Patent GB-958578-A (GB)
Title: Electronic circuits using negative resistance diodes
IPC: H03K19/10
Filed: 1960-06-16
Abstract: 958,578. Tunnel-diode switching circuits. RADIO CORPORATION OF AMERICA. June 16, 1960 [June 25, 1959], No. 21248/60. Heading H3T. An element in a logic circuit comprises a first tunnel 10 connected in parallel with the series combination of a similarly-poled tunnel diode 30 and resistor 36, the diodes being braced in the forward direction by a constant current source 42, input signals being applied also so as to bias the diodes in the forward direction via a resistor 46 to the junction point of the two diodes and output signals being taken from across the resistor 36. In the circuits described the constant-current source 42 supplies pulses synchronized with the input pulses 50; presence of an input pulse denotes binary " one " and its absence binary " zero." Fig. 6 shows an inverter circuit in which a large amplitude output pulse appears at terminal 52 only when the input pulse 50 is absent. Curve 60, Fig. 7, represents the forward currentvoltage characteristic curve for the series combination of diode 30 and resistor 36, the positive value of resistor 36 being greater the negative resistance exhibited by the diode 30 over the central portion of its characteristic, Fig. 2 (not shown). Curve 62 represents the characteristic curve of the diode 10 but inverted and displaced along the current axis by an amount equal to the magnitude of the current pulses supplied by source 42; thus where the two curves intersect the total current consumed is equal to that supplied by the source and such points of intersection represent possible states of the circuit, of which those represented by points 66 and 68 are stable. Thus in the absence of a pulse 50, i.e. binary " zero " input, the circuit assumes the state represented by point 66 when current is supplied from source 42 so that a large current flows through diode 30 and a large amplitude, or binary " one," pulse is developed at terminal 52. If a pulse 50 representing binary " one " is applied the curve 62 is shifted to the broken-line position 62<SP>1</SP> so that it has only one intersection with curve 60; hence when current is supplied from source 42 the circuit takes up the state represented by the point 70. The current through the diode 30 is small so that a small-amplitude output signal representing binary " zero " is developed at terminal 52. The circuit may be modified to function as an "exclusive-or " circuit by including a further input terminal also connected through a resistor to the junction of the diodes, Fig. 9 (not shown). The amplitude of the constantcurrent pulses is chosen to give two characteristic curves which intersect as shown in Fig. 10. Only the application of a single pulse input, displacing the curve 62 to 62<SP>1</SP> permits the stable point 112<SP>1</SP> to be achieved at which a large current flows in diode 30 to give a largeamplitude pulse output at terminal 52. The same circuit may also be made to function as an inhibitor circuit. A sufficiently large auxiliary input pulse can shift the curve 62 to 6211 so preventing a large amplitude pulse output being obtained whether or not an input pulse 50 is applied. Alternatively the inhibiting pulse may be of small amplitude so that without an input pulse 50 it is insufficient to displace the curve 62 sufficiently to prevent intersection 110 from taking place and yet sufficient when assisted by an input pulse 50 to prevent intersection 112 from taking place. Fig. 11 shows an inhibitor circuit as just described; the input pulses thereto are provided by an and-gate comprising tunnel diode 120, energizing source 126 for the diode 120 supplying pulses 128 synchronized with those from source 42 and input terminals connected to the junction between diode 120 and source 126 through resistors 136, 138, 140. The current amplitudes of energizing pulses 128 and signal input pulses are so chosen that only when an input is applied to all three input terminals is the amplitude sufficient to trigger the diode to its high voltage state. In the circuit of Fig. 8 (not shown) two networks, each comprising a tunnel diode in parallel with the series combination of a tunnel diode and resistor as shown in Fig. 6, are connected in series with a constant-voltage pulse source, the junction point between the two networks being supplied with constant-current pulses and input pulses. Output pulses inverted with respect to the input are taken off across the resistor in one of the networks.