Patent GB-1376462-A (GB)
Title: Amplifiers
IPC: H03F1/56
Filed: 1972-02-08
Abstract: 1376462 Amplifiers WESTERN ELECTRIC CO Inc 8 Feb 1972 [8 Feb 1971 (3) 22 March 1971 6 Dec 1971 (2)] 5765/72 Heading H3T [Also in Division H1] An amplifier coupling between an input signal source and output load, both of specified impedances, includes a pair of active amplifier stages whose transmission coefficients are substantially equal, whose input reflection coefficients relative to the source impedance are substantially equal in magnitude but opposite in sign and whose output reflection coefficients relative to the load impedance are substantially equal in magnitude but opposite in sign, an input multiport coupler one port of which comprises the input port of the amplifier, an output multiport coupler one port of which comprises the output port of the amplifier, each of the amplifier stages being coupled between a different port of the input coupler and a different port of the output coupler, and a matching impedance connected to at least one port of each of the couplers for matching the source impedance and the load. The arrangement in general comprises input and output 3dB hybrid couplers, e.g. magic T couplers or hybrid transformers 10, 11 respectively, Fig. 1, each coupler having four branches arranged in pairs 1-2 and 3-4 and 1<SP>1</SP>-2<SP>1</SP>, 3<SP>1</SP>-4<SP>1</SP> respectively, where the branches of each pair are conjugate to each other and in coupling relationship with the branches of the other pairs: the coupled signals are either in phase of 180 degrees out of phase. The amplifiers 12, 13 are such that the product of their input impedances is equal to the source impedance and the product of their output impedances equal to the load impedance: output and input of the arrangement are connected to ports 1, 1<SP>1</SP> respectively and terminating resistors 14, 15 respectively of the same value as the source and load impedances are connected to ports 2, 2<SP>1</SP> respectively. One embodiment uses couplers comprising input transformers T1, T2, Fig. 3, and output transformers T1<SP>1</SP>, T2<SP>1</SP>: amplifier 30 comprises a grounded base transistor and amplifier 31 a grounded collector transistor, together with impedance transforming transformers T3, T4 and T5, T6 respectively. The pairs of transformers T1, T3; T2; T5; T2<SP>1</SP>, T4 and T1<SP>1</SP>, T6 may be replaced by single transformers (Fig. 4, not shown): in a simplification of this a single input transformer T40, Fig. 5, and output transformer T40<SP>1</SP> are used. The transistors may be replaced by corresponding Darlington pairs (Fig. 7, not shown). Amplifiers utilizing combinations of a grounded base stage and a grounded collector stage to provide either high input and output impedance or low input and output impedance may also be used (Figs. 8A, 8B and 9, not shown). The arrangement may be applied, as a coupling circuit utilizing amplifiers 30, 31, Fig. 6, to the type of amplifier in which the output from a main signal amplifier 42 is combined with the output from an auxiliary amplifier 44 which amplifies only distortion and noise signals, whereby the distortion and noise are cancelled out in the output load 43. In a further embodiment, six port input and output hybrid couplers (see Division H1) 90, 91 respectively, are used Ports 4a, 4b are connected in series and coupled to the bases of parallelconnected emitter-followers 106, 107 while ports 3a, 3b are connected in parallel and drive grounded-base transistors 104, 105 in push-pull: the commoned emitters of transistors 106, 107 are connected to ports 3a<SP>1</SP>, 3b<SP>1</SP> arranged in parallel, while the collectors of transistors 104, 105 drive into ports 4a<SP>1</SP>, 4b<SP>1</SP> arranged in series. In a modification, the emitters of transistors 106, 107 are not connected together, but the one is connected to port 3a<SP>1</SP> and the other to port 3b<SP>1</SP>, these ports also being separated [Fig. 11 not shown). Transistors 105, 107 may alternatively be omitted, coupler sub-branches 3a and 4b<SP>1</SP> then being grounded. The Specification also describes modified arrangements in which the power is not equally divided between the two branches of the amplifier (Figs. 13, 14, not shown). In one embodiment of this kind, the input and outputs connections comprise auto-transformers 190, 190, Fig. 15, and the matching impedances 194, 195 respectively are connected across the outer ends of the windings. The Specification describes further modifications using impedance-transforming transformers or auto-transformers (Figs. 16-21, not shown). In a final embodiment, the signal from source 117, Fig. 22, having internal impedance 126 is directly connected to amplifier 12 which has high input impedance and low output impedance, and to amplifier 13 which has low input impedance and high output impedance, via series-connected matching impedance 171. A similar arrangement is used to couple the outputs of the amplifiers to the load 18.