Bipolar transistor arrangement with distortion compensation

Abstract: The invention relates to a bipolar transistor arrangement with distortion compensation to compensate for the distortion component (Id) in the collector current (Io + Id) of a transistor (T1), which component is caused by the logarithmic base-emitter voltage thereof. In accordance with the invention a sub-current (Is) proportional to the emitter current (I + Ie) is generated, which sub-current is fed through an element (7) comprising at least one semiconductor junction. By means of a voltage-to-current converter (8) the logarithmic voltage appearing across this element is converted into a correction current (Ir) proportional to the distortion component (Id) and is applied to the collector of the transistor (T1) in order to compensate for the distortion component (Id) in a load circuit (Rc) connected to the collector. The invention is suitable for use in voltage-to-current converters formed by means of bipolar transistors.

Description: The invention relates to a bipolar transistor circuit with compensation for a distortion component of a transistor collector current which is determined by a base-emitter voltage of the transistor, said circuit comprising: an input terminal for receiving a signal voltage, an output terminal for connection to a load circuit, at least one main transistor having a collector coupled to the output terminal, a base coupled to the input terminal, an element for developing a voltage across the element as a function of a current flowing therein, means coupled to the main transistor for supplying a sub-current to the element which is proportional to the collector current through the main transistor, the means comprising a parallel transistor of the same conductivity type as the main transistor and having its base connected to the base of the main transistor and having its collector coupled to the element in a collector terminal, and voltage/current conversion means coupled to the element and to the output terminal for supplying a correction current to the output terminal which is proportional to the voltage across the element to compensate the distortion component, the voltage/current conversion means comprising a first conversion transistor of the same conductivity type as the main transistor and having its base connected to the collector terminal. Such a bipolar transistor arrangement is known from EP-A-0 133 724. In addition to the D.C. bias current and the signal current the collector current of the main transistor contains an undesirable distortion component which is dictated mainly by the logarithmic voltage across the base-emitter junction of the main transistor. As the emitter current increases, the distortion component also increases and limits the maximum voltage amplitude of the output signal to a value smaller than the maximum output swing attainable with a given supply voltage. This may be a disadvantage in particular in transistor arrangements operating with a comparatively low supply voltage. In the known bipolar amplifier arrangement the emitters of the main and of the parallel transistor are connected to signal ground via separate emitter resistors. The element is a simple resistor connected to the collector of the parallel transistor. The base of the first conversion transistor is connected to the collector of the parallel transistor and the emitter of the first conversion transistor is connected to the collector of the main transistor and operates as an emitter follower, thereby forcing a signal voltage at the load terminal which is nearly equal to the signal voltage at the collector of the parallel transistor. In order to work well the voltage gain of the main and parallel transistors should be equal and the resistance of the emitter resistor of the parallel transistor should be much larger than that of the emitter resistor of the main transistor. GB-A-2 118 394 discloses a bipolar amplifier arrangement in which the emitters of the main and of the parallel transistor are connected to signal ground via separate emitter resistors. The element is a single diode connected to the collector of the parallel transistor. The base and collector of the first conversion transistor are connected in parallel with the diode to form a current mirror, thereby adding a current to the load terminal which is proportional to the collector current through the parallel transistor. It is an basic object of the invention to minimise the influence of the distortion component in the output signal of the transistor arrangement. This is achieved in that the element comprises at least one semiconductor junction, the parallel transistor has a smaller emitter area than that of the main transistor, the emitter of the parallel transistor is connected to the emitter of the main transistor, the main transistor and the parallel transistor thereby forming a common base terminal and a common emitter terminal, the collector of the parallel transistor being coupled to the element and to the voltage/current conversion means, and the voltage/current conversion means comprise a second conversion transistor of the same conductivity type as the main transistor and a first impedance, the emitters of the first and second conversion transistors being coupled via the first impedance and the collector of the second conversion transistor being coupled to the output terminal. The invention is based on the idea of adding to the collector current of the main transistor a correction current derived from the emitter current. For this purpose a smaller sub-current, which is proportional to the current in the emitter of the main transistor, is generated. By means of this smaller sub-current a replica of the base-emitter voltage of the main transistor is produced by passing this sub-current through one or more elements comprising a semiconductor junction. This results in a logarithmic voltage drop across these elements, which voltage drop is a replica of the logarithmic base-emitter voltage of the main transistor which dictates the distortion component in the collector current. If subsequently this logarithmic voltage drop is suitably converted into a correction current of the same magnitude as the distortion component in the collector current of the main transistor, an effective compensation for said distortion component in the current through the load circuit is obtained, enabling substantially the maximum output voltage swing in a given circuit arrangement to be utilised. Since the replica of the base-emitter voltage is generated by means of a correction circuit via a sub-current which can be substantially smaller than the emitter current in the main transistor, the inevitable distortion components in the correction circuit remain below a level which is negligible relative to the correction current to be generated. For generating a sub-current which is proportional to the emitter current of the main transistor it is possible inter alia to employ a current-mirror circuit in the emitter line of the main transistor. However, the addition of circuit elements in the collector-emitter path of the transistor has the drawback that this leads to an undesirable reduction of the output swing of the relevant transistor. In order to preclude this, in the arrangement in accordance with the invention the means for supplying the sub-current comprise a parallel transistor of the same conductivity type as and having a smaller emitter area than the main transistor, the base-emitter junctions of the transistors being arranged in parallel, thereby constituting a common base and emitter terminal. Through compensation of the distortion component in the output current of the main transistor, this output current can be made to depend accurately and in a desired manner on an input signal. A further embodiment of the invention based on this is characterized in that the main transistor constitutes a first branch of a differential transistor arrangement having a second branch including: a second main transistor and a second parallel transistor, both of the same conductivity type as the first main transistor, and having their respective base-emitter junctions connected in parallel to form a second common base terminal and a second common emitter terminal, the second parallel transistor having a smaller emitter area than the second main transistor, a second element comprising at least one semiconductor junction coupled to the collector of the second parallel transistor in a second collector terminal, the base of the second transistor being connected to the second collector terminal, and in that the bipolar transistor arrangement further includes: a second impedance connected between the first and second common emitter terminals, and first and second bias current sources, coupled to the first common emitter terminal and the second common emitter terminal, respectively. This transistor arrangement constitutes a very accurate balanced voltage-current converter suitable as a component for use in analog multiplier circuits, analog-to-digital converters etc. The embodiment may be further characterized in that the bipolar transistor arrangement further comprises a third bias current source coupled to the emitter of the first conversion transistor and a fourth bias current source coupled to the second conversion transistor. The use of a conversion means having a similar construction to that of the balanced voltage-current converter results in a total arrangement which can be dimensioned simply. It is possible to demonstrate that an optimum distortion compensation is achieved when the first and second elements each comprise a series arrangement of m diodes or m diode-connected transistors, m being an integer greater than 1, the emitter areas of the first and second main transistors being substantially equal and the emitter areas of the first and second parallel transistors being substantially equal and in that the first and second impedances comprise a first and a second resistor, respectively, whose resistance values are in a ratio of m : 1. The embodiment may alternatively be further characterized in that the first main transistor comprises two sub-transistors of the same conductivity type, the sum of the emitter areas of the two sub-transistors being equal to the emitter area of the first main transistor, the base-emitter junctions of the two sub-transistors being connected in parallel, the collector of one of the two sub-transistors being connected to the emitter of the first conversion transistor and the collector of the other sub-transistor being connected to the emitter of the second conversion transistor. For biasing the first and second conversion transistors this embodiment does not require any separate bias current sources. The use of sub-transistors further reduces the D.C. component of the current in the output circuit, as a result of which the voltage amplitude across the load circuit, for example a load resistor, can approximate more closely the maximum output swing imposed by the supply voltage. Optimum compensation can be achieved in this embodiment when the first and second elements each comprise a series arrangement of m diodes or m diode-connected transistors, m being an integer greater than 1, the sum of the emitter areas of the two sub-transistors and the first parallel transistor being substantially in a ratio of 2n : 1 and the emitter areas of the second main transistor and the second parallel transistor also being substantially in a ratio of 2n : 1, n being a positive number, and in that the first and second impedances comprise a first and a second resistor, respectively, whose resistance values are in a ratio of (1 + 2n)m/n : 1. The transistor arrangement in accordance with the invention can readily be extended to form an arrangement with controllable gain. An embodiment thereof is characterized in that the output terminal is connected to a common emitter terminal of a differential transistor pair, the collector of one of the transistors of the differential transistor pair constituting a controlled output terminal for connection of the load circuit and the bases of the transistors of the differential transistor pair constituting terminals for applying a control voltage for controlling the current to the controlled output terminal. A further embodiment which is based thereon is characterized in that the transistor whose collector is connected to the output terminal is constructed as a multi-collector transistor, each of the individual collectors of the multi-collector transistor being coupled to a respective common emitter terminal of a plurality of said differential transistor pairs having a respective collector connected to the controlled output terminal. This arrangement is very suitable for control by means of a digital control signal. The invention will now be described in more detail, by way of example, with reference to the accompanying drawings. Fig. 1 shows diagrammatically a transistor arrangement with distortion compensation in accordance with the invention. Fig. 2 shows the circuit diagram of a voltage-to-current converter with distortion compensation in accordance with the invention. Fig. 3 shows a modification of the arrangement shown in Fig. 2. Fig. 4 shows an arrangement as shown in Fig. 3, comprising a gain-control circuit. Fig. 5 shows a further embodiment of the arrangement shown in Fig. 4 constructed to provide digital gain control. In Fig. 1 an NPN transistor T1 is shown, which in principle may form part of a more extensive transistor arrangement having power-supply terminals 1, 2. The collector of the transistor T1 constitutes a collector terminal 3 a resistor Rc, by way of example, being arranged between this terminal and the power-supply terminal 1. In the present example a resistor Re is arranged between the emitter of the transistor T1, having an emitter terminal 4, and the power-supply terminal 2. The base of the transistor T1 constitutes a base terminal 5 for connection of a signal-voltage source Vi, as shown. For the sake of clarity the d.c. bias means of the transistor T1 are not shown. If the material resistance of the base emitter junction of the transistor T1 is ignored the following relationship is valid. Vi=Vbe+(I+Ie)Re=(kT/q)ln(I+Ie)+(I+Ie)Re where k = Boltzmann's constant T = absolute temperature q = elementary charge Vbe = base emitter voltage I = emitter direct current, and Ie = emitter signal current. The logarithmic term gives rise to a distortion component Id in the collector current, which component limits the output swing of the transistor. The influence of this distortion component depends on the signal current Ie and the d.c. setting of the transistor T1. The invention provides means 6, connected to the emitter terminal 4 of the transistor 1, to generate a sub-current Is which is proportional to the emitter current, i.e. the d.c. component I and the signal current component Ie of this emitter current. This sub-current Is flows through an element 7 comprising at least one semiconductor junction. Said at least one element 7 may comprise, for example, a series arrangement of a plurality of diodes or a plurality of diode connected transistors. If subsequently a voltage-to-current converter 8 converts the logarithmic voltage drop across said at least one element 7 into a correction current Ir, having a polarity as indicated by the arrow in the Figure, in such a way that this correction current is equal to the distortion component Id in the collector current, an effective compensation for the distortion component Id through the collector resistance Rc is achieved. Then only the current Io of the arrangement flows through said collector resistance Rc, which current in the present case is dictated by the instantaneous signal voltage Vi, the emitter resistance Re, the current-gain factor of the transistor T1 and the d.c. setting. The circuit diagram in Fig. 1 clearly shows that in order to achieve the desired compensation for the distortion component no means have to be arranged in the collector-emitter path of the transistor T1. This means that the output voltage of the arrangement on, for example, the collector terminal 3 can assume the value of the supply voltage applied to the power-supply terminal 1, 2 of the transistor arrangement. The means 6 for generating a replica of the emitter current of the transistor T1 may comprise, for example, a current-mirror circuit, in a manner known per se. However, this implies that further electronic components must be arranged in the emitter line of the transistor T1, which has an adverse effect on the output swing of the transister T1. In accordance with the invention this drawback can be avoided by arranging the base-emitter junction of a further transistor in parallel with the base-emitter junction of the transistor T1. When this further transistor is given a smaller emitter area than the transistor T1 a replica of the emitter current of the transistor T1 is obtained, the magnitude of this emitter-current replica being dictated by the ratio between the respective emitter areas. This sub-current can subsequently be employed for generating a correction current. Fig. 2 shows the circuit diagram of a transistor arrangement in accordance with the invention, in which the transistor T1 constitutes a first branch and the NPN transistor T2 constitutes a second branch of a voltage-to-current converter. The respective bases of the transistors T1 and T2 constitute the input terminals 9, 10 of the arrangement, for receiving a signal voltage Vi, while the collectors of the two transistors T1 and T2 constitute the respective collector terminals 11, 12 for the connection of a load circuit. In the embodiment shown in Fig. 2 the collector terminal 12 is connected directly to the power supply terminal 1 of the arrangement and the collector terminal 11 is connected to this power-supply terminal via a load resistor R3. To obtain the d.c. bias of the transistors T1 and T2 their respective emitter terminals 13, 14 are each connected to the power-supply terminal 2 of the arrangement via a current-reference circuit 15, 16. The term "current-reference circuit" is to be understood to mean a circuit through which a specific substantially constant direct current flows and whose impedance for a signal current is comparatively high. Such circuits are generally known per se and require no further explanation. Moreover, the emitters of the transistors T1 and T2 are interconnected via an impedance, in the present embodiment a resistor R1. A signal voltage Vi applied to the input terminals 9, 10 is converted into a proportional signal current I1 through the resistor R1, which signal current flows via the two collector-emitter paths of the transistors T1 and T2 and the load resistor R3. As described above, the base-emitter junctions of the transistors T1 and T2 will give rise to a distortion component. If it is assumed that two reference-signal sources 15, 16 each carry a direct current It the signal voltage Vi may be expressed as follows in terms of signal current I1: Vi = Vbe2 + I1 R1 · Vbe1 where Vbe1 = the base-emitter voltage of the transistor T1 and Vbe2 = the base-emitter voltage of the transistor T2. Using the logarithmic relationship between the base-emitter voltage and the base-emitter current it follows that: Vi=(kT/q)ln {(It+I1)/(It-I1)} + R1 I1 The logarithmic term dictates the distortion component Id in the current through the load resistor R3. In order to obtain a replica of the respective emitter currents of the transistors T1 and T2, in accordance with the invention, the NPN transistors T3 and T4 are provided in the arrangement. The transistor T3 has its base-emitter junction connected in parallel with the base-emitter junction of the transistor T1 and the transistor T4 has its base-emitter junction connected in parallel with the base-emitter junction of the transistor T2. The collector terminals 17, 18 of the transistor T3 and T4 respectively are each connected to the power-supply terminal 1 via series arrangements 19, 20 comprising two elements with a semiconductor junction. In the Figure, the series arrangements 19, 20 comprise diode-connected transistors, but it is obvious that these may be replaced by conventional diodes. Although the Figure shows two elements in each series arrangement these series arrangements may generally comprise m elements, where m is an integer larger than 1. If the emitter areas of the transistors are in the following ratio: T1 : T2 : T3 : T4 = 2n : 2n : 1 : 1 where n = a positive integer, a sub-current equal to (It - I1)/(2n + 1) will flow through the series arrangement 19 and a sub-current equal to (It + I1)/(2n + 1) will flow through the series arrangement 20. This results in a logarithmic voltage Vf between the collector terminals 17, 18 of the transistors T3 and T4 respectively, which voltage is equal to: Vf = m(kT/q) ln [{(It+I1)/(2n+1)}/{(It-I1)/(2n+1)}] = m(kT/q) ln {(It+I1)/(It-I1)} which relates to the general case in which the series arrangements 19, 20 each comprise m elements with a semiconductor junction. When the factor m is ignored the voltage Vf depends on the emitter current of the transistors T1 and T2 in the same way as the respective base-emitter voltages. In accordance with the invention a further voltage to current converter is provided to convert the voltage Vf into a correction current for the distortion component of the current through the load resistor R3, which converter comprises the NPN transistors T5 and T6, a resistor R2 and current-reference circuits 21, 22. The bases of the transistors T5 and T6 are connected to the collector terminals 17, 18 respectively, the collector of the transistor T5 being connected to the power-supply terminal 1 and the collector of the transistor T6 being connected to the collector terminal 11 of the transistor T1. In the same way as in the voltage-to-current converter comprising the transistors T1 and T2, the emitters of the transistors T5 and T6 are interconnected via a resistor R2 and their d.c. settings are provided by current reference circuits 21, 22. The d.c. bias current Iv of the current-reference circuits 21, 22 can be substantially smaller than the bias current It of the current-reference circuits 15, 16 because the transistors T5 and T6 need supply only a current of the same magnitude as the distortion component. This means that the collector currents of the transistors T5 and T6 themselves will exhibit in a negligible distortion component. Using relationship (2) it follows that the current in the collector of the transistor T6 is then equal to Iv+I2=Iv-Vf/R2=Iv-m kT/(qR2) ln{(It+I1)/(It-I1)} Subsequently, using equations (1) and (3) it follows that the current Io through the load resistor R3 is: Io = It-I1+Iv+I2 Io = It-Vi/R1+kT/(qR1) ln{(It+I1)/(It-I1)} + Iv-m kT/(qR2) ln{(It+I1)/(It-I1)} The logarithmic distortion component can now be compensated for effectively if: m/R2 = 1/R1 or R2 = m R1 This simple relationship follows from the fact that the circuit for generating the correction component employs a voltage-to-current converter of a construction similar to that used in the transistor arrangement itself. Fig. 3 shows a voltage-to-current converter similar to the arrangement shown in Fig. 2 but in which the transistor T1 is split up into two sub-transistors T1′ and T1″. The base-emitter junctions of these sub-transistors T1′ and T1″ are arranged in parallel, the emitters of the transistors T5 and T6 being connected to the respective collectors of said sub-transistors. The load resistor R3 is arranged in the collector line of the transistor T6, the collector of the transistor T5 being connected directly to the power-supply terminal 1. The two sub-transistors T1′ and T1″ provide the d.c. settings of the transistors T5 and T6, so that in contradistinction to the arrangement shown in Fig. 2 no separate current-reference circuits 21, 22 are needed. In a similar way as for the arrangement shown in Fig. 2 it can be demonstrated that if the emitter areas of the transistors are in the following ratio: T1′ : T1″ : T2 : T3 : T4 = n : n : 2n : 1 : 1 the distortion component in the current Io is compensated for effectively if: R1 : R2 = 1 : (2n + 1) m/n In addition to the advantage that separate current-reference circuits 21, 22 may be dispensed with, splitting the transistor T1 in two sub-transistors T1′, T1″,has the advantage that the d.c. component through the load resistor R3 in the given example is approximately half the direct current through the load resistor R3 in the arrangement shown in Fig. 2. As a result of this, the output swing of the arrangement will be situated even closer to the maximum output swing as dictated by the power-supply voltage. If an arrangement having a symmetrical output is required the transistor T2, in the same way as the transistor T1, can be divided into two sub-transistors to which a voltage-to-current converter comprising the transistors T5 and T6 and a resistor R2 (not shown) is connected. Fig. 4 shows the circuit diagram of a voltage-to-current converter based on the arrangement shown in Fig. 3 and comprising a control circuit for controlling the current through the load resistor R3. This control circuit comprises the NPN transistors T8 and T9, which are arranged as a differential pair 23 and to whose common emitter terminal the collector of the transistor T6 is connected. The collector of the transistor T9 is connected directly to the power-supply terminal 1, and the collector of the transistor T8 constitutes an output terminal 24 for connecting a load circuit, in the present case the resistor R3. The current through the resistor R3 can be influenced by applying a control voltage to the bases of the transistors T8 and T9. Fig. 5 shows a further embodiment based on the principle illustrated in Fig. 4, in which a plurality of differential transistor pairs 21 are connected to the collector of the transistor T5, which for this purpose comprises a multi-collector terminal. As is shown, the base of one transistor T9 of the differential pairs is connected to the power-supply terminal 2 and the base of the other transistor T8 is provided with a terminal 25, 27 for applying a control voltage. The current through the load resistor R3 can be controlled in steps, for example by means of a digital signal. Although only two differential pairs 23 are shown it is obvious that the arrangement may be extended to comprise further differential pairs. In the embodiment of the invention shown herein all the transistors are NPN transistors. Of course, it is possible to replace these by PNP transistors, in which case, for example, for the voltage-to-current converter in the correction circuit and for the transistors T5 and T6 field-effect transistors may be used instead of the bipolar transistors, or voltage-to-current converters of a different construction. Instead of the resistors R1, R2, R3 it is possible to utilise, for example, frequency-dependent impedances or further semiconductor components. Instead of a symmetrical input the voltage-to-current converter comprising the transistors T1 and T2 may have an asymmetrical input, which can be achieved for example by connecting the base terminal 19 to the power-supply terminal 2. The invention is very suitable for use in integrated circuits, for example to form an analog multiplexer with very good distortion characteristics, for which purpose the resistor R3 may be provided with a plurality of compensation circuits which can be selected by means of differential current switches.

Claims: A bipolar transistor circuit with compensation for a distortion component of a transistor collector current which is determined by a base-emitter voltage of the transistor, said circuit comprising: an input terminal (5; 9) for receiving a signal voltage, an output terminal (3; 11) for connection to a load circuit (R c ; R₃), at least one main transistor (T₁) having a collector coupled to the output terminal (3; 11), a base coupled to the input terminal (5; 9), an element (7; 19) for developing a voltage across the element as a function of a current flowing therein, means (6; T₃) coupled to the main transistor (T₁) for supplying a sub-current to the element (7; 19) which is proportional to the collector current through the main transistor (T₁), the means (6; T₃) comprising a parallel transistor (T₃) of the same conductivity type as the main transistor (T₁) and having its base connected to the base of the main transistor (T₁) and having its collector coupled to the element in a collector terminal (17), and voltage/current conversion means (8) coupled to the element (7; 19) and to the output terminal (3; 11) for supplying a correction current to the output terminal (3; 11) which is proportional to the voltage across the element to compensate the distortion component, the voltage/current conversion means comprising a first conversion transistor (T₅) of the same conductivity type as the main transistor (T₁) and having its base connected to the collector terminal (17), characterized in that the element (7; 19) comprises at least one semiconductor junction, the parallel transistor (T₃) has a smaller emitter area than that of the main transistor (T₁), the emitter of the parallel transistor (T₃) is connected to the emitter of the main transistor (T₁), the main transistor (T₁) and the parallel transistor (T₃) thereby forming a common base terminal (9) and a common emitter terminal (13), the collector of the parallel transistor (T₃) being coupled to the element (7; 19) and to the voltage/current conversion means (8), and the voltage/current conversion means (8) comprise a second conversion transistor (T₆) of the same conductivity type as the main transistor (T₁) and a first impedance (R₂), the emitters of the first (T₅) and second (T₆) conversion transistors being coupled via the first impedance (R₂) and the collector of the second conversion transistor (T₆) being coupled to the output terminal (3; 11). A bipolar transistor arrangement as claimed in Claim 1, characterized in that the main transistor (T₁) constitutes a first branch of a differential transistor arrangement having a second branch including: a second main transistor (T₂) and a second parallel transistor (T₄), both of the same conductivity type as the first main transistor (T₁), and having their respective base-emitter junctions connected in parallel to form a second common base terminal (10) and a second common emitter terminal (14), the second parallel transistor (T₄) having a smaller emitter area than the second main transistor (T₂), a second element (20) comprising at least one semiconductor junction coupled to the collector of the second parallel transistor (T₄) in a second collector terminal (18), the base of the second transistor (T₆) being connected to the second collector terminal (18), and in that the bipolar transistor arrangement further includes: a second impedance (R₁) connected between the first (13) and second (14) common emitter terminals, and first (15) and second (16) bias current sources, coupled to the first common emitter terminal (13) and the second common emitter terminal (14); respectively. A bipolar transistor arrangement as claimed in Claim 2, characterized in that the bipolar transistor arrangement further comprises a third bias current source (21) coupled to the emitter of the first conversion transistor (T₅) and a fourth bias current source (22) coupled to the second conversion transistor (T₆). A bipolar transistor arrangement as claimed in Claim 2, characterized in that the first main transistor (T₁) comprises two sub-transistors (T₁′, T₁″) of the same conductivity type, the sum of the emitter areas of the two sub-transistors (T₁′, T₁″) being equal to the emitter area of the first main transistor (T₁), the base-emitter junctions of the two sub-transistors (T₁′, T₁″) being connected in parallel, the collector of one of the two sub-transistors (T₁′) being connected to the emitter of the first conversion transistor (T₅) and the collector of the other sub-transistor (T₁″) being connected to the emitter of the second conversion transistor (T₆). A bipolar transistor arrangement as claimed in Claim 3, characterized in that the first (19) and second (20) elements each comprise a series arrangement of m diodes or m diode-connected transistors, m being an integer greater than 1, the emitter areas of the first (T₁) and second (T₂) main transistors being substantially equal and the emitter areas of the first (T₃) and second (T₄) parallel transistors being substantially equal and in that the first (R₂) and second (R₁) impedances comprise a first (R₂) and a second (R₁) resistor, respectively, whose resistance values are in a ratio of m : 1. A bipolar transistor arrangement as claimed in Claim 4, characterized in that the first (19) and second (20) elements each comprise a series arrangement of m diodes or m diode-connected transistors, m being an integer greater than 1, the sum of the emitter areas of the two sub-transistors (T₁′, T₁″) and the first parallel transistor (T₃) being substantially in a ratio of 2n : 1 and the emitter areas of the second main transistor (T₂) and the second parallel transistor (T₄) also being substantially in a ratio of 2n : 1, n being a positive number, and in that the first (R₂) and second (R₁) impedances comprise a first (R₂) and a second (R₁) resistor, respectively, whose resistance values are in a ratio of (1 + 2n)m/n : 1. A bipolar transistor arrangement as claimed in any one of the preceding Claims, characterized in that the output terminal is connected to a common emitter terminal of a differential transistor pair (23), the collector of one of the transistors (T₈) of the differential transistor pair (23) constituting a controlled output terminal (24) for connection of the load circuit (R₃) and the bases of the transistors of the differential transistor pair (23) constituting terminals (25, 26) for applying a control voltage for controlling the current to the controlled output terminal (24). A bipolar transistor arrangement as claimed in Claim 8, characterized in that the transistor (T₆) whose collector is connected to the output terminal is constructed as a multi-collector transistor, each of the individual collectors of the multi-collector transistor being coupled to a respective common emitter terminal of a plurality of said differential transistor pairs having a respective collector connected to the controlled output terminal (24).

Inventors: RUTTEN IVO WILHELMUS JOHANNES, VAN DE GRIFT ROBERT EMILE JOHA, RUTTEN, IVO WILHELMUS JOHANNES MARIE, VAN DE GRIFT, ROBERT EMILE JOHAN
Applicants: PHILIPS ELECTRONICS NV, PHILIPS ELECTRONICS N.V.
Application year: 1990
Main classification: H03F1
IPC codes: H03F3, H03G3, H03F1