Patent GB-654909-A (GB)
Title: Improvements in or relating to electric delay devices employing semi-conductors
Inventor: REEVES ALEC HARLEY
IPC: H03K23/00
Filed: 1948-10-27
Abstract: 654,909. Semi-conductor relay circuits. STANDARD TELEPHONES & CABLES, Ltd. Oct. 27, 1948, No. 27895. [Class 40 (iv)] [Also in Group XL (c)] In a pulse delay circuit comprising a semi-conducting material having a base electrode and at least two pointcontact electrodes, a trigger circuit is associated with each point contact electrode. An input pulse trips one of the trigger circuits which transmits a coupling pulse over the semi-conducting surface to trip the adjacent trigger circuit and thus generate an output pulse after a delay dependent on the separations of the point-contact electrodes. Figs. 1 and 2 show a semi-conducting device comprising a germanium crystal 1 mounted in a base 2 having a metallic shank electrode 3. A number of fine wire cat's-whiskers 4 are arranged in a row in contact with the upper edge of the crystal. Fig. 4 shows a pulse delaying circuit in which the electrodes 5 and 6 and the base electrode 3 form two separate rectifiers which are biassed to the centre of the negative resistance region of their characteristic and thus operate as simple self-restoring trigger circuits as described in Specification 650,007. A negative-going input pulse applied at terminal 12 trips the first trigger circuit comprising electrodes 3, 5 which restores itself and thus trips the second trigger circuit comprising electrodes 3, 6 which produces a delayed output pulse at terminal 14. Since the delay is dependent on the potential of electrode 6, if a regularly recurring pulse train is applied at 12 and a varying control voltage is applied at 17, a phase-modulated output pulse train is produced at 14. Fig. 5 shows a pulse counter or frequency divider circuit comprising a number of rectifier units 3, 19; 3, 20, &c., each of which operates as a trigger circuit. Positive-going input pulses are applied to the base 3 and the first trigger circuit 3, 19 has an additional bias voltage 31 so that it is tripped by the first incoming pulse and conditions the second trigger circuit 3, 20 which is thus tripped by the second incoming pulse and conditions the third circuit. This action thus spreads down the chain until the circuit 3, 23 is triggered when an output pulse is obtained at terminal 37 for a predetermined number of input pulses. The trigger circuits are restored to their initial state ready for a further count either by the application of a negative-going pulse to electrode 3 from the output circuit via the trigger circuit 35 which may be of any well-known type or by rendering the last trigger circuit self restoring by the provision of capacitor 36 and making electrode 23 a multi-contact or " comb " electrode, the current-carrying capacity of which is equal to the total current-carrying capacity of all the remaining trigger circuits combined. In a modification, Fig. 6 (not shown), the auxiliary bias source of the first trigger circuit is dispensed with and the initial coupling pulse is provided by an auxiliary electrode which is unaffected by the input pulse train. Fig. 7 shows a pulse counter or frequency divider circuit in which the trigger pair contacts are arranged round the crystal 1 which is in the form of an annular ring as shown in Fig. 3. The electrodes 3, 42; 3, 43, &c. operate as self-restoring trigger circuits and input pulses are applied to electrode 3 from the input 52 via the delay network 54. The elements of the counting ring are caused to trigger consecutively in a clockwise direction by applying the input pulse train to an auxiliary pulse generator 55 which applies a negative-going " start " pulse to electrode 42 so that this is the first circuit to be triggered and a positive-going " hold-off " pulse to the next adjacent electrode 47 in the counter-clockwise direction. The " hold-off " pulse is of sufficient duration to prevent electrode 42 from being tripped by either of the first two incoming pulses, Fig. 8 (not shown). The single point-contact electrodes shown in Figs. 1-3 may each be replaced by a pair of electrodes spaced close together so that each pair with the base electrode functions as a crystal triode. Fig. 9 shows a pulse-delaying circuit which is similar to that of Fig. 4, but in which crystal triodes are used as the trigger circuit. Each trigger circuit is biassed so that the circuit just does not oscillate and capacitors 71, 72 render each circuit self-restoring so that in response to a positive-going input pulse applied at 73 a delayed output pulse is obtained at 76. A train of input pulses may be phasemodulated by applying a control signal across 77, 78. Each trigger-pair circuit could be connected as a blocking oscillator arranged to be tripped into oscillation by an incoming or coupling pulse. The counting or frequency dividing circuit of Fig. 5 may be modified to use crystal triodes, Fig. 10 (not shown). In a further modification, Fig. 11 (not shown), an annular crystal is used as in Fig. 7 and a counting or frequency dividing circuit is produced by a ring type connection of crystal triode trigger circuit. The Provisional Specification states that lead sulphide may be used as the semi-conductive material when the diode trigger circuits are used and that silicon carbide, copper oxide, silver sulphide, thallium sulphide or barium titanate may be used for the crystal element when triode circuits are used.