Low-dissipation output stage for binary transmitters

Abstract

Two driving transistors controlled in push-pull by an input stage responsive to incoming binary signals are connected in a common-collector mode across a direct-current source in series with a high-current generator, with interposition of two switching transistors between this generator and the emitters of the driving transistors. The line wires are tied to these emitters and also to two low-current generators each shunting the combination of the high-current generator with the respective switching transistor. The input stage comprises two control transistors operated in push-pull--directly or via respective pilot transistors--by the incoming signal; the collectors of these control transistors are tied to the bases of the driving transistors while their emitters are joined in parallel to another low-current generator connected in series therewith across the source. The bases of the switching transistors are biased by the input stage to turn either of them on when the respectively associated driving transistor is in a high-impedance state whereby line current passes through the other driving transistor, the conductive switching transistor and the high-current generator.