JP3558868B2 - Amplifier circuit - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an improvement in the structure of a bipolar transistor, and more particularly to an improvement in the structure of a bipolar transistor for improving electrical characteristics of the bipolar transistor.
[0002]
[Prior art]
Conventionally, NPN type and PNP type bipolar transistors have been known. This bipolar transistor has a collector made of an n-type or p-type semiconductor and a base joined to the collector and made of a semiconductor of a type different from the collector (that is, p-type if the collector is n-type and n-type if the collector is p-type) And an emitter joined to the base and made of the same type of semiconductor as the collector.
[0003]
This bipolar transistor controls a current path including the collector-emitter so that when a base current flows between an external signal source and the base, an amount of current substantially proportional to the base current flows between the collector and the emitter. I do.
[0004]
[Problems to be solved by the invention]
In order to allow a substantial amount of base current to flow in this bipolar transistor, a base-emitter voltage of about 0.6 volt is normally required. For this reason, a time lag occurs between the transition of the voltage of the signal supplied to the base and the transition of the on / off state of the bipolar transistor, which causes a delay in signal propagation.
[0005]
For example, for a digital input that rises from a low state below 0.6 volts to a high state above 0.6 volts for a finite period of time, the time it takes for the input to go from low to 0.6 volts is: The rise of the output does not start, which appears as a propagation delay.
[0006]
The amount of base current that can flow in the non-saturated state of the bipolar transistor is a function of the base-emitter voltage, but the value of the base current flowing under a constant base-emitter voltage also depends on temperature. . The rate of change of the base current with respect to temperature increases as the base-emitter voltage increases.
[0007]
For this reason, depending on the application, it is necessary to use a configuration for compensating the fluctuation of the base current with respect to temperature, such as a differential amplifier, and the number of bipolar transistors required to achieve the application increases, and the complexity of the device increases. In addition, the power consumption increases.
[0008]
SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and facilitates the manufacture of an amplifier circuit that amplifies a signal in a state where the voltage of a signal input terminal is substantially equal to the ground potential, and facilitates the manufacture of such an amplifier circuit. It is an object to provide a semiconductor device.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, a semiconductor device according to a first aspect of the present invention includes:
A first semiconductor layer of a first conductivity type;
A second conductivity type second semiconductor layer joined to the first semiconductor layer;
A third semiconductor layer of a first conductivity type joined to the second semiconductor layer;
A first conductivity type fourth semiconductor layer joined to the second semiconductor layer;
A fifth semiconductor layer of a second conductivity type joined to the fourth semiconductor layer,
The first, second, and third semiconductor layers are such that the second semiconductor layer functions as a base, and one of the first and third semiconductor layers functions as a collector, and the other functions as an emitter. Without a bipolar transistor,
The second, fourth and fifth semiconductor layers are such that the fourth semiconductor layer functions as a base, one of the second and fifth semiconductor layers functions as a collector, and the other functions as an emitter. A bipolar transistor,
It is characterized by the following.
[0010]
According to such a semiconductor element, for example, by operating the first bipolar transistor in the common emitter mode, operating the second semiconductor layer as the emitter of the second bipolar transistor, and operating the fifth semiconductor layer as the collector , The potential of the fourth semiconductor layer becomes substantially equal to the ground potential.
Further, for example, the first bipolar transistor is operated in the common emitter mode, the fifth semiconductor layer is operated as the emitter of the second bipolar transistor, the second semiconductor layer is operated as the collector, and the second bipolar transistor is saturated. Even so, the potential of the fourth semiconductor layer becomes substantially equal to the ground potential.
Therefore, according to such a semiconductor element, it becomes easy to manufacture an amplifier circuit that amplifies a signal in a state where the voltage of the signal input terminal is substantially equal to the ground potential.
[0011]
The area of the junction between the base and the emitter of the first bipolar transistor may be smaller than the area of the junction between the collector and the base of the first bipolar transistor.
[0012]
Thus, the amount of carriers injected from the emitters of the first and second bipolar transistors to the collectors can be controlled by a small base current flowing to the base of each bipolar transistor. That is, the input impedances of the bases of the first and second bipolar transistors increase, and the current amplification factors of the first and second bipolar transistors increase.
[0013]
Further, since the area of the junction between the base and the emitter of the first and second bipolar transistors is reduced, the junction capacitance of the capacitor formed by the junction is also reduced, and the frequency of the first and second bipolar transistors is reduced. The characteristics are improved.
[0014]
Further, a semiconductor device according to a second aspect of the present invention includes:
A first semiconductor layer of a first conductivity type;
A second conductivity type second semiconductor layer joined to the first semiconductor layer;
A third semiconductor layer of a first conductivity type joined to the second semiconductor layer;
A first conductivity type fourth semiconductor layer joined to the second semiconductor layer;
A fifth semiconductor layer of a second conductivity type joined to the fourth semiconductor layer,
The first, second, and third semiconductor layers are, in order from one pole of an external power supply, a first current that reaches the other pole of the power supply through the first, second, and third semiconductor layers. Form a path,
The second, fourth, and fifth semiconductor layers are, in order from one pole of the power supply, a second current path that reaches the other pole of the power supply through the fifth, fourth, and second semiconductor layers. Forming a
It is characterized by the following.
[0015]
The first, second, and third semiconductor layers of such a semiconductor device form a first bipolar transistor by, for example, functioning as a collector, a base, and an emitter, respectively, and form second, fourth, and fifth semiconductors. The layers form a second bipolar transistor, for example, by functioning as an emitter, a base and a collector.
Then, for example, by operating the first bipolar transistor in the common emitter mode, the potential of the fourth semiconductor layer becomes substantially equal to the ground potential.
Therefore, according to such a semiconductor element, it becomes easy to manufacture an amplifier circuit that amplifies a signal in a state where the voltage of the signal input terminal is substantially equal to the ground potential.
[0016]
Further, a semiconductor device according to a third aspect of the present invention includes:
A first semiconductor layer of a first conductivity type;
A second conductivity type second semiconductor layer joined to the first semiconductor layer;
A third semiconductor layer of a first conductivity type joined to the second semiconductor layer;
A first conductivity type fourth semiconductor layer joined to the second semiconductor layer;
A fifth semiconductor layer of a second conductivity type joined to the fourth semiconductor layer,
The first, second, and third semiconductor layers are, in order from one pole of an external power supply, a first current that reaches the other pole of the power supply through the first, second, and third semiconductor layers. Form a path,
The second, fourth, and fifth semiconductor layers are, in order from one pole of the power supply, a second current path that reaches the other pole of the power supply through the second, fourth, and fifth semiconductor layers. Forming a
It is characterized by the following.
[0017]
The first, second, and third semiconductor layers of such a semiconductor device form a first bipolar transistor by, for example, functioning as a collector, a base, and an emitter, respectively, and form second, fourth, and fifth semiconductors. The layers form a second bipolar transistor, for example, by functioning as a collector, a base and an emitter.
Then, for example, when the first bipolar transistor is operated in the common emitter mode and the second bipolar transistor is saturated, the potential of the fourth semiconductor layer becomes substantially equal to the ground potential.
Therefore, according to such a semiconductor element, it becomes easy to manufacture an amplifier circuit that amplifies a signal in a state where the voltage of the signal input terminal is substantially equal to the ground potential.
[0018]
Further, an amplifier circuit according to a fourth aspect of the present invention includes:
A first semiconductor layer of a first conductivity type; a second semiconductor layer of a second conductivity type joined to the first semiconductor layer; and a first semiconductor layer of a first conductivity type joined to the second semiconductor layer. A third conductive semiconductor layer, a first conductive fourth semiconductor layer bonded to the second semiconductor layer, a second conductive fifth semiconductor layer bonded to the fourth semiconductor layer, Wherein the first, second and third semiconductor layers comprise: The first semiconductor layer functions as a collector, The second semiconductor layer functions as a base, The third semiconductor layer functions as an emitter Forming a first bipolar transistor, wherein the second, fourth and fifth semiconductor layers are such that the second semiconductor layer functions as an emitter and the fourth semiconductor layer functions as a base; The fifth semiconductor layer functions as a collector A semiconductor element forming a second bipolar transistor;
The said 2 Said bipolar transistor Emitter A current path including the collector and the emitter of the first bipolar transistor. Led A current path including a collector and an emitter of the second bipolar transistor connected to the base of the second bipolar transistor. Led Bias means for supplying a bias current for passing
Input means for supplying an input signal to the base of the second bipolar transistor;
Means for applying a voltage generated by the emitter of the second bipolar transistor to the base of the first bipolar transistor;
Cascaded to a current path including the collector and the emitter of the first bipolar transistor Negative Output means for supplying an output signal representing the magnitude of the current flowing through the load to the outside,
It is characterized by having.
[0019]
According to such an amplifier circuit, the voltage between the base and the emitter of the first bipolar transistor is substantially canceled by the voltage between the base and the emitter of the second bipolar transistor, and the voltage of the base of the second bipolar transistor is reduced. The potential is substantially equal to the potential of the emitter of the first bipolar transistor.
Therefore, for example, if the emitter of the first bipolar transistor is grounded, the amplifier circuit receives the input signal with the potential of the base of the second bipolar transistor, which is the input terminal of the input signal, substantially equal to the ground potential. Performs signal amplification.
[0020]
Further, an amplifier circuit according to a fifth aspect of the present invention includes:
A first semiconductor layer of a first conductivity type; a second semiconductor layer of a second conductivity type joined to the first semiconductor layer; and a first semiconductor layer of a first conductivity type joined to the second semiconductor layer. A third conductive semiconductor layer, a first conductive fourth semiconductor layer bonded to the second semiconductor layer, a second conductive fifth semiconductor layer bonded to the fourth semiconductor layer, Wherein the first, second and third semiconductor layers comprise: The first semiconductor layer functions as a collector, The second semiconductor layer functions as a base, The third semiconductor layer functions as an emitter Forming a first bipolar transistor, wherein the second, fourth and fifth semiconductor layers are such that the second semiconductor layer functions as an emitter and the fourth semiconductor layer functions as a base; The fifth semiconductor layer functions as a collector A semiconductor element forming a second bipolar transistor;
The said 2 Said bipolar transistor Emitter A current path including the collector and the emitter of the first bipolar transistor. Led A current path including a collector and an emitter of the second bipolar transistor connected to the base of the second bipolar transistor. Get tired of Bias means for supplying a bias current for summing;
Input means for supplying an input signal to the base of the second bipolar transistor;
Means for supplying a current flowing through a current path including the collector and the emitter of the second bipolar transistor to the base of the first bipolar transistor;
A cascade connected to a current path including the collector and the emitter of the first bipolar transistor; Negative Output means for supplying an output signal representing the magnitude of the current flowing through the load to the outside,
It is characterized by having.
[0021]
According to such an amplifier circuit, the voltage between the base and the emitter of the first bipolar transistor is substantially canceled by the voltage between the collector and the base of the second bipolar transistor, and the voltage between the base and the emitter of the second bipolar transistor is reduced. The potential is substantially equal to the potential of the emitter of the first bipolar transistor.
Therefore, for example, if the first bipolar transistor is operating in the common-emitter mode, the amplifier circuit operates in a state where the potential of the base of the second bipolar transistor, which is the input terminal of the input signal, is substantially equal to the ground potential. Amplifies the input signal.
[0022]
Further, an amplifier circuit according to a sixth aspect of the present invention includes:
A first semiconductor layer of a first conductivity type; a second semiconductor layer of a second conductivity type joined to the first semiconductor layer; and a first semiconductor layer of a first conductivity type joined to the second semiconductor layer. A third semiconductor layer, a fourth semiconductor layer of the first conductivity type joined to the second semiconductor layer, a fifth semiconductor layer of the second conductivity type joined to the fourth semiconductor layer, Wherein the first, second and third semiconductor layers comprise: The first semiconductor layer functions as a collector, The second semiconductor layer functions as a base, The third semiconductor layer functions as an emitter Forming a first bipolar transistor, wherein the second, fourth and fifth semiconductor layers are such that the second semiconductor layer functions as an emitter and the fourth semiconductor layer functions as a base; The fifth semiconductor layer functions as a collector A semiconductor element forming a second bipolar transistor;
The said 2 Said bipolar transistor Emitter A current path including the collector and the emitter of the first bipolar transistor. Led A current path including a collector and an emitter of the second bipolar transistor connected to the base of the second bipolar transistor. Noh Bias means for supplying a bias current for conducting in the active region;
Input means comprising: an input terminal; and a means for supplying a current representing an input signal applied to the input terminal to the base of the second bipolar transistor.
Potential fixing means for controlling a voltage between the input terminal and the base of the second bipolar transistor so that the potential of the input terminal is substantially equal to the potential of the emitter of the first bipolar transistor;
Means for supplying a current flowing through a current path including the collector and the emitter of the second bipolar transistor to the base of the first bipolar transistor;
Cascaded to a current path including the collector and the emitter of the first bipolar transistor Negative Output means for supplying an output signal representing the magnitude of the current flowing through the load to the outside,
It is characterized by having.
[0023]
According to such an amplifier circuit, while the second bipolar transistor operates in the active region, the potential of the input terminal becomes substantially equal to the potential of the emitter of the first bipolar transistor by the potential regulating means.
Therefore, for example, if the first bipolar transistor operates in the common emitter mode and the emitter of the first bipolar transistor is grounded, the amplifier circuit operates in a state where the potential of the input terminal is substantially equal to the ground potential. Amplifies the input signal.
[0024]
Further, in such an amplifier circuit, the current between the collector and the emitter of the first bipolar transistor changes in a phase substantially opposite to the change in the voltage of the input signal. For this reason, for example, when the first bipolar transistor operates with the emitter grounded and the voltage of the collector of the first bipolar transistor is used as the output signal, the output signal changes in phase with the input signal.
[0025]
The bias means includes negative feedback means for reducing the magnitude of the bias current supplied to the base of the second bipolar transistor substantially in proportion to an increase in the current flowing to the load. May be.
Accordingly, the first bipolar transistor is substantially self-biased, for example, and operates stably with respect to a change in ambient temperature. Further, the frequency characteristics of the amplifier circuit are also improved.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
[0027]
(Transistor)
FIG. 1 is a diagram schematically showing a configuration of a transistor according to an embodiment of the present invention. As shown, the transistor includes first to fifth semiconductor layers 1 to 5.
[0028]
The first semiconductor layer 1 includes an n-type semiconductor region (hereinafter, referred to as an n-type region) and is joined to the second semiconductor layer 2. A collector terminal tC for external connection is connected to the first semiconductor layer 1.
[0029]
The second semiconductor layer 2 includes a p-type semiconductor region (hereinafter, referred to as a p-type region). A bias terminal tBIAS for external connection is connected to the second semiconductor layer 2.
[0030]
The third semiconductor layer 3 is formed of an n-type region, is joined to the second semiconductor layer 2, and is connected to a first emitter terminal tE1 for external connection.
[0031]
The fourth semiconductor layer 4 is formed of an n-type region, and is joined to the second semiconductor layer 2 without being in contact with the third semiconductor layer 3. A base terminal tB for external connection is connected to the fourth semiconductor layer 4.
[0032]
The fifth semiconductor layer 5 is formed of a p-type region, is joined to the fourth semiconductor layer 4, and is connected to a second emitter terminal tE2 for external connection.
[0033]
As shown in FIG. 1, in this transistor, the first to third semiconductor layers 1 to 3 form an NPN-type first bipolar transistor, and the second, fourth and fifth semiconductor layers 2, 4 And 5 form a second bipolar transistor of the PNP type.
[0034]
The first semiconductor layer 1 functions as a collector of the first bipolar transistor.
The second semiconductor layer 2 functions as a base of the first bipolar transistor and an emitter of the second bipolar transistor. The third semiconductor layer 3 functions as an emitter of the first bipolar transistor.
The fourth semiconductor layer 4 functions as a base of the second bipolar transistor. The fifth semiconductor layer 5 functions as a collector of the second bipolar transistor.
[0035]
However, as described below, the second semiconductor layer 2 may perform the function of the emitter of the second bipolar transistor. When the second semiconductor layer 2 performs the function of the emitter of the second bipolar transistor, the fifth semiconductor layer 5 performs the function of the collector of the second bipolar transistor.
[0036]
(Amplifier circuit)
Next, an amplifier circuit according to an embodiment of the present invention will be described.
FIG. 2 is a circuit diagram showing the configuration of this amplifier circuit.
As shown, the amplifier circuit includes a transistor Q, resistors R1 to R3, an input terminal IN, and an output terminal OUT.
[0037]
The transistor Q is substantially the same as the transistor shown in FIG. However, in the transistor Q of this amplifier circuit, the fifth semiconductor layer 5 performs the function of the collector of the second bipolar transistor, and the second semiconductor performs the function of the emitter of the second bipolar transistor. Layer 2.
[0038]
The resistor R1 is connected between the collector terminal tC of the transistor Q and the positive terminal of the external DC power supply, and the output terminal OUT is connected to the collector terminal tC. The first emitter terminal tE1 and the second emitter terminal tE2 are both grounded, and the negative pole of the DC power supply is also grounded. A resistor R2 is connected between the bias terminal tBIAS and the positive terminal of the DC power supply. The input terminal IN is connected to the base terminal tB, one end of a resistor R3 is connected to the base terminal tB, and the other end of the resistor R3 is grounded.
[0039]
The resistance values of the resistors R1 to R3 are selected such that the above-described first and second bipolar transistors included in the transistor Q perform substantially class A operation. That is, the resistance value of each of the resistors R1 to R3 is substantially equal between the collector and the emitter of the first and second bipolar transistors when a signal is not substantially supplied from the input terminal IN. It is set so that almost half of the current flowing when completely turned on flows.
[0040]
In the circuit of FIG. 2, when a power supply voltage is applied from both poles of the DC power supply, the current flowing between the collector and the emitter of the first and second bipolar transistors when these bipolar transistors are almost completely turned on is reduced. Almost half the current flows.
[0041]
Then, a forward voltage is generated between the second and third semiconductor layers 2 and 3 according to the forward characteristics of the diode formed by the second and third semiconductor layers 2 and 3. Specifically, the voltage of the base of the first bipolar transistor (ie, the second semiconductor layer 2) with respect to the emitter of the first bipolar transistor (ie, the third semiconductor layer 3) is, for example, about 0.6 volts. It becomes.
[0042]
Also, a forward voltage is generated between the second and fourth semiconductor layers 2 and 4 according to the forward characteristics of the diode formed by the second and fourth semiconductor layers 2 and 4. Therefore, the voltage of the base of the second bipolar transistor (ie, the fourth semiconductor layer 4) with respect to the emitter of the second bipolar transistor (ie, the second semiconductor layer 2) is, for example, about 0.6 volt.
[0043]
Therefore, the absolute value of the forward voltage of the diode formed by the second and third semiconductor layers 2 and 3 and the absolute value of the forward voltage of the diode formed by the second and fourth semiconductor layers 2 and 4 are different. If they are substantially equal to each other, the voltage between the third and fourth semiconductor layers 3 and 4 will be substantially zero. That is, the voltage of the input terminal IN connected to the fourth semiconductor layer 4 becomes substantially equal to the ground potential.
[0044]
When an input signal to be amplified is applied to the input terminal IN, the current flowing between the collector and the emitter of the second bipolar transistor is substantially proportional to the amplitude of the input signal when the input signal has a positive polarity. And increases substantially in proportion to the amplitude of the input signal when the input signal has a negative polarity.
[0045]
Accordingly, the voltage of the second semiconductor layer 2 which performs the function of the base of the second bipolar transistor rises in proportion to the ground potential in proportion to the amplitude of the input signal when the input signal is positive, and the voltage of the input signal becomes negative. In the case of sex, it falls in proportion to the amplitude of the input signal.
[0046]
The current flowing between the collector and the emitter of the first bipolar transistor increases as the voltage of the second semiconductor layer 2 increases, and decreases as the voltage of the second semiconductor layer 2 decreases.
Therefore, the current flowing between the collector and the emitter of the first bipolar transistor increases when the voltage of the input signal applied to the input terminal IN increases, and decreases when the voltage decreases.
[0047]
As a result, the voltage of the output terminal OUT connected to the first semiconductor layer 1 decreases when the voltage of the input signal applied to the input terminal IN increases, and increases when the voltage of the input signal decreases. That is, the voltage at the output terminal OUT represents a signal obtained by inverting the polarity of the voltage at the input terminal IN.
[0048]
FIG. 3 shows an example of a potential waveform at the output terminal OUT when a sine wave whose instantaneous value oscillates across the ground potential is supplied to the input terminal IN of the amplifier circuit shown in FIG. As shown in the figure, even if the potential of the input terminal IN rises and falls with the ground potential interposed therebetween, the output terminal OUT supplies a potential corresponding to a change in the potential of the input terminal IN that is amplified in the opposite phase.
[0049]
Note that, in the amplifier circuit of FIG. 2, the first and second bipolar transistors included in the transistor Q do not need to substantially perform the class A operation. What is necessary is just to be substantially in the active area in the state where it is not supplied. In other words, the first and second bipolar transistors are such that when a signal is newly supplied from the input terminal IN, the change in the current flowing between each collector and the emitter is obtained by amplifying the change in each base current. It suffices if a current corresponding to the current flows.
[0050]
The amplifier circuit according to the embodiment of the present invention may have, for example, the configuration shown in FIG. As shown, the amplifier circuit includes a transistor Q, resistors R1 to R3, an input terminal IN, and an output terminal OUT.
[0051]
In the amplifier circuit of FIG. 4, the transistor Q is substantially the same as the transistor shown in FIG. However, in the transistor Q of this amplifier circuit, the second semiconductor layer 2 performs the function of the collector of the second bipolar transistor, and the fifth semiconductor performs the function of the emitter of the second bipolar transistor. Layer 5.
[0052]
Further, in the amplifier circuit of FIG. 4, a resistor R1 is connected between the collector terminal tC of the transistor Q and the positive electrode of the external DC power supply, and the collector terminal tC Is connected to the output terminal OUT. The input terminal IN and one end of the resistor R3 are connected to the base terminal tB, and the other end of the resistor R3 is grounded. The first emitter terminal tE1 and the negative electrode of the DC power supply are also grounded.
[0053]
On the other hand, in the amplifier circuit of FIG. 4, the resistor R2 is connected between the second emitter terminal tE2 of the transistor Q and the positive electrode of the DC power supply. The bias terminal tBIAS is open.
[0054]
In the amplifier circuit of FIG. 4, the resistance values of the resistors R1 to R3 are such that the first bipolar transistor of the transistor Q performs substantially class A operation and the second bipolar transistor of the transistor Q substantially saturates. Is chosen.
[0055]
In the amplifier circuit of FIG. 4, when a power supply voltage is applied from both poles of the DC power supply, the second bipolar transistor saturates, and from the emitter to the collector of the second bipolar transistor (ie, from the fifth semiconductor layer 5 to the second The saturation current flowing in the semiconductor layer 2) flows into the base of the first bipolar transistor.
[0056]
The first bipolar transistor is driven by the saturation current, and the first bipolar transistor is almost completely driven from the collector to the emitter of the first bipolar transistor (that is, from the first semiconductor layer 1 to the third semiconductor layer 3). Approximately half the current that flows when the switch is turned on flows.
[0057]
Then, a forward voltage is generated between the second and third semiconductor layers 2 and 3 in accordance with the forward characteristics of the diode formed by the second and third semiconductor layers 2 and 3, and the second and third semiconductor layers 2 and 3 generate a forward voltage. A forward voltage is generated between the fourth semiconductor layers 2 and 4 in accordance with the forward characteristics of the diode formed by the second and fourth semiconductor layers 2 and 4.
Therefore, as in the amplifier circuit of FIG. 2, the voltage between the third and fourth semiconductor layers 3 and 4 is substantially zero, and the voltage at the input terminal IN is substantially equal to the ground potential.
[0058]
It is assumed that an input signal to be amplified is supplied to the input terminal IN while a power supply voltage is applied from the DC power supply.
In this case, since the second bipolar transistor is saturated, the voltage between the second and fifth semiconductor layers 2 and 5 is substantially 0, and the voltage applied across the resistor R2 is It is substantially equal to the voltage of the DC power supply minus the forward voltage of the diode formed by the second and third semiconductor layers 2 and 3. Therefore, the magnitude of the current flowing through the resistor R2 is substantially constant.
[0059]
Therefore, almost all of the current flowing through the base of the second bipolar transistor (that is, the fourth semiconductor layer 4) due to the input signal supplied to the input terminal IN is the second bipolar transistor, which is the base of the first bipolar transistor. It flows through the semiconductor layer 2 as a base current.
[0060]
Then, the current flowing from the input terminal IN to the second semiconductor layer 2 is amplified by the first bipolar transistor. Therefore, the amplitude of the input signal is substantially between the collector of the first bipolar transistor (ie, the first semiconductor layer 1) and the emitter of the first bipolar transistor (ie, the third semiconductor layer 3). A current that increases or decreases in proportion to the current flows.
[0061]
As a result, when the voltage of the input signal applied to the input terminal IN increases, the voltage of the output terminal OUT connected to the first semiconductor layer 1 decreases substantially in proportion to the amount of increase of the input signal. However, if the voltage of the input signal drops, it rises substantially in proportion to the amount of drop of the input signal. That is, the voltage at the output terminal OUT is substantially proportional to the magnitude of the signal obtained by inverting the polarity of the voltage at the input terminal IN.
[0062]
FIG. 5 shows an example of a voltage waveform at the output terminal OUT when a sine wave whose instantaneous value oscillates across the ground potential is supplied to the input terminal IN of the amplifier circuit shown in FIG. As shown in the figure, also in the amplifier circuit of FIG. 4, a voltage substantially equal to a voltage obtained by amplifying the voltage of the input terminal IN which goes up and down with respect to the ground potential in opposite phases is output from the output terminal OUT.
[0063]
In the amplifier circuit of FIG. 2 described above, the amount of change in the voltage between the base and the emitter of the first bipolar transistor is substantially proportional to the amount of change in the voltage of the input signal. The magnitude of the base current of the bipolar transistor is substantially proportional to the exponential function of the amount of change in the voltage between the base and the emitter of the bipolar transistor. For this reason, in the amplifier circuit of FIG. 2, the amount of change in the voltage at the output terminal OUT cannot be considered to be proportional to the amount of change in the voltage at the input terminal IN, and the distortion may not be ignored.
[0064]
Specifically, for example, as shown in FIG. 3, in a portion where the potential is high in the output waveform, the first bipolar transistor is substantially turned off, so that an ideal output waveform (the waveform shown by the broken line in FIG. 3) is obtained. ) Is generated at the output terminal OUT, and the nonlinear distortion increases.
[0065]
On the other hand, in the amplifier circuit shown in FIG. 4, as described above, the amount of change in the base current of the first bipolar transistor is substantially proportional to the amount of change in the voltage of the input signal. For this reason, the amplifier circuit of FIG. 4 has better linearity of the output signal with respect to the input signal than the amplifier circuit of FIG. 2, and for example, as shown in FIG. 5, less nonlinear distortion than the output waveform shown in FIG. An output waveform is obtained.
[0066]
In the amplifier circuit shown in FIG. 4, the first bipolar transistor Q does not need to perform the class A operation substantially, and substantially does not have the active region when no signal is supplied from the input terminal IN. Should be there.
[0067]
The amplifier circuit according to the embodiment of the present invention may have, for example, the configuration shown in FIG.
The amplifier circuit of FIG. 6 is substantially the same as the amplifier circuit of FIG. 4 except that the resistor R2 is connected between the second emitter terminal tE2 and the collector terminal tC of the transistor Q as shown. Is the same as
[0068]
Further, the resistance values of the resistors R2 and R3 are similar to those of the amplifier circuit of FIG. 4 in that the first bipolar transistor of the transistor Q substantially performs class A operation and the second bipolar transistor of the transistor Q substantially The value is selected so that it is saturated.
[0069]
In the amplifier circuit of FIG. 6 as well, when a power supply voltage is applied from both poles of the DC power supply, the second bipolar transistor is saturated and the first bipolar transistor is almost completely turned on from the collector to the emitter of the first bipolar transistor. A half of the current that flows when the current flows.
[0070]
Therefore, the voltage at the input terminal IN is equal to the forward voltage of the diode formed by the second and third semiconductor layers 2 and 3, and the forward voltage of the diode formed by the second and fourth semiconductor layers 2 and 4. Is approximately equal to the difference That is, the voltage of the input terminal IN becomes substantially equal to the ground potential.
[0071]
It is assumed that an input signal to be amplified is supplied to the input terminal IN while a power supply voltage is applied from the DC power supply.
In this case, the voltage between the second and fifth semiconductor layers 2 and 5 is substantially zero because the second bipolar transistor is saturated. The voltage applied to both ends of the resistor R2 is obtained by subtracting the voltage across the resistor R1 from the voltage of the DC power supply, and furthermore, the forward voltage of the diode formed by the second and third semiconductor layers 2 and 3 is changed. Substantially equal to the voltage subtracted.
The voltage drop across the resistor R1 is caused by the current flowing between the collector and the emitter of the first bipolar transistor flowing through the resistor R1.
[0072]
Therefore, the magnitude of the base current flowing through the first bipolar transistor decreases substantially in proportion to the increase in the current flowing through the resistor R1, and decreases when the current flowing through the resistor R1 decreases. Increases substantially in proportion to That is, the first bipolar transistor is substantially self-biased, and a change in current between the collector and the emitter of the first bipolar transistor is negatively fed back to the base.
[0073]
Then, almost all of the current flowing through the base of the second bipolar transistor flows through the base of the first bipolar transistor due to the input signal supplied from the input terminal IN, and this current is amplified by the first bipolar transistor.
[0074]
As a result, the voltage at the output terminal OUT is substantially proportional to the magnitude of the signal obtained by inverting the polarity of the voltage at the input terminal IN. The rate of change of the voltage of the output terminal OUT with respect to the change of the voltage of the input terminal IN is as follows. The current amplification factor of the first bipolar transistor and the change in the current between the collector and the emitter of the first bipolar transistor are negatively fed back to the base current. (Ie, the ratio of the change amount of the base current to the change amount of the current flowing through the resistor R1).
[0075]
In the amplifier circuit of FIG. 6, as a result of the first bipolar transistor being substantially self-biased, the operating point of the first bipolar transistor becomes stable with respect to the temperature around the transistor Q.
Also, the voltage gain of a bipolar transistor in the common emitter mode generally decreases according to the Miller effect as the frequency of the signal to be amplified increases. However, in the amplifier circuit of FIG. 6, since the first bipolar transistor is subjected to negative feedback as described above, the cutoff frequency of the amplifier circuit of FIG. 6 is higher than that of the amplifier circuit of FIG. That is, the frequency characteristics are improved.
[0076]
In the amplifier circuit of FIG. 6, the first bipolar transistor of the transistor Q does not substantially need to perform the class A operation, and is substantially active in a state where a signal is not substantially supplied from the input terminal IN. It only has to be in the area.
[0077]
The amplifier circuit according to the embodiment of the present invention may have, for example, the configuration shown in FIG.
As shown, the amplifier circuit includes a transistor Q, a diode D, resistors R4 to R8, an input terminal IN, and an output terminal OUT.
[0078]
The transistor Q is substantially the same as the transistor shown in FIG. However, in the transistor Q of this amplifier circuit, the second semiconductor layer 2 performs the function of the collector of the second bipolar transistor, and the fifth semiconductor performs the function of the emitter of the second bipolar transistor. Layer 5.
[0079]
The resistor R4 is connected between the collector terminal tC of the transistor Q and the positive terminal of the external DC power supply, and the output terminal OUT is connected to the collector terminal tC. A resistor R5 is connected between the collector terminal tC and the second emitter terminal tE2, and a resistor R6 is connected between the first emitter terminal tE1 and the second emitter terminal tE2. The first emitter terminal tE1 and the negative electrode of the DC power supply are grounded. The resistor R7 is connected between the positive terminal of the DC power supply and the base terminal tB, the anode of the diode D is connected to the base terminal tB, and the cathode of the diode D is connected to the input terminal IN. A resistor R8 is connected between the input terminal IN and the first emitter terminal tE1.
[0080]
The resistance values of the resistors R4 to R8 are selected such that the first bipolar transistor of the transistor Q substantially performs the class A operation, and the potential of the input terminal IN becomes substantially equal to the ground potential.
[0081]
For example, assume that the voltage at the base of the second bipolar transistor (ie, the fourth semiconductor layer 4) relative to the emitter of the second bipolar transistor (ie, the fifth semiconductor layer 5) is about -0.7 volts. . Further, a forward voltage generated between both ends of the diode D (that is, an anode and a cathode) due to a current from the positive electrode of the DC power supply to the negative electrode of the DC power supply via the resistor R7, the diode D, and the resistor R8 is connected to the ground. About +0.5 volts.
In this case, the resistance values of the resistors R4 to R8 are selected such that the voltage at the emitter of the second bipolar transistor is approximately +1.2 volts with respect to ground.
[0082]
In the amplifier circuit of FIG. 7, when a power supply voltage is applied from both poles of the DC power supply, the current flowing from the collector to the emitter of the first bipolar transistor is substantially half of the current flowing when the first bipolar transistor is almost completely turned on. Electric current flows.
[0083]
Further, a forward voltage of a diode formed by the second semiconductor layer 2 and the third semiconductor layer 3 is applied to the collector of the second bipolar transistor (that is, the second semiconductor layer 2).
The forward voltage generated between both ends of the diode formed by the fourth semiconductor layer 4 and the fifth semiconductor layer 5 and the forward voltage generated between both ends of the diode D are provided to the emitter of the second bipolar transistor. A voltage substantially equal to the sum of the voltages is applied.
[0084]
Therefore, the potential of the collector of the second bipolar transistor is lower than the potential of the emitter by about 0.6 volts, and the second bipolar transistor operates in the active region. Note that the voltage at the input terminal IN becomes substantially 0 as a result of the resistance values of the resistors R4 to R8 being selected as described above.
[0085]
It is assumed that an input signal to be amplified is supplied to the input terminal IN while a power supply voltage is applied from the DC power supply. In this case, the magnitude of the current supplied to the fourth semiconductor layer 4, which is the base of the second bipolar transistor, decreases substantially in proportion to the amount of increase in the voltage of the input signal. It increases substantially in proportion to the amount of voltage decrease.
[0086]
Then, the magnitude of the current flowing from the emitter to the collector of the second bipolar transistor increases and decreases substantially in proportion to the amount of increase and decrease of the current supplied to the base of the second bipolar transistor.
[0087]
The current flowing between the emitter and the collector of the second bipolar transistor also flows between the second and third semiconductor layers 2 and 3 as the base current of the first bipolar transistor. A current obtained by amplifying the base current flows between the emitter and the collector of the first bipolar transistor.
[0088]
The voltage generated at both ends of the resistor R4 is proportional to the magnitude of the current flowing between the emitter and the collector of the first bipolar transistor. The voltage between the emitter and the collector of the first bipolar transistor is different from the power supply voltage. Substantially equal to the voltage across resistor R4 minus the voltage.
[0089]
As a result, the voltage at the output terminal OUT increases substantially in proportion to the amount of increase in the voltage at the input terminal IN, and also decreases substantially in proportion to the amount of decrease in the voltage at the input terminal IN. That is, the amplifier circuit shown in FIG. 7 generates, at the output terminal OUT, a voltage obtained by amplifying the voltage applied to the input terminal IN in substantially the same phase.
[0090]
In the amplifier circuit shown in FIG. 7, when the current flowing between the collector and the emitter of the first bipolar transistor increases, the voltage of the collector of the first bipolar transistor drops. The potential of the connected emitter of the second bipolar transistor also drops.
For this reason, the potential difference between the base and the emitter of the second bipolar transistor is reduced, and the current flowing between the emitter and the collector of the second bipolar transistor (that is, the base current of the first bipolar transistor) is reduced. The current flowing between the collector and the emitter of one bipolar transistor also decreases.
[0091]
Accordingly, the first bipolar transistor is substantially self-biased similarly to the first bipolar transistor in the amplifier circuit of FIG. 6, and the change in current between the collector and the emitter of the first bipolar transistor is negatively fed back to the base. You.
Thereby, also in the amplifier circuit of FIG. 7, the operating point of the first bipolar transistor becomes stable with respect to the temperature around the transistor Q, and the frequency characteristics of the entire amplifier circuit are improved.
[0092]
In the amplifier circuit shown in FIG. 7, the rate of change of the voltage of the output terminal OUT with respect to the change of the voltage of the input terminal IN depends on the current amplification rates of the first and second bipolar transistors and the collector-emitter of the first bipolar transistor. The change in the current during the period is determined by the feedback rate at which the base current is negatively fed back.
[0093]
Further, in the amplifier circuit of FIG. 7, the first bipolar transistor included in the transistor Q does not need to perform the class A operation substantially, and the signal is substantially transmitted from the input terminal IN similarly to the second bipolar transistor. It is sufficient if the power supply is substantially in the active area in a state where the power supply is not supplied.
[0094]
Note that the configuration of the transistor according to the embodiment of the present invention is not limited to the above.
For example, the conductivity type (impurity type) of the first semiconductor layer 1, the third semiconductor layer 3, and the fourth semiconductor layer 4 need not be n-type, but may be p-type. When the first semiconductor layer 1, the third semiconductor layer 3, and the fourth semiconductor layer 4 are p-type, the second semiconductor layer 2 and the fifth semiconductor layer 5 may be n-type.
[0095]
The operation of this transistor when the first semiconductor layer 1, the third semiconductor layer 3, and the fourth semiconductor layer 4 are p-type and the second semiconductor layer 2 and the fifth semiconductor layer 5 are n-type The first semiconductor layer 1, the third semiconductor layer 3, and the fourth semiconductor layer 4 are n-type, and the second semiconductor layer 2 and the The operation is substantially the same as the operation of this transistor when the semiconductor layer 5 is p-type.
[0096]
In addition, the first semiconductor layer 1 and the collector terminal tC perform the functions of the third semiconductor layer 3 and the first emitter terminal tE1, and the third semiconductor layer 3 and the first emitter terminal tE1 correspond to the first semiconductor layer 3 and the first emitter terminal tE1. The functions of the semiconductor layer 1 and the collector terminal tC may be performed.
[0097]
In addition, in the transistor according to the embodiment of the present invention, as shown in FIGS. 8A and 8B, for example, the area of the junction surface between the second semiconductor layer 2 and the third The area may be smaller than the area of the joint surface between the second semiconductor layer 2 and the fourth semiconductor layer 4.
As shown in FIG. 8A, the area of the bonding surface between the fourth semiconductor layer 4 and the fifth semiconductor layer 5 is equal to the area of the bonding surface between the second semiconductor layer 2 and the fourth semiconductor layer 4. It may be smaller. Further, as shown in FIG. 8B, the area of the bonding surface between the second semiconductor layer 2 and the fourth semiconductor layer 4 is equal to the area of the bonding surface between the fourth semiconductor layer 4 and the fifth semiconductor layer 5. It may be smaller.
[0098]
Thus, the amount of carriers injected from the emitter to the collector of the first and second bipolar transistors included in this transistor can be controlled by a small base current flowing to the base of each bipolar transistor. That is, the input impedances of the bases of the first and second bipolar transistors increase, and the current amplification factors of the first and second bipolar transistors increase.
[0099]
The minority carriers flowing from the emitter of each bipolar transistor into the base diffuse widely into the base and are absorbed as a collector current flowing through the collector of each bipolar transistor.
[0100]
Also, by reducing the area of the junction surface between the base and the emitter of each bipolar transistor, the junction capacitance of the capacitor formed by these junctions also decreases. Therefore, in this transistor, good frequency characteristics can be obtained (that is, the transition frequency of the first and second bipolar transistors included in this transistor can be increased).
[0101]
The conventional high power transistor has a drawback that the current amplification factor is small and the frequency characteristics are poor. On the other hand, the transistors illustrated in FIGS. 8A and 8B can be used widely for power control because the transistors can be easily controlled for low power as well as for high power.
[0102]
【The invention's effect】
As described above, according to the present invention, an amplifier circuit for amplifying a signal in a state where a voltage of a signal input terminal is substantially equal to a ground potential, and a semiconductor for facilitating the manufacture of such an amplifier circuit An element is realized.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view illustrating a configuration of a transistor according to an embodiment of the present invention.
FIG. 2 is a circuit diagram showing a configuration of an amplifier circuit according to the embodiment of the present invention.
FIG. 3 is a graph showing voltage waveforms at an input terminal and an output terminal of the amplifier circuit of FIG. 2;
FIG. 4 is a circuit diagram showing a configuration of a modification of the amplifier circuit of FIG. 2;
FIG. 5 is a graph showing voltage waveforms at an input terminal and an output terminal of the amplifier circuit of FIG. 4;
FIG. 6 is a circuit diagram showing a configuration of a modification of the amplifier circuit of FIG. 2;
FIG. 7 is a circuit diagram showing a configuration of a modification of the amplifier circuit of FIG. 2;
8A and 8B are schematic cross-sectional views illustrating a configuration of a modification of the transistor in FIG.
[Explanation of symbols]
1 First semiconductor layer
2 Second semiconductor layer
3 Third semiconductor layer
4. Fourth semiconductor layer
5 Fifth semiconductor layer
D diode
Q transistor
tB base terminal
tBIAS bias terminal
tC Collector terminal
tE1 first emitter terminal
tE2 Second emitter terminal
R1-R8 resistor

Claims (6)

A first semiconductor layer of a first conductivity type;
A second conductivity type second semiconductor layer joined to the first semiconductor layer;
A third semiconductor layer of a first conductivity type joined to the second semiconductor layer;
A first conductivity type fourth semiconductor layer joined to the second semiconductor layer;
A fifth semiconductor layer of the second conductivity type joined to the fourth semiconductor layer;
With
The first, second, and third semiconductor layers are such that the first semiconductor layer functions as a collector, the second semiconductor layer functions as a base, and the third semiconductor layer functions as an emitter . A second bipolar transistor, wherein the second, fourth and fifth semiconductor layers are such that the second semiconductor layer functions as an emitter , the fourth semiconductor layer functions as a base, and the fifth semiconductor layer A semiconductor element forming a second bipolar transistor whose layer functions as a collector ;
Said emitter of said second bipolar transistor, supplies a bias current for through guide the current path including the collector and the emitter of the first bipolar transistor, said base of said second bipolar transistor, a bias means for supplying a bias current for through guide the current path including the collector and the emitter of said second bipolar transistor,
Input means for supplying an input signal to the base of the second bipolar transistor;
Means for applying a voltage generated by the emitter of the second bipolar transistor to the base of the first bipolar transistor;
And the collector and output means for supplying an output signal to the outside of the current path represents the magnitude of the current flowing to the load that will be connected in a cascade comprising said emitter of said first bipolar transistor,
An amplifier circuit comprising:   A first semiconductor layer of a second conductivity type;
  A second semiconductor layer of a first conductivity type joined to the first semiconductor layer;
  A third semiconductor layer of a second conductivity type joined to the second semiconductor layer;
  A fourth semiconductor layer of a second conductivity type joined to the second semiconductor layer;
  A fifth semiconductor layer of the first conductivity type joined to the fourth semiconductor layer;
  With
  The first, second, and third semiconductor layers are such that the first semiconductor layer functions as an emitter, the second semiconductor layer functions as a base, and the third semiconductor layer functions as a collector. A second bipolar transistor, wherein the second, fourth and fifth semiconductor layers are such that the second semiconductor layer functions as a collector, the fourth semiconductor layer functions as a base, and the fifth semiconductor layer A semiconductor element forming a second bipolar transistor whose layer functions as an emitter;
  A bias current for supplying a current path including the emitter and the collector of the first bipolar transistor to the collector of the second bipolar transistor is supplied to the collector of the second bipolar transistor. Bias means for supplying a bias current for conducting a current path including the emitter and the collector of the second bipolar transistor;
  Input means for supplying an input signal to the base of the second bipolar transistor;
  Means for applying a voltage generated by the collector of the second bipolar transistor to the base of the first bipolar transistor;
  Output means for externally supplying an output signal indicating a magnitude of a current flowing to a load cascaded to a current path including the emitter and the collector of the first bipolar transistor;
  An amplifier circuit comprising: A first semiconductor layer of a first conductivity type;
A second conductivity type second semiconductor layer joined to the first semiconductor layer;
A third semiconductor layer of a first conductivity type joined to the second semiconductor layer;
A first conductivity type fourth semiconductor layer joined to the second semiconductor layer;
A fifth semiconductor layer of the second conductivity type joined to the fourth semiconductor layer;
With
The first, second, and third semiconductor layers are such that the first semiconductor layer functions as a collector, the second semiconductor layer functions as a base, and the third semiconductor layer functions as an emitter . A second bipolar transistor, wherein the second, fourth and fifth semiconductor layers are such that the second semiconductor layer functions as an emitter , the fourth semiconductor layer functions as a base, and the fifth semiconductor layer A semiconductor element forming a second bipolar transistor whose layer functions as a collector ;
Said emitter of said second bipolar transistor, supplies a bias current for through guide the current path including the collector and the emitter of the first bipolar transistor, said base of said second bipolar transistor, a bias means for supplying a bias current for saturating the current path including the collector and the emitter of said second bipolar transistor,
Input means for supplying an input signal to the base of the second bipolar transistor;
Means for supplying a current flowing through a current path including the collector and the emitter of the second bipolar transistor to the base of the first bipolar transistor;
And the collector and output means for supplying an output signal to the outside of the current path represents the magnitude of the current flowing to the load that will be connected in a cascade comprising said emitter of said first bipolar transistor,
An amplifier circuit comprising:   A first semiconductor layer of a second conductivity type;
  A second semiconductor layer of a first conductivity type joined to the first semiconductor layer;
  A third semiconductor layer of a second conductivity type joined to the second semiconductor layer;
  A fourth semiconductor layer of a second conductivity type joined to the second semiconductor layer;
  A fifth semiconductor layer of a first conductivity type joined to the fourth semiconductor layer;
  With
  The first, second, and third semiconductor layers are such that the first semiconductor layer functions as an emitter, the second semiconductor layer functions as a base, and the third semiconductor layer functions as a collector. A second bipolar transistor, wherein the second, fourth and fifth semiconductor layers are such that the second semiconductor layer functions as a collector, the fourth semiconductor layer functions as a base, and the fifth semiconductor layer A semiconductor element forming a second bipolar transistor whose layer functions as an emitter;
  A bias current for supplying a current path including the emitter and the collector of the first bipolar transistor to the collector of the second bipolar transistor is supplied to the collector of the second bipolar transistor. Bias means for supplying a bias current for saturating a current path including the emitter and the collector of the second bipolar transistor;
  Input means for supplying an input signal to the base of the second bipolar transistor;
  Means for supplying a current flowing through a current path including the emitter and the collector of the second bipolar transistor to the base of the first bipolar transistor;
  Output means for externally supplying an output signal indicating a magnitude of a current flowing to a load cascaded to a current path including the emitter and the collector of the first bipolar transistor;
  An amplifier circuit comprising: A first semiconductor layer of a first conductivity type;
A second conductivity type second semiconductor layer joined to the first semiconductor layer;
A third semiconductor layer of a first conductivity type joined to the second semiconductor layer;
A first conductivity type fourth semiconductor layer joined to the second semiconductor layer;
A fifth semiconductor layer of the second conductivity type joined to the fourth semiconductor layer;
With
The first, second, and third semiconductor layers are such that the first semiconductor layer functions as a collector, the second semiconductor layer functions as a base, and the third semiconductor layer functions as an emitter . A second bipolar transistor, wherein the second, fourth and fifth semiconductor layers are such that the second semiconductor layer functions as an emitter , the fourth semiconductor layer functions as a base, and the fifth semiconductor layer A semiconductor element forming a second bipolar transistor whose layer functions as a collector ;
Said emitter of said second bipolar transistor, supplies a bias current for through guide the current path including the collector and the emitter of the first bipolar transistor, said base of said second bipolar transistor, a bias means for supplying a bias current for conducting current path including said collector and said emitter of said second bipolar transistor in the ability moving area,
Input means comprising: an input terminal; and a means for supplying a current representing an input signal applied to the input terminal to the base of the second bipolar transistor.
Potential fixing means for controlling a voltage between the input terminal and the base of the second bipolar transistor so that the potential of the input terminal is substantially equal to the potential of the emitter of the first bipolar transistor;
Means for supplying a current flowing through a current path including the collector and the emitter of the second bipolar transistor to the base of the first bipolar transistor;
And the collector and output means for supplying an output signal to the outside of the current path represents the magnitude of the current flowing to the load that will be connected in a cascade comprising said emitter of said first bipolar transistor,
An amplifier circuit comprising:   A first semiconductor layer of a second conductivity type;
  A second semiconductor layer of a first conductivity type joined to the first semiconductor layer;
  A third semiconductor layer of a second conductivity type joined to the second semiconductor layer;
  A fourth semiconductor layer of a second conductivity type joined to the second semiconductor layer;
  A fifth semiconductor layer of the first conductivity type joined to the fourth semiconductor layer;
  With
  The first, second, and third semiconductor layers are such that the first semiconductor layer functions as an emitter, the second semiconductor layer functions as a base, and the third semiconductor layer functions as a collector. A second bipolar transistor, wherein the second, fourth and fifth semiconductor layers are such that the second semiconductor layer functions as a collector, the fourth semiconductor layer functions as a base, and the fifth semiconductor layer A semiconductor element forming a second bipolar transistor whose layer functions as an emitter;
  A bias current for conducting a current path including the emitter and the collector of the first bipolar transistor is supplied to the collector of the second bipolar transistor, and the base of the second bipolar transistor is supplied with the bias current. Bias means for supplying a bias current for conducting a current path including the emitter and the collector of the second bipolar transistor in an active region;
  Input means comprising: an input terminal; and a means for supplying a current representing an input signal applied to the input terminal to the base of the second bipolar transistor.
  Potential fixing means for controlling a voltage between the input terminal and the base of the second bipolar transistor so that the potential of the input terminal is substantially equal to the potential of the collector of the first bipolar transistor;
  Means for supplying a current flowing through a current path including the collector and the emitter of the second bipolar transistor to the base of the first bipolar transistor;
  Output means for supplying an output signal indicating the magnitude of a current flowing to a load cascaded to a current path including the collector and the emitter of the first bipolar transistor,
  An amplifier circuit comprising:

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