GB1100262A - Improvements in or relating to logic circuits - Google Patents

Abstract

1,100,262. Half adders. PLESSEY UK Ltd. 23 July, 1964 [31 July, 1963], No. 30408/63. Heading G4A. [Also in Division H3] A logic circuit suitable for use in an adding circuit comprises two transistors each connected with a third to form a long tail pair, the output voltage of the third transistor switching between two levels one of which is determined by saturation of the transistor. Fig. 7 shows a circuit for producing a " carry " signal by performing the logic operation (A.B) + (B.C) + (C.A) in which transistor sections J 13B and J 14B for negative signals perform the operation A.B at the common emitter connection and sections J 14A and J 15B and J 13A , J 15A similarly perform the operations B.C and C.A. The multi-emitter transistor J 8 then performs the required OR operation, the " 1 " signal level being defined at the collector of J 8 by its saturation voltage and at the output of the succeeding emitter follower in addition by the voltage of the emitter junction of the emitter follower. The 0 level is defined by the voltage drop across transistor J 11 connected as a diode and the emitter base voltage of the emitter follower. In alternative AND, OR arrangements the multi emitter transistors are replaced by a single transistor and the diode connected transistor J 11 by a potentiometer formed by the collector resistor (R 2 , Fig. 1, not shown) and a resistor (R 3 ) from the collector to earth. The circuits described may be followed by inverters (Figs. 2, 5 and 8, not shown) comprising common emitter pairs with outputs derived from either or both collectors via a resistor circuit (R 6 , R 7 ) or via a transistor (J 12 ) strapped as a diode.