GB881182A - Improvements in or relating to transistor switching circuits - Google Patents

Abstract

881,182. Transistor pulse amplifying circuits. AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd. Aug. 17, 1960 [Sept. 18, 1959], No. 31805/59. Class 40(6). In a transistor pulse amplifying circuit rectangular positive-going pulses are applied to the base of an NPN transistor TX1 which is normally biased to cut-off by a negative bias over resistor R1, and drive it to saturation. Amplified pulses from the collector circuit are applied to the bases of a number of parallel-connected PNP transistors TX2, each of which is normally biased to cut-off by a. positive bias over an individual resistor R3, again driving them to saturation. To prevent lengthening of the pulses due to charge-storage in the transistors at saturation, they are also applied over a differentiating circuit Cl, R2 to a further PNP transistor TX3 which is normally biased to cut-off by a positive bias over resistor R2. The negative-going "spikes" produced by differentiation from the trailing edges of the incoming pulses drive transistor TX3 conductive to discharge the bases of each of the transistors TX2, via individual diodes Dl, and return these transistors to the cut-off state at the ends of the incoming pulses. To prevent ringing due to stray capacity and caused by the transistor TX3 being still driven by the differentiated pulses when transistors TX2 have returned to cut-off, a conductive path may be provided for its collector current in the shape of diode D2.