GB817094A - Improvements in and relating to electric signal translating circuits employing semi-conductor devices - Google Patents

Abstract

817,094. Transistor switching and pulse modulation circuits. ENGLISH ELECTRIC CO. Ltd. Dec. 23, 1955 [Dec. 24, 1954], No. 37391/54. Classes 40 (5) and 40 (6). In a switching or gating circuit, the emittercollector path of a junction transistor is connected in a controlled circuit, potentials being applied to the base so that one potential has a value such that the transistor operates in the bottomed condition. In this condition the base current is equal to or greater than that corresponding to the greatest curvature of the base current/emitter-collector potential curve. In a series gate, Fig. 7, when the potential to which the base resistor Rb is lowered sufficiently there is a negligible potential drop between the emitter and collector and the potential appearing across the load R L is that of the source Eg diminished by the potential drop across the internal impedance Rg. In the cut-off condition the potential appearing across the load is only that due to leakage current. A shunt gate, Fig. 8, is arranged so that when the transistor is off the source potential appears across the load R L diminished by the drop across the internal impedance Rg. When the transistor is on, there is a virtual short-circuit across the load. Pulse amplitude modulation circuit.-By applying a pulse train S 1 , Fig. 9b, to the resistor Rb in Fig. 7 and a modulating signal as the source Eg, an output wave e o appears across the load R L . In a similar manner by employing a pulse train S 1 , Fig. 10b, applied to the base of the transistor in Fig. 8, a wave C o may be derived from the load R L .