Bias-Controlled Tunnel-Pair Logic Circuits

A three-terminal network consisting of two matched tunnel diodes and a fixed resistor is introduced as a basic element for performing peak threshold summation logic. The characteristic between two terminals resembles a tunnel diode curve where application of a signal or bias current to the third terminal causes reduction of the observed peak current. Decrease of this peak current below a fixed load line allows switching from the low- to the high-voltage state for logic-function circuit operation. Such bias-controlled tunnel pairs are shown to be unilateral to a considerable extent (30 db). This is advantageous in logic networks since it allows directional flow of information without the provision of multiphase power supplies or backward diodes, as needed in conventional tunnel diode logic circuits to eliminate back-switching. Circuits are described based on this principle, consisting entirely of tunnel junctions and resistors, for performing OR, MAJORITY, AND and NOR logic. Generalized design equations for circuits with a fan-in of M and a fan-out of N are derived. Test circuits based upon the generalized equations with a fan-in of 9 and a fan-out of 5 were found to operate over a temperature range from ¿70° to +60°C. A sample switching speed measurement for an OR gate using 1-ma tunnel diodes and a normal degree of drive showed a 7.5-nsec rise time which was triple that observed with a single tunnel diode under similar conditions.