JPS6089112A - Transistor amplifier circuit - Google Patents

Abstract

PURPOSE:To prevent completely generation of an offset at no signal or at operation by adding plural current source circuits to a differential amplifier. CONSTITUTION:The differential amplifier 7 consists of differential pair transistors (TR) T1, T2, a power supply TRT3 and an active load circuit 8. Then a current I1 from a current source circuit 9 becomes a current I1/beta via a TRT8 and flows to a current source circuit 10. Then the current I1/beta is drawn from the base side. On the other hand, a current I2 is drawn from a current source circuit 12, becomes a current I2/beta via a TRT13 and flows to a current source circuit 13. Thus, the current I2/beta is drawn from the base side of the TRT2 to the current source circuit 13. Then a current equal to the base current is drawn from the respective base of the TRs T1, T2. The generation of offset at no signal or at operation is prevented completely.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transistor amplifier circuit having high input impedance characteristics to prevent offset voltage from occurring.

FIG. 1 shows a differential amplifier circuit disclosed by the present applicant in Japanese Patent Application No. 57-99047. Such a differential amplifier 20fd
Current source transistor T23 and transistor T2. ,
It is formed from a differential pair consisting of T,2 and an active load circuit consisting of a diode D23 and a transistor T2□.

When there is no signal, an offset current flows between the emitter and base of the transistor T21 on the signal input side, but the current source transistor T2 is connected to the transistor T25 which has the same electrical characteristics as the transistors forming the transistor differential pair.
A current I equivalent to the current flowing through the transistor T21 is supplied through the transistor T4. Therefore, transistor T2. A base current 7 of 2 is passed into a current mirror circuit 21 formed from a diode 22 and a transistor T26'HT2B. A current approximately equal to the base current 1 flows through the diode D22, and the transistors T26, T2. A state is reached in which collector current A can flow. Note that a constant current I flows through the diode D21, and the diode D21 and the transistors T23 and T24 are formed from a current mirror circuit. A current of 2I flows through the transistor T23. Further, resistors R1 and R2 are a reference voltage source circuit 22.

In this way, when there is no signal, each transistor T21 . A β current equal to Y is drawn from T2□, equalizing the current flowing to the load of the transistor differential pair and eliminating the offset.

However, when the amplifier circuit 20 is in operation, the offset current varies in proportion to the base current of each differential pair of transistors because the voltage between the base and emitter of each differential pair differs, and the offset current changes in proportion to the base current of each differential pair. Δ■ flows into the resistor R2, and the potential of the input terminal 4 fluctuates. Therefore, the potential of the reference voltage source fluctuates, which is undesirable when the differential amplifier is used at a low power level or voltage, or when used in a high-precision device, or when such a differential amplifier is used in a comparator or the like.

The present invention has been made in view of the above, and its main purpose is to provide a transistor amplifier circuit that eliminates offset voltage.

The purpose of the 1030 is to provide a transistor amplifier circuit with high input impedance.

Furthermore, the purpose of the transistor amplifier circuit is to provide a transistor amplifier circuit that eliminates offset components that differ depending on the base current portions flowing through the differential pair of transistors, thereby preventing the occurrence of offset.

The transistor amplification circuit of the present invention has a potential difference caused by the difference in base-emitter voltage, so-called between the signal input terminals, due to the base current flowing through each of the transistor differential pairs, not only when there is no signal but also during operation. This prevents a potential difference from occurring as an offset.

The following is a second description of the transistor amplifier circuit according to the present invention.
This will be explained based on the drawings and FIG.

In Figure 2, l and 2 are terminals for power supply voltage supply, 3.4
is a signal input terminal, and 5 is an output terminal. 7 is a differential amplifier, which includes a current source transistor T3 and a transistor T1.
．． It is formed from a differential pair consisting of T2, a diode D4 and an active load circuit 8 comprising transistors T4 and T,,'re. 9 to 13 are current source circuits forming a current mirror circuit or the like, including a diode D1 and transistors 'rs and 'rt.

also forms a current mirror circuit. In addition, the transistors 'rs and 7.3 are transistors T,,T.

It is formed of transistors that have the same electrical characteristics as a differential pair consisting of.

The operation of the transistor differential amplifier circuit of the present invention will be explained. A constant current I is supplied to the differential pair of transistors of the differential amplifier 7 through a current source transistor T3, and collector currents 1 to 1 are supplied to the transistors T, T2, respectively. , I2 is flowing. When there is no signal, ideally the collector currents are 11 and 12.
It's like bamboo. On the other hand, since the active load circuit 7 forms a current mirror circuit, the collector VIL of the transistor T2
The current I2 is also the collector VT of the transistor TI, l'r
Since a current equal to c and I t is about to flow, a current monograph of the difference (hI+) appears as an output.

Next, a detailed explanation of the current source circuit attached to the differential amplifier 7 will be given. The bias side of the current mirror circuit 9 consisting of the transistor T7 and the diode D2 is connected to the collector of the transistor T11 of the active load circuit 8, and a current equivalent to the collector current 11 of the transistor TI is drawn from the current mirror circuit 9 by the transistor Ts. Therefore, the mirror 'M of transistor T7, current 11
Is it true through T8? Jt flow is current mirror circuit I
Flows into O. And through transistor T9, I.

A current of approximately j is drawn from the base side of the transistor T1. Similarly, β is the current amplification factor of the transistor T8, and the transistors T1, T2, and Tta also have the same electrical characteristics as the transistor T8. On the other hand, the transistor T6 of the active load circuit 8 is connected to the current source transistor Tso to Il.
draws a current of Further, since the 'F14 current I flows into the transistor T6E current mirror circuit 11 via the transistor T1o, the current I2 corresponding to the difference flows into the current mirror circuit 11. And diode D6
and a current mirror circuit 12 consisting of a transistor T1□
From 1□■2■, a current is drawn in, and the current j flows into the current mirror circuit 13 via the transistor T13. Therefore, the current in the base-side curve of the transistor T2 is drawn into the current mirror circuit 13. Accordingly, transistors T1 . of the transistor differential pair. Since a current equal to the base current is drawn from the base side of each T2, even in the operating state (a), it is possible to perform aging with high precision.

Therefore, it is not only possible to completely prevent offset from occurring when there is no signal or during operation, but it is also extremely suitable as a transistor amplifier circuit used at a low power supply voltage of 2 to 3 volts. Still, even when the trans/') star amplifier circuit of the present invention is used as a comparator, a highly reliable comparator can be provided without any abnormal current flowing into the reference voltage source that causes an offset. Furthermore, it has a feature that its input impedance is extremely high.

Figure 3 shows an embodiment of the song of the transistor amplifier circuit of the present invention, but even if transistors with opposite polarity to the embodiment of Figure 2 are used, it is possible to erase the offset based on the same concept. Needless to say. In addition, parts with the same function are denoted by the same reference numerals.

In addition, in Figures 2 and 3, generally the diode DI
%D7 is typically formed by a diode-connected transistor.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a conventional transistor amplifier circuit, FIG. 2 is a circuit diagram showing an embodiment of the transistor amplifier circuit according to the present invention, and FIG. 3 is a circuit diagram showing an embodiment of the song of the transistor amplifier circuit according to the present invention. FIG. 7: Differential amplifier, 8: Active load circuit. 9 to 13F current source circuit Toko Co., Ltd. Figure 1

Claims (5)

[Claims] (1) A differential amplifier circuit formed from an active load circuit including a first current source transistor, a differential pair of transistors, and a first and second transistor, and a first current that flows into the first transistor. a second current source circuit that draws current from the first current source circuit through a third transistor having the same electrical characteristics as the transistors forming the transistor differential pair; a second current source transistor that causes a current equal to the current flowing through the transistor to flow into the second transistor and the third current source circuit of the active load circuit; a fourth current source circuit that draws an equal current from the fourth current source circuit through a sixth transistor; a fifth current source circuit that draws current from the base of one transistor of the transistor differential pair; A current equivalent to a base current flowing through each transistor of the transistor differential pair is drawn into the second current source circuit from the other transistor differential pair of the transistor differential pair into the fifth current source circuit. A transistor amplifier circuit characterized in that the load currents flowing from each transistor/transistor of the transistor differential pair to the active load circuit are made equal to each other, thereby preventing the occurrence of an offset. (2) The transistor amplifier circuit according to claim 1, wherein the third and fourth transistors have characteristics equal to the electrical characteristics of the transistors forming the transistor differential pair. (3) The transistor amplifier circuit according to claim 1, wherein the active load circuit including the first and second transistors is a current mirror circuit. (4) The transistor amplifier circuit according to claim 1, which is formed of a current mirror circuit together with the first and second current source transistor diodes. (5) The transistor amplifier circuit according to claim 1, wherein each of the first to fifth current source circuits forms a current mirror circuit.