WO1986004196A1

WO1986004196A1 - Active circuit element

Info

Publication number: WO1986004196A1
Application number: PCT/HU1985/000081
Authority: WO
Inventors: Gábor HUSZTI
Original assignee: Licencia Találmányokat Értékesito^" És Innovációs
Priority date: 1984-12-29
Filing date: 1985-12-29
Publication date: 1986-07-17
Also published as: EP0205539A1; AU5308486A

Abstract

Active circuit element, constituting a transistor comprising a basis terminal (1), an emitter terminal (2) and a collector terminal (3). The proposed active circuit element is characterized by comprising four transistors wherein the first, the third and the fourth (4, 6, 8) are of type opposite to the type of the second transistor (5) and the basis of the first transistor (4) constitutes the basis terminal (1), the emitter of the second transistor (5) is connected to the emitter terminal (2) and the third and fourth transistors (8) are connected with their respective emitters to the collector terminal (3), further the third transistor (6) is connected through its basis to the basis and the collector of the fourth transistor (8) and over its collector to the emitter of the first transistor (4) and to the basis of the second transistor (5), wherein the collector of the first transistor (4) is connected to the emitter of the second transistor (5).

Description

ACTIVE CIRCUIT ELEMENT

The invention relates to an active circuit element constituting a transistor comprising a basis terminal, an emitter terminal and a collector terminal. The proposed active circuit element is characterized by a linear characteristics: the output current is a linear function of the input voltage. The known active circuit elements are characterized by the fact that their output current changes in a nonlinear way with the input voltage. An example of the known devices forming the art in the field of the active elements is the bipolar transistor having exponential characteristics, the field--effect transistor showing a quadratic characteristics etc. The nonlinear characteristics is in most cases disadvantageous and is the source of generating harmonic frequency signals of relatively high level. The effects of the nonlinear characteristics can be diminished by applying negative feedback. The networks comprising negative feedback loops are not satisfactory under aspect of the transient processes. Another disadvantage of the known devices should be seen in strong temperature dependency of the characteristics: at different temperatures the same input voltage results in different outpuit currents. This disadvantageous feature can be avoided by application of compensating circuits especially in case of high currents.

The technical development requires active circuit elements with theoretically unlimited input voltage - output current characteristics wherein an outer resistor can make the characteristics be linear with slope determined by the reciprocal value of an outer resistor connected to one of the terminals of the circuit element. This device can be called linear transistor, which is thermally compensated and thereby shows a theoretical independency of the characteristics on the temperature.

Hence, the object of the invention is to create an active circuit element having linear characteristics. The invention is based on the recognition that the known bipolar transistors can form a desired active circuit element when connected to each other as shown herebelow.

The recognition mentioned above means that subtracting the basis-emitter voltage of two bipolar transistor from one another and ensuring a linear coupling between the collector currents of the two transistors it can be achieved that the difference of the basis-emitter voltages of the transistors remains constant during the work of the transistors. By realising a low heat resistance heat flow path between the two transistors, e.g. by integrating them in a common chip the temperature dependency of their P - N junctions is the same.

The proposed active circuit element constituting a transistor comprising a basis terminal, an emitter terminal and a collector terminal Is a device comprising four transistors, the first, the third and the fourth of them being of type opposite to the type of the second transistor, wherein the basis of the first transistor constitutes the basis terminal, the emitter of the second transistor is con nected to the emitter terminal and the third and fourth transistors are connected via their respective emitters to the collector terminal, further the third transistor is connected through its basis to the basis and the collector of the fourth transistor and over its collector to the emitter of first transistor and to the basis σf the second transistor, wherein the collector of the first transistor is connected to the emitter of the second transistor.

It is advantageous to Integrate the transistors in a common chip together with a resistor between the emitter and the second transistor and the emitter terminal, whereby the slope of the characteristics can be adjusted.

The type of the second transistor is the type of the proposed active circuit element which is - it will be described in more detail - a pnp-type element when the first, third and fourth transistors are of npn-type and vice versa. The proposed active circuit element constitutes a transistor-type device having a linear characteristics without or with very low level of dependency on temperature, of harmonic distorsion, ensuring output current following the input voltage according to a linear function.

The invention will be now described in more detail with reference to the accompanying drawings, wherein the single Figure shows the proposed circuit element connected to some terminals offan outer operating circuit.

The active circuit element according to the invention (Figure) comprises a basis terminal 1, an emitter terminal 2 and a collector terminal 3 with four transistors thereamong. A first transistor 4 is coupled through its basis to the basis terminal 1, through its collector to the emitter of a second transistor 5 and through its emitter to the basis of the second transistor 5 and to the collector of a third transistor 6. The basis of the third transistor 6 is coupled to the basis and the collector of a fourth transistor 8 forming thereby a diode. The voltage drop on this fourth transistor 8 ensures the input voltage of the third transistor 6. The emitter of the third transistor 6 is connected with the emitter of the fourth transistor 8 and their common point is connected to the collector terminal 3. The common point of the emitter of the first transistor 4 and of the collector of the second transistor 5 form the emitter terminal 2, wherein a resistor 9 can be included between the mentioned common point and the emitter terminal 2.

The first, third and fourth transistors 4, 6 and 8 are of the same type, e.g. npn-type oppositely to the type of the second transistor, e.g. pnp-type, wherein the type of the second transistor 5 determines the transistor type of the active circuit element proposed by the invention.

It is important that the forward voltages of the first and second transistors 4 and 5 show a constant difference; this requires the same values of their emitter currents realised by the third and the fourth transistors 6 and 8 wherein a current should be driven through the first transistor 4 which has the same intensity as the current flowing over the second transistor 5.

As shown in the Figure, the active circuit element according to the invention can be connected in an outer circuit by applying input voltage U_be between a terminal 11 and the basis terminal 1 obtaining thereby output current I_ki flowing be tween a terminal 12 and the collector terminal 3 through an outer resistor 10. Between the terminal 12 and the terminal 13 a supply voltage U_tap is applied. The terminals 11 and 13 are common and they are connected to a pole of the resistor 9. In normal operating conditions the input voltage U_be is an alternating voltage supervening a direct voltage, the supply voltage U_tap is a direct voltage and the output current I_ki is an alternating current supervening a direct current. When applying the operated active circuit element according to the Invention works in the following way, wittcut taking into account the basis currents of the transistors.

The voltage U₂ of the emitter terminal 2 can be determined as

U₂ = U_be + U_BE4 - U_BE5 , wherein U_BE is the basis-emitter voltage of the first and second transistors 4 and 5 and U_be is the input voltage applied between the terminal 11 and the basis terminal 1.

The basis-emitter voltage of a transistor depends on a specific thermic potential T, on the collector current I and a constant value I_O characterizing the transistor. It can be expressed by the function U_BE = Tlnl/I_O. Therefore the voltage U₂ is

wherein 4 and 5 are indices relating to the first and second transistors 4 and 5. The third and the fourth transistors are connected in a way as to ensure the equality of their basis-emitter voltage. This means that U_BE6 = U_BE8. Therefore

The interconnection of the transistors in the active circuit element of the invention ensures that I₄₌I₆ (3)

I₅ = I₈ (4)

(in the above expressions the indices 4, 5, 6, 8 relate to the corresponding transistor shown in the Figure).

Replacing in (1) the appropriate items by the expressions (2), (3) and (4) it follows that

wherein

The conclusion is that according to (5)

U₂ = U_be + K (7) i.e. the voltage of the emitter terminal 2 is equal to the input voltage shifted by a constant level signed by K in the expressions given above.

The output current flowing between the terminal 12 and the collector terminal 3 through the outer resistor 10 can be expressed in the following form: I_ki = I₈ + I₆ Because of (3) and (4)

I_ki = I₅ + I₄ and this is even the current flowing through the resistor 9, which can be signed by I_R9. According to the general laws

Hence,

wherein R is the resistance of the resistor 9. This means that the output current I_ki is a linear function of the input, voltage U_be and the slope characterizing this linear function is 1/R, i.e. the reciprocal value of the resistance R. In (8) K/R is a constant value, of course.

When the transistors 4, 5, 6 and 8 and eventually the resistor 9 are integrated in a chip the thermic dependency of the values characterizing the transistors is the same for all of the mentioned transistors and therefore it has no influence on the thermic behaviour of the active circuit element of the invention. This means, the proposed circuit element in integrated form shows a very low level of thermic sensitivity.

The proposed active circuit element can be applied in every case when linear signal transmission and amplification is required what can be done without feedback and thermic problems. The circuits realised on the basis of the proposed element comprise less elements, show higher linea rity and lower level of transient errors than the circuits realised on the basis of the elements known up to date. The proposed circuit element can be produced by well known technological processes of integrating or by simple interconnecting transistors of appropriate types, e.g. bipolar transistors. Its most important advantage is the linearity of the characteristics.

Claims

1. Active circuit element, constituting a transistor comprising a basis terminal, an emitter terminal and a collector terminal c h a r a c t e r i z e d in comprising four transistors wherein the first, the third and the fourth (6, 4, 8) are of type opposite to the type of the second transistor (5) and the basis of the first transistor (4) constitutes the basis terminal (1), the emitter of the second transistor (5) is connected to the emitter terminal (2) and the third and fourth transistors (8) are connected with their respectives to the collector terminal (3), further the third transistor (6) is connected through its basis to the bais and the collector of the forth transistor (8) and over its collector to the emitter of the first transistor (4) and to the basis of the second transistor

(5), wherein the collector of the first transistor (4) is connected to the emitter of the second transistor (5).

2. An active circuit element as claimed in claim 1, c h a r a c t e r i z e d in comprising a resistor (9) between the emitter of the second transistor (5) and the emitter terminal (2).

3. An active circuit element as claimed in claim 1 or 2, c h a r a c t e r i z e d in comprising three transistors of pnp-type.

4. An active circuit element as claimed in claim 1 or 2, c h a r a c t e r i z e d in comprising three transistors of npn-type.

5. An active circuit element as claimed in any preceding claim, c h a r a c t e r i z e d in forming by the transistors (4, 5, 6, 8) and their connection an integrated circuit.

6. An active circuit element as claimed in claim 5, c h a r a c t e r i z e d in comprising a resistor (9) integrated between the emitter point of the second transistor (5) and the emitter terminal (2).