GB1164167A - Improvements in and relating to Switching Circuits - Google Patents

Abstract

1,164,167. Transistor current switching logic circuits. INTERNATIONAL BUSINESS MACHINES CORP. 13 Oct., 1966 [14 Oct., 1965], No. 45731/66. Heading H3T. The threshold of a current-switching type transistor logic circuit is varied in the same sense as the input signal but with a time delay. In the embodiments the reference signal is constituted by a delayed and reduced amplitude version of the input signal (Fig. 6) so that switching action at V and W takes place more quickly after the beginning of the pulse than when a fixed mean-value reference is used. A further increase in speed of response may be obtained by providing positive feedback to the reference potential so that, as in Fig. 28, the reference initially moves towards the input potential. The delayed attenuated signal may be obtained from the output (Fig. 2, not shown) or from the input (Fig. 17, not shown). In Fig. 1 the current switching logic circuit comprising a plurality of input transistors Q1, Q1n sharing a common emitter load with transistor Q2 and feeding an output stage Q3, Q4. A voltage of the same sense of the input signal but of reduced magnitude is obtained from resistors R4 and R5 and applied as the reference voltage to transistor Q2, the delay of the reference voltage being provided by inherent delays in the circuit, assisted if necessary by capacitance at point 22 (C1, Fig. 15, not shown). The reference voltage may alternatively be obtained from a potentiometer connected between the collector of Q3 and earth (Fig. 22, not shown) or, via a further transistor, from the collector of Q4 (Fig. 23, not shown) or from the emitter of Q4 (Fig. 25, not shown). The positive feedback required by Fig. 28 type circuits may be obtained by means of a capacitor or a resistor connected between the collector of Q1 and the base of Q2 (C3 or R85, Figs. 26 and 27, not shown). In Fig. 24 (not shown) the push-pull output stage is replaced by a single transistor (Q36) providing the delayed reference voltage from a potentiometer (R64, R66) connected to the collector. In a further embodiment (Fig. 16, not shown) the delayed reference voltage is obtained by feedback from the collector of Q2 to a capacitor in its base circuit (Q22<SP>1</SP>a and C2, Fig. 16, not shown). A pulse oscillator may be formed by coupling the output of transistor Q4 via a delay line to the input of transistor Q1 (Fig. 14, not shown).