Patent GB-984233-A (GB)
Title: Logic system employing tunnel diodes
IPC: G06F7/50
Filed: 1962-03-14
Abstract: 984,233. Tunnel diode logic circuits. NATIONAL CASH REGISTER CO. March 14, 1962 [April 17, 1961], No. 9823/62. Heading H3T. In a logic circuit comprising a plurality of successive stages each comprising a tunnel diode and being responsive, on the application of a clock pulse, to the voltage levels applied thereto from both the immediately preceding and immediately succeeding stages, the stages are interconnected by delay lines differing alternately in their delay times and the clock pulses applied to successive stages are delayed respectively by amounts equal to the delay times of the corresponding delay lines, the repetition periods of the clock pulses being equal to the sum of two successive delay times so that two sets of clock pulses are established differing in phase but of equal period, the pulses of one set being applied to every other stage and those of the other set being applied to the intermediate stages, whereby the flow of information through the circuit is rendered unidirectional. In the preferred embodiment, each stage comprises a tunnel diode 10 connected in series with a load resistor 12 and the primary winding of an output transformer 13, input signals from the preceding stage being applied at terminals A, B to the junction point of the diode and the primary winding. The values of the resistor 12 and of the bias voltage Vc are so chosen that the diode is normally biased to a mono-stable condition on the low-voltage portion of its characteristics, Fig. 3 (not shown), and is excited to its unstable state by positive-going clock pulses applied at terminal C, the input signals being either of zero or negative value with the negative input signals inhibiting the action of the clock pulses so that the diode is triggered to its unstable state only when the input signals occurring simultaneously with a positive-going clock pulse are of zero value. In order to produce sharply defined output pulses at output terminals 14a, 14b, the clock pulses comprise two closely spaced pulses, a positive pulse followed by a negative pulse, the latter pulse switching the diode back, after excitation by the positive pulse, from its unstable to its stable state. It will thus be seen that if zerolevel signals are given the value zero and negative signals the value unity, terminal 14b delivers a conventional OR-output, and terminal 14a delivers the converse of this, i.e. a NOT-AND output, in which a unity output occurs only when both inputs are zero. Figs. 4 and 6 (not shown) illustrate a plurality of such circuits connected in cascade, Fig. 4 showing how successive circuits are coupled through delay lines in order to control the direction of flow of information through the system. Clock pulses Cb are delayed 2T with respect to clock pulses Ca; hence, signals generated by clock pulses Ca in stage 1 are received at stage 2 at the same time as clock pulses are applied thereto. Similarly, the delay between a clock pulse Cb and the successive clock pulse Ca is T so that signals from stage 2 appear at stage 3 but not at stage 1 in coincidence with clock pulses Ca. Specification 984,234 is referred to.