Patent GB-745227-A (GB)
Title: Improvements in or relating to electrical coincidence responsive circuits
Inventor: RIDLER DESMOND SYDNEY
IPC: H03K17/52
Filed: 1953-04-30
Abstract: 745,227. Multi-stable state and coincidence circuits. STANDARD TELEPHONES & CABLES, Ltd. April 30, 1953, No. 11933/53. Class 40 (6). Fig. 1 shows a coincidence circuit in which a two stable state trigger circuit comprising cold cathode tubes CTA, CTB is triggered by pulses derived from the anode circuits of either tube G1 or G2. On coincidence of a positive pulse on input 1 and a negative pulse on input 2, tube G1 fires until the negative pulse on input 2 ceases when it is extinguished, inductor L1 " rings " and produces a positive going half sine wave which triggers tube CTA and extinguishes CTB by virtue of the common anode resistor R1. Similarly tube G2 fires when coincidence occurs between a positive and a negative pulse on inputs 3 and 4 respectively and tube CTB fires if it is not already discharging when the input at 4 ceases. In a modification, Fig. 2 (not shown), three coincidence cold cathode tubes are associated with three further tubes having a common anode load so that one only of the latter tubes can be conductive at any given time. In a modification shown in Fig. 3 which uses hard valves, valves VA, VB are cross-connected as a conventional trigger pair circuit and triggering pulses are applied to their respective control grids from the coincidence valves V1, V2 which conduct during the coincidence of a positive pulse at input 1 or 4 and a negative pulse at input 2 or 3, the valves being rendered non-conducting when the pulses at any input ceases. Diodes D1, D2 and D3, D4 isolate their respective trigger pair valves VA, VB from the negative pulses produced when V1 or V2 conduct, but pass the pulses produced when V1 or V2 cut off. Fig. 4 shows a hard valve trigger-pair circuit in which valve VC is normally conductive and VD cut-off. Negative-going clock pulses at input 1 are differentiated by network C4, R7 so that when the resulting negative going pip coincides with a positive pulse at input 2 valve VD conducts and VC is cut-off. The positive going pip resulting from differentiation of the negative pulse at input 1 causes VC to conduct and VD to be cut-off, the rise in anode voltage of valve VD triggering cold-cathode tube CT to produce an output across its cathode resistor R11. Tube CT is reset by a negative pulse applied at terminal RESET to its anode. Tube CT as shown in Fig. 7 may form one tube of a trigger circuit CT, CQ, each tube of which is associated with a circuit as shown in Fig. 4. In a futher modification shown in Fig. 8 cold cathode tubes CTG, CTH form a trigger pair circuit in which positive clock pulses applied at input 1 are differentiated by network C7, R13 and applied to trigger tube CTG during the coincidence of a negative pulse applied to its cathode from input 2, tube CTH being extinguished by the commutating action of capacitor C6. When tube CTH is cut-off capacitor C9 charges from HT+ via resistor R16. On the trailing edge of a clock pulse the sharp negative pulse produced by network C7, R13 is phase reversed by step-up transformer T1 to produce a large positive pulse which triggers tube CTH and extinguishes tube CTG. The resulting large negative pulse across cathode resistor R17 is differentiated by network C10, R18 and fires tube CT to produce an output pulse across its cathode resistor. As described in connection with Fig. 7 tube CT could form one tube of a trigger pair circuit the other tube of which is triggered by a further trigger circuit having two inputs. In a further modification shown in Fig. 10 the cold cathode tubes are replaced by metal rectifiers of the type described in Specification 686,958 which have a negative resistance portion in their characteristic and two stable conditions of operation. The rectifiers NGA, NGB are biased near to the # turnover point " so that normally NGB is # on " in its state of high current and NGA is #off in its state of low current. During the coincidence of a positive pulse on the anode of NGA, which occurs at the leading edge of a negative clock pulse at input 1 differentiated by network C12, R21 and inverted in transformer T2, and a negative pulse at input 2, rectifier NGA is switched " on " and NGB "off" the sharp positive pulse occurring at the end of the differentiated pulse of input 1 restoring the trigger circuit so that the rectifier NGB is # on ". The resulting positive pulse across resistor R22 triggers rectifier NGT to its " on " condition to produce a positive output pulse. The rectifier NGT may form half of a trigger circuit using a second rectifier of the same type.