GB984985A - Tunnel diode-transistor logic circuits - Google Patents

Abstract

984,985. Semi-conductor logic; circuits. STANDARD TELEPHONES & CABLES Ltd. Jan. 23, 1963, No. 2878/63. Heading H3T. A semi-conductor logical circuit comprises a transistor T1 in common-emitter configuration and a tunnel diode D1 connected between the base input to the transistor and a point whose potential is such that the emitter-base junction of the transistor has a small forward bias. The arrangement is such that the circuit has a first state in which the transistor is cut off and a second state in which the transistor is bottomed. The NAND unit of Fig. 3 is provided with a bias current I B and a series of input terminals ABCD, the transistor switching from a non- conducting state to a conducting state if there are two or more inputs on the terminals ABCD. The transistor remains in this state after the removal of inputs <SP>I</SP>IN until the circuit is switched back to its first stage by its base. By increasing the bias current I B the unit becomes a NOR circuit when the circuit switches from the first state to the second when one or more inputs are present. The circuit of Fig. 3 may be used as a store reading circuit, Fig. 4 (not shown), by applying accurately timed strobe pulses to one of the input terminals and a read-out signal to another of the inputs, the circuit changing from the first state to the second when the input pulses are coincident. In order that the circuit of Fig. 3 may function as a gating circuit without storage, source I B may be omitted but the inputs I IN must be of sufficient magnitude to switch the circuit, the circuit returning to its initial state when inputs I IN are removed. In an alternative embodiment, Fig. 5, the collector of transistor T1 is connected via delay line L4 to the junction of resistors R4, R 5 through which bias current I B flows. With the transistor cut off the diode is in its high current low voltage state but when a pulse I IN occurs on one of the inputs the tunnel diode switches to its high voltage-low current state, the transistor bottoms and the voltage at its collector falls. This fall in voltage is transmitted via the delay line LD and resistor R5 to the base input resulting in I B becoming zero so that only I IN is present. When I IN is removed the diode switches back to its low voltage state and switches the transistor off, the output of the circuit thus following the input.