JPH0374528B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an amplifier circuit used in low frequency circuits such as radio receivers and tape recorders.

Configuration of conventional example and its problems Figure 1 shows a conventional amplifier circuit. In the figure, amplifier 3 has a positive input terminal +, a negative input terminal -, and an output terminal Q. By setting the bias voltage of Q to an intermediate voltage between one power supply Vcc and the other power supply, a signal with a large amplitude can be extracted. Therefore, the resistors R ₁ and R ₂ are set to approximately the same value, and the bias voltage of the positive input terminal + is set to be approximately an intermediate voltage between one power supply Vcc and the other power supply (earth). Then, negative feedback is applied to the negative input terminal - from the output terminal Q through the resistor _R3 , so that the voltage at the output terminal Q is approximately the middle voltage between one power supply Vcc and the other power supply. .

FIG. 2 shows more specifically the inside of the amplifier 3 shown in FIG. 1, and as the amplifier 3, a differential amplifier consisting of two transistors 12 and 13 is often used. In FIG. 2, the base of transistor 12 is a positive input terminal, and the base of transistor 13 is a negative input terminal. The values of the resistors R ₁ and R ₂ are made almost the same so that the base of the transistor 12, that is, the positive input terminal, has a voltage that is approximately half that of one power supply Vcc and the other power supply (earth). From this, transistors 12,1
The contact potential difference V _BE between the base and emitter of 3 is approximately
Since the voltage is 0.7V, the emitter voltage of transistors 12 and 13 is approximately lower than that of the base of transistor 12.
This means that it is operating at a higher voltage by 0.7V.
Therefore, when one power supply Vcc becomes 1.4V or less, the voltage between the base of transistor 12 and one power supply Vcc becomes 0.7V or less, and the voltage between the emitters and bases of transistors 12 and 13 becomes 0.7V or less, and current flows through transistors 12 and 13. stops flowing and stops working. Further, the output section of the amplifier 3 shown in FIG. 2 uses transistors 24 and 25 that perform class B push-pull operation. the transistor 12,
The output signal of the differential amplifier 13 is applied to the base of the transistor 17 from the collectors of the transistors 13 and 15, and is amplified. By applying the signal of transistor 20 to the base of transistor 25, transistors 24 and 25 perform class B push-pull operation. At this time, transistor 2
0 performs phase inversion operation. The signal at the output terminal Q is applied to the speaker 7 via the capacitor 6 to operate the speaker 7.

In order to set the bias current of transistors 24 and 25 constituting the output section of this amplifier 3, connect the connection point P of the series connection of the diode-connected transistor 22 and the resistor 23 from the output terminal Q to the emitter of the phase inverting transistor 20. The bases of the transistors 20 and 24 are biased by a diode-connected transistor 21. The base of the transistor 24 has a contact voltage between the base and emitter of the transistor, which is higher than the output terminal Q.
V _BE is a higher voltage by about 0.7V. Therefore, when one power supply Vcc becomes 1.4V or less, the output terminal Q
The voltage between and one power supply Vcc becomes 0.7V or less,
Current no longer flows through the transistor 24, and normal class B push-pull operation no longer occurs.

As described above, in the amplifier circuit shown in Figure 2, the input differential amplifier circuit and the output circuit are connected to the power supply voltage Vcc.
The drawback was that it did not work at low voltages below 1.4V.

OBJECTS OF THE INVENTION The present invention aims to eliminate the above-mentioned conventional drawbacks, and to provide an excellent amplifier circuit that can operate satisfactorily even at lower voltages.

Composition of the Invention In order to achieve the above object, the present invention provides that the bias voltage between the positive input terminal and the negative input terminal of an amplifier having a positive input terminal, a negative input terminal, and an output terminal is set to a contact potential difference V between the base and emitter of the transistor. It is designed to operate even at a voltage sufficiently lower than _BE ,
The collectors of first and second transistors of different polarity that operate as push-pull output are connected to form an output terminal, and the collector of a third transistor of different polarity than the first transistor is connected to the base of the first transistor. a fourth transistor of opposite polarity to the base of the second transistor;
Connect the collectors of the transistors of the third transistor and
biasing the emitter of the fourth transistor using a diode or a contact potential difference between the base and emitter of the transistor; biasing the emitter of the third transistor to a voltage lower than the output terminal; is biased to a higher voltage than the output terminal, and the third and fourth
biasing between the bases of the transistors using a diode or a contact potential difference between the base and emitter of the transistor, applying a signal to the bases of the third and fourth transistors, and applying the signal to the collectors of the first and second transistors. This device is characterized in that it is constructed so that the output signal is taken out from the connection point, and has the advantage of being able to operate satisfactorily even when the power supply voltage drops significantly.

DESCRIPTION OF EMBODIMENTS FIG. 3 is an electrical wiring diagram of an embodiment of the amplifier circuit of the present invention.

In Figure 3, the value of resistor R ₁ is, for example, 17KΩ,
Assuming that the value of resistor R ₂ is 3KΩ and the power supply voltage Vcc is 1V, there will be a voltage drop of approximately 0.15V across resistor _R1 . From this, the base voltage of transistor 12 is 0.15V
Therefore, the base voltage of transistor 13 is also approximately
Set it to 0.15V. If the voltage at the output terminal Q is set to 1/2 of the power supply voltage Vcc, a large output voltage can be obtained.

Therefore, if the value of the resistor _R4 is 3KΩ and the negative feedback resistor _R3 is 7KΩ, the transistor 12,
The base voltage of 13 is approximately 0.15V.

In other words, if the value of R ₂ /R ₁ +R ₂ ×Vcc and the value of R ₄ /R ₃ +R ₄ ×Vcc/2 are made equal to each other, the voltage at the output terminal Q will be approximately 1/2 of the power supply voltage Vcc. voltage, and a large signal can be output to the output terminal Q.

In this case, the emitter voltage of transistors 12 and 13 is approximately 0.85V (the base is approximately
Since the voltage between the base and emitter is approximately 0.7V at 0.15V), and the power supply voltage Vcc is 1V, transistor 1
Sufficient current flows through 2 and 13 to operate. Furthermore, transistors that operate when the voltage between the collector and emitter of the transistors 12 and 13 is 0.15 V or more are used. In this circuit, the contact potential between the base and emitter of diode-connected transistors 14 and 15 is about 0.7V, and the voltage between the collectors and emitters of transistors 12 and 13 is about 0.15V, so that it operates satisfactorily. Since the voltage drop caused by the resistors R ₂ and R ₄ is about 0.15V, it can be operated satisfactorily even with the power supply voltage Vcc of 1V.

Note that as long as the voltage drop across the resistors R ₂ and R ₄ is 0.7V or less, the device can operate even if the power supply voltage Vcc is 1.4V or less.

Next, to explain the output section of amplifier 3, PNP
The collector of the transistor 24 and the collector of the NPN transistor 25 are connected to each other, and the base of the PNP transistor 24 is connected to the NPN transistor 3.
The collector of PNP transistor 32 is connected to the base of NPN transistor 25. Furthermore, a resistor 34 and a diode-connected transistor 3 are connected between the power supply Vcc and ground.
3. The resistors 35 are connected in series, the emitter of the transistor 31 is connected to the connection point E between the resistor 35 and the transistor 33, and the emitter of the transistor 32 is connected to the connection point between the resistor 34 and the transistor 33. This transistor 33 is a diode-connected transistor, and the base of the transistor
Biasing is performed using the contact electrode difference between the emitters. Furthermore, a transistor 30 is connected between the bases of transistors 31 and 32. The resistor 36 connected to the collector of this transistor 30 is not necessarily required. At this time, the transistor 30 operates as a diode-connected transistor, and biases the bases of the transistors 31 and 32 by the contact potential difference between the base and emitter. When the resistor 36 is connected, the current flowing through the transistor 17 also flows to the collector of the transistor 30, causing a voltage drop at the resistor 36, and the contact potential between the base and emitter of the transistor 30 is used to bias the voltage to a lower voltage by the voltage drop across the resistor 36. be able to.

Then, it is amplified by the transistors 12 and 13 that constitute the differential amplifier in the input section, and the transistor 1
A diode-connected transistor 14 and a transistor 15 of a current mirror circuit are provided on the collector side of transistors 2 and 13, and the collector signals of transistors 13 and 15 are applied to the base of transistor 17, and from the collector of transistor 17 to transistors 32 and 3.
In addition to the base of 1, the collector signals of transistors 31 and 32 are added to the bases of transistors 24 and 25, and an output signal is taken out to the connection point Q of the collectors of transistors 24 and 25, and the speaker 7 is operated via a capacitor 6. I can do it.

Here, the means for applying the emitter potential of these transistors 31 and 32 is different from the conventional one. That is, the resistors 34 and 35 and the diode-connected transistor 3
3, and the resistors 34 and 35 are made to have substantially the same resistance value. Therefore, the contact potential between the base and emitter of the diode-connected transistor 33 is approximately 0.7V.
Therefore, point E is about 0.15V, point D is about 0.85V,
The voltage at point E is lower than that at point Q, and the voltage at point D is higher than that at point Q.

Also, when the voltage drops by about 0.1V across the resistor 36, the voltage between the emitter and collector of the transistor 30 is about 0.6V.
becomes. Also between the bases of transistors 31 and 32
It becomes 0.6V. Assuming that 5mA flows through the output transistor and the H _FE of the transistor is 100, the collector current of transistors 31 and 32 is 0.05mA.
Since it is only necessary to allow the current to flow, the contact potential between the base and emitter of the transistors 31 and 32 becomes small (for example, 0.65 V), and the biases match exactly.

The base point A of transistor 31 is 0.15 (point E) + 0.65 = 0.80, and the base point B of transistor 32 is 0.8V (point A) - 0.6V (emitter-collector voltage of transistor 30) = 0.85V (point D )−0.65V=0.2V. Therefore, the voltage between the collector and emitter of the transistors 31 and 32 is 0.15V, and the transistors 31 and 32 operate at this potential, and the collector of the transistor 17 is 0.1V, and the transistor 17 operates at this potential. This is because a transistor that operates at 0.1V or more between the emitter and collector is used.

Furthermore, the output transistors 24 and 25 are conventional second transistors.
Since transistors having the same polarity as the transistors 24 and 25 shown in the figure are not used, it is possible to operate down to a low voltage.

In the above embodiment, a resistor 36 is connected to the collector of the transistor 30, and a voltage lower than V _BE is used using the contact potential difference V _BE of the transistor. However, as shown in FIG. resistor 52,5 with a contact potential difference of 30
Even if it is divided into 3 and used, it can operate in the same way.

In FIG. 5, constant current operating transistors 41 and 43 are used in place of the resistors 11 and 19 in FIG. 3. These transistors 41 and 43 use a constant current circuit 44 whose current does not change much with changes in power supply voltage, so that the diode or diode-connected transistor 42 and the transistors 41 and 43 perform current mirror operation. In addition, a resistor 5 is connected between the dividing point of resistors R ₁ and R ₂ and the base of the transistor 12.
The same operation can be achieved by connecting 1 to 1 to increase the input impedance.

Effects of the Invention As explained above, according to the present invention, by updating the bias of the input circuit and the bias of the output circuit, it is possible to obtain an excellent amplifier circuit that operates down to a low voltage, which is extremely advantageous in practice. It is something.

[Brief explanation of drawings]

Figure 1 is an electrical wiring diagram of a conventional amplifier circuit;
3 is an electrical wiring diagram of one embodiment of the amplifier circuit of the present invention, and FIG. 4 is a wiring diagram showing another embodiment of the essential part of the amplifier circuit,
FIG. 5 is an electrical wiring diagram showing another embodiment of the present invention. 1... Signal input terminal, 2, 5, 6, 16... Capacitor, R ₁ , R ₂ , R ₃ , R 4 , ₄ , 11, 19,
23, 34, 35, 36, 52, 53, 51...
Resistance, 12, 13, 15, 17, 20, 21, 2
4, 25, 30, 31, 32...transistor,
14, 21, 22, 30, 33...Diode or diode-connected transistor, Q...Output terminal, 7...Speaker.

Claims (1)

[Claims] 1 A differential amplifier is provided in the input stage in which the emitters of two transistors are connected to each other, the emitter side of the transistor is connected to the other power supply side, and the collector side of the transistor is connected to one power supply side, and the differential amplifier is connected to the one power supply side. A connection point between a first resistor and a second resistor connected in series with the other power supply is connected to the positive input terminal of the differential amplifier, and a resistor connected in series with the other power supply is connected to the positive input terminal of the differential amplifier. the third connected to
and the fourth resistor are connected to the negative input terminal of the differential amplifier, and the voltage values of the positive input terminal and the negative input terminal are approximately equal, and the first and third resistors are connected to each other. The transistor operates satisfactorily even when the voltage drop across the resistor is less than the contact potential between the base and emitter of the transistor, and the collectors of the first and second transistors of different polarity that operate as a class B pushable output are connected. The output terminal is connected to the base of the first transistor to the collector of a third transistor having a different polarity from the first transistor, and to the base of the second transistor to the collector of a third transistor having a different polarity from the second transistor. Connect the collectors of the transistors and connect the third and fourth transistors.
If the third and fourth transistors are NPN transistors and PNP transistors, the emitters of the third transistor are biased using a diode or a contact potential difference between the base and emitter of the transistor. biasing the emitter of the fourth transistor to a voltage lower than the output terminal and biasing the emitter of the fourth transistor to a voltage higher than the output terminal;
When the fourth transistor is a PNP transistor or an NPN transistor, the emitter of the third transistor is biased to a voltage higher than the output terminal, and the emitter of the fourth transistor is biased to a voltage lower than the output terminal. biasing between the bases of the third and fourth transistors using a diode or a connection potential between the base and emitter of the transistors, and applying a signal to the bases of the third and fourth transistors;
An amplifier circuit characterized in that the output signal is extracted from the collector connection point of the first and second transistors.