GB1048012A - Improvements in or relating to transistor switching circuits - Google Patents

Abstract

1,048,012. Transistor switching circuits. INTERNATIONAL BUSINESS MACHINES CORPORATION. July 4, 1963, No. 26474/63. Heading H3T. A transistor has a load switchable between high and low resistance states and is arranged such that when the resistance state is high the transistor is saturated and when it is low it is unsaturated and carries a higher current. In Fig. 3, when the load transistors 20 and 60 are non-conducting transistor 23 is saturated and its emitter current flows to its base. If either or both transistors 20 or 60 are rendered conductive transistor 28 comes out of saturation and an output signal is available at the collectors 20 and/or 60 or at the collector of 28. The circuit may be inhibited by rendering conducting a transistor 68 so as to divert the emitter current supply from 28. An inverted output may be obtained from the collector of a further transistor 92 (Fig. 4, not shown) having its emitter connected to the base of 28, the further transistor being rendered conducting by the base current of 28 when the load transistors 20 and 60 are non-conducting. An " exclusive OR " circuit may be formed (Fig. 7) from two sub-circuits each comprising transistors 20, 28 and 68 with each input signal applied in parallel to the normal input of a respective one and the inhibit input of the other. No output current flows when both signals are " 0 " or both " 1 " but if either alone is " 1 " an output will be obtained from the common collector load of the transistors 20. Fig. 7 illustrates a 3-level circuit. When V IN is positive transistor 20 cuts off and - V appears at the output terminal. When V IN is near earth, transistor 100 becomes unsaturated and its current flows in the output circuit. If V IN is positive both transistors 100 and 28 become unsaturation and a higher current flows in the output circuit.