WO2008038998A1

WO2008038998A1 - Darlington circuit with constant voltage source and integrated circuit device integrated the darlington circuit with constant voltage source

Info

Publication number: WO2008038998A1
Application number: PCT/KR2007/004703
Authority: WO
Inventors: Ok-Sang Jin
Original assignee: Ok-Sang Jin
Priority date: 2006-09-28
Filing date: 2007-09-27
Publication date: 2008-04-03

Abstract

A Darlington circuit with a constant voltage source includes a first transistor that has a base, which is connected to an input terminal, and is supplied with an input signal from the input terminal as a bias current, a second transistor that is supplied with part of an emitter current of the first transistor as a bias current and outputs an amplified current through an emitter thereof, a resistor, one end of which is connected to a contact of an emitter of the first transistor and a base of the second transistor, and a constant voltage source that is connected between the other end of the resistor and the emitter of the second transistor. The constant voltage source is composed of a transistor having the same operational characteristic as that of at least one of the first and second transistors.

Description

DARLINGTON CIRCUIT WITH CONSTANT VOLTAGE

SOURCE AND INTEGRATED CIRCUIT DEVICE INTEGRATED

THE DARLINGTON CIRCUIT WITH CONSTANT VOLTAGE

SOURCE Technical Field

[1] The present invention relates to a Darlington circuit with a constant voltage source and an integrated circuit device having the same integrated therein. In particular, the present invention relates to a Darlington circuit with a constant voltage source that has excellent operational characteristics, while achieving low manufacturing costs, and an integrated circuit device having the same integrated therein. Background Art

[2] Generally, as shown in FIG. 1, in a Darlington circuit with a constant voltage source, a constant voltage source (constant voltage circuit) (CV) CV31 is additionally connected to an emitter of a second transistor Q32 to increase a voltage across both ends of a resistor R31 connected to an emitter of a first transistor Q31, such that an operation point of the first transistor Q31 is within a linear region on a characteristic curve. In addition, the resistor R31 serves as a constant current load of the first transistor Q31 to improve amplification characteristics.

[3] The Darlington circuit with a constant voltage source shown in FIG. 1 also has a constant current function. Thus, it is called "constant current Darlington circuit" or "CCD (Constant Current Darlington)".

[4] The operation of the Darlington circuit with a constant voltage source shown in

FIG. 1 will now be described.

[5] If an input signal of an input terminal IN3 increases, a current ibe31 increases, and a current ice31 of the first transistor Q31 also increases. Since most of the current ice31 passes through the resistor R31, the voltage across both ends of the resistor R31 increases by a current iR31, and accordingly a voltage on a contact (node) A rises. In addition, as the voltage on the contact A rises, a current ibe32 of the second transistor Q32 increases, a collector current ice32 of the second transistor Q32 also increases. Then, the collector-emitter impedance of the second transistor Q32 is lowered. Since a voltage across both ends of the constant voltage source (CV) CV31 connected to the emitter of the second transistor Q32, a potential on a contact B increases by a load (LD) LD31, and a potential on a contact C also increases. If the potential on the contact C rises, the voltage across both ends of the resistor R31 decreases. Then, the current iR31 decreases, and the current ice31 also decreases. Accordingly, the current ice31 maintains the previous state (a constant current operation of the resistor R31). At this time, the current ibe31 also decreases and maintains the previous state. The second transistor Q32 controls the current ice31 so as to be constant. As the input signal increases, the voltage on the contact B and the voltage across both ends of the load (LD) LD31 increase.

[6] That is, the first transistor Q31 and the second transistor Q32 are the same as those in a basic Darlington circuit. In addition, the constant voltage source (CV) CV31 is connected to the emitter of the second transistor Q32, and the resistor R31 is provided on the emitter side of the first transistor Q31. Here, a base-emitter voltage Vbe_Q32 of the second transistor Q32 and a current flowing in the resistor R31 by the constant voltage source (CV) CV31 are controlled by the second transistor Q32 to be constant. Therefore, a collector-emitter current of the first transistor Q31 is constant, and the base current ibe31 of the first transistor Q31 is constant. The fact that the base current of the first transistor Q31 is constant means that a current does not flow in alternating current wise. That is, a signal current by the voltage of the input signal does not flow to the base of the first transistor Q31, and thus the first transistor Q31 serves as a voltage amplifying element.

[7] As described above, since the second transistor Q32 operates to allow the current ibe31 to be constant, input impedance on the input terminal IN3 side is high, and the input signal that is input to the input terminal IN3 is not transformed. Therefore, full amplification can be performed.

[8] To obtain such excellent characteristics, the constant voltage source (CV) provided on the emitter side of the second transistor Q32 is important. In addition, the characteristics of the constant voltage source does not need to be changed according to a change in voltage or frequency of the input signal and a change in the collector-emitter current of the second transistor Q32.

[9] In the related art, as the constant voltage source provided on the emitter side of the second transistor Q32, a diode or a Zener diode has been mainly used.

[10] FIG. 2 shows a case where a diode is used as a constant voltage source. If a diode

D41 is provided on the emitter side of a second transistor Q42 in a forward direction, a voltage V_D41 across both ends of the diode D41, which is approximately 0.6 V, is generated by a current flowing in the emitter of the second transistor Q42. With the voltage V_D41 across both ends of the diode D41 and a base-emitter voltage Vbe_Q42 of the second transistor Q42, a voltage V_R41 across both ends of a resistor R41 is represented by Equation 1.

[11] (Equation 1)

[12] V_R41 = Vbe_Q42 + V_D41 [13] A collector-emitter current Ice_Q41 of a first transistor Q41 is represented by

Equation 2.

[14] (Equation 2)

[15] Ice_Q41 = V_R41/R41

[16] Ice_Q41 = ( Vbe_Q42 + V_D41 )/R41

[17] To allow the collector-emitter current Ice_Q41 of the first transistor Q41 to be constant, the base-emitter voltage Vbe_Q42 of the second transistor Q42 and the voltage V_D41 across both ends of the diode D41 serving as the constant current source need to be constant.

[18] The base-emitter voltage Vbe_Q42 of the second transistor Q42 may be constant within the operational range of the second transistor Q42. The voltage across both ends of the diode D41 may vary according to the component characteristics of the diode D41. As shown in FIG. 3, when the collector-emitter current Ice_Q42 of the second transistor Q42 is smaller than the rated forward characteristics of the diode, an operation point exists in a non-linear portion of the characteristic curve of the diode D41. The voltage across both ends of the diode D41 is non-linearly changed according to a change in the current Ice_Q42, and a reference voltage across both ends of the resistor R41 is changed. Then, a current I_R41 flowing in resistor R41 is changed, and accordingly the base current of the first transistor Q41 is changed. For this reason, the input signal is transformed, and the amplification characteristics of the first transistor Q41 are changed. As a result, an amplified signal is distorted.

[19] In particular, if the diode D41 has high capacitance, when an operating current between the collector and the emitter of the second transistor Q42 is small, the amplified signal is excessively distorted. Meanwhile, if the diode D41 has low capacitance, there are many cases when it is difficult to select a diode that is compatible with the operational characteristic of the second transistor Q42. That is, since the second transistor Q42 has a three-electrode structure, and the diode D41 has a two- electrode structure, it is almost impossible to make the operational characteristics be compatible with each other.

[20] FIG. 4 shows a case where a Zener diode is used as a constant voltage source. If a

Zener diode ZD51 is provided on an emitter side of a second transistor Q52 in a backward direction, a voltage V_ZD51 across both ends of the Zener diode ZD51 is generated by a collector-emitter current of the second transistor Q52 as a Zener voltage.

[21] A voltage V_R51 that is applied to both ends of a resistor R51 by the voltage

V_ZD51 across both ends of the Zener diode ZD51 and a base-emitter voltage Vbe_Q52 of the second transistor Q52 is represented by Equation 3.

[22] (Equation 3) [23] V_R51 = Vbe_Q52 + V_ZD51

[24] A collector-emitter current Ice_Q51 of a first transistor Q51 is represented by

Equation 4.

[25] (Equation 4)

[26] Ice_Q51 = V_R51/R51

[27] Ice_Q51 = (Vbe_Q52 + V_ZD51 )/R51

[28] To allow the collector-emitter current Ice_Q51 of the first transistor Q51 to be constant, the base-emitter voltage Vbe_Q52 of the second transistor Q52 and the voltage V_ZD51 across both ends of the Zener diode ZD51 serving as the constant current source need to be constant.

[29] The base-emitter voltage Vbe_Q52 of the second transistor Q52 may be constant within the operational range of the second transistor Q52. The voltage across both ends of the Zener diode ZD51 may vary according to the component characteristics of the Zener diode ZD51. As shown in FIG. 5, when the collector-emitter current Ice_Q52 of the second transistor Q52 is smaller than the rated backward characteristics of the Zener diode ZD51, the operation point exists in a non-linear portion of a characteristic curve. The voltage across both ends of the Zener diode ZD51 is non-linearly changed according to a change in the current Ice_Q52, and the voltage across both ends of the resistor R51 is changed. Then, a current I_R51 flowing in the resistor R51 is changed, and accordingly the base current of the first transistor Q51 is changed. For this reason, the input signal is transformed, and the amplification characteristics of the first transistor Q51 are changed. As a result, an amplified signal is distorted.

[30] In particular, when a low- voltage Zener diode is used as the Zener diode ZD51, a

Zener voltage excessively changes even while using a small current. Then, when the collector-emitter current of the second transistor Q52 is small, the amplified signal is excessively distorted. In addition, even if the Zener diode ZD51 has low capacitance, there are many cases when it is difficult to select a Zener diode that is compatible with the operational characteristic of the second transistor Q52.

[31] When a diode or a Zener diode is used as the above-described constant voltage source, in order to form a device having a constant current Darlington circuit integrated therein (for example, a constant current Darlington transistor), two transistors, one resistor, and one diode or one Zener diode may be arranged on a circuit board as individual components.

[32] In this case, however, since the area for the components is large, there is a limitation in reducing the size of a product. In addition, since many steps are needed, this is disadvantageous for mass production. Furthermore, since manufacturing costs may be increased, the price is not comparable to cost.

[33] In order to manufacture the constant current Darlington transistor, surface mounting components are used and assembled on a circuit board, thereby reducing the mounting area. In this way, the mounting area of the components can be reduced. However, many steps are still needed, and this is disadvantageous for mass production.

[34] At present, there are known several methods known manufacture the constant current Darlington transistor with a single component.

[35] First, there is known a method that arranges individual components on a circuit board and assembles the components as a module. This method is suitable for reducing the size since the surface mounting (SMD) components are used. According to this method, since the individual components are used, the costs for the components are not reduced as much, and a predetermined amount of the mounting area may be somewhat needed. Therefore, the constant current Darlington transistor manufactured by this method is regarded as a module, not a single component.

[36] Second, there is known a method that integrates portions having the same characteristics of individual components in a semiconductor substrate with a semiconductor by a semiconductor manufacturing process. This method is appropriately used to manufacture the constant current Darlington transistor as a single component. If it is assumed that two transistors, one resistor, and one diode or one Zener diode, which form the constant current Darlington transistor, are formed in the semiconductor substrate, portions having the characteristics of the transistors, the resistor, and the diode or the Zener diode need to be formed in the same semiconductor substrate.

[37] Here, in order to obtain the individual characteristics in forming the three types of components, holes (P-type region) or electrons (N-type region) are injected with different quantities. Then, in order to form the portions corresponding to the individual components in the semiconductor substrate, the transistor portions are formed, then the resistor portion is formed, and subsequently the diode or Zener diode portion is formed. That is, three steps are needed.

[38] Of course, the constant current Darlington transistor may be manufactured using a voltage reference diode or a shunt regulator, which has excellent constant voltage control characteristics, as compared with the diode or the Zener diode. In this case, however, many steps are also needed.

[39] That is, the larger the number of steps for processing a semiconductor substrate is, the more manufacturing costs are required, and mass production becomes difficult. In addition, the yield is reduced, and an error rate is increased. Disclosure of Invention Technical Problem

[40] The invention has been finalized in order to solve the problems inherent in the related art. An object of the invention is to provide a Darlington circuit with a constant voltage source that has excellent operational characteristics while achieving low manufacturing costs, and an integrated circuit device having the same integrated therein. Technical Solution

[41] According to an aspect of the invention, a Darlington circuit with a constant voltage source includes a first transistor that has a base, which is connected to an input terminal, and is supplied with an input signal from the input terminal as a bias current, a second transistor that is supplied with part of an emitter current of the first transistor as a bias current and outputs an amplified current through an emitter thereof, a resistor, one end of which is connected to a contact of an emitter of the first transistor and a base of the second transistor, and a constant voltage source that is connected between the other end of the resistor and the emitter of the second transistor. The constant voltage source is composed of a transistor having the same operational characteristic as that of at least one of the first and second transistors.

[42] At least one transistor may form the current voltage source.

[43] A base and a collector of the transistor, which forms the constant voltage source, may be connected with each other.

[44] According to another aspect of the invention, an integrated circuit device having a

Darlington circuit with a constant voltage source that is integrated therein integrates a Darlington circuit with a constant voltage source therein. The Darlington circuit with a constant voltage source includes a first transistor that has a base, which is connected to an input terminal, and is supplied with an input signal from the input terminal as a bias current, a second transistor that is supplied with part of an emitter current of the first transistor and outputs an amplified current through an emitter thereof, a resistor, one end of which is connected to a contact of an emitter of the first transistor and a base of the second transistor, and a constant voltage source that is connected between the other end of the resistor and the emitter of the second transistor, and is composed of a transistor having the same operational characteristic as that of at least one of the first and second transistors.

[45] The second transistor and the constant voltage source may be manufactured together by the same manufacturing process.

[46] The first transistor, the second transistor, and the constant voltage source may be manufactured together by the same manufacturing process.

Advantageous Effects

[47] As described below in detail, according to the invention, the constant voltage source is composed of a transistor having the same operational characteristic as that of at least one of two transistors forming the Darlington circuit, thereby implementing a constant current Darlington transistor. Therefore, a constant current Darlington transistor having excellent operational characteristics is obtained. [48] Like the invention, when a device to be used as a constant voltage source is selected, if a transistor having the same three-electrode structure as the transistor, which forms the Darlington circuit, it is possible to simply and accurately adjust the operational characteristic thereof, compared with the related art where a diode or a

Zener diode is selected and the operational characteristic thereof is adjusted. Therefore, it is possible to easily select a component to be used as the constant voltage source. [49] In manufacturing the constant current Darlington transistor using semiconductors, the number of steps can be reduced, which reduces the manufacturing costs, as compared with the related art where a diode or a Zener diode is used.

Brief Description of the Drawings [50] FIG. 1 is a circuit diagram illustrating a general Darlington circuit with a constant voltage source. [51] FIG. 2 is a circuit diagram showing a case where a diode is used as a constant voltage source shown in FIG. 1. [52] FIG. 3 is a graph showing the operational characteristics of the diode shown in FIG.

2. [53] FIG. 4 is a circuit diagram showing a case where a Zener diode is used as a constant voltage source shown in FIG. 1. [54] FIG. 5 is a graph showing the operational characteristics of the Zener diode shown in FIG. 4. [55] FIG. 6 is a circuit diagram showing a Darlington circuit with a constant voltage source according to a first embodiment of the invention. [56] FIG. 7 is a diagram showing a case where the Darlington circuit shown in FIG. 6 is mounted on a circuit board with individual components. [57] FIG. 8 is a cross-sectional view showing a case where the Darlington circuit shown in FIG. 6 is manufactured in a semiconductor substrate. [58] FIG. 9 is a circuit diagram showing a Darlington circuit with a constant voltage source according to a second embodiment of the invention. [59] <Description of Reference Numerals and Signs>

[60] Q 1 , Q21 : FIRST TRANSISTOR

[61] Q2, Q22: SECOND TRANSISTOR

[62] Q3, Q23: THIRD TRANSISTOR

[63] Q24: FOURTH TRANSISTOR

[64] Rl, R21: RESISTOR

Best Mode for Carrying Out the Invention [65] A Darlington circuit with a constant voltage source according to an embodiment of the invention and an integrated circuit device having the same integrated therein will now be described with reference to the accompanying drawings.

[66] FIG. 6 is a circuit diagram showing a Darlington circuit with a constant voltage source according to a first embodiment of the invention.

[67] The Darlington circuit with a constant voltage source according to the first embodiment includes a first transistor Ql that has a base, which is connected to an input terminal Bl, and is supplied with an input signal from the input terminal Bl as a bias current, a second transistor Q2 that is supplied with part of an emitter current of the first transistor Ql as a bias current and outputs an amplified current through an emitter thereof, and a third transistor Q3 that has a base and a collector, which are connected to the emitter of the second transistor Q2, and an emitter, which is connected to the emitter of the first transistor Ql and a base of the second transistor Q2 through a resistor Rl.

[68] The third transistor Q3 is used as a constant voltage source. The third transistor Q3 is manufactured to have the same operational characteristic as the second transistor Q2.

[69] A constant voltage circuit that uses the third transistor Q3, the base and collector of which are connected with each other, as the constant voltage source generates a constant voltage of approximately 0.6 V. It is used in a portion of an electronic circuit that requires the constant voltage of 0.6 V. In the constant voltage circuit composed of a transistor, a relatively stable voltage is generated, and a collector-emitter current of the transistor is in a wide range.

[70] The constant voltage circuit that is composed of a transistor, the base and collector of which are connected with each other, that is, the third transistor Q3 operates such that a current obtained by amplifying a current Ibe flowing from the base to the emitter due to a current amplification ratio hfe flows to the collector and emitter. If so, the voltage is maintained at a base-emitter voltage Vbe of the transistor Q3, that is, 0.6 V. The constant voltage circuit composed of a transistor operates if a current flowing therein is a minimum base current Ibe or more. A current exceeding the minimum base current Ibe flows from the collector to the base, and thus the voltage is maintained to the base-emitter voltage vbe. Therefore, in a small-current circuit, a stable constant voltage can be maintained. (Description 1)

[71] When the Darlington circuit with a constant voltage source shown in FIG. 6 is integrated in a single component (device), it may be called a constant current Darlington transistor. At this time, a base of the single component becomes a first base B 1, an emitter thereof becomes a first emitter El, and a collector thereof becomes a first collector Cl.

[72] In FIG. 6, the emitter of the third transistor Q3 is connected to a load LD (not shown), like FIG. 1. [73] The configuration shown in FIG. 6 may be manufactured by assembling individual components in a circuit board as a module, as shown in FIG. 7. Most preferably, the configuration shown in FIG. 6 is integrated with a semiconductor, as shown in FIG. 8. At this time, the number of steps required in the semiconductor manufacturing process needs to be as small as possible, and a difference in the characteristic that corresponds to a deviation in process needs to be small. As a result, yield can be increased and manufacturing costs can be reduced.

[74] In FIG. 8, there are many methods that can be used to manufacture the constant current Darlington transistor in the semiconductor substrate using a semiconductor manufacturing method.

[75] Among the methods, a first preferred method is as follows. If the first transistor Ql is designed to have a different characteristic, and the second transistor Q2 and the third transistor Q3 have the same characteristic, a collector region of the first transistor Ql is first formed, then a base region thereof is formed, and subsequently an emitter region thereof is formed. Since the second transistor Q2 and the third transistor Q3 can be simultaneously formed, collector regions for two transistor regions are simultaneously formed, then base regions for the two transistor regions are simultaneously formed, and subsequently emitter regions for the two transistor regions are simultaneously formed. Although the number of transistors is 3, only two steps are needed. Therefore, the amount of work time needed can be reduced, resulting in saving manufacturing costs. Finally, a region for the resistor Rl is formed, thereby completing a semiconductor substrate process.

[76] A second preferred method is as follows. If the first transistor Ql, the second transistor Q2, and the third transistor Q3 are designed to have the same characteristic, collector regions for three transistor regions are simultaneously formed, then base regions for the three transistor regions are simultaneously formed, and subsequently emitter regions for the three transistor regions are simultaneously formed. Although the number of transistors is 3, only one step is needed. Therefore, the work time required is only needed to manufacture one transistor, resulting in reduced manufacturing costs. Finally, a region for the resistor Rl is formed, thereby completing a semiconductor substrate process.

[77] When a constant current Darlington transistor is manufactured in a semiconductor substrate by a semiconductor manufacturing method, in forming the transistors, if the first transistor Ql, the second transistor Q2, and the third transistor Q3 are formed by the same process, the doping areas for the collectors, the bases, and the emitters may be the same, or may be different according to the characteristics of the individual transistors.

[78] As described above, the Darlington circuit with a constant voltage source (a constant current Darlington circuit) or a device having the constant current Darlington circuit (that is, a constant current Darlington transistor) integrated therein shown in FIG. 6 that uses a transistor, the base and collector of which are connected with each other, has the following characteristics.

[79] First, when the circuit shown in FIG. 6 operates, an operation current that flows between the collector and the emitter of the second transistor Q2 also flows to the collector and the emitter of the third transistor Q3. If the third transistor Q3 having the same operational characteristic as the second transistor Q2 or a similar operational characteristic thereto is used as the constant voltage source, an excellent constant voltage characteristic is obtained, and a stable operation of the operation current is achieved. If the second transistor Q2 and the third transistor Q3 have different operational characteristics, a voltage to be generated varies, and it is difficult for the transistor to function as a constant voltage source. For this reason, the third transistor Q3 having the same operational characteristic as the second transistor Q2 is preferably used as the constant voltage source. (Description 2)

[80] Particularly, in the case of selecting a component, since the third transistor Q3 has the same three-electrode structure as the second transistor Q2, among transistors having various operational characteristics, it is easy to select a transistor having the same operational characteristic as the second transistor Q2, as compared with a case where a diode or a Zener diode is selected. (Description 3)

[81] Second, as shown in FIG. 8, a case where a constant current Darlington transistor is manufactured as a single component by a semiconductor manufacturing method will be described. Here, in view of the number of steps, one step refers to a step of forming a device having a different characteristic.

[82] In FIG. 8, when the first transistor Ql, the second transistor Q2, and the third transistor Q3 are designed to have different characteristics, there are four steps needed in total, that is, a step of forming the first transistor Ql, a step of forming the second transistor Q2, a step of forming the third transistor Q3, and a step of forming the resistor Rl.

[83] In contrast, if the second transistor Q2 and the third transistor Q3 are designed to have the same characteristic, there are needed three steps in total, that is, a step of forming the first transistor Ql, a step of simultaneously forming the second transistor Q2 and the third transistor Q3, and a step of forming the resistor Rl. That is, the second transistor Q2 and the third transistor Q3 can be formed in one step. Furthermore, in the constant current Darlington transistor, the first transistor Ql and the second transistor Q2 may have the same characteristic. Accordingly, if the first transistor Ql, the second transistor Q2, and the third transistor Q3 are designed to have the same characteristic, two steps are needed in total, that is, a step of forming the first transistor Ql, the second transistor Q2, and the third transistor Q3, and a step of forming the resistor Rl. That is, the first transistor Ql, the second transistor Q2, and the third transistor Q3 can be formed in one step. (Description 4)

[84] If a transistor is used as the constant voltage source of the constant current

Darlington transistor, as described in Description 1, the difference in characteristic that corresponds to the deviation during the process can be made uniform. In addition, as described in Description 2, a constant current Darlington transistor having excellent operational characteristics can be obtained. Furthermore, as described in Description 3, it is possible to easily select a device that is to be used as the constant voltage source, and as described in Description 4, the number of steps in the manufacturing process with a semiconductor can be reduced.

[85] FIG. 9 is a circuit diagram showing a Darlington circuit with a constant voltage source according to a second embodiment of the invention. The circuit diagram of FIG. 9 is different from the circuit diagram of FIG. 6 in that, in FIG. 9, two transistors are used as a constant voltage source. That is, while a transistor used as a constant voltage source is the third transistor Q3 in FIG. 6, a transistor used as a constant voltage source is the third and fourth transistors Q23 and Q24 in FIG. 9. In FIG. 9, the third transistor Q23 may serve as a first constant voltage source, and the fourth transistor Q24 may serve as a second constant voltage source.

[86] The transistor Q21 shown in FIG. 9 corresponds to the first transistor Ql shown in

FIG. 6, and the transistor Q22 shown in FIG. 9 corresponds to the second transistor Q2 shown in FIG. 6.

[87] The transistor forming the constant voltage source according to the first embodiment (that is, the third transistor Q3) has the same operational characteristic as the transistors Q23 and Q24 of the constant voltage source according to the second embodiment. The number of transistors is determined depending on a voltage of the constant voltage source that is required by the constant current Darlington transistor.

[88] A voltage when the constant voltage circuits, in each of which the collector and base of the transistor are connected with each other, are connected in series is the sum of the base-emitter voltages Vbe of the individual transistors. Accordingly, referring to FIG. 9, in the constant current Darlington transistor, the higher the voltage of the constant voltage source is, the more the constant current flowing in the resistor R21 is precisely controlled.

[89] In FIG. 9, the emitter of the fourth transistor Q24 is connected to a load LD (not shown), like FIG. 1.

[90] It should be understood that the invention is not limited to the above-described embodiments, but various modifications and changes can be made without departing from the subject matter of the invention. In addition, all modifications and changes that fall within metes and bounds of the claims, or equivalents of such metes and bounds are intended to be embraced by the claims.

Claims

[1] A Darlington circuit with a constant voltage source, comprising: a first transistor that has a base, which is connected to an input terminal, and is supplied with an input signal from the input terminal as a bias current; a second transistor that is supplied with part of an emitter current of the first transistor and outputs an amplified current through an emitter thereof; a resistor, one end of which is connected to a contact of an emitter of the first transistor and a base of the second transistor; and a constant voltage source that is connected between the other end of the resistor and the emitter of the second transistor, wherein the constant voltage source is composed of a transistor having the same operational characteristic as that of at least one of the first and second transistors. [2] The Darlington circuit as set forth in claim 1, wherein at least one transistor forms the constant voltage source. [3] The Darlington circuit as set forth in claim 1 or 2, wherein a base and a collector of the transistor, which forms the constant voltage source, are connected with each other. [4] An integrated circuit device having the Darlington circuit with a constant voltage source integrated therein as set forth in claim 1 or 2. [5] The integrated circuit device as set forth in claim 4, wherein the second transistor and the constant voltage source are manufactured together by the same manufacturing process. [6] The integrated circuit device as set forth in claim 4, wherein the first transistor, the second transistor, and the constant voltage source are manufactured together by the same manufacturing process. [7] An integrated circuit device having the Darlington circuit with a constant voltage source integrated therein as set forth in claim 3.