Patent GB-746490-A (GB)
Title: Electrical circuits using two-electrode devices
Inventor: ODELL ALEXANDER DOUGLAS
IPC: H03K3/313
Filed: 1953-05-22
Abstract: 746,490. Semi-conductor circuits. STANDARD TELEPHONES & CABLES, Ltd. May 22, 1953, No. 14478/53. Class 40 (6). The invention relates to semi-conductor diode devices of the kind described in Specification 686,958 and having a reverse characteristic exhibiting negative-resistance properties as shown in Fig. 1. Such devices are referred to in the Specification as " negativegap diodes ". Owing to the negative-resistance properties of these devices they have two stable states for certain operating voltages, one being a high-conduction or " on " state and the other being a low-conduction or " off " state. The Specification describes a number of circuits in which negative-gap diodes alternately assume their " on " and " off states; in particular circuits are described employing two reciprocally coupled negative-gap diodes although other circuits employing only one such diode or employing more than two such diodes are also described. Circuits employing two reciprocally coupled diodes (Figs. 4, 6, 8, 9, 11, 12 and 14). Fig. 4 shows a bistable circuit which is changed from a condition wherein one of the diodes NG1, NG2 conducts to one wherein the other one conducts by the alternate application of positive pulses to the inputs marked P1, P2. Assuming diode NG1 is in its low-current condition, the application of a positive pulse at P1 causes the voltage applied across the diode to move to the left in the diagram of Fig. 1 so that provided the pulse is of sufficient amplitude the diode changes over to its " on condition. The potential at the upper end of resistor R3 consequently rises, thus applying a positivepulse to the " cathode of the diode NG2 (assumed to be in its " on " condition), thereby reducing the voltage across this diode and so causing it to assume its " off " condition. The application of a further positive-pulse at P2 restores the original condition of the diodes. In a modification, Fig. 6, the " anode " circuits of the diodes include a common resistor R7 which provides the coupling between the two diodes. The application of a positive-pulse to a diode in its " off " condition changes it to its " on " condition, thus producing a fall of potential at the " anode " of the other diode, thus causing it to cease conducting since the potential at its " cathode " is maintained by the condenser in parallel with its " cathode " resistor. The resistor R7 may be replaced by resistors individual to the two diodes and crosscoupled by a condenser. The circuit of Fig. 8 is similar to that of Fig. 6 but the resistor R7 is replaced by an inductor L1. The metal rectifier MR3 prevents ringing in the inductor L1. The " cathode " resistors R5, R6 are returned to a point of negative-potential in order to decrease the time taken for the " cathode" potentials to return to zero at which they are held by the metal rectifiers MR4, MR5. Fig. 9 shows a binary pair based on the circuit of Fig. 8. Assuming that NG1 is " on " and NG2 " off," the rectifier MR6 is biased positively by the " cathode " potential of the diode NG1 while the rectifier MR9 is unbiased. Upon the application of a positive pulse at the common pulse input P, rectifiers MR7, MR8 are also biased positively and the coincidence gate comprising the rectifiers MR6, MR7 consequently closes allowing the potential at Y to rise triggering NG2 to its " on " condition. Since rectifier MR9 is not biased, the potential at X cannot rise and the diode NG1 changes to its off condition as previously described in connection with Figs. 6 and 8. Fig. 11 illustrates a shift register comprising a plurality of circuits as shown in Fig. 8, two such circuits being shown in the Figure. Upon the application of a " shift " pulse to the inputs P, the diode NGB1 assumes the state previously held by diode NGA1 and diode NGB2 assumes that held by diode NGA2. Similarly diodes NGA1, NGA2 assume the states held by the immediately previous pair of diodes in the chain and those immediately following diodes NGB1, NGB2 assume the states held by these diodes.. Thus on the application of each " shift " pulse, the pattern of information stored by the diodes is moved one space along in the register. Fig. 12 illustrates another multistage circuit, each stage being similar to that of Fig. 4, and the circuit as a whole operating as a binary counter. Fig. 14 shows a two-element astable circuit similar to a multivibrator. Assuming when the circuit is switched on that diode D1 conducts first the potentials at X and Y initially have low values, that at Y rising due to charging of condensers C18, C19 until diode D2 conducts. Condenser C19 discharges through diode D2 to deliver an output pulse across resistor R26 and the consequent fall in potential at Y is transmitted to X to cut the diode D1 off. The circuit stays in this condition until the potential at X has risen sufficiently to permit diode D1 to assume its " on " condition diode D2 then being cut off as before and the cycle of operations repeated. Fig. 15 (not shown), illustrates a mono-stable circuit similar to that of Fig. 14, the potential at point X being derived from a potential divider.  Further counter circuits (Figs. 10 and 13). Fig. 10 shows a ring counter having a scale factor equal to the member of negative-gap diodes. The operation of the circuit is similar to that of Fig. 9; considering diode NG1 to be in its " on " state, the application of a positivepulse at P permits the potential at the junction of rectifiers MR12, MR14 to rise; the rectifier MR12 being biased by the potential at the cathode of the diode NG1, thus switching diode NG2 on. The diode NG1 is simultaneously switched off by the potential drop produced across the inductor L2. This the diodes NG1, NG2, &c. assume their " on " states in succession, the final diode of the chain being coupled back to diode NG1 by components R12, MR13, MR16. Fig. 13 shows a binary counter in which each stage comprises a single negative-gap diode. If diode D1 is " off," the application of a positive pulse via condenser C14 switches it to its " on " condition and a negative pulse is sent to diode D2 to switch that on if it is non-conducting. However, if the diode D1 is conducting it is switched off by the trailing edge of the positive-pulse but no pulse is sent to the diode D2 due to the low impedance of the rectifier in parallel with the inductor L3 to positive-going signals. Hence a pulse is sent to diode D2 each time diode D1 is switched on, these pulses switching diode D2 alternately " on " and " off " but sending pulses to diode D3 only when D2 is switched " on," and consequently the circuit operates as a binary counter. Pulse generating and re-generating circuits (Fig. 16). In the circuit of Fig. 16 a positive potential source is connected through an artificial delay line to the negative-gap diode D. When the circuit is switched on, the potential at the " anode " of D eventually rises sufficiently for it to assume its " on " state, whereupon it discharges the line and sends a negative-step waveform back along the line which after reflection at the far end returns and switches the diode off. This process is repeated and thus a continuous train of pulses is generated. Synchronizing pulses may be applied at terminal SP. In a modification, Fig. 17 (not shown), operating as a pulse regenerator, the positive supply potential is of itself insufficient to cause to the diode to assume its " on " condition, a further connection being made to the anode of the diode to permit the application of triggering pulses thereto. Fig. 18 (not shown) illustrates the application of a plurality of such diodes connected in parallel to a delay line for storing information on a magnetic drum or similar memory device.