JPH0786843A - Amplifier circuit - Google Patents

Abstract

PURPOSE:To stabilize the bias current by detecting the voltage difference between the emitters of transistors, supplying a voltage corresponding to the voltage difference to the base of the transistor and obtaining output signals from a resistor. CONSTITUTION:When the current made flow from the emitter of the transistor 26 towards the collector of the transistor 32 increases by temperature rising, the voltage drop of the resistors 28 and 34 increases as well. A differential amplifier 54 detects the increased voltage drop and when the output voltage rises, the base voltage of the transistor 44 rises as well. Thus, the current made flow to the resistor 42 is reduced and the voltage drop of the resistor 42 is lowered as well. Then, the base voltage of the transistor 26 is lowered and the current made flow to the transistor 26, that is the current made flow to the resistor 28, is reduced as well. Thus, the bias current is stabilized. When a temperature falls, operations for which increase (rise) and reduction (drop) are inverted are performed and the bias current is stabilized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplifier circuit whose bias is stabilized without being affected by temperature.

[0002]

2. Description of the Related Art An operational amplifier is used in various electronic circuits, and a buffer amplifier having a gain of 1 can be easily realized, and is a very effective circuit. In an amplifier circuit using an operational amplifier, if a large amount of output current needs to flow, a bipolar transistor circuit is added to the output terminal of the operational amplifier.

A conventional example of such an amplifier circuit is shown in FIG. In FIG. 3, operational amplifier 10 receives an input signal from input terminal 12 at its non-inverting input terminal. The output terminal of the operational amplifier 10 is coupled to the positive voltage source terminal 18 via the diode 14 and the resistor 16, and is coupled to the negative voltage source terminal 24 via the diode 20 and the resistor 22. The NPN transistor 26 has a collector coupled to the positive voltage source terminal 18, and a base connected to the diode 14 and the resistor 16.
, And the emitter is coupled to the output terminal 30 via the resistor 28. This output terminal 30 is coupled to the inverting input of the operational amplifier 10. The PNP transistor 32 having a conductivity type different from that of the transistor 26 has a collector coupled to the negative voltage source terminal 24, a base coupled to a common connection point of the diode 20 and the resistor 22, and an emitter coupled to the output terminal 30 via the resistor 34. To do. Such an amplifier circuit is a non-inverting amplifier having a gain of 1, that is, a buffer amplifier because the inverting input terminal of the operational amplifier 10 and the output terminal 30 are coupled to each other.

When the junction temperature of the transistor rises, the collector-base leakage current ICBO increases, the base-emitter voltage VBE decreases, and the collector current increases. This increase in collector current also increases collector loss. At this time, since the transistor generates heat, if the heat cannot be efficiently dissipated, the junction temperature of the transistor may cumulatively increase and the transistor may be destroyed. Moreover, even if the current is not destroyed, if the current changes due to the temperature change, the characteristics of the entire amplifier circuit are affected by the temperature. Therefore, it is necessary to compensate the bias current so that it does not depend on temperature.

In the amplifier circuit of FIG. 3, the diode 14 compensates the change in VBE of the transistor 26 and the diode 20 compensates the change in VBE of the transistor 32. This utilizes the characteristic that the diode also reduces the potential difference for the same current due to the temperature rise, like the transistor.

Transistors 26 and 3 of the amplifier circuit of FIG.
2 is often replaced by Darlington-connected transistors 26A, 26B and 32A, 32B, as shown in FIG. In FIG. 4, the same elements as those in FIG. 3 are designated by the same reference numerals. In the case of FIG. 4, the transistor 26
Two diodes 14A and 14B are used to compensate the temperature characteristics of A and 26B, and two diodes 2 are used to compensate the temperature characteristics of the transistors 32A and 32B.
0A and 20B are used.

[0007]

In the amplifier circuits of FIGS. 3 and 4, a diode is used for compensating the temperature characteristic of the transistor. However, there is a slight difference in the temperature characteristic between the transistor and the diode. Cannot completely compensate for the effect of. Therefore, there is also a method of using a transistor in which a base and a collector are connected in place of the compensation diode. This method can be used to some extent in the amplifier circuit of FIG.

However, the transistors used as diodes and the transistors 26A, 26B, 32A and 32B
And the characteristics do not exactly match. The amplifier circuit of FIG. 4 uses Darlington connection composed of two transistors and uses two diodes each. Therefore, even if the transistors are diode-connected, the error between the voltage as the diode and VBE of the Darlington-connected transistor is accumulated, and the transistors 26A, 26
In some cases, no bias current may flow through B, 32A, and 32B, or these transistors may remain conductive.

Further, in the amplifier circuits of FIGS. 3 and 4,
The resistor 28 (or 34) is connected to the transistor 26 (or 3).
It compensates for the increase in ICBO in 2). However, when it is desired to take out a large-current output signal from the output terminal 30, the values of these resistors must be reduced, and the effect of compensating for ICBO will be reduced. Also, in these amplifier circuits, unless the bias current is increased to some extent,
Zero cross distortion cannot be eliminated. By increasing the bias current, the change in bias due to temperature change also increases.

Therefore, an object of the present invention is to provide an amplifier circuit which overcomes the above-mentioned drawbacks of temperature compensation by canceling the VBE of the transistor and the diode voltage when stabilizing the bias current.

[0011]

An amplifier circuit according to a first aspect of the present invention includes an operational amplifier having a non-inverting input terminal for receiving an input signal and an output terminal coupled to a first voltage source through a first resistor; A first transistor whose collector is coupled to the output of the operational amplifier via a second resistor and whose emitter is coupled to a second voltage source via a third resistor; and whose base is coupled to the collector of this first transistor, A second transistor having a conductivity type different from that of the first transistor; a base coupled to an output terminal of the operational amplifier, an emitter coupled to an emitter of the second transistor through a fourth resistor, and a first transistor having the same conductivity type as the first transistor. And a differential amplifier that detects a voltage difference between the emitters of the second and third transistors and supplies a voltage corresponding to the voltage difference to the base of the first transistor. With obtaining the force signal, and supplies the output signal to the inverting input of the operational amplifier.

Further, the amplifier circuit of the second invention of the present application includes an operational amplifier which receives an input signal at a non-inverting input terminal; a collector is coupled to an output terminal of the operational amplifier through a first resistor, and an emitter is connected to a second resistor. A first transistor coupled to the first voltage source via; a collector coupled to the output terminal of the operational amplifier via a third resistor, and an emitter coupled to the second terminal via a fourth resistor.
A second transistor coupled to the voltage source and having a conductivity type different from that of the first transistor; a third transistor having a base coupled to the collector of the first transistor and having a conductivity type different from that of the first transistor.
A transistor; a base coupled to the collector of the second transistor, an emitter coupled to the emitter of the third transistor through a series circuit of a fifth resistor and a sixth resistor, and a fourth transistor having the same conductivity type as the first transistor. ; Third
A first differential amplifier that detects a voltage difference between an emitter of the transistor and a common connection point of the fifth and sixth resistors, and supplies a voltage according to the voltage difference to a base of the second transistor; A second differential amplifier that detects a voltage difference between the emitter and the common connection point of the fifth and sixth resistors, and supplies a voltage corresponding to the voltage difference to the base of the first transistor. An output signal is obtained from the common connection point of the 6 resistors, and this output signal is supplied to the inverting input terminal of the operational amplifier. It should be noted that the components with ordinal numbers do not match in the first invention and the second invention.

[0013]

1 is a circuit diagram of a first preferred embodiment of the present invention. The operational amplifier 10 receives the input signal from the input terminal 12 at its non-inverting input terminal. In addition, the operational amplifier 10
The output terminal of the PNP transistor 44 is coupled to the negative voltage source terminal 24 via the resistor 40 and the PNP transistor 44 via the resistor 42.
To the collector of. The emitter of transistor 44 is coupled to positive voltage source terminal 18 via variable resistor 46. The base of NPN transistor 26 of a different conductivity type from transistor 44 is coupled to the collector of transistor 44, which is coupled to positive voltage source terminal 18.
The base of a PNP transistor 32, which is of the same conductivity type as the transistor 44, is coupled to the output of the operational amplifier 10, its collector is coupled to the negative voltage source terminal 24, and its emitter is connected to the transistor 26 via resistors 34 and 28. Coupled to the emitter of.

The non-inverting input of operational amplifier 48 is coupled to the emitter of transistor 26, and its inverting input is coupled to the emitter of transistor 32 via resistor 50. A resistor 52 is inserted between the inverting input and the output of operational amplifier 48, and the output of operational amplifier 48 is coupled to the base of transistor 44. The operational amplifier 48 and the resistors 50 and 52 have a gain of R52 / R50 (R52: resistor 52
, R50: the value of the resistor 50), the difference voltage between the emitters of the transistors 26 and 32 is detected, and the transistor 44 is detected.
The differential amplifier 54 is supplied to the base of the. The common connection point of the resistors 28 and 34 is the output terminal 30 and the operational amplifier 1.
Connect to inverting input of 0.

Next, the operation of the embodiment shown in FIG. 1 will be described. Due to the temperature rise, the transistor 26 and the transistor 32
As I CBO increases and the current flowing from the emitter of transistor 26 to the collector of transistor 32 increases, so does the voltage drop across resistors 28 and 34. When the differential amplifier 54 detects this increased voltage drop and its output voltage rises, the base voltage of the transistor 44 also rises. Therefore, the current flowing through the resistor 42 decreases, and the voltage drop of the resistor 42 also decreases. Then, the base voltage of the transistor 26 drops, and the current flowing in the transistor 26
That is, the current flowing through the resistor 28 also decreases. Therefore,
Bias current is stabilized. When the temperature decreases, the above-described increase (increase) and decrease (decrease) operations are reversed to stabilize the bias current. That is, in the present invention, in order to stabilize the bias current, the bias current itself is detected and feedback is performed. The resistance 46 is varied to adjust the bias current.

FIG. 2 is a circuit diagram of the second embodiment of the present invention. The same elements as those in FIG. 1 are designated by the same reference numerals, and only the differences will be described. A resistor 56, an NPN transistor 58 and a resistor 60 are inserted between the output terminal of the operational amplifier 10 and the negative voltage source terminal 24, and the base of the transistor 32 is connected to the collector of the transistor 60. The differential amplifier 68 configured by the resistors 64 and 66 and the operational amplifier 62 includes a resistor 28
The base voltage of the transistor 60 is controlled by detecting the voltage difference between both ends of the. A differential amplifier 76 composed of resistors 70 and 72 and an operational amplifier 74 detects a voltage difference across the resistor 34 and controls the base voltage of the transistor 44.

In the amplifier circuit of FIG. 2, the differential amplifier 68 detects the current flowing through the resistor 28, that is, the emitter current of the transistor 26, controls the VBE of the transistor 32, and controls the current flowing through the resistor 34. . Similarly, resistor 3
4 is detected by the differential amplifier 76, that is, the emitter current of the transistor 32, and V of the transistor 26 is detected.
The BE is controlled to control the current flowing through the resistor 28. In this way, although the amplifier circuit of FIG. 2 controls crossing,
Since the upper half and the lower half of FIG. 2 are configured symmetrically,
The bias current can be stabilized in the same manner as in the above case. Further, even if an attempt is made to extract a high current from the output terminal 30 and the voltage drop of the resistor 28 increases, the VBE of the transistor 32 is controlled instead of the VBE of the transistor 26.
There is no reduction in the current flowing through 8. Similarly, even if the current flowing from the load to the output terminal 30 increases and the voltage drop of the resistor 34 increases, the VBE of the transistor 26 is controlled instead of the VBE of the transistor 32, so that the current flowing through the resistor 34 is not reduced. . That is, the amplifier circuit of FIG. 2 can obtain a larger output current than the amplifier circuit of FIG. 1 while stabilizing the bias current under no load.

[0018]

As described above, according to the present invention, the bias current itself is detected, and the detection result is fed back to stabilize the bias current, so that the elements having similar temperature characteristics as in the prior art are canceled. The bias current can be further stabilized than in the case of. Also, the final stage transistor 2
Even if 6 and 32 are changed to the Darlington configuration, the bias current can be stabilized without changing other circuit configurations.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a first embodiment of an amplifier circuit of the present invention.

FIG. 2 is a circuit diagram of a second embodiment of the amplifier circuit according to the present invention.

FIG. 3 is a circuit diagram of a conventional amplifier circuit.

FIG. 4 is a circuit diagram of another conventional amplifier circuit.

[Explanation of symbols]

 10 operational amplifier 12 input terminal 26, 32, 44, 58 transistor 30 output terminal 54 differential amplifier 68 first differential amplifier 72 second differential amplifier

Claims (2)

[Claims] 1. An operational amplifier whose non-inverting input terminal receives an input signal and whose output terminal is coupled to a first voltage source via a first resistor; and whose output terminal is the output terminal of the operational amplifier via a second resistor. A first transistor having an emitter coupled to a second voltage source through a third resistor, and a base having a base coupled to the collector of the first transistor and having a conductivity type different from that of the first transistor. A base coupled to an output terminal of the operational amplifier, an emitter coupled to an emitter of the second transistor through a fourth resistor, a third transistor having the same conductivity type as the first transistor, the second and the third transistors. A differential amplifier that detects a voltage difference between the emitters of the three transistors and supplies a voltage corresponding to the voltage difference to the base of the first transistor, and outputs an output signal from the fourth resistor. Rutotomoni, amplifying circuit for supplying the output signal to the inverting input terminal of the operational amplifier. 2. An operational amplifier receiving an input signal at a non-inverting input terminal, a collector coupled to an output terminal of the operational amplifier via a first resistor, and an emitter coupled to a first voltage source via a second resistor. And a collector connected to the output terminal of the operational amplifier via a third resistor, and an emitter connected to a second voltage source via a fourth resistor, the conductivity type of which is different from that of the first transistor. A second transistor, a base coupled to the collector of the first transistor, a third transistor having a conductivity type different from that of the first transistor, a base coupled to the collector of the second transistor, an emitter of the fifth resistor and a fifth resistor A fourth transistor coupled to the emitter of the third transistor via a 6-resistor series circuit and having the same conductivity type as the first transistor; and the third transistor. Emitter and the fifth and sixth
A first differential amplifier that detects a voltage difference between common connection points of resistors and supplies a voltage according to the voltage difference to the base of the second transistor, an emitter of the fourth transistor, and the fifth and fifth transistors. 6
A second differential amplifier that detects a voltage difference between common connection points of the resistors and supplies a voltage corresponding to the voltage difference to the base of the first transistor, and the common connection of the fifth and sixth resistors. An amplifier circuit that obtains an output signal from a point and supplies the output signal to the inverting input terminal of the operational amplifier.