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A fresh approach is made to computer circuitry in which due prominence is given to the electrical characteristics of the logical interconnection network. The necessity for matching active logic elements to a screened transmission system rules against the use of diode-gate transistor amplifier circuits of the type which has become familiar. An amplifier circuit is described which has a virtual-earth input combined with a non-linear response suitable for threshold logic. This circuit exploits the high-speed amplifying and standardizing properties of a tunnel diode in conjunction with the ability of a transistor to direct and buffer information flow. Unlike most hybrid circuits, the transistor is allowed to give current gain without loss of speed. The action of the amplifier is inverting and latching, i.e. it is bi-stable. The degree of latching may be controlled by the use of delayed negative feedback, and other useful variations are possible. Preliminary experiments have been carried out with slow tunnel diodes, the circuits being suitable for 30 Mc/s operation if used in a synchronous mode.