GB970415A - Improvements relating to electronic coupling circuits - Google Patents

Abstract

970,415. Transistor amplifying circuits. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. July 26, 1961 [Aug. 16, 1960], No. 28312/60. Heading H3T. In a coupling circuit comprising a first transistor T2 with the input applied to its base, and the output taken from its collector, the emitter circuit includes a constant current device and the collector load comprises the emitter collector circuit of a second transistor T3, the base of which is capacity coupled to the emitter of transistor T2. The constant current device comprises a further transistor T1 whose base is connected to a constant potential. When an input signal is applied to T2, its emitter moves in phase with the signal applied to its base and the change in potential is transmitted through capacitor C1 to the base of transistor T3. This transistor functions as an emitter follower so that the potential at its emitter, and at the collector of T2, also follows the input signal. Thus both emitter and collector of T2 follow the base giving a high input impedance. Resistors R4, R5, R6 control the voltage drop across T2 and T3, and a further capacitor C2 is connected between the junction of T2, T3 and the junction between R5, R6 to magnify the value of R5 and thus reduce its shunting effect.