JP6646475B2 - Diode drive circuit and diode drive system - Google Patents

Description

  The present invention relates to a diode drive circuit and a diode drive system.

2. Description of the Related Art Conventionally, a technology using a current mirror circuit in a diode drive circuit is known (for example, see Patent Document 1).
Patent Document 1 JP 2005-26410 A

  However, in the conventional diode drive circuit, a difference occurs in the drain-source voltage in the mirror source and mirror destination transistors of the current mirror circuit, and the linearity of the output current with respect to the input current deteriorates.

  According to a first aspect of the present invention, there is provided a diode driving circuit for driving a diode, the circuit including a first transistor and a second transistor connected to the diode, and a current flowing through the first transistor. A first current mirror circuit that mirrors the current to a second transistor, a current setting unit that sets a current flowing through the first transistor to a predetermined current value, and a first current mirror circuit that is connected to a drain terminal of the first transistor. A voltage setting unit configured to set a voltage of a drain terminal of the one transistor to a predetermined voltage.

  According to a second aspect of the present invention, there is provided a diode driving system including a diode driving circuit and a diode connected to a drain terminal of a second transistor.

  The above summary of the present invention is not an exhaustive listing of all features of the present invention. Further, a sub-combination of these feature groups can also be an invention.

1 shows an outline of a configuration of a diode drive system 200 according to a first embodiment. 2 illustrates a specific circuit configuration of the diode drive system 200 according to the first embodiment. 7 shows an example of the configuration of a diode drive circuit 500 according to Comparative Example 1. 7 shows an example of the input / output characteristics of the diode drive circuit 500 according to Comparative Example 1. 3 shows an example of a specific circuit configuration of the control circuit 30. 9 shows an example of a configuration of a diode drive system 200 according to a second embodiment. 9 shows a specific circuit configuration of the diode drive system 200 according to the second embodiment. 10 illustrates an example of a configuration of a diode drive system 200 according to a third embodiment. 9 shows a specific circuit configuration of the diode drive system 200 according to the third embodiment.

  Hereinafter, the present invention will be described through embodiments of the invention, but the following embodiments do not limit the invention according to the claims. In addition, not all combinations of the features described in the embodiments are necessarily essential to the solution of the invention.

[Example 1]
FIG. 1 illustrates an outline of a configuration of a diode driving system 200 according to the first embodiment. The diode drive system 200 of the present example includes the diode drive circuit 100 and the diode 50. The diode drive circuit 100 includes a current mirror circuit 10, a voltage setting unit 20, and a current setting unit 40. The voltage setting unit 20 includes a transistor unit 25 and a control circuit 30.

  The current mirror circuit 10 generates an output current Iout that mirrors the input current Iin. In one example, the current mirror circuit 10 includes two transistors, a mirror source transistor TR1 and a mirror destination transistor TR2. The current mirror circuit 10 is connected to the current setting unit 40 and the diode 50. The current mirror circuit 10 outputs an output current Iout corresponding to the input current Iin set by the current setting unit 40 to the diode 50.

The voltage setting unit 20 sets the drain voltage of the transistor TR1 as the mirror source of the current mirror circuit 10 to a predetermined voltage. In this specification, a drain voltage refers to a voltage of a drain terminal of a transistor. The drain voltage set by the voltage setting unit 20 in this example is set to _{VD_TR1} . The drain voltage _{VD_TR1} may be determined according to the size of the transistors TR1, TR2, and the like. In one example, the transistor section 25 has a transistor TR3.

The control circuit 30 controls the gate voltage of the transistor TR3. The control circuit 30 of the present example sets the gate voltage of the transistor TR3 to the control voltage _Vctrl . Control voltage _{V ctrl} may be determined according to the size of the drain voltage _{V D_TR1} of the transistor TR1 to be set. Thus, the voltage setting unit 20, in accordance with the control voltage _{V ctrl} of the control circuit 30 outputs, to control the drain voltage _{V D_TR1} of the transistor TR1. The control circuit 30 is an example of a control unit included in the voltage setting unit 20. Note that in this specification, a gate voltage refers to a voltage of a gate terminal of a transistor.

  The current setting unit 40 generates a predetermined input current Iin. The current setting unit 40 is electrically connected to the current mirror circuit 10. The current setting unit 40 sets the drain current of the mirror-source transistor TR1 of the current mirror circuit 10 to the input current Iin. The magnitude of the input current Iin may be appropriately changed according to the drive current of the diode 50.

  The diode 50 is electrically connected to the current mirror circuit 10. The diode 50 is driven by the output current Iout output from the current mirror circuit 10.

  FIG. 2 illustrates a more specific circuit configuration of the diode drive system 200 according to the first embodiment.

  The current mirror circuit 10 includes a PMOS transistor TR1 and a transistor TR2. However, the current mirror circuit 10 may be configured as an NMOS type. The gate terminals of the transistor TR1 and the transistor TR2 are connected to each other to form a current mirror circuit.

  The transistor TR1 is a mirror source transistor of the current mirror circuit. The source terminal of the transistor TR1 is connected to a power supply terminal set to the power supply voltage VDD. The drain terminal of the transistor TR1 is connected to the voltage setting unit 20.

  The transistor TR2 is a transistor at the mirror destination of the current mirror circuit. The source terminal of the transistor TR2 is connected to a power supply terminal set to the power supply voltage VDD. The drain terminal of the transistor TR2 is connected to the diode 50.

  Voltage setting unit 20 sets the voltage at the drain terminal of transistor TR1 to a predetermined voltage. The transistor section 25 included in the voltage setting section 20 includes a transistor TR3. The transistor TR3 of this example is a PMOS transistor. The source terminal of the transistor TR3 is connected to the drain terminal of the transistor TR1. The drain terminal of the transistor TR3 is connected to the current setting unit 40.

Control circuit 30, so that a voltage value drain voltage _{V D_TR1} is predetermined transistor TR1, to set the control voltage _{V ctrl.} In one example, the control circuit 30, the source voltage of the transistor TR3, that is, the drain voltage _{V D_TR1} the transistor TR1, so that the same potential as the drain voltage _{V D_TR2} of the transistor TR2, which control the gate voltage of the transistor TR3. Note that in this specification, a source voltage refers to a voltage of a source terminal of a transistor.

  The current setting unit 40 includes a constant current source CG1. One end of the constant current source CG1 of this example is connected to the drain terminal of the transistor TR3, and the other end is connected to a reference terminal such as ground. The constant current source CG1 generates a predetermined constant current and sets the constant current as the drain current of the transistor TR1. In one example, the constant current source CG1 sets the input current Iin to the drive current of the diode 50. Further, a switch SW for switching the connection may be provided between the transistor TR3 and the constant current source CG1.

  The diode 50 is connected to the drain terminal of the transistor TR2. The diode 50 is driven by the output current Iout output from the current mirror circuit 10. For example, the diode 50 is a laser diode (LD: LASER DIODE).

As described above, the diode drive circuit 100 of the present example _controls the drain voltage _{VD_TR1} of the transistor TR1 so as to be a predetermined voltage value. By setting to the same value as the drain voltage _{V D_TR2} of the drain voltage _{V D_TR1} transistor TR2 transistor TR1, the diode drive circuit 100, thereby improving the linearity with respect to the input current Iin of the output current Iout.

[Comparative Example 1]
FIG. 3 shows an example of the configuration of the diode drive circuit 500 according to Comparative Example 1. The diode drive circuit 500 includes a current mirror circuit 510, a current setting unit 540, and a diode 550.

The current mirror circuit 510 has a transistor P1 and a transistor P2. The transistor P1 and the transistor P2 are PMOS transistors, respectively. The transistor P1 is diode-connected. The current mirror circuit 510 allows the input current Iin flowing in the mirror source transistor P1 to flow to the mirror destination transistor P2 as the output current Iout. _{VDS_P1} indicates a drain-source voltage of the transistor P1. _{VDS_P2} indicates a drain-source voltage of the transistor P2.

  The current setting unit 540 has a constant current source. The constant current source sets the input current Iin to the drain current of the transistor P1. The constant current source is connected to the drain terminal of the transistor P1.

  The diode 550 is driven by the output current Iout output from the current mirror circuit 510. The diode 550 of this example is a laser diode.

  FIG. 4 shows an example of the input / output characteristics of the diode drive circuit 500 according to Comparative Example 1. The vertical axis indicates the output current Iout, and the horizontal axis indicates the input current Iin. The solid line indicates the actual characteristics of the diode drive circuit 500 in which the linearity has deteriorated. The broken line indicates an ideal characteristic in which the linearity has not deteriorated.

  In this specification, for the sake of simplicity, the current mirror circuit included in the diode driving circuit is based on the assumption that the current ratio of the drain current flowing in the mirror source transistor to the mirror destination transistor is 1: 1. For example, in the calculation of this example, it is assumed that the current ratio between the mirror source transistor and the mirror destination transistor is 1: 1 and that Iout = Iin = Id. Id is the drain current of the mirror source and mirror destination transistors.

ここで、Ｒ_ｌｏａｄは、ダイオード５５０の駆動時のインピーダンスを示す。（数１）式より、ドレイン電流が大きいほどトランジスタＰ２のドレイン・ソース間電圧Ｖ_{ＤＳ＿Ｐ２}は低くなる。 In the diode drive circuit 500 according to Comparative Example 1, the drain-source voltage _{VDS_P2} of the transistor P2 is determined by the output current Iout of the drive circuit and the impedance of the diode 550 that is a drive load. The drain-source voltage _{VDS_P2} of the transistor P2 is _expressed by the following equation.

Here, R _load indicates the impedance when the diode 550 is driven. From equation (1), the drain-source voltage _{VDS_P2} of the transistor P2 decreases as the drain current increases.

On the other hand, the drain-source voltage _{VDS_P1} of the transistor P1 is determined by the input current Iin and the characteristics of the transistor P1. The drain current Id of a general PMOS transistor is expressed by the following equation in a saturation region.

  In the equation (2), the coefficient Kp is represented by Kp = μp · Cox · W / L. μp is the surface mobility of the channel carrier, Cox is the gate oxide film capacitance of the PMOS transistor, W is the channel width of the PMOS transistor, L is the channel length of the PMOS transistor, and Vgs is the source-gate voltage of the PMOS transistor. The absolute value and Vth indicate the absolute value of the threshold voltage of the PMOS transistor, respectively.

In this case, the drain-source voltage of the transistor P1 is expressed by the following equation.

Equation (3) shows that the larger the drain current Id, the higher the drain-source voltage _{VDS_P1 of} the transistor P1. As the drain current Id increases, a drain-source voltage difference between the transistor P1 and the transistor P2 occurs. As a result, in the diode drive circuit 500, the linearity of the output current Iout with respect to the input current Iin deteriorates.

  For example, when the diode driving circuit 500 drives the LD as the diode 550, the potential of the drain terminal of the transistor P2 when the LD emits light is about 2V. However, as the drive current of the diode 550 increases, the potential of the drain terminal of the transistor P2 increases. On the other hand, as the drive current of the diode 550 increases, the potential of the gate terminal of the transistor P2 decreases, and the operation region of the transistor P2 approaches the linear region from the saturation region. As a result, as shown by the solid line, the linearity of the input / output characteristics may be greatly deteriorated.

  FIG. 5 illustrates an example of a specific circuit configuration of the control circuit 30 according to the embodiment. The control circuit 30 of this example includes an operational amplifier 31, a transistor TR8, a resistor R1, a resistor R2, a constant current source CG3, and a constant current source CG4.

The operational amplifier 31 has an output terminal, a positive input terminal, and a negative input terminal. The output terminal of the operational amplifier 31 is connected to the gate terminal of the transistor TR8. The operational amplifier 31 sets the gate voltage of the transistor TR8 to the control voltage V _ctrl . The positive input terminal of the operational amplifier 31 is set to, for example, the reference voltage V _BIAS . On the other hand, the negative input terminal of the operational amplifier 31 is connected to the constant current source CG3 via the resistor R1. The negative input terminal of the operational amplifier 31 is connected to the constant current source CG4 via the resistor R2. Note that the output terminal of the operational amplifier 31 may be connected to the gate terminal of the transistor TR3.

  The transistor TR8 is a transistor having characteristics corresponding to the transistor TR3. In one example, the transistor TR8 is a PMOS transistor having the same size or a proportional size as the transistor TR3. The transistor TR8 of this example has the same size as the transistor TR3. Further, the transistor TR8 of the present example is a PMOS transistor. The gate terminal of the transistor TR8 is connected to the output terminal of the operational amplifier 31. The source terminal of the transistor TR8 is connected to the constant current source CG3. The drain terminal of the transistor TR8 is connected to the constant current source CG4.

  One end of the resistor R1 is connected to the constant current source CG3, and the other end is connected to the negative input terminal of the operational amplifier 31. One end of the resistor R2 is connected to the constant current source CG4, and the other end is connected to the negative input terminal of the operational amplifier 31. The transistor TR8 is set similarly to the transistor TR3 in which the bias state is inserted. Note that in this specification, it is assumed that the current flowing through the transistor TR3 and the transistor TR8 is 1: 1.

Constant current source CG3 passes a current _I A + _{I B} determined in advance. Constant current source CG4 passes a predetermined current _{I B.} Current _{I A} flows through the resistors R1 and R2 connected in series. The current _{I B} flows through the transistor TR8.

Here, if _{(R1 + R2) × I A} = 2V, R2 × I A = V BIAS, the source terminal of the transistor TR8 by the feedback loop becomes 2.0 V. Therefore, the control circuit 30, by controlling the gate terminal of the transistor PMOS3 control voltage _{V ctrl,} can set the drain-source voltage _{V DS_TR1} transistor TR1 around 2V. Thereby, the diode drive circuit 100 of the present example can improve the linearity of the output current Iout with respect to the input current Iin as compared with the diode drive circuit 500 according to Comparative Example 1.

[Example 2]
FIG. 6 illustrates an example of a configuration of the diode drive system 200 according to the second embodiment. The diode drive system 200 includes the diode drive circuit 100 and the diode 50. The diode drive circuit 100 of the present example includes a replica unit 11, an output unit 12, a voltage setting unit 20, a second current mirror circuit 60, and a current comparison unit 70. The voltage setting unit 20 includes a transistor unit 25 and a control circuit 30. The replica unit 11 and the output unit 12 are examples of the current mirror circuit 10. The second current mirror circuit 60 and the current comparison unit 70 are an example of the current setting unit 40.

The replica unit 11 has a transistor TR1. The output unit 12 has a transistor TR2. The gate terminals of the transistor TR1 and the transistor TR2 are connected to each other. The gate potential _{VG_TR1_TR2} indicates the potential of the gate terminals of the transistor TR1 and the transistor TR2.

  The second current mirror circuit 60 generates a mirror current of the drain current Id flowing through the transistor TR1 of the replica unit 11. The output current Iout ′ corresponding to the drain current Id is input from the replica unit 11 to the second current mirror circuit 60 of the present example. The second current mirror circuit 60 generates a mirror current Iout ′ obtained by mirroring the input output current Iout ′. The second current mirror circuit 60 outputs the generated mirror current Iout ′ to the current comparison unit 70.

The current comparison unit 70 compares the input mirror current Iout ′ with the generated input current Iin. When the mirror current Iout ′ is larger than the input current Iin, the current comparison unit 70 increases the gate potential _{VG_TR1_TR2} . On the other hand, when the mirror current Iout ′ is smaller than the input current Iin, the current comparison unit 70 lowers the gate potential _{VG_TR1_TR2} . As described above, the current comparison unit 70 feeds _back the gate potential _{VG_TR1_TR2} so that the output current Iout and the input current Iin are equalized by the current balance between the mirror current Iout ′ and the input current Iin.

  FIG. 7 illustrates a more specific circuit configuration of the diode drive system 200 according to the second embodiment. The replica unit 11 has a transistor TR1. The output unit 12 has a transistor TR2. The second current mirror circuit 60 has transistors TR4, TR5, TR6, and TR7. Further, the current comparison unit 70 has a transistor TR7 and a constant current source CG2. Note that the control circuit 30 may have the configuration shown in FIG.

  Transistor TR4 and transistor TR5 form a current mirror circuit. The current mirror circuit mirrors the current flowing in the transistor TR4 to the transistor TR5. The transistor TR4 and the transistor TR5 of this example are NMOS transistors. The drain terminal of the transistor TR4 is connected to the drain terminal of the transistor TR3. The drain terminal of the transistor TR5 is connected to the drain terminal of the transistor TR6.

  Transistor TR6 and transistor TR7 form a current mirror circuit. The current mirror circuit mirrors the current flowing in the transistor TR6 to the transistor TR7. The transistor TR6 and the transistor TR7 in this example are PMOS transistors. A current Iout ′ corresponding to the drain current Iout ′ flowing through the transistor TR1 flows through the transistor TR7.

The constant current source CG2 of the current comparison unit 70 generates an input current Iin. The constant current source CG2 of the current comparison unit 70 is connected to the drain terminal of the transistor TR7. A node between the transistor TR7 and the constant current source CG2 is connected to the gate terminals of the transistor TR1 and the transistor TR2. Accordingly, if the drain current Iout ′ of the transistor TR7 is larger than the input current Iin, the current comparison unit 70 increases the gate potential _{VG_TR1_TR2} . On the other hand, if the drain current Iout ′ of the transistor TR7 is smaller than the input current Iin, the current comparison unit 70 decreases the gate potential _{VG_TR1_TR2} . That is, the current comparison unit 70 feeds _back the gate potential _{VG_TR1_TR2} so that the drain current Iout ′ of the transistor TR7 corresponding to the drain current of the transistor TR1 becomes the input current Iin.

  Here, the diode drive circuit 100 of this example is based on the assumption that all the MOS transistors operate in the saturation region. However, when the power supply voltage VDD changes in a higher direction, the MOS transistor of the transistor TR3 may operate in the linear region. This is because the voltage at the drain terminal of the transistor TR3 depends on the power supply voltage VDD.

（数４）式は、電源電圧ＶＤＤが高くなるとトランジスタＴＲ３のドレイン電圧が上昇することを示す。ここで、トランジスタＴＲ３が飽和領域で動作する為の条件は、次式で示される。

なお、上式では、ＰＭＯＳトランジスタについて計算しているので、絶対値としている。

ここに（数４）式及び、Ｖ_{Ｓ＿ＴＲ３}＝Ｖ_{Ｄ＿ＴＲ１}、Ｖ_{ＧＳ＿ＴＲ３}＝Ｖ_ｃｔｒｌ−Ｖ_{Ｄ＿ＴＲ１}を代入し整理すると、次式が得られる。

（数７）式の条件が満たせなくなると、トランジスタＴＲ３は、ドレイン・ソース間電圧を確保できず、リニア領域で動作する。リニア領域で動作すると、ドレイン電圧Ｖ_{Ｄ＿ＴＲ１}が意図した電圧で抑えられなくなる場合がある。 The voltage at the drain terminal of the transistor TR3 is expressed by the following equation.

Equation (4) shows that the drain voltage of the transistor TR3 increases as the power supply voltage VDD increases. Here, the condition for the transistor TR3 to operate in the saturation region is expressed by the following equation.

In the above formula, since the calculation is performed for the PMOS transistor, the absolute value is used.

Here (number 4) _{and, V S_TR3} = V _{D_TR1,} and rearranging substituting _{V GS_TR3} = _{V ctrl -V D_TR1,} the following equation is obtained.

If the condition of Expression 7 cannot be satisfied, the transistor TR3 cannot operate in the linear region because the drain-source voltage cannot be secured. When operating in the linear region, the drain voltage _{VD_TR1} may not be suppressed to the intended voltage.

  However, since the diode drive circuit 100 of the present example sets the drain voltage of the transistor TR3 to the gate-source voltage VGS_TR4 of the transistor TR4, it is not limited by the power supply voltage VDD. Therefore, the diode driving circuit 100 of the present example does not have the restriction as in the equation (7). Therefore, the diode drive circuit 100 of the present example easily operates the transistor TR3 in the saturation region, and has a wider range of operable power supply voltage VDD than the diode drive circuit 500 according to the comparative example.

As described above, the diode drive circuit 100 of the present example _adjusts the gate potential _{VG_TR1_TR2} of the transistor TR1 and the transistor TR2 based on the current balance between the input current Iin and the drain current Iout ′ of the transistor TR7. Thus, the diode drive circuit 100 of the present example can improve the linearity of the output current Iout with respect to the input current Iin in a wide range of the power supply voltage VDD.

[Example 3]
FIG. 8 illustrates an example of a configuration of a diode drive system 200 according to the third embodiment. The diode drive system 200 includes the diode drive circuit 100 and the diode 50. The diode drive circuit 100 of the present example includes a replica unit 11, an output unit 12, a voltage setting unit 20, a second current mirror circuit 60, and a current comparison unit 70. The voltage setting unit 20 includes a transistor unit 25 and a control circuit 30. In the present embodiment, a configuration different from the diode drive circuit 100 according to the second embodiment will be particularly described.

The control circuit 30 controls the transistor unit 25 using the generated control voltage V _ctrl . The drain voltage _{VD_TR2 of the} transistor TR2 included in the output unit 12 is input to the control circuit 30 of the present example. The control circuit 30 based on the drain voltage _{V D_TR2,} controls the control voltage _{V ctrl.}

Diode drive circuit 100 of the present example, as the drain voltage _{V D_TR1} of the transistor TR1 becomes equal to the drain voltage _{V D_TR2} transistor TR2, and feedback to the gate potential of the transistor TR3. Accordingly, even when the drain voltage _{V D_TR2} of the transistor TR2 is varied, can be controlled drain voltage _{V D_TR2} of the transistor TR2 in the same drain voltage _{V D_TR1} of the transistor TR1.

  FIG. 9 illustrates a more specific circuit configuration of the diode drive circuit 100 according to the third embodiment. In the present embodiment, a configuration different from the diode drive circuit 100 according to the second embodiment will be particularly described.

The control circuit 30 controls the gate voltage of the transistor TR3 based on the drain voltage _{VD_TR2} of the transistor TR2. The control circuit 30 of the present example has an operational amplifier AMP. The output terminal of the operational amplifier AMP is connected to the gate terminal of the transistor TR3. The inverting input terminal of the operational amplifier AMP is connected to the drain terminal of the transistor TR1. The non-inverting input terminal of the operational amplifier AMP is connected to the drain terminal of the transistor TR2.

Diode drive circuit 100 of this embodiment, the drain voltage _{V D_TR1} transistor TR1 equal to the drain voltage _{V D_TR2} of the transistor TR2 _{(i.e., V D_TR1 =} V _{D_TR2)} controlled to be. Thus, if the transistor TR1 and the transistor TR2 operate normally as a current mirror circuit in the saturation region, the diode drive circuit 100 can suppress an error in the drain current of the transistor TR1 and the transistor TR2.

Here, when the diode driving circuit 100 drives the diode 50 with a large current, the drain voltage _{VD_TR2} of the transistor TR2 may increase. When the drain voltage _{VD_TR2} of the transistor TR2 increases and becomes higher than the drain voltage _{VD_TR1} of the transistor TR1 (that is, _{VD_TR1} < _{VD_TR2} ), the output current Iout becomes lower than the drain current of the transistor TR1.

On the other hand, the diode drive circuit 100 of the present example, even when a large current operation, controls the drain voltage _{V D_TR2} of the transistor TR2 in the same drain voltage _{V D_TR1} of the transistor TR1. Thus, the diode drive circuit 100 can improve the linearity of the output current Iout with respect to the input current Iin even during a large current operation.

  As described above, the present invention has been described using the embodiments, but the technical scope of the present invention is not limited to the scope described in the above embodiments. It is apparent to those skilled in the art that various changes or improvements can be made to the above embodiment. It is apparent from the description of the appended claims that embodiments with such changes or improvements can be included in the technical scope of the present invention.

  The order of execution of processes such as operations, procedures, steps, and steps in the apparatuses, systems, programs, and methods shown in the claims, the description, and the drawings is particularly “before” or “before”. It should be noted that they can be realized in any order as long as the output of the previous process is not used in the subsequent process. Even if the operation flow in the claims, the specification, and the drawings is described using “first,” “second,” or the like for convenience, it means that it is essential to perform the operation in this order. Not something.

DESCRIPTION OF SYMBOLS 10 ... Current mirror circuit, 11 ... Replica part, 12 ... Output part, 20 ... Voltage setting part, 25 ... Transistor part, 30 ... Control circuit, 31 ... Operational amplifier , 40: current setting unit, 50: diode, 60: second current mirror circuit, 70: current comparison unit, 100: diode driving circuit, 200: diode driving system, 500 ... Diode drive circuit, 510 ... Current mirror circuit, 540 ... Current setting unit, 550 ... Diode

Claims (9)

A diode drive circuit for driving a diode,
A first current mirror circuit having a first transistor and a second transistor connected to the diode, and mirroring a current flowing through the first transistor to the second transistor;
A current setting unit that sets a current flowing through the first transistor to a predetermined current value;
A voltage setting unit connected to a drain terminal of the first transistor and setting a voltage of the drain terminal of the first transistor to a predetermined voltage ;
The voltage setting unit,
A third transistor having a source terminal connected to a drain terminal of the first transistor
Including
The current setting unit,
A second current mirror circuit having a fourth transistor and a fifth transistor, and mirroring a current flowing through the fourth transistor to the fifth transistor;
A third current mirror circuit having a sixth transistor and a seventh transistor, and mirroring a current flowing through the sixth transistor to the seventh transistor;
A second constant current source connected to a drain terminal of the seventh transistor;
Including
A drain terminal of the fourth transistor is connected to a drain terminal of the third transistor;
A drain terminal of the fifth transistor is connected to a drain terminal of the sixth transistor;
Gate terminals of the first transistor and the second transistor are connected to a connection node between the seventh transistor and the second constant current source.
Diode drive circuit. The voltage setting unit,
Includes a control unit for controlling the voltage of the gate terminal of said third transistor,
The control unit includes:
An operational amplifier having an output terminal connected to the gate terminal of the third transistor;
An eighth transistor having a gate terminal connected to the output terminal of the operational amplifier;
A third constant current source connected to the source terminal of the eighth transistor;
A fourth constant current source connected to a drain terminal of the eighth transistor;
A first resistor having one end connected to the third constant current source and the other end connected to an inverting input terminal of the operational amplifier;
A second resistor having one end connected to the fourth constant current source and the other end connected to the inverting input terminal of the operational amplifier.
The diode drive circuit according to claim 1 . The voltage setting unit,
Includes a control unit for controlling the voltage of the gate terminal of said third transistor,
The control unit includes:
An operational amplifier having an output terminal connected to the gate terminal of the third transistor, an inverting input terminal connected to the drain terminal of the first transistor, and a non-inverting input terminal connected to the drain terminal of the second transistor. The diode drive circuit according to claim 1 , comprising:   A diode drive circuit for driving a diode,
  A first current mirror circuit having a first transistor and a second transistor connected to the diode, and mirroring a current flowing through the first transistor to the second transistor;
  A current setting unit that sets a current flowing through the first transistor to a predetermined current value;
  A voltage setting unit that is connected to a drain terminal of the first transistor and sets a voltage of the drain terminal of the first transistor to a predetermined voltage;
  With
  The voltage setting unit,
  A third transistor having a source terminal connected to a drain terminal of the first transistor;
  A control unit for controlling a voltage of a gate terminal of the third transistor;
  Including
  The control unit includes:
  An operational amplifier having an output terminal connected to the gate terminal of the third transistor;
  An eighth transistor having a gate terminal connected to the output terminal of the operational amplifier;
  A third constant current source connected to the source terminal of the eighth transistor;
  A fourth constant current source connected to a drain terminal of the eighth transistor;
  A first resistor having one end connected to the third constant current source and the other end connected to an inverting input terminal of the operational amplifier;
  A second resistor having one end connected to the fourth constant current source and the other end connected to an inverting input terminal of the operational amplifier;
  Having
  Diode drive circuit.   A diode drive circuit for driving a diode,
  A first current mirror circuit having a first transistor and a second transistor connected to the diode, and mirroring a current flowing through the first transistor to the second transistor;
  A current setting unit that sets a current flowing through the first transistor to a predetermined current value;
  A voltage setting unit that is connected to a drain terminal of the first transistor and sets a voltage of the drain terminal of the first transistor to a predetermined voltage;
  With
  The voltage setting unit,
  A third transistor having a source terminal connected to a drain terminal of the first transistor;
  A control unit for controlling a voltage of a gate terminal of the third transistor;
  Including
  The control unit includes:
  An operational amplifier having an output terminal connected to the gate terminal of the third transistor, an inverting input terminal connected to the drain terminal of the first transistor, and a non-inverting input terminal connected to the drain terminal of the second transistor. Having
  Diode drive circuit.   The current setting unit includes a first constant current source connected to a drain terminal of the third transistor.
  A diode drive circuit according to claim 4.   The non-inverting input terminal of the operational amplifier has a product of a current value of a difference between a current value of the third constant current source and a current value of the fourth constant current source, and a resistance value of the second resistor. Is set to the reference voltage corresponding to
  The diode drive circuit according to claim 2. A diode drive circuit according to any one of claims 1 to 7,
A diode connected to a drain terminal of the second transistor.   9. The diode driving system according to claim 8, wherein the diode is a laser diode.

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