Circuit logique à transistor

摘要

1,118,640. Logic circuits. HITACHI Ltd. 3 Nov., 1965 [21 Nov., 1964; 28 June, 1965], No. 46580/65. Heading H3T. A logic circuit comprises a plurality of transistors having their emitters connected via a common resistor to a power supply point and their collectors via another common resistor to another power supply point, means being provided to detect changes in the collector/emitter voltages and to feed such changes back to the common collectors. Such a circuit provides direct and inverted outputs and can be coupled to one or more succeeding stages. The collector resistor also serves to prevent ringing if the load is capacitative, by feeding back a voltage through the base-collector capacitance when this becomes forward biased. It is arranged that the transistor becomes saturated only on the overshoot of voltage due to ringing, thus preserving fast response. Fig. 3 shows two cascaded AND circuits with extra transistors Tr1 and Tr2 which stabilize the emitter-collector potentials of the logic transistors and thus facilitate the elimination of the ringing. Transistors Tr1 and Tr2 are normally cut off but if the collector voltage at c or c1 falls or rises emitter current will flow in Tr1 or Tr2 respectively to restore the voltage to its former level. R 1 and R 1 1 may be replaced by diodes, and R 3 and R 3 1 may be omitted; stabilization may be improved by a further resistor between the emitter of Tr1 or Tr2 and c or c1 respectively (Fig. 8, not shown).