier circuit that generates a voltage of a desired positive magnification using the voltage generated by the temperature coefficient circuit 101 Output from the amplifier circuit 103, the level shift circuit 104 that shifts the level of the voltage output from the inverting amplifier circuit 102, and the non-inverting amplifier circuit 103. A level shift circuit 105 for shifting the voltage level and two emitter followers 106 and 107 for outputting the higher voltage by superimposing two voltages generated by the level shift circuits 104 and 105 on each other. And a voltage / current conversion circuit 108 that converts a voltage generated by the superposition output circuit 110 into a bias current for driving the laser diode LD1. Each of the circuit blocks 101 to 109 is connected between the power supply Vcc and the ground GND.

  The level shift circuits 104 and 105 constitute level shift means. The superimposition output circuit 110 and the voltage / current conversion circuit 108 receive two output signals from the previous circuit, select one of the two output signals, and generate a bias current based on the two signals. The circuit is configured.

  LD1 is a surface-emitting laser diode, and is composed of, for example, a VCSEL (vertical surface-emitting laser). One end of the laser diode LD1 is connected to the power supply Vcc, and the other end is connected to the current control transistor of the voltage / current conversion circuit 108. A high-speed modulation circuit 111 that supplies a high-speed modulated current signal (modulation current) is connected in parallel to both ends of the bias current output unit including the current control transistor of the voltage / current conversion circuit 108. The high-speed modulation circuit 111 is composed of, for example, a current source I4 that supplies a modulated pulse current. A high-speed modulation signal (modulation current) is applied to the bias current.

The temperature coefficient circuit 101 is also called a VT reference circuit, and can generate a voltage proportional to temperature by multiplying kT / q by a positive coefficient. Here, k represents the Boltzmann constant, q represents the charge, and T represents the absolute temperature. The temperature coefficient circuit 101 generates a voltage having a positive temperature coefficient using, for example, the temperature dependency of the transistor. The voltage having a positive slope with respect to the temperature generated by the temperature coefficient circuit 101 is supplied to the inverting amplifier circuit 102 and the non-inverting amplifier circuit 103.
The inverting amplifier circuit 102 includes an operational amplifier U1 and resistors R1 and R2. The voltage from the temperature coefficient circuit 101 is input to the negative terminal via the resistor R1, and the voltage from the reference voltage circuit 109 is input to the positive terminal. A resistor R2 is connected between the negative terminal and the output terminal. The non-inverting amplifier circuit 103 includes an operational amplifier U2 and resistors R3 and R4. The voltage from the temperature coefficient circuit 101 is input to the plus terminal, the minus terminal is connected to the ground GND via the resistor R4, and the minus terminal. And a resistor R3 is connected between the output terminals.

  The inverting amplifier circuit 102 can set the amplification factor by the ratio of the resistor R1 and the resistor R2, and the slope of the output voltage is inverted with respect to the input voltage. Therefore, the output of the inverting amplifier circuit 102 has a negative slope (negative temperature coefficient) with respect to the temperature, and the negative slope with respect to the temperature can be set by setting the amplification factor by the resistors R1 and R2.

  The non-inverting amplifier circuit 103 can set the amplification factor by the ratio of the resistor R3 and the resistor R4, and the slope of the output voltage is the same as the input voltage (non-inverted). Therefore, the output of the non-inverting amplifier circuit 103 has a positive slope (positive temperature coefficient) with respect to the temperature, and the positive slope with respect to the temperature can be set by setting the amplification factor by the resistors R3 and R4.

  The reason why the positive / negative slope is created with respect to the temperature matches the temperature characteristics (for example, temperature vs. threshold current shown in FIG. 10) of the VCSEL (vertical surface emitting laser) as the optical semiconductor light emitting device used in the first embodiment. This is because it is desired to change the slope of the voltage at a certain temperature point. For that purpose, it is necessary to change the slope at the desired temperature point. The temperature point that changes the slope is called the inflection point. It is necessary to form one or more inflection points according to the temperature characteristics of the surface emitting laser diode LD1.

  The inverting amplifier circuit 102 and the non-inverting amplifier circuit 103 can obtain a positive / negative gradient (positive / negative temperature coefficient) with respect to the temperature. However, it is not always possible to change the inclination at a desired temperature point even if they are superimposed as they are. However, it is possible to obtain a desired curve whose slope is changed at a desired temperature point by appropriately adjusting the voltage level by the level shift circuits 104, 105 and 112, respectively.

  The voltages level-shifted by the level shift circuits 104 and 105 are superimposed through the emitter followers 106 and 107 constituting the superimposed output circuit 110, respectively. The emitter follower 106 is configured by connecting the collector / emitter of the transistor Q1 and the constant current source I1 in series between the power source Vcc and the ground GND, and the output voltage of the level shift circuit 104 is input to the base of the transistor Q1. The emitter follower 107 is configured by connecting the collector / emitter of the transistor Q2 and the constant current source I2 in series between the power source Vcc and the ground GND, and the output voltage of the level shift circuit 105 is input to the base of the transistor Q2. The emitters of the transistors Q1 and Q2 are connected in common, and the common emitter output is output to the voltage / current conversion circuit 108 in the next stage. Since the voltage at the point overlapped by the emitter followers 106 and 107 is clamped to a higher potential, the higher voltage generated by the level shift circuits 104 and 105 is output from the superimposed output circuit 110.

  In the superimposed output circuit 110, the constant current sources I1 and I2 of the emitter followers 106 and 107 may be replaced with one constant current source or one resistor.

  The voltage / current conversion circuit 108 includes an operational amplifier U3 for error amplifier, an NPN bipolar transistor Q4 for current control, and a resistor R5, and has a function of outputting a current proportional to the input voltage. The output voltage of the superimposed output circuit 110 is input as the input voltage Vin to the plus terminal of the operational amplifier U3 for error amplifier. The error voltage output from the operational amplifier U3 is input to the base of the current control transistor Q4, and the collector of the transistor Q4 is Connected to one end of the negative pole of the laser diode LD1, the emitter of the transistor Q4 is connected to the ground terminal via the resistor R5 connected to the negative terminal of the operational amplifier U3, and the voltage generated in the resistor R5 by the current flowing through the transistor Q4 is the operational amplifier. It is configured to be fed back to the negative terminal of U3. This is because if the input voltage of the operational amplifier U3 is Vin and the current flowing through the resistor R5 is Ibias, the error amplifier U3 works so that the voltage drop Ibias · R5 caused by the current flowing through the resistor R5 becomes equal to Vin, and the current Ibias is controlled. It is to be done. Therefore, Ibias = Vin / R5. An FET can be used instead of the bipolar transistor Q4. The absolute value of the current can be adjusted by the resistor R5, and in this way, the bias current Ibias following the temperature change of the surface emitting laser diode LD1 can be supplied to the laser diode LD1.

  In the configuration of FIG. 1 described above, a voltage having a temperature coefficient is generated by utilizing the temperature dependence of the transistor, inverted amplification and non-inversion amplification are performed, and a level shift is appropriately performed to thereby obtain a desired negative slope. And a voltage having a desired positive slope. Then, by superimposing these voltages, a higher voltage is output with respect to the ambient temperature, and the voltage is converted into a current, which is used as a bias current for the surface emitting laser diode. As a result, the bias current has a temperature characteristic that follows the temperature characteristic of the threshold current of the surface emitting laser diode. Therefore, even if the threshold current of the laser diode fluctuates due to changes in the ambient temperature, the fluctuation Thus, it is possible to generate a light output without deterioration of extinction ratio characteristics due to temperature change and without eye pattern deterioration due to temperature change.

  In the first embodiment, the temperature curve of the bias current Ibias is created with the slope with respect to the positive and negative temperatures. However, the bias current Ibias may be created with positive or negative slopes having different slopes with respect to the temperature. In addition, by generating a voltage having a positive / negative slope with respect to temperature by using a band gap reference type reference voltage circuit 109 capable of generating a reference voltage with accuracy with respect to temperature and power supply voltage, it is possible to prevent fluctuations in power supply voltage. It is possible to stabilize, level shift is performed by attaching a voltage follower, a circuit equivalent to the emitter followers 106 and 107 is added, and the above-described voltage is supplied, so that the threshold current with respect to the temperature change can be obtained. It is also possible to obtain a tracking bias current.

FIG. 2 is a circuit diagram showing an embodiment of the temperature coefficient circuit 101.
The temperature coefficient circuit 101 shown in FIG. 2 includes a start-up circuit 115 including transistors Q11 to Q13 and a resistor R9 as a starting circuit when power is turned on, and transistors Q6 to Q10 between a power source V1 (for example, 3.3 V) and GND. And a temperature coefficient signal generation circuit 116 that outputs a voltage proportional to the ambient temperature using the temperature dependence of the transistor.

  The start-up circuit 115 has two transistors Q12 and Q13 connected in series between the power source V1 and the ground GND, the resistor R9 and the collector and base connected in series, and the connection point between the resistor R9 and the transistor Q12 is connected between the base and the emitter. Are connected to the collector current path of the temperature coefficient signal generation circuit 116 through the collector and emitter of the transistor Q11 connected in common.

  When the temperature coefficient signal generation circuit 116 is turned on, the start-up circuit 115 rapidly activates the transistor Q11 because the collector voltage of the diode-connected transistors Q12 and Q13 rises rapidly. As a result, the temperature coefficient signal The current is transferred to the commonly connected bases of the transistors Q8 and Q9 of the generation circuit 116, thereby causing the temperature coefficient signal generation circuit 116 to start operation.

  The temperature coefficient signal generation circuit 116 includes two PNP type transistors Q6 and Q7. These two transistors have the emitter connected to the power supply V1 and the base connected in common, and the base of the transistor Q7. A collector is commonly connected, and includes a current mirror circuit that outputs the same current Ic to each collector of the transistors Q6 and Q7, and two NPN transistors Q8 and Q9 having different emitter areas, and the emitters of the transistors Q8 and Q9. The area ratio is 1: 4, the collector of the transistor Q8 is connected to the collector of the transistor Q6, the collector of the transistor Q9 is connected to the collector of the transistor Q7, and the collector and base of the transistor Q8 are connected in common. The bases of the transistors Q8 and Q9 are connected in common, The emitter of the star Q9 is connected to the ground GND through the resistor R7, and the emitter of the transistor Q8 is directly connected to the ground GND, and a thermal circuit for obtaining a current proportional to the ambient temperature as the collector current Ic, The transistor Q10 has an emitter connected to the power source V1, a base connected to the common base of the transistors Q6 and Q7, a collector connected to the ground GND via the resistor R8, and a resistor R8 connected in series with the resistor R8. And an output circuit for outputting a voltage Vout proportional to the temperature at one end of R8.

Hereinafter, the operation of the temperature coefficient signal generation circuit 116 will be described using mathematical expressions.
The following equation holds for the bipolar transistor used.
Ic = Is · exp (VBE / VT) (1)
Where Is is a saturation current, VBE is a base-emitter voltage, VT is kT / q, k is a Boltzmann constant, q is an elementary charge, and T is an absolute temperature.

  If the transistors Q6 and Q7 are PNP transistors of the same size, the collector currents Ic flowing through the transistors Q6 and Q7 are the same.

From the above equation (1), assuming that the base-emitter voltages of the transistors Q8 and Q9 are VBE8 and VBE9,
VBE8 ＝ VT ・ ln (Ic / Is) (2)
VBE9 = VT · ln {Ic / (4 · Is)} (3)
Since Ic is the same as the collector current flowing through transistor Q9, Ic = (VBE8-VBE9) / R1 (4)
Therefore,
Ic = VT ・ ln (Ic / Is ・ 4Is / Ic) (5)
Ic ＝ VT ・ ln (4) (6)
∴ Ic is a current proportional to temperature.

The voltage Vout generated in the resistor R8 is Vout = R8 · Ic (7)
Therefore, the output voltage Vout is proportional to the temperature.

  FIG. 3 is a graph showing the results of measuring the relationship between temperature and voltage obtained by the temperature coefficient circuit (temperature coefficient signal generation circuit) of FIG. A voltage output proportional to temperature is obtained.

FIG. 4 is a circuit diagram showing one embodiment of the band gap reference type reference voltage circuit 109. In FIG.
A band gap reference type reference voltage circuit 109 shown in FIG. 4 has a circuit in which a constant current source I11 and the collector and emitter of an NPN transistor Q15 are connected in series between a power supply Vcc and a ground GND, and a collector connected to the power supply Vcc. The transistor Q14 has a base connected to the collector of the transistor Q15 and two PNP transistors Q16 and Q17 having different emitter areas. The ratio of the emitter areas of the transistors Q16 and Q17 is N: 1. Is connected to the emitter of the transistor Q14 via a resistor R13, the emitter of Q16 is connected to the ground GND via a resistor R11, and the collector of the transistor Q17 is connected to the emitter of the transistor Q14 via a resistor R12. Is connected in common to the base of the transistor Q16, and the collector of Q17 And a circuit for outputting a constant bandgap reference voltage VBG independent of temperature from a connection point between the transistor Q14 and the resistor R12. .

Hereinafter, the operation of the band gap reference type reference voltage circuit 109 will be described using mathematical expressions.
As for the bipolar transistor to be used, the following equation holds as in the above equation (1).
Ic = Is · exp (VBE / VT)
Where Is is a saturation current, VBE is a base-emitter voltage, VT is kT / q, k is a Boltzmann constant, q is an elementary charge, and T is an absolute temperature. The base-emitter voltages of the transistors Q15, Q16, Q17 are VBE15, VBE16, VBE17, respectively, and the saturation currents Is of Q15, Q16, Q17 are Is15, Is16, Is17, respectively.

Also, if the same transistor is paired, Is is proportional to the emitter area.
From VBE15 = VBE17 Is15 = Is17
Further, since the emitter area of the transistor Q16 is N times the emitter area of the transistor Q17, Is16 = N · Is17.

VBE17 = VBE16 + I2 ・ R11
∴ VBE17−VBE16 ＝ I2 ・ R11
VBE17−VBE16 = Vt · ln (I1 / Is17) −VT · ln (I2 / Is16)
＝ VT ・ ln (I1 ・ Is16) / (I2 ・ Is17) ...... (8)
Assuming VBE17 = VBE15 I1 ・ R12 ＝ I2 ・ R13 ...... (9)
From the above formulas (8) and (9), I2 = (VBE17-VBE16) / R11 = VT / R11 · ln (I1 · Is16) / (I2 · Is17)
＝ VT / R11 ・ ln (R13 ・ Is16) / (R12 ・ Is17) …… (10)
Vref = I2 · R13 + VBE15 = R13 / R11 · VT · ln (R13 · Is16) / (R12 · Is17) + VBE15
It becomes. here
VT ＝ k ・ T / q (k: Boltzmann constant q: elementary charge)
So VT has a positive slope with respect to temperature.

  It is generally known that VBE15 has a negative slope with respect to temperature. Therefore, it is possible to obtain a constant voltage with respect to temperature by adjusting the VT term.

  FIG. 5 is a circuit diagram showing an embodiment of the level shift circuit 104 (or 105). The level shift circuit 104 has a configuration in which a collector / emitter of a PNP transistor Q, a resistor R, and a constant current source I are connected in series between a power supply Vcc and a ground GND. When the output voltage from the inverting amplifier circuit 102 in the previous stage is input to the base of the transistor Q, a voltage level-shifted by the voltage I × R is output from the connection point of the resistor R and the constant current source I, and the emitter follower in the next stage is output. 106 is supplied to the base of the transistor Q1.

  6A to 6C are diagrams for explaining the operation of the superimposed output circuit 110 composed of the two emitter followers 106 and 107 described above. The level-shifted output voltage from the level shift circuit 104 as shown in FIG. 6A and having a negative slope (negative temperature coefficient) with respect to the temperature T, and the level shift from the level shift circuit 105 and The output voltage having a positive slope (positive temperature coefficient) with respect to the temperature T is superimposed by the superposition output circuit 110 as shown in FIG. 6B, and clamped to the higher voltage. As shown in FIG. 6C, an output voltage having a V-shaped characteristic in which the voltage increases at the low temperature side and the high temperature side with respect to the temperature T is generated.

  According to the first embodiment of the present invention, the bias current Ibias can be made to follow the temperature characteristic of the threshold current Ith even in an optical semiconductor light emitting element driving circuit using a surface emitting laser diode such as a VCSEL. Therefore, it is possible to suppress the fluctuation of the extinction ratio characteristic based on the change of the threshold current.

  FIG. 6C illustrates a case where a bias current having a temperature characteristic following the threshold current is generated for a laser diode having a temperature characteristic of a threshold current having one inflection point. The present invention is applied to a case where a bias current having a temperature characteristic following a threshold current is generated for a laser diode having a temperature characteristic of a threshold current having a plurality of inflection points as shown in the second and third embodiments. can do.

  FIG. 7 shows the temperature characteristic c of the bias current Ibias with respect to the temperature generated in the first embodiment. X-axis is temperature (° C), Y-axis is current value when current value at 25 ° C is 0 mA (current values shown in this graph are actual current value at ambient temperature and actual current at 25 ° C It is indicated by the difference from the value). As the bias current Ibias, a shape approximating the temperature characteristic of the threshold current of the VCSEL can be obtained.

According to the first embodiment of the present invention, a bias current is supplied in the vicinity of the threshold current in the entire temperature range used for a laser diode having a V-shaped temperature characteristic of the threshold current having one inflection point. Therefore, eye pattern deterioration due to temperature change is reduced, and good transmission characteristics can be obtained.
Further, when a laser diode having a characteristic that the threshold current is larger than the room temperature (25 ° C.) on the low temperature side and the threshold current is larger than the room temperature (25 ° C.) on the high temperature side, such as VCSEL, Since the deterioration of the pattern is reduced, good transmission characteristics can be obtained.

  Furthermore, by using a reference voltage source that does not depend on temperature, a voltage or current having a positive or negative slope can be generated with reference to this, so that stable control is possible.

  Further, by using the temperature characteristics of the transistor and a stable reference voltage, a voltage or current having a stable slope with respect to temperature can be obtained. That is, by using a temperature coefficient generation circuit having a temperature characteristic proportional to temperature and a stable reference voltage source, a voltage or current having a stable gradient with respect to temperature can be obtained.

Also, a stable high speed operation can be obtained by applying a high speed modulation signal to the bias current.
Note that the temperature coefficient circuit 101 as the temperature coefficient signal generation circuit has been described in the case where the voltage characteristic with respect to temperature has a positive (or negative) slope, but the current characteristic with respect to temperature has a positive (or negative) slope. The same can be applied to the case of having.
[Embodiment 2]

  FIG. 11 shows a configuration diagram of an optical semiconductor light emitting element driving circuit according to Embodiment 2 of the present invention. The same parts as those shown in FIG.

  An optical transmission module 100A shown in FIG. 11 includes an optical semiconductor light emitting element driving circuit 200A and a surface emitting laser diode LD1 as an optical semiconductor light emitting element.

  In FIG. 11, an optical semiconductor light emitting element driving circuit 200A generates a bias current for generating a bias current Ibias for driving a laser diode following the temperature characteristic of the threshold current Ith of a surface emitting laser diode LD1 which is an optical semiconductor light emitting element. A circuit (101 to 109, 112, 113), and a high-speed modulation circuit 111 that generates a current signal (modulation current Im) modulated at high speed and applies it to the bias current Ibias supplied from the bias current generation circuit; It is equipped with. The high-speed modulation circuit 111 includes a current source I4 that supplies a current signal (for example, a pulse current signal) modulated at high speed, and is connected to both ends of the bias current output unit of the optical semiconductor light emitting element driving circuit 200A. This is the same as the case of 1.

  The difference from the configuration of FIG. 1 is that a level shift circuit 112 is provided and a corresponding emitter follower 113 is provided. The level shift circuit 112 constitutes a level shift means together with the existing level shift circuits 104 and 105, and the emitter follower 113 constitutes a superimposed output circuit 110A together with the existing emitter followers 106 and 107. The other configurations are the same as those in FIG. 1, but the following description will focus on the configurations of the different points, and the description of the same parts as those in FIG. 1 will be omitted.

  Therefore, the configuration of the level shift means includes a level shift circuit 104 that shifts the level of the voltage output from the inverting amplifier circuit 102, a level shift circuit 105 that shifts the level of the voltage output from the non-inverting amplifier circuit 103, And a level shift circuit 112 that shifts the level of the reference voltage independent of the temperature output from the reference voltage circuit 109 configured by a bandgap reference type reference voltage circuit.

  The voltages level-shifted by the level shift circuits 104, 105, and 112 are superposed through the three emitter followers 106, 107, and 113 constituting the superposition output circuit 110A, respectively.

  The three emitter followers 106, 107, and 113 constituting the superimposed output circuit 110A superimpose the three voltages generated by the level shift circuits 104, 105, and 112 on the previous stage, and output the higher voltage.

  The emitter follower 106 is configured by connecting the collector / emitter of the transistor Q1 and the constant current source I1 in series between the power source Vcc and the ground GND, and the output voltage of the level shift circuit 104 is input to the base of the transistor Q1. The emitter follower 107 is configured by connecting the collector / emitter of the transistor Q2 and the constant current source I2 in series between the power source Vcc and the ground GND, and the output voltage of the level shift circuit 105 is input to the base of the transistor Q2. The emitter follower 113 is configured by connecting the collector / emitter of the transistor Q3 and the constant current source I3 in series between the power source Vcc and the ground GND, and the output voltage of the level shift circuit 112 is input to the base of the transistor Q3.

  The emitters of the transistors Q1, Q2, and Q3 are connected in common, and the common emitter output is output to the voltage / current conversion circuit 108 in the next stage. Since the voltage at the point overlapped by the emitter followers 106, 107, 113 is clamped to a higher potential, the higher voltage generated by the level shift circuits 104, 105, 112 is output from the superimposed output circuit 110A. Is output.

  The level shift circuits 104, 105, and 112 constitute level shift means. The superimposition output circuit 110A and the voltage / current conversion circuit 108 receive three output signals from the previous stage, select one of the three output signals, and generate a bias current based on that signal. The circuit is configured.

  Further, in the superimposed output circuit 110A, the constant current sources I1, I2, and I3 of the emitter followers 106, 107, and 113 may be replaced with one constant current source or one resistor.

  In the configuration of FIG. 11 described above, a stable reference voltage that does not depend on temperature is generated, while a voltage having a temperature coefficient is generated using the temperature dependence of the transistor, and is inverted and non-inverted. By appropriately level-shifting, a voltage having a desired negative slope, a voltage having a desired positive slope, and a voltage that is constant with respect to temperature change (that is, constant independent of temperature) are obtained. Then, by superimposing these voltages, any one of the highest voltages is output with respect to the ambient temperature, and the voltage is converted into a current to be used as a bias current for the surface emitting laser diode. As a result, the bias current has a temperature characteristic that follows the temperature characteristic of the threshold current of the surface emitting laser diode. Therefore, even if the threshold current of the laser diode fluctuates due to changes in the ambient temperature, the fluctuation Thus, it is possible to generate a light output without deterioration of extinction ratio characteristics due to temperature change and without eye pattern deterioration due to temperature change.

  FIGS. 12A to 12C are diagrams for explaining the operation of the superimposed output circuit 110A composed of the three emitter followers 106, 107, and 113 described above. The level-shifted output voltage from the level shift circuit 104 as shown in FIG. 12 (a) and having a negative slope (negative temperature coefficient) with respect to the temperature T, and the level shift from the level shift circuit 105 and An output voltage having a positive slope (positive temperature coefficient) with respect to the temperature T and a reference voltage level-shifted from the reference voltage circuit 109 and independent of the temperature T are shown in FIG. As shown in FIG. 12, the superposed output circuit 110 superimposes and clamps to the higher voltage, resulting in a parabolic shape in which the voltage increases at the low temperature side and the high temperature side with respect to the temperature T as shown in FIG. An output voltage having the characteristics is generated.

  FIG. 13 shows a change characteristic c of the bias current Ibias generated in the second embodiment with respect to the ambient temperature. The temperature characteristic b of the threshold current of the VCSEL is also shown. However, the X axis is the temperature (° C), the Y axis is the current value when the current value at 25 ° C is 0 mA (the current value shown in this graph is the actual current value at the ambient temperature and the actual value at 25 ° C It is shown by the difference with the current value of

  Although it is not strict because there are few acquisition points of the temperature characteristics of the threshold current of the VCSEL, a shape matching the temperature characteristics b of the threshold current of the VCSEL is obtained as the bias current Ibias supplied to the VCSEL. By further increasing the number of circuits having different slopes of the output voltage with respect to the temperature and providing a plurality of inflection points, it is possible to perform matching more accurately. Note that point a indicates the lowest voltage point.

According to the second embodiment of the present invention, for a laser diode having a parabolic temperature characteristic of a threshold current having at least one inflection point, a bias current in the vicinity of the threshold current in the entire temperature range to be used. Therefore, deterioration of the eye pattern due to temperature change is reduced, and good transmission characteristics can be obtained.
Further, when a laser diode having a characteristic that the threshold current is larger than the room temperature (25 ° C.) on the low temperature side and the threshold current is larger than the room temperature (25 ° C.) on the high temperature side, such as VCSEL, Since the deterioration of the pattern is reduced, good transmission characteristics can be obtained.

  Furthermore, by using a reference voltage source that does not depend on temperature, a voltage or current having a positive or negative slope can be generated with reference to this, so that stable control is possible.

  Further, by using the temperature characteristics of the transistor and a stable reference voltage, a voltage or current having a stable slope with respect to temperature can be obtained. That is, by using a temperature coefficient signal generation circuit having a temperature characteristic proportional to temperature and a stable reference voltage source, a voltage or current having a stable slope with respect to temperature can be obtained.

Also, a stable high speed operation can be obtained by applying a high speed modulation signal to the bias current.
Note that the temperature coefficient circuit 101 as the temperature coefficient signal generation circuit has been described in the case where the voltage characteristic with respect to temperature has a positive (or negative) slope, but the current characteristic with respect to temperature has a positive (or negative) slope. The same can be applied to the case of having.
[Embodiment 3]

  FIG. 14 shows a configuration diagram of an optical semiconductor light emitting element driving circuit according to Embodiment 3 of the present invention. FIG. 14 shows a configuration example of an optical transmission module 100B having an optical semiconductor light emitting element driving circuit 200B and a surface emitting laser diode LD11 as an optical semiconductor light emitting element driven thereby.

  In FIG. 14, the optical semiconductor light emitting element driving circuit 200B generates a bias current for generating a bias current Ibias for driving the laser diode following the temperature characteristic of the threshold current Ith of the surface emitting laser diode LD11 which is an optical semiconductor light emitting element. Circuit (202, 203, 209, 214 to 222) and a high-speed modulation circuit for generating a current signal (modulation current Im) modulated at high speed and applying it to the bias current Ibias supplied from the bias current generation circuit 223. The high-speed modulation circuit 223 includes a current source I15 that supplies a current signal (for example, a pulse current signal) modulated at high speed, and is connected to both ends of the bias current output unit of the optical semiconductor light emitting element driving circuit 200B. 1 and FIG. 2 are the same.

  The bias current generation circuits (202, 203, 209, 214 to 222) are voltage levels of a band gap reference type reference voltage circuit 209 that generates a stable voltage independent of temperature, and a band gap reference type reference voltage circuit 209. Is shifted in the direction of higher voltage to obtain a voltage having a negative temperature coefficient with a gradual slope, and the voltage from the band gap reference type reference voltage circuit 209 is used to obtain a negative voltage. The second temperature coefficient circuit 215 that obtains a voltage having a temperature gradient (negative temperature coefficient) and a plurality of resistance voltage dividing circuits, and the voltage generated by the first temperature coefficient circuit 214 is divided by resistors. A voltage dividing circuit 216 for obtaining a plurality of desired voltage levels, and a voltage generated by the second temperature coefficient circuit 215 and one obtained by dividing the voltage by the voltage dividing circuit 216. The voltage is input, and the inverting amplifier circuit 217 as an output unit of the second temperature coefficient circuit 215 that performs inverting amplification, and the voltage output from the inverting amplifier circuit 217 and one voltage obtained by dividing by the voltage dividing circuit 216 Are input to the inverting amplifier circuit 202 as the first amplifier circuit for inverting amplification, the voltage output from the inverting amplifier circuit 217 and one voltage obtained by dividing by the voltage dividing circuit 216, and An inverting amplifier circuit 218 to be amplified, a voltage output from the inverting amplifier circuit 218 and one voltage obtained by dividing the voltage by the voltage dividing circuit 216 are input, and an inverting amplifier circuit 203 to perform inverting amplification is configured. Inverting amplifier circuits 218 and 203 functioning as a second amplifier circuit that performs non-inverting amplification by the circuit 218 and the inverting amplifier circuit 203, and the voltage output from the inverting amplifier circuit 217 and the voltage dividing circuit 21 The voltage amplified by the inverting amplifier circuits 202, 203, and 219 is composed of an inverting amplifier circuit 219 as a third amplifier circuit for inverting and amplifying the voltage obtained by dividing the voltage by the inverting amplifier circuits 202, 203, and 219. Are superimposed on each other to generate the higher voltage, the superimposed output circuit 220, the voltage / current conversion circuit 221 that converts the voltage generated by the superimposed output circuit 220 into current, and the voltage / current conversion circuit 221. A current mirror circuit 222 for supplying the generated current as a bias current to the laser diode LD11. Each circuit block 202, 203, 209, 214-222 is connected between the power supply Vcc and the ground GND.

  Note that the first temperature coefficient circuit 214, the second temperature coefficient circuit 215, the reference voltage circuit 209, and the inverting amplifier circuit 217 generate a voltage or current having a positive slope or a negative slope with respect to the ambient temperature. A temperature coefficient signal generation circuit is configured. The voltage dividing circuit 216 includes a plurality of resistance voltage dividing circuits, inputs a signal obtained from the temperature coefficient signal generation circuit to the plurality of resistance voltage dividing circuits, and performs first, second, and third amplification. Level shift means for shifting the level of the signal output to each circuit is configured. Further, the superimposition output circuit 220, the voltage / current conversion circuit 221 and the current mirror circuit 222 are inputted with three output signals from the previous stage, select one of the three output signals, and bias based on the signals. An output circuit for generating a current is configured.

  The first temperature coefficient circuit 214 has a negative temperature coefficient with respect to the temperature as compared with the reference voltage circuit 209. However, the inclination is smaller than that of the second temperature coefficient circuit 215.

  The voltage dividing circuit 216 includes a plurality of resistance voltage dividing circuits, and divides the voltage generated by the first temperature coefficient circuit 214 to generate a plurality of divided voltages. This corresponds to the level shift means of the first and second embodiments. The plurality of divided voltages obtained by the voltage dividing circuit 216 are input as reference voltages to the plus terminals of the inverting amplifier circuits 202, 203, 217, 218, and 219.

  The voltage dividing circuit 216 has a configuration in which, for example, five resistance voltage dividing circuits are connected in parallel. That is, between the output line of the voltage generated by the first temperature coefficient circuit 214 and the ground GND, the first resistor voltage dividing circuit by the resistor R21 and the resistor R22, and the second resistor voltage dividing by the resistor R43 and the resistor R44. A circuit, a third resistor voltage divider circuit with resistors R25 and R26, a fourth resistor voltage divider circuit with resistors R31 and R32, and a fifth resistor divider circuit with resistors R29 and R30 are arranged in parallel. It has a connected configuration.

  The band gap reference type reference voltage circuit 209 may be the same as the circuit configuration shown in FIG.

  A circuit example of the first temperature coefficient circuit 214 is shown in FIG. The first temperature coefficient circuit 214 uses the fact that the base-emitter voltage VBE of the transistor has a negative temperature coefficient to generate a voltage having a negative temperature coefficient.

  In FIG. 15, the first temperature coefficient circuit 214 includes a resistor R53, a collector / emitter of a transistor Q41, between a power supply terminal of the reference voltage VBG supplied from the bandgap reference type reference voltage voltage circuit 209 and the ground GND. A resistor R52 is connected in series, the collector and base of the transistor Q41 are connected in common, and a resistor R51 is connected between the base and the ground GND, and an operational amplifier U21 is provided. And a voltage follower having a base voltage V1 of Q41 as input and a negative terminal and an output terminal connected in common.

Hereinafter, the operation of the second temperature coefficient circuit 215 will be described using mathematical expressions.
If the current flowing through the resistor R53 is I3,
V1 ＝ VBG−R53 ・ I3 (11)
I3 = V1 / R51 + (V1-VBE) / R52 (12)
From equation (11) and equation (12) V1 = A + B · VBE
Is obtained. Therefore, V1 has a negative slope with respect to temperature.

Where A = VBG / (1 + R53 / R51 + R53 / R52) ... constant with temperature B = (R53 / R52) / (1 + R53 / R51 + R53 / R52)
It is.

  A circuit example of the second temperature coefficient circuit 215 is shown in FIG. The second temperature coefficient circuit 215 generates a voltage having a negative temperature coefficient by utilizing the fact that the base-emitter voltage VBE of the transistor has a negative temperature coefficient.

  In FIG. 16, the second temperature coefficient circuit 215 includes a resistor R62, a collector / emitter of a transistor Q51, a power supply terminal of a reference voltage VBG supplied from a bandgap reference type reference voltage circuit 209, and a ground GND. The resistor R63 is connected in series, the collector and the base of the transistor Q51 are connected in common, and the resistor R61 is connected between the base and the ground GND. The voltage generated at the base (= collector) of the transistor Q51 is the sum of the voltage generated at the resistor R63 and the base-emitter voltage VBE of Q51. Therefore, since the temperature characteristic of the collector voltage Vout of the transistor Q51 is proportional to the temperature characteristic of VBE, it has a negative slope. VBG is a voltage that is obtained from the bandgap reference type reference voltage circuit 209 and is constant with respect to temperature (that is, constant independent of temperature).

  Another circuit example of the second temperature coefficient circuit 215 is shown in FIG. The second temperature coefficient circuit 215 generates a voltage having a negative temperature coefficient by utilizing the fact that the base-emitter voltage VBE of the transistor has a negative temperature coefficient.

  In FIG. 17, the second temperature coefficient circuit 215 has a resistor R71 and a resistor R72 connected in series between the power supply terminal of the reference voltage VBG supplied from the bandgap reference type reference voltage circuit 209 and the ground GND, and the power supply Vcc. A circuit in which a constant current source I12 and a collector / emitter of an NPN transistor Q61 are connected in series between a resistor and a series connection point of the resistors R71 and R72, and a collector and a base of the transistor Q61 are connected in common. The operational amplifier U22 is provided with a voltage follower in which the base voltage of the transistor Q61 is input to the positive terminal and the negative terminal and the output terminal are connected in common.

  In such a configuration of FIG. 17, the current I12 of the constant current source I12 is a constant current with respect to temperature, and VBG is a band gap reference voltage. Accordingly, the voltage V2 obtained by dividing the band gap reference voltage VBG by the resistors R71 and R72 is a constant voltage with respect to the temperature. Since the base-emitter voltage VBE of the transistor Q61 has a negative slope with respect to temperature, a voltage having a negative slope with respect to the output voltage Vout can be obtained.

Returning to FIG. 14, the configuration of the inverting amplifier circuits 202, 203, 217, 218, and 219 will be described.
The inverting amplifier circuit 217 includes an operational amplifier U11 and resistors R23 and R24. The divided voltage from the first resistor voltage dividing circuit is input to the plus terminal, and the minus terminal is connected to the second temperature coefficient circuit 215 via the resistor R23. The resistor R24 is connected between the negative terminal and the output terminal. The amplification factor can be set by the ratio of the resistor R23 and the resistor R24.

The inverting amplifier circuit 202 includes an operational amplifier U14 and resistors R33 and R34. A divided voltage from the fifth resistor voltage dividing circuit is input to the positive terminal, and a voltage from the inverting amplifier circuit 217 is input to the negative terminal via the resistor R33. The resistor R34 is connected between the negative terminal and the output terminal. The amplification factor can be set by the ratio of the resistor R33 and the resistor R34, and R33 <R34 is set. In the inverting amplifier circuit 202, an inverting output having a positive slope from the inverting amplifier circuit 217 can be input, and a voltage having a negative slope with respect to temperature can be output.
The inverting amplifier circuit 218 includes an operational amplifier U17 and resistors R45 and R46. A divided voltage from the second resistor voltage dividing circuit is input to the plus terminal, and a voltage from the inverting amplifier circuit 217 is input to the minus terminal via the resistor R45. The resistor R46 is connected between the negative terminal and the output terminal. The amplification factor can be set by the ratio of the resistor R45 and the resistor R46.

The inverting amplifier circuit 203 includes an operational amplifier U15 and resistors R37 and R38. A divided voltage from the third resistor voltage dividing circuit is input to the plus terminal, and a voltage from the inverting amplifier circuit 218 is input to the minus terminal via the resistor R37. The resistor R38 is connected between the negative terminal and the output terminal. The amplification factor can be set by the ratio of the resistor R37 and the resistor R38, and R37 <R38 is set. In the inverting amplifier circuit 203, an output obtained by inverting and amplifying the inverting output having a positive slope from the inverting amplifier circuit 217 by the inverting amplifier circuit 218 in the previous stage is input, and a voltage having a positive slope with respect to the temperature is output. Can do.
The inverting amplifier circuit 219 includes an operational amplifier U13 and resistors R41 and R42, and the divided voltage from the fourth resistor voltage dividing circuit is input to the plus terminal, and the voltage from the inverting amplifier circuit 217 is input to the minus terminal via the resistor R41. The resistor R42 is connected between the negative terminal and the output terminal. The amplification factor can be set by the ratio of the resistor R41 and the resistor R42, and R41≈R42 is set. In the inverting amplifier circuit 219, an inverting output having a positive slope from the inverting amplifier circuit 217 can be input, and a voltage having a substantially zero slope with respect to temperature can be output.

  The voltage generated by the second temperature coefficient circuit 215 is inverted and amplified by the inverting amplifier circuit 217. Therefore, the output voltage from the inverting amplifier circuit 217 has a positive slope with respect to temperature. The voltage generated by the inverting amplifier circuit 217 is input to the negative terminals of the inverting amplifier circuits 202, 218, and 219. The inverting amplifier circuit 202 generates a voltage having a desired negative temperature gradient (negative temperature coefficient) as described in the inverting amplifier circuit 102 of the first and second embodiments. Further, in the inverting amplifier circuit 219, the temperature gradient of the output voltage is adjusted so as to be constant with respect to the ambient temperature.

  The inverting amplifier circuit 218 serves as a buffer for the inverting amplifier circuit 203 that generates a voltage having a positive temperature gradient (positive temperature coefficient). That is, if the output voltage of the second temperature coefficient circuit 215 is directly inverted and amplified by the inverting amplifier circuit 203, the level of the output voltage of the inverting amplifier circuit 203 is far from the level of the output voltage of the inverting amplifier circuits 202 and 219, and the emitter follower. There is a possibility that the output voltage of the superimposition output circuit 220 configured as shown in FIG. For this reason, the inverting amplification circuit 218 amplifies the slope to some extent, so that the inverting amplification level of the inverting amplification circuit 203 can be easily adjusted.

  The inverting amplifier circuit 203 is an amplifier that generates a voltage having a positive temperature gradient, as described in the non-inverting amplifier circuit 103 of the first and second embodiments. A voltage having a temperature coefficient is generated.

  The superimposed output circuit 220 includes three transistors Q21, Q22, Q23 having a collector connected in common and an emitter connected in common between a power supply Vcc and a ground GND, and a constant current source connected between the common emitter and the ground GND. I12, the output voltage of the inverting amplifier circuit 202 is input to the base of the transistor Q21, the output voltage of the inverting amplifier circuit 219 is input to the base of the transistor Q22, and the output voltage of the inverting amplifier circuit 203 is input to the base of the transistor Q23. The input voltage is obtained from the common emitter.

  When the voltages generated by the inverting amplifier circuits 202, 219, and 203 are superimposed by the superimposition output circuit 220, the highest voltage among the three voltages is clamped and output from the superimposition output circuit 220.

  The voltage / current conversion circuit 221 includes a voltage / current conversion unit including a transistor Q29, an operational amplifier U18, constant current sources I13 and I14, transistors Q28 and Q31, resistors R47 and R48, and a current including transistors Q30 and Q24. And a mirror section. That is, the voltage / current conversion circuit 221 has constant current sources I13 and I14, one end of which is connected to the power supply Vcc, an emitter connected to the constant current source I13, a collector connected to the ground GND, and a base connected to the previous common emitter. The PNP transistor Q29 to which the output voltage is input, the PNP transistor Q28 whose emitter is connected to the constant current source I14, the collector is connected to the ground GND, the emitter of the transistor Q29 is connected to the plus terminal, and minus An operational amplifier U18 having the terminal connected to the emitter of the transistor Q28 and two PNP transistors Q30 and Q24 are provided. These transistors Q30 and Q24 have the emitter connected to the power source Vcc and the base connected in common. And the base and collector of the transistor Q30 are connected in common, and the transistors Q30 and Q24 A current mirror section for outputting a current of the same magnitude to the transistor, an NPN transistor Q31 having a collector connected to the collector of the transistor Q30 and an emitter connected to the ground GND via a resistor R47, and one end of the transistor Q24 And a resistor R48 having the other end connected to the ground GND.

  The current mirror circuit 222 has a base connected in common to the bases of the previous transistors Q24 and Q30, an emitter connected to the power source Vcc, a collector and a base connected in common, and a collector connected to the transistor Q25. NPN transistor Q26 having an emitter connected to ground GND, a base connected in common to the base of transistor Q26, an emitter connected to ground GND, and a collector connected to the negative electrode of laser diode LD11. And an NPN transistor Q27 connected to one end. Transistor Q26 and transistor Q27 form a current mirror. A laser diode LD11 as a load is connected between the power source Vcc and the collector of the transistor Q27.

  In the voltage / current conversion circuit 221, the transistor Q29 is inserted to increase the voltage level by the base-emitter voltage VBE. This is to prevent the operational amplifier U18 from operating when the input voltage of the operational amplifier U18 is low. The current generated by the operational amplifier U18, the transistor Q31, and the resistor R47 is mirrored by the transistor Q30, and the same current flows through the transistor Q24. The current flowing through the transistor Q24 is converted into a voltage by the resistor R48, and the voltage is input to the base of the transistor Q28, thereby forming a feedback loop to the negative terminal of the operational amplifier U18. The transistor Q28 functions as a variable resistor whose resistance value varies depending on the base voltage. As a result, the current flowing through the resistor R48 is controlled so that the voltage at the negative terminal of the operational amplifier U18 is the same as the voltage input to the positive terminal.

  A bias current is supplied to the laser diode LD11 by turning back the mirror current of the transistor Q30 by the current mirrors of the transistors Q25 and Q27. This bias current follows the temperature characteristic of the threshold current of the laser diode LD11.

  The LD 11 is a surface emitting laser diode, and is composed of, for example, a VCSEL (vertical surface emitting laser). One end of the laser diode LD11 is connected to the power source Vcc, and the other end is connected to one end of the transistor Q27. A high-speed modulation circuit 223 that supplies a high-speed modulated current signal (modulation current) is connected in parallel to both ends of the transistor Q27 of the bias current output unit of the current mirror circuit 222. The high-speed modulation circuit 223 is composed of, for example, a current source I15 that supplies a modulated pulse current.

  In the configuration of FIG. 14 described above, a voltage having a temperature coefficient is created based on the voltage of the reference voltage circuit that generates a stable voltage that does not depend on the temperature, and a level shift is appropriately performed to thereby generate a desired negative voltage. , A voltage having a desired positive slope, and a voltage that is constant (that is, constant independent of temperature) with respect to a temperature change. Then, by superimposing these voltages, the highest voltage is output with respect to the ambient temperature, and the voltage is converted into a current, which is used as a bias current for the surface emitting laser diode. As a result, the bias current is a current that follows the temperature characteristics of the threshold current of the surface emitting laser diode. Therefore, even if the threshold current of the laser diode fluctuates due to changes in the ambient temperature, the bias current that follows the fluctuation As a result, it is possible to generate a light output without deterioration of the extinction ratio characteristic due to temperature change and without eye pattern deterioration due to temperature change.

  FIGS. 18A to 18C are diagrams for explaining the operation of the superimposed output circuit 220 including the emitter follower. As shown in FIG. 18A, the output voltage is level-shifted from the inverting amplifier circuit 202 and has a negative slope (negative temperature coefficient) with respect to the temperature T, and the level-shifted from the inverting amplifier circuit 203 and An output voltage having a positive slope (positive temperature coefficient) with respect to the temperature T and a constant voltage that is level-shifted from the inverting amplifier circuit 219 and has no dependency on the temperature T are shown in FIG. As shown in FIG. 18, as a result of being superposed by the superposition output circuit 220 and clamped to one of the highest voltages, the voltage T is high on the low temperature side and high temperature side as shown in FIG. An output voltage having a parabolic characteristic is generated.

  FIG. 19 shows the temperature characteristic c of the bias current Ibias with respect to temperature, generated in the third embodiment. X-axis is temperature (° C), Y-axis is current value when current value at 25 ° C is 0 mA (current values shown in this graph are actual current value at ambient temperature and actual current at 25 ° C It is indicated by the difference from the value). As the bias current Ibias, it is possible to obtain a shape that follows the temperature characteristics of the threshold current of the VCSEL. By further increasing the number of circuits having different slopes of the output voltage with respect to the temperature and providing a plurality of inflection points, it is possible to perform matching more accurately.

According to the third embodiment of the present invention, since the level shift means is constituted by a plurality of resistance voltage dividing circuits, an effect of easily adjusting the level of the temperature characteristic can be obtained. This is because, when an integrated circuit is formed, the resistance value itself may vary if the ratio of the magnitudes of two resistors such as the voltage dividing circuit 216 is the same. This is because the ratio of the two resistance values can be adjusted relatively easily if they are formed in the same place on the same semiconductor wafer. A laser diode having a parabolic temperature characteristic of a threshold current having at least one inflection point can supply a bias current in the vicinity of the threshold current in the entire temperature range used. Deterioration is reduced and good transmission characteristics can be obtained.
Further, when a laser diode having a characteristic that the threshold current is larger than the room temperature (25 ° C.) on the low temperature side and the threshold current is larger than the room temperature (25 ° C.) on the high temperature side, such as VCSEL, Since the deterioration of the pattern is reduced, good transmission characteristics can be obtained.

Furthermore, by using a reference voltage source that does not depend on temperature, a voltage or current having a positive or negative slope can be generated with reference to this, so that stable control is possible.
Further, by using the temperature characteristics of the transistor and a stable reference voltage, a voltage or current having a stable slope with respect to temperature can be obtained. That is, by using a temperature coefficient signal generation circuit having a temperature characteristic proportional to temperature and a stable reference voltage source, a voltage or current having a stable slope with respect to temperature can be obtained.
Also, a stable high speed operation can be obtained by applying a high speed modulation signal to the bias current.

  Next, as described with reference to FIG. 8, as the bias current Ibias supplied to the laser diode LD1, the bias current Ibias is a constant current having no temperature characteristics, and the modulation current Im supplied to the laser diode LD1 is a surface emitting type. Embodiments 4 to 6 will be described in the case where the laser diode LD1 is configured to generate the modulation current Im following the temperature characteristic of the threshold current Ith of the laser diode LD1.

That is, in the fourth to sixth embodiments, the optical semiconductor light emitting element driving circuit includes a bias current generating circuit that always generates a substantially constant current as the bias current Ibias without depending on the ambient temperature, and a surface emitting laser diode LD1. A high-speed modulation signal (modulation current Im) for driving a laser diode following the temperature characteristic of the threshold current Ith is generated, and this high-speed modulation signal (modulation current Im) is applied to the bias current Ibias supplied from the bias current generation circuit. And a high-speed modulation circuit to be applied. The bias current Ibias may be a constant current corresponding to the threshold current Ith of the surface emitting laser diode LD1 at room temperature (25 ° C.).
[Embodiment 4]

FIG. 20 shows a configuration diagram of an optical semiconductor light emitting element driving circuit according to Embodiment 4 of the present invention. The fourth embodiment corresponds to the first embodiment in FIG. 1, and the same reference numerals are given to the same parts having the same functions as those in FIG.
FIG. 20 shows a configuration example of an optical transmission module 100C having an optical semiconductor light emitting element driving circuit 200C and a surface emitting laser diode LD1 as an optical semiconductor light emitting element driven thereby.

  20 differs from the configuration of FIG. 1 in that an external data signal generating circuit (in series with the collector of the transistor Q4 of the voltage / current conversion circuit 108A between the laser diode LD1 and the voltage / current conversion circuit 108A). By inserting a switch circuit S1 that is turned on and off by a data signal (pulse signal corresponding to a digital signal of “1” and “0”) generated by a data signal (not shown), the threshold value of the surface emitting laser diode LD1 While constituting a high-speed modulation circuit (101 to 107, 108A, 109) for generating a high-speed modulated current signal (modulation current Im) for driving a laser diode following the temperature characteristic of the current Ith, it depends on the ambient temperature. The bias current generation circuit 111A is configured to generate a constant current that is always constant as the bias current Ibias. The bias current generation circuit 111A includes a constant current source I4A having a temperature characteristic that does not depend on the ambient temperature.

In FIG. 20, the amplitude of the pulse current (modulation current) as the data signal changes following the temperature characteristics of the threshold current Ith of the surface emitting laser diode LD1 in response to the change in the ambient temperature. By applying an appropriate constant bias current Ibias to the pulse current (modulation current), the same operation and effect as in FIG. 1 can be obtained. That is, when the temperature characteristic of the threshold current Ith of the surface emitting laser diode LD1 used is a V-shaped characteristic having one inflection point or a parabolic characteristic close thereto, the laser diode is driven accordingly. The temperature characteristic of the current can be followed.
[Embodiment 5]

FIG. 21 shows a configuration diagram of an optical semiconductor light emitting element driving circuit according to Embodiment 5 of the present invention. The fifth embodiment corresponds to the second embodiment of FIG. 11, and the same portions having the same functions as those of FIG.
FIG. 21 shows a configuration example of an optical transmission module 100D having an optical semiconductor light emitting element driving circuit 200D and a surface emitting laser diode LD1 as an optical semiconductor light emitting element driven thereby.

  21 is different from the configuration of FIG. 11 in that an external data signal generation circuit (in FIG. 21) is connected in series with the collector of the transistor Q4 of the voltage / current conversion circuit 108A between the laser diode LD1 and the voltage / current conversion circuit 108A. By inserting a switch circuit S1 that is turned on and off by a data signal (pulse signal corresponding to a digital signal of “1” and “0”) generated by a data signal (not shown), the threshold value of the surface emitting laser diode LD1 While constituting a high-speed modulation circuit (101 to 107, 108A, 109, 112, 113) for generating a high-speed modulated current signal (modulation current Im) for driving a laser diode following the temperature characteristic of the current Ith, The bias current generation circuit 111A is configured to always generate a substantially constant constant current as the bias current Ibias without depending on the temperature.The bias current generation circuit 111A includes a constant current source I4A having a temperature characteristic that does not depend on the ambient temperature.

In FIG. 21, the amplitude of the pulse current (modulation current) as the data signal changes following the temperature characteristics of the threshold current Ith of the surface emitting laser diode LD1 in response to the change in the ambient temperature. By applying an appropriate constant bias current Ibias to the pulse current (modulation current), the same operation and effect as in FIG. 11 can be obtained. That is, when the temperature characteristic of the threshold current Ith of the surface emitting laser diode LD1 to be used is a parabolic characteristic having at least one inflection point, the temperature characteristic of the laser diode driving current is corresponding to this. Can be made to follow.
[Embodiment 6]

FIG. 22 shows a configuration diagram of an optical semiconductor light emitting element driving circuit according to Embodiment 6 of the present invention. The sixth embodiment corresponds to the third embodiment of FIG. 14, and the same parts having the same functions as those of FIG.
FIG. 22 shows a configuration example of an optical transmission module 100E having an optical semiconductor light emitting element driving circuit 200E and a surface emitting laser diode LD11 as an optical semiconductor light emitting element driven thereby.

  FIG. 22 differs from the configuration of FIG. 14 in that an external data signal generation circuit (not shown) is connected in series with the collector of the transistor Q27 of the current mirror circuit 222A between the laser diode LD1 and the current mirror circuit 222A. The temperature of the threshold current Ith of the surface emitting laser diode LD11 is inserted by inserting a switch circuit S2 that is turned on and off by the data signal generated in step (a pulse signal corresponding to the digital signal of “1” and “0”). While constituting a high-speed modulation circuit (202, 203, 209, 214 to 221, 222A) for generating a high-speed modulated current signal (modulation current Im) for driving a laser diode following the characteristics, it depends on the ambient temperature. A bias current generation circuit 223A that always generates a substantially constant constant current as the bias current Ibias is configured. . The bias current generation circuit 223A includes a constant current source I15A having a temperature characteristic that does not depend on the ambient temperature.

  In FIG. 22, the amplitude of the pulse current (modulation current) as the data signal changes following the temperature characteristics of the threshold current Ith of the surface emitting laser diode LD1 corresponding to the change in the ambient temperature. By applying an appropriate constant bias current Ibias to the pulse current (modulation current), the same operation and effect as in FIG. 14 can be obtained. That is, when the temperature characteristic of the threshold current Ith of the surface emitting laser diode LD11 to be used is a parabolic characteristic having at least one inflection point, the temperature characteristic of the laser diode driving current is corresponding to this. Can be made to follow.

1 is a configuration diagram of an optical semiconductor light emitting element driving circuit according to Embodiment 1 of the present invention. FIG. The circuit diagram which shows one Example of the temperature coefficient circuit of FIG. The graph which shows the relationship of the temperature versus voltage obtained by the temperature coefficient circuit (temperature coefficient signal generation circuit) of FIG. The circuit diagram which shows one Example of the band gap reference type | mold reference voltage circuit of FIG. FIG. 2 is a circuit diagram showing an embodiment of the level shift circuit of FIG. 1. FIG. 3 is a diagram for explaining the operation of the superimposed output circuit of FIG. 1. FIG. 4 is a diagram illustrating a temperature characteristic c of a bias current Ibias with respect to temperature, generated in the first embodiment. 1 is an overall view of an optical transmission module according to the present invention. The figure which shows the electric current versus optical output characteristic of a laser diode. The figure which shows the temperature characteristic of the threshold current of a surface emitting type laser diode. The block diagram of the optical semiconductor light-emitting device drive circuit by Embodiment 2 of this invention. FIG. 12 is a diagram for explaining the operation of the superimposed output circuit of FIG. 11. The figure which shows the temperature characteristic c of the bias current Ibias which followed the temperature characteristic of the threshold current of VCSEL produced | generated in Embodiment 2. FIG. The block diagram of the optical semiconductor light-emitting device drive circuit by Embodiment 3 of this invention. The circuit diagram which shows one Example of the 1st temperature coefficient circuit of FIG. The circuit diagram which shows one Example of the 2nd temperature coefficient circuit of FIG. The circuit diagram which shows the other Example of the 2nd temperature coefficient circuit of FIG. FIG. 15 is a diagram for explaining the operation of the superimposed output circuit of FIG. 14. The figure which shows the temperature characteristic c of the bias current Ibias with respect to temperature produced | generated in Embodiment 3. FIG. The block diagram of the optical semiconductor light-emitting device drive circuit by Embodiment 4 of this invention. The block diagram of the optical semiconductor light-emitting device drive circuit by Embodiment 5 of this invention. The block diagram of the optical semiconductor light-emitting device drive circuit by Embodiment 6 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Temperature coefficient circuit 102, 103 ... Amplifier circuit 104, 105 ... Level shift circuit 108 ... Voltage / current conversion circuit 110 ... Superimposition output circuit 200 ... Optical semiconductor light emitting element drive circuit

Claims (5)

A temperature coefficient signal generation circuit that generates a voltage or current having a positive slope or a negative slope with respect to the ambient temperature; and
A first amplifier circuit that receives the voltage or current of the temperature coefficient signal generation circuit, inverts the voltage or current to a predetermined temperature gradient, and outputs the first output signal;
A second amplification circuit that receives the voltage or current of the temperature coefficient signal generation circuit and outputs the second output signal without inverting the voltage or current at a predetermined temperature gradient;
The first output signal and the second output signal are input, and either the first output signal or the second output signal is selected, and a bias current or a modulation current is selected based on the signal. An output circuit to generate,
An optical semiconductor light-emitting element driving circuit comprising: A temperature coefficient signal generation circuit that generates a voltage or current having a positive slope or a negative slope with respect to the ambient temperature; and
A reference signal generation circuit that generates a reference signal having a substantially zero slope with respect to the ambient temperature;
An inverting amplifier circuit that receives the voltage or current of the temperature coefficient signal of the temperature coefficient signal generation circuit, inverts the voltage or current to a predetermined temperature gradient, and outputs the inverted signal as a first output signal;
A non-inverting amplifier circuit that receives the voltage or current of the temperature coefficient signal of the temperature coefficient signal generation circuit and outputs the second output signal without inverting the voltage or current at a predetermined temperature gradient;
The first output signal, the second output signal, and the reference signal are input, and one of the first output signal, the second output signal, and the reference signal is selected, and the signal is An output circuit for generating a bias current or a modulation current based on the output circuit;
An optical semiconductor light-emitting element driving circuit comprising: A temperature coefficient signal generation circuit that generates a voltage or current having a positive slope or a negative slope with respect to the ambient temperature; and
A first amplifier circuit that receives the voltage or current of the temperature coefficient signal generation circuit, inverts the voltage or current to a predetermined temperature gradient, and outputs the first output signal;
A voltage or current of the temperature coefficient signal generation circuit is input, and at least two or more inverting amplification circuits are used to output the voltage or current as a second output signal without being inverted at a predetermined temperature gradient. An amplifier circuit;
A voltage or current of the temperature coefficient signal generation circuit is input, the voltage or current is inverted to a substantially zero temperature gradient, and a third output signal having a substantially zero gradient with respect to the ambient temperature is output. An amplifier circuit of
The first output signal, the second output signal, and the third output signal are input, and any one of the first output signal, the second output signal, and the third output signal is obtained. An output circuit that selects and generates a bias current or a modulation current based on the signal;
An optical semiconductor light-emitting element driving circuit comprising: 3. The optical semiconductor light emitting element driving according to claim 1, further comprising level shift means provided in a preceding stage of the output circuit and configured to shift levels of a plurality of signals output to the output circuit. circuit. It is composed of a plurality of resistance voltage dividing circuits provided in front of the first, second and third amplifier circuits, and a signal obtained from the temperature coefficient signal generation circuit is input to the plurality of resistance voltage dividing circuits, 4. The optical semiconductor light emitting element drive circuit according to claim 3, further comprising level shift means for shifting the level of a signal output to each of the first, second and third amplifier circuits.

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