GB1275645A - Transistor switching circuit - Google Patents

Abstract

1275645 Transistor logic circuits PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 12 June 1969 [15 June 1968 26 Sept 1968] 29783/69 Heading H3T [Also in Division H1] An integrated gating circuit has two transistors such as T7, T10 the base of one T7 receiving two inputs via respectively a diode D5, and the other transistor T10, which has its collector connected to T7 base, its base through a resistor to the supply, and its emitter (of which it has at least one) to the second input. T7 base will go negative if a negative potential is applied to the diode D5 cathode, or to the T10 emitter since the base emitter current causes a substantial voltage drop across the base resistor. If the T10 emitter is positive, the base potential of T10 is able to go positive and this causes forward conduction of T10 collector junction to apply a positive potential to T7 base, provided D5 is also receiving a positive input. The circuit of Fig. 4 (block diagram, Fig. 3, not shown) incorporating this gating circuit is a clocked D-type bi-stable. The two pairs of transistors T1, T2 and T3, T4 are cross-coupled through the diode D3 in one direction, and in the other through gating transistors T7, T8, T10, T11. The transistors T7, T8 and also T5, T6 are all in parallel and constitute effectively a NOR gate (1) inupt to the transistor T4 of the bi-stable. The transistors T11, T10 and also T9 effectively constitute AND gates (3, 4, 5) feeding respective inputs T8, T7, T6 of the NOR gate (1) and each receives two inputs: T11 (3) receives the Q2 output of the bi-stable from T2 collector, and a clock pulse double-inverted by T15, T16 (7, 8) from D10; T10 (4) receives the Q2 output also, and the D input from D5; and T9 (5) receives an inverted clock pulse from T13, and the D input from D6. T5 receives the reset input R from T12. The diodes D5, D6 are said to be better able to withstand the higher voltage signals which they apply from an external source to an integrated circuit than are the emitter-base diodes whose use in the gate circuits is confined to lower voltage signals originating within the i.c. The diodes D5, D6 are formed as collector-emitter functions. A diode D1 reduces collector currents, and also limits the collector voltage of, for example, T13, T16 when these are non-conductive this voltage being applied to the emitters of the gating transistors T9, T11. A simple bi-stable (Fig. 2, not shown) has two transistors (T2, T4) similar to T7 cross-coupled through their respective associated transistors (T1, T3) such as T10. The collector loads (of T2, T4) each comprise a resistor and a diode, their commoned emitters are connected through series diodes to the supply, and the respective diodes (D1, D2) corresponding to D5 receive set and reset signals.