GB2210527A

GB2210527A - An integratable push-pull amplifier

Info

Publication number: GB2210527A
Application number: GB8822377A
Authority: GB
Inventors: Johann Mattfield
Original assignee: Telefunken Electronic GmbH
Current assignee: Telefunken Electronic GmbH
Priority date: 1987-09-30
Filing date: 1988-09-23
Publication date: 1989-06-07
Anticipated expiration: 2008-09-23
Also published as: GB2210527B; DE3732872C1; GB8822377D0; JPH01109805A; KR890005976A

Description

2210527 Integrated Transistor Push-Pull Amplifier The invention relates to

a transistor push-pull ampli fier having a complementary push-pull B final stage and complementary driver transistors, with one driver tran sistor and one transistor of the final stage together constituting a complementary Darlington circuit.

A transistor push-pull amplifier having a push-pull driver stage, two complementary transistors and a push pull B final stage likewise containing two complementary transistors is known from DE-PS 25 54 770.

Figure 1 shows the circuit of a transistor push-pull amplifier in accordance with the above publication, where the complementary driver transistors (T 31 T4), whose emitters are directly connected to one another, are used to actuate the complementary push-pull B final stage (T1, T2). Since the DC voltage potential of these emit ters is about half the operating voltage potential, these emitters can be connected to the link between the two collectors of the final stage transistors (T1, T2). The connection of the two collectors of the end-stage tran sistors must have a DC voltage corresponding to half the operating voltage in order to attain a high power output.

To avoid amplification-reducing negative feedback this connection is made via a filter section-comprising two resistors (R,, R 6) and a capacitor C.

A transistor push-pull amplifier having this circuit structure cannot be integrated, since the capacitor C of the filter section cannot be integrated into this cir cuit because of the high capacitance value (22 pP in the 2 cited reference). Therefore the connection point between the filter section resistors (Rp R 6) and the emitters of the driver transistors T 3' T 4 would have to be design ed as an external connection point, entailing additional costs. A further drawback of this circuit according to the prior art is that the minimum operating voltage of approx. 2.3 V is relatively high. This value results from the fact that there ar.e up to four diodes connected between the terminals of the operating voltage sources in this circuit.

The object of the invention is therefore to provide a transistor push-pull amplifier of the type mentioned at the outset that is integratable and so designed that the minimum permissible operating voltage is less than 2 V.

The object is achieved in accordance with the invention by the bases or emitters of the driver transistors being connected to one another by a diode in each case, by the emitters of a complementary transistor pair being con nected in cross-coupled manner and with the same elec trical direction to one emitter each of the driver tran sistors, by the collectors of the transistor pair each being connected to one terminal of the operating voltage source, by a first or second resistor being connected between the first or second terminal respectively of the operating voltage source and the base of the transistor of'the transistor pair that is connected to said first or second terminal, and by three series-connected diodes connecting the two bases of the transistors of the tran sistor pair.

In an advantageous embodiment of the invention the diodes of the transistor push-pull amplifier are connected in 3 the conducting direction as regards the operating volt age.

This circuit is integratable thanks to the embodiment of the transistor push-pull amplifier in accordance with the invention, with its manufacture not entailing any unacceptable modification of the technology. In addition, there is a minimum permissible operating voltage of 1.7 V, as there cannot be more than three flow paths of diodes or transistors between the termina'ls of the ope rating voltage source. In addition, the circuit portion between the emitters of the driver transistors T 3 and T4 and the reference potential has dynamic low impedance and is designed so that around half the operating volt age drops at these emitters.

An embodiment of the invention is shown in Figure 2 and is described in detail in the following.

The integratable transistor push-pull amplifier accord ing to the invention and shown in Figure 2 has two con nections 1, 2 for supplying AC signals of voltage UE to be amplified by the amplifier, where connection 2 is earthed and connection 1 is linked to the base of a tran sistor T 5 via a capacitor C E' the emitter of said tran sistor being connected to earth potential and the collec tor of said transistor being connected firstly to the base of a pnp-driver transistor T 4 and secondly to the base of the npn-driver transistor T 3 via a diode D 1 con nected in the conduction direction as regards the operat ing voltage, such that the transistors T 3 and T 4 form a complementary push-pull driver stage whose emitters are connected to one another via a diode D2. The base of the driver transistor T 3 is in addition connected via a cur- 4 rent source Q, to a connection 3 of an operating voltage source supplying a positive DC voltage U B Whereas the collectors of-the transistors T1 and T2 are directly connected to one another, the collector of the driver transistor T3 is connected to the base of the pnp-tran sistor T1 and the collector of driver transistor T 4 to the base of the npn-transistor T 2. Transistor T 1 and T2 constitute a complementary push-pull B final stage, with the emitter of the final stage transistor T1 being con nected to the positive operating potential of connection 3 and the emitter of the final stage transistor T2 being connected to earth potential.

The two interconnected collectors of the final stage transistors T 1 and T2 are firstly connected to a connec tion 4 via a capacitor C L$ said connection constituting together with a connection 5 at earth potential the out put of the transistor push-pull amplifier. Secondly, the connection point between the collectors of the final stage transistors is connected to the base of the input transistor T 5 via a resistor R2. A resistor R 1 is provid ed between the base of this input transistor and the reference potential. The capacitor CE is used for cou pling the input signal U E Apart from the complementary transistors T 3 and T 41 and T 1 and T 2 in the driver stage and in the push-pull B final stage respectively, ' the transistorg T 1 and T 31 and T 2 and T4 respectively are also complementary to one another.

A further complementary transistor pair crises the transistors T and T whose emitters are mutually inter- 6 71 connected to the emitters of the driver transistors T 3 and T 4 such that the emitter of the npn-transistor T6 is connected to ' the emitter of the pnp-transistor T4 and at the same time to the anode of diode D 21 and the emitter of pnp-transistor T 7 to the emitter of npn-transistor T 3 and at the same time to the cathode of diode D2, while the collector of transistor T 6 or T 7 is connected to the positive operating potential of connection 3 or to the earth potential respectively. In addition, the base of transistor T 6 is connected via a resistor R 3 to the po sitive operating potential of connection 3, and the base of transistor T 7 via the resistor R 4 to earth potential.

Furthermore, the bases of transistors T 6 and T 7 are con nected via three diodes D 31 D 41 and D 5 connected in series and in the conducting direction as regards the operating voltage, thereby providing a voltage divider together with resistors R 3 and R 4 The identically sized resistors R 3 and R 4 ensure that the DC voltage at the emitters of transistors T 3 and T 4 corresponds to approx imately half of the operating voltage. Since there are a maximum of three diodes in each series circuit between the terminals of the operating voltage source in this circuit array according to the invention, the resultant minimum permissible operating voltage is around 1,7 V.

6

Claims

Patent-Claims

1) A transistor push-pull amplifier having complementary push-pull B final stage (T1, T 2) and a complementary driver transistors (T 31 T 4), with one driver transistor (T3 or T4) together with one transistor of the final stage (T1 or T 2) each constituting a complementary Dar lington circuit, wherein the bases or emitters of the driver transistors (T 31 T 4) are connected to one another by a diode D 1 or D 2 respectively, wherein the emitters of a complementary transistor pair (T6, T 7) are connect ed in cross-coupled manner and with the same electrical direction to one emitter each of the driver transistors (T 33 T 4), wherein the collectors of the transistor pair (T6) T7) are each connected to one terminal of the ope rating voltage source, wherein a first or second resis tor (R3 or R 4) is provided between the first or second terminal respectively of the operating voltage source and the base of that transistor of the transistor pair that is connected to said first or second terminal, and wherein three series-connected diodes D 31 D 41 and D 5 connect the two bases of the transistors of the transi stor pair (T 62 T7).

2) A transistor push-pull amplifier according to Claim 1, wherein the diodes (D1, D2, D 31 D41 and D 5) are connected in the conducting direction as regards the operating voltage.

7 3 A transistor push-pull amplifier having a complementary push-pull B final stage and complemdntary driver transistors, with one driver transistor and one transistor of the final stage together constituting a complementary Rarlington circuit, wherein the respective bases and re^spective emitters of the two driver transistors are each connected by a diode, and wherein a further complementary transistor pair, with a potential divider formed of resistors and diodes. connected across the operating voltage source of the amplifier provides a suitable reduced operating potential between the emitters of the driver transistors.

4TP. Further copies m a Published 1988 at The Patent, OricE. Sta,e House. 6671 High Holborr'. London WC1R ' be obtained from The Patent Office, Sales Branch. S, Many Cray. Orpington, Kent BR5 3RD, Printed by Multiplex techniques ltd. St Mary Cray, Kent. Con 1187 -