Monolithic Integrable Constant Current Source For Transistors Connected As Current Stabilizing Elements

Abstract

To reduce sensitivity to battery voltage variation in a multiple transistor monolithically integrated constant current source, the control transistor is replaced by an amplifier. Only a fraction of the sum of base currents of the source transistors is applied to the input of the amplifier. Also, the number of source transistors is not as limited by current gain factor as it is when a control transistor is used.

Description

From the technical journal "IEEE Transactions on Circuit Theory," December 1965, pp. 586 to 590 it is known to operate transistors or transistor structures, when being correspondingly controlled, as so-called constant current sources. Relative thereto, the transistor serving as the current stabilizing element, as shown in FIG. 1 with reference to the transistors T.sub.0 and T.sub.1, is connected with its emitter to the voltage-conducting pole of the source of supply voltage U.sub.B, and with its base to a control circuit consisting of the transistor T.sub.0 and the resistor R.sub.0. The collector of the current stabilizing transistor T.sub.1 is connected to a suitable point of any kind of circuit arrangement to which the constant current is to be applied, this being indicated by the arrow points in the drawings. The control circuit, in the conventional arrangement, consists of a transistor of the same conductivity type which, with its emitter is likewise connected to the voltage-conducting pole of the source of supply voltage U.sub.B, while the collector and the base thereof are directly connected to one another and, across a resistor R.sub.0, are connected to the other pole of the supply voltage which, in the drawings, is identical to the zero point of the circuit. The current stabilizing transistor T.sub.1 is controlled in that the base thereof is connected to the base of the control transistor T.sub.0 with respect to direct current. As will be shown later on, the current which is capable of being taken from the collector of the current stabilizing transistor T.sub.1, can be adjusted by varying the resistance value of R.sub.0.

Such transistors connected as current stabilizing elements, are very versatile in use. Thus, for example, it is known from the technical journal "IEEE Journal of Solid-State Circuits," June 1969, pp. 110 to 123, in particular page 115 et seq., to use in monolithic integrated circuits such types of current stabilizing transistors for acting as the decoupling elements between individual stages of the circuits. A further use of such constant current sources is known from the German technical journal "radio mentor", September 1967, pp. 702 and 703; in this case the transistor connected as a current stabilizing element, serves as the collector resistance of another transistor in a monolithic integrated circuit.

Also in circuit arrangements composed of individual components in the usual way, hence in a so-called discrete configuration, it is already known to use current stabilizing transistors, cf. the book "Siemens-Halbleiter-Schaltbeispiele" (Siemens semi-conductor circuit examples), April 1964, pp. 57 and 58; here there is concerned a highly sensitive dc zero point amplifier in which a transistor connected as a current stabilizing element is used as the collector resistance of a transistor amplifier.

Moreover, it is known in the art to operate also several transistors connected as current stabilizing elements, from one single control circuit. In this case the individual base lead-in conductors of the current stabilizing transistors are connected to one another as is denoted in FIG. 1 with reference to the transistors T.sub.2 to T.sub.n. From the German Valvo handbook on "Integrated Circuits 1968", April 1968, page 171 there is known the basic circuit diagram of a monolithic integrated multi-stage differential amplifier in which such a multiple constant current source is used as emitter resistances of the individual differential amplifying stages. From the Swiss Pat. No. 484.521 corresponding to the German published application (DOS) 1.911.934 and the French printed application 2.012.426, finally, there has become known a monolithic integrated multiple onstant current source whose individual transistors serving as current stabilizing elements, serve as the collector resistances of bistable multivibrator circuits.

As a control circuit in the multiple constant current source according to the last-mentioned Swiss patent specification there is likewise provided a circuit arrangement corresponding to the control circuit according to FIG. 1 of the accompanying drawings, i.e., which is substantially identical to the circuit of the transistor T.sub.0 and of the resistor R.sub.0.

Based on the aforementioned prior art, the present invention relates to a monolithic integrable control circuit for one or several transistors or transistor structures of the one conductivity type connected as current stabilizing elements, and having the same or different emitter configurations and which, is discretely designed or integrated circuits, serve as a substitute of ohmic resistors, preferably as substitutes of high-ohmic resistors, with the base-emitter sections thereof, in the case of several current-stabilizing elements, being connected in parallel in the same direction, with the control circuit consisting of one control transistor (-structure) of the one conductivity type, whose base-emitter section is connected in parallel in the same direction to the base-emitter section of the current stabilizing transistor (transistor structure), and whose collector is connected to the base thereof and, via one collector resistance, is connected to the one pole of the source of supply voltage.

For explaining the problem on which the invention is based and for explaining the object of the invention as resulting therefrom, there will first of all be briefly explained the mode of operation of the control circuit upon the multiple constant current source with reference to FIG. 1. For the sake of simplicity, it be assumed that the individual transistors or transistor structures T.sub.0 to T.sub.n all have the same emitter configuration, because in this case the collector currents flowing in the current stabilizing transistors T.sub.1 to T.sub.n are alike, as well as the individual base currents. The invention, however, is in no way restricted to this equal emitter configuration. In the case of an unequal (unalike) emitter configuration different currents depending on the respective configuration, flow in the individual collector circuits, so that in this way it is possible to obtain a multiple constant current source in the individual branches of which, quite depending on requirements, different currents may be provided for.

The graphical representation of FIG. 1 is made in such a way that the point connecting the base of the control transistor T.sub.0 to the common base connection of the current stabilizing transistors T.sub.1 to T.sub.n is either referred to as connecting point A or as the first connecting point. Moreover, the point connecting the collector of the control transistor T.sub.0 and the collector resistor R.sub.0 is referred to as D or as the second connecting point.

To this circuit, under dc voltage operating conditions, there apply the following simple relations. Across resistor R.sub.0 there drops off a voltage which is equal to the supply voltage U.sub.B less the base-emitter voltage U.sub.BE of the control transistor T.sub.0. In the collector circuit of the control transistor T.sub.0 there is flowing the collector current I.sub.C while in the connecting line extending between the connecting points A and D there is flowing the total base current of all transistors T.sub.0 to T.sub.n which, in the assumed case of equal transistors, corresponds to (n+1) times the value of one individual base current, i.e., there is flowing the current (n+1)I.sub.B. The current I.sub.R flowing through the collector resistor R.sub.0, therefore, is equal to the sum of the currents flowing to the connecting point D and, on account of Ohm's law, there apply the following equations which will be understandable without further ado:

I.sub.R = I.sub.C + (n+1)I.sub.B = U.sub.R /R.sub.0 = U.sub.B - U.sub.BE /R.sub.0

where I.sub.R is the collector resistance current, I.sub.C is the current flowing in the collector of the current transistor, I.sub.B is the value of one individual base current, R.sub.0 is the value of the collector resistor, U.sub.B is the value of the supply voltage, U.sub.BE is the base-emitter voltage of the control transistor and U.sub.R is the value of potential across the collector resistor.

Accordingly, the following will result with respect to the collector current I.sub.C of the control transistor T.sub.0 :

I.sub.C = (U.sub.B - U.sub.BE /R.sub.0) - (n+1)I.sub.B

The collector current of the control transistor T.sub.0, however, is linked to the base current thereof through the direct current gain factor B in a grounded emitter circuit according to the equation

I.sub.B = I.sub.C /B

where B is the direct current gain factor, this analogously also applying to the linkage between the base and the collector current of the current stabilizing transistors T.sub.1 to T.sub.n. The equation relating to the collector current of the control transistor, therefore, may also be written in the following form:

I.sub.C = (U.sub.B - U.sub.BE /R.sub.0 (1 + n+1/B))

Since on the other hand, however, under the aforementioned condition of an equal emitter configuration, also the collector currents of the individual transistors are identical to one another, i.e., the following is applicable I.sub.C = I.sub.C = I.sub.C = I.sub.C , this equation indicates the current flowing in each collector circuit of the transistor.

This current, as already briefly mentioned hereinbefore, can be adjusted with the aid of the resistance value of the collector resistor R.sub.0. However, it is not only dependent upon this value, but also upon the number n of transistors serving as current stabilizing elements, and on the direct current gain factor B thereof.

There are some cases of practical application in which the problem arises to supply circuits or circuit units with a certain minimum current and which may not be fallen short of. Since in the case of circuits which are to be realized concretely, the parameters of individual discrete transistors, or else in the case of a monolithic integration, those of the transistor structures T.sub.0 to T.sub.n as a whole, are subjected to manufacturing tolerances, which is in particular noticeable from the different values of the direct current gain factor B, it is necessary in dimensioning the resistance value of resistor R.sub.0, to proceed in a way assuming a most unfavourable value for the direct current gain factor B, and calculating the resistor R.sub.0 associated therewith.

Especially in the monolithic integration, the manufacturing tolerances cause variations of the direct current gain factors B of the individual production batches so that in cases of dimensioning according to the lowest direct current gain factor B a greater collector current will flow in switching circuits with a higher B than would be actually necessary. This leads to an unnecessarily high current consumption of the equipment equipped with the entire (integrated) circuit, this having a very disadvantageous effect upon the service life of the battery in cases where equipments are to be operated from a dry battery of restricted charge.

For solving this problem it is possible, according to the Swiss patent specification 484.521 to supplement each of the current stabilizing transistors by one further transistor taking care that the relationship (n+1)/B as mentioned in the foregoing equation, remains substantially smaller than 1. However, as already mentioned in this particular patent specification, this again causes other disadvantages, especially as regards compensation of the temperature coefficient.

In addition to the dependence of the current gain factor upon the setting of the individual collector currents as described in detail hereinbefore, the conventional control circuit still has the further disadvantage that voltage variations superimposed upon the supply voltage, for example, the slow dropping of the battery voltage as occurring during the long service life of a dry battery, is noticed as a variation or fluctuation of the collector current flowing over the individual constant current transistors.

It, therefore, is the object of the present invention to eliminate this current gain factor dependence and, if possible, also the voltage dependence of the setting of the currents flowing in the collector circuits of the individual constant current transistors. That portion of the problem relating to the dependency of the setting upon the current gain factor may also be formulated in such a way that even in the case of a large number (n+1) of transistors T.sub.0 to T.sub.n and a relatively small current gain factor B, to relationship (n+1)/B shall always be small with respect to unity (1).

By the monolithic integrable control circuit described in detail hereinbefore, this problem is solved in that the connecting line extending between the connecting point of the base of the control transistor and the base (bases) of the one (or more) current stabilizing transistors, i.e., the first connecting point, and the connecting point of the collector resistance with the collector of the control transistor, i.e., the second connecting point, is split up or seperated, that between the two connecting points there is inserted a dc regulating amplifier via the output thereof there is flowing the common current of the current stabilizing transistors (transistor structures) as well as of the control transistor, and via the input thereof there is only flowing a fraction of this common base current, and that said dc regulating amplifier serves to compare the potential as applied to the second connecting point with the potential of a source of reference voltage as regards one common reference point, in such a way that the potential difference between the potential of the second connecting point and the potential of the source of reference voltage becomes zero with respect to said common reference point .

Further developments and types of embodiments of the inventive circuit arrangement are characterized in the claims, and will now be described in detail with reference to the further FIGS. 1 to 7 shown in the accompanying drawings, in which:

FIG. 1 shows a prior art circuit having the disadvantages described above,

FIG. 2 shows one type of embodiment of the invention in which the source of reference voltage is connected to the voltage-conducting pole of the source of supply voltage,

FIG. 3 shows one type of embodiment of the invention in which the source of reference voltage is connected to the zero point of the circuit,

FIG. 4 shows one circuit realized according to the basic circuit diagram shown in FIG. 2.

FIG. 5 shows one circuit realized according to the basic circuit diagram shown in FIG. 3,

FIG. 6 shows another circuit realized according to the basic circuit diagram shown in FIG. 3, and,

FIG. 7 shows a modified embodiment of the circuit arrangement according to FIG. 6.

The circuit arrangement according to FIG. 2 consists of the transistors T.sub.1 to T.sub.n connected as current stabilizing elements, and of the control transistor T.sub.0 which are all connected in the same way as regards their base-emitter sections, as has already been described hereinbefore with reference to FIG. 1. For solving theproblem on which this invention is based, the dc regulating amplifier V is now connected into the line extending between the connecting points A and D, via the output of which there is flowing the common base current (n+1)I.sub.B of the transistors T.sub.1 to T.sub.n connected as constant-current elements, and of the transistor T.sub.0, and via the input thereof which is connected to the connecting point D, there only flows a fraction of this common base current. This fraction is given by the total dc gain factor v of the dc regulating amplifier V. Moreover, a second input of the dc regulating amplifier V is connected to the source of reference voltage U.sub.ref, with the other pole thereof being connected to the voltage-conducting pole of the source of supply voltage U.sub.B. The dc regulating amplifier V has the property of causing the potential difference between the connecting point D and the potential of the source of reference voltage U.sub.ref to become zero with respect to the common reference point, hence in this particular case with respect to the voltage-conducting pole of the source of supply voltage U.sub.B.

By interconnecting this special type of dc regulating amplifier, the influence of the factor (n+1)/B in the abovementioned equation is reduced by the total dc gain factor v of this amplifier, so that variations in the current gain factor B of the individual transistors or of the individual integrated circuits of different production batches will no longer have an influence upon the selection of the resistance value of the collector resistor R.sub.0 of the control transistor T.sub.0. In fact, it is possible to select the resistance value intended for a minimum current consumption, because manufacturing tolerances and the spread between units will practically no longer have an influence upon the voltage U.sub.R as dropping off across the collector resistor R.sub.0.

The circuit arrangement according to FIG. 3, as regards the interconnection of the dc regulating amplifier V between the connecting points A and D, corresponds to that shown in FIG. 2 with the exception, however, that the source of reference voltage U.sub.ref, instead of being connected to the voltage-conducting pole of the source of supply voltage U.sub.B, is connected to the zero point of the circuit. In this particular case the dc regulating amplifier V has the property of making the potential difference between the connecting point D and the reference voltage U.sub.ref equal to zero as regards the zero point of the circuit. In this case, too, there results the current reduction which is essential in the invention, by the total current gain factor v of the dc regulating amplifier V. As an additional advantage offered by this particular type of embodiment of the invention there is to be regarded the fact that supply voltage fluctuations or variations of long duration of this particular voltage will no longer have an influence upon the collector currents of the transistors T.sub.1 to T.sub.n which are to be stabilized.

FIG. 4 shows a circuit arrangement representing a type of embodiment according to the basic circuit diagram shown in FIG. 2. The dc regulating amplifier consists of the two transistors T.sub.V and T.sub.V . The transistor T.sub.V is of the same conductivity type as the control transistor T.sub.0 and the current stabilizing transistors T.sub.1 to T.sub.n while the transistor T.sub.V is complementary to these transistors. In embodying the invention, the base-emitter section of the transistor T.sub.V simultaneously serves as the source of reference voltage U.sub.ref, thus resulting in a considerable simplification of the entire circuit. It will be seen that the emitter of this transistor is connected to the voltage-conducting pole of the source of supply voltage U.sub.B while the base thereof is connected to the point D connecting the collector resistor R.sub.0 and the collector of the control transistor T.sub.0. To the base of the transistor T.sub.V the collector of the transistor T.sub.V is connected directly galvanically, with the emitter thereof being connected to the zero point of the circuit, while the collector thereof is connected to the point A, hence to the common base terminal of the transistors T.sub.0 to T.sub.n. The total current gain factor v of this dc regulating amplifier is equal to the product from the current gain factors B.sub.1 and B.sub.2 of the transistors T.sub.V and T.sub.V . Therefore, in the base lead-in conductor of the transistor T.sub.V there is flowing the base current (n+1)I.sub.B /B.sub.1 B.sub.2.

FIG. 5 shows a circuit arrangement corresponding to the basic circuit diagram shown in FIG. 3. The dc regulating amplifier V consists of the transistors T.sub.V and T.sub.V , with the transistor T.sub.V being of the same conductivity type as transistors T.sub.0 to T.sub.n and the transistor T.sub.V being complementary to these transistors. In this particular example of embodiment the base-emitter section of the transistor T.sub.V serves as the source of reference voltage, with the emitter of this transistor being connected to the zero point of the circuit while its base is connected to the ollector of the control transistor T.sub.0 and to the collector resistor R.sub.0, hence to the connecting point D. The collector of transistor T.sub.V is connected directly galvanically to the base of transistor T.sub.V , with the emitter thereof being connected to he voltage conducting pole of the source of supply voltage U.sub.B, and the collector thereof being connected directly galvanically to the common base terminal of the transistors T.sub.0 to T.sub.n and, on the other hand, to the zero point of the circuit across a resistor R.sub.V . The total current gain factor v of this dc regulating amplifier, when neglecting the current flowing across the register R.sub.V , is equal to the product from the current gain factors B.sub.3 and B.sub.4 of the transistors T.sub.V and T.sub.V . Accordingly, only that particular portion of the common base current of the transistors T.sub.0 to T.sub.n reduced by this factor is flowing across the collector resistor R.sub.0.

The circuit arrangement shown in FIG. 6 represents another variety relating to the basic circuit diagram shown in FIG. 3, in which the reference voltage U.sub.ref is connected to the zero point of the circuit. Also in this case the base-emitter section of a transistor is used as the source of reference voltage. The dc regulating amplifier, in this particular variety, again is composed of the transistor T.sub.V which is complementary to the transistors T.sub.0 to T.sub.n, and of a further transistor T.sub.V which is complementary to these transistors, i.e., the transistors T.sub.V and T.sub.V are of the same conductivity type but complementary in relation to the transistors T.sub.0 to T.sub.n.

The base-emitter section of the transistor T.sub.V is connected in the same way as in the example of embodiment according to FIG. 5, and also the collector is led galvanically directly to the base of transistor T.sub.V , whereas the collector, however, is connected across a resistor R.sub.V to the voltage-conducting pole of the supply voltage U.sub.B. The emitter of transistor T.sub.V is applied to the zero point of the circuit while the collector thereof is connected directly galvanically to the common base terminal of the transistors T.sub.0 to T.sub.n.

The collector-emitter section of transistor T.sub.V may be connected in parallel to the resistor R.sub.V , with the emitter of transistor T.sub.V being connected to the voltage-conducting pole of the supply voltage. In the examples of embodiment according to FIGS. 6 and 7 there is flowing in the base lead-in conductor of the transistor T.sub.V approximately the total base current (n+1)I.sub.B /B.sub.3 B.sub.5 as reduced by the product B.sub.3 B.sub.5. The current gain factors of the transistors T.sub.V and T.sub.V are indicated by the references B.sub.3 and B.sub.5.

In addition to the already mentioned advantages, the individual circuit arrangements according to the present invention still have the property of behaving differently with respect to the temperature coefficient. Thus, for example, the circuit arrangement according to FIG. 4 shows to have a positive temperature coefficient while the circuit arrangements according to FIGS. 5 to 7 show to have a negative temperature coefficient. Therefore, quite depending on the specific type of circuit in which the current stabilizing transistors are being used, it is possible to select a circuit adapting the entire circuit to the temperature range expected during operation. Thus, it may be of advantage to use a circuit having a negative temperature coefficient because especially in the case of temperatures ranging about the freezing point, the current gain factor of transistors or transistor structures shows to have a strong current-dependent behaviour. If, for this reason, the collector currents of the current stabilizing transistors decrease in the case of low temperatures, this may be compensated for to a certain extent by the negative temperature coefficient.

The examples of embodiment according to FIGS. 2 to 7 have been explained with reference to circuits in which the current-stabilizing transistors are connected to the voltage-conducting pole of a source of supply voltage U.sub.B. As a rule, this corresponds to a practical use where the current stabilizing transistors are employed as collector resistors, i.e., where the current stabilizing transistors are applied to a potential ranging near the supply voltage. However, as is known from the aforementioned German Valvo handbook, the current-stabilizing transistors, for example, may also be used as emitter resistors of differential amplifiers. In that case the current-stabilizing transistors are at a relatively low potential, mostly even at a potential which is negative with respect to the zero point of the circuit in the case where npn-transistors are used as differential transistor amplifiers. The individual varieties of the control circuit with corresponding circuit or arrangement of the source of reference voltage, may also be chosen with respect to this case of practical application, in such a way that quite depending on the desired characteristic there will be obtained either a positive or a negative temperature coefficient and an additional voltage stabilization.

The inventive control circuit is above all of advantage to circuits operating with low voltages and small currents. Such types of circuits, for example, are multi-stage frequency divider circuits consisting of flip flop stages as used in the digital technique for storages, shift registers, translators, etc., or as may be employed in organs and in clocks or watches controlled by a standard frequency generator.

Claims

What is claimed is:

1. A monolithic integrable constant current source comprising:

a source of supply voltage having a voltage conducting pole and a zero voltage pole;

a plurality of current stabilizing transistors of one conductivity type having base-emitter sections connected in parallel and in the same direction;

a control transistor having a base-emitter section connected in the same direction and parallel to the base-emitter section of one of said plurality of current stabilizing transistors;

a resistor coupled between the collector of said control transistor and said second pole; and

a DC regulating amplifier receiving at its input a fraction of the common base current and delivering at its output the total common base current, said amplifier coupled between the junction of said resistor and collector of said control transistor and the junction of the bases of said plurality of current stabilizing transistors for comparing a reference voltage with the voltage at the junction of said resistor and control transistor collector

for adjusting the difference to equal the potential at a common reference point, said regulating amplifier comprising:

a first transistor having an emitter coupled to the voltage conducting pole of said reference voltage, and a base coupled to the junction of said resistor and the collector of said control transistor, the voltage across said voltage conducting pole and said base establishing said reference voltage; and

a second transistor having a base coupled to the collector of said first transistor, and emitter coupled to the zero pole of said supply voltage and a collector coupled to the junction of the bases of said plurality of current stabilizing transistors.