The invention relates to an active circuit element con¬ stituting a transistor comprising a basis terminal, an emit¬ ter terminal and a collector terminal. The proposed active circuit element is characterized y 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 form¬ ing the art in the field of the active elements is the bipo- lar transistor having exponential characteristics, the field- -effect transistor showing a quadratic characteristics etc. The nonlinear characteristics is in most cases disadvan¬ tageous 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 feed¬ back. 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 dif- ferent temperatures the same input voltage results in differ _¬ ent 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 ele- ents 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 there- by shows a theoretical independency of the characteristics on the temperature.

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

The recognition mentioned above means that subtract- ing the basis-emitter voltage of two bipolar transistor from one another and ensuring a linear coupling between the col- lector 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 tran¬ sistors. 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 - Ε 3unc¬ ions 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 tran- sistors, 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 tran¬ sistors are connected via their respective emitters to the collector terminal, further the third transistor is connect¬ ed through its basis to the basis and the collector of the 5 ^' fourth transistor and over its collector to the emitter of the first transistor and to the basis σf the second transis¬ tor, wherein the collector of the first transistor is con¬ nected to the emitter of the second transistor.

It is advantageous to Integrate the transistors in a 0 common chip together with a resistor between the emitter and the second transistor and the emitter terminal, wπereby the slope of the characteristics can be a_i: ^" sted.

The type of the second transistor is _r_e type of the proposed active circuit element w ich is - it will be de- 5 ^' scribed in more detail - a pnp-type element when the first, third and fourth transistors are of npn-tvte and vice versa. The proposed active circuit element ci stitutes a tran¬ sistor-type device having a linear characteristics wit::out or with very low level of dependency on t=.t.t rature. i 0 harmonic distorsion, ensuring output current fcllowi _r the input voltage according to a linear functi.n.

The invention will be now described in more detail wit _h reference to the accompanying drawings, w::erein the single Figure shows the proposed circuit element connected to some ^~~ terminals offan outer operating circuit.

The active circuit element according tc the invention (Figure) comprises a basis terminal 1, an emitter terminal 2 and a collector terminal 3 with four transistors there- among. A first transiεtor 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 form- ing thereby a diode. The voltage drop on this fourth tran¬ sistor 8 ensures the input voltage of the third transistor 6. The emitter of the third transistor 6 is connected wita 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, where¬ in 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 tr.e type ct the second transistor, e.g. pnp-type, wherein the type of the sec¬ ond transistor 5 determines the transistor type of the active circuit element proposed by the invention.

It is important that the forward voltages cf 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 wαerβ- in 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 ac _¬ cording to the invention can be connected in an outer circuit by applying input voltage U _b _ between a terminal 11 and the basis terminal 1 obtaining thereby output current I. , flow- i_rι ing 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.. is applied. The termi¬ nals 11 and 13 are common and they are connected to a pole of the resistor 9. In normal operating conditions the input voltage U _fcα is an alternating voltage supervening a direct voltage, the supply voltage U. is a direct voltage and the output cur- u a p rent I.C_l. is an alternating current supervening a direct . cur- rent. When applying the operated active circuit element ac¬ cording to the Invention works in the following way, wittcut taking into account the basis currents of the transistors.

The voltage O- of the emitter terminal 2 can 'be deter¬ mined as

^U 2 = ^U be ^{+ ϋ} BE4 ^{" U} BE5 ' wherein U _BE is the basis-emitter voltage of the first and second transistors 4 and 5 and U _fce is the input voltage applied between the terminal 11 and the basis terminal 1.

The basis-emitter voltage of a transistor depends on a spe¬ cific thermic potential T, on the collector current I anf a constant value I _Q characterizing the transistor. It ca be expressed by the function U _BE = Tlnl/I ₀ . Therefore tπe voltage U- is

U- =. u, _{+ TlQ} ain! . .

2 be ^Ω I ₅ I ₀₄ (1)

wherein 4 and 5 are indices relating to the first and sec _¬ ond 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

Λ __ -___£ ₌ . constant (2)

^I 8 ^I 08

The interconnection of the transistors in the active cir¬ cuit element of the invention ensures that

I ₅ - I _B (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

K = U ln— — 25. _ constant (6)

I I 08 ^04

The conclusion is that according to (5)

^U 2 = ^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 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 = ^τ S ^{+ I} 6 Because of (3) and (4)

-kl = -5 + - and this is even the current flowing through the resistor 9, which can be signed by I _RQ . According to the general laws

Hence,

wherein R is the resistance of the resistor 9. This means that the output current I.. is a linear function of the in¬ put, voltage U, 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, ~ 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 amplifi¬ cation 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 inter¬ connecting transistors- of appropriate types, e.g. bipolar transistors. Its most important advantage is the linearity of the characteristics.