Patent GB-907492-A (GB)
Title: Delay circuits
IPC: H03K3/49
Filed: 1960-07-01
Abstract: 907,492. Controlled non-linear inductors. NATIONAL CASH REGISTER CO. July 1, 1960 [July 22, 1959], No. 23079/60. Class 40 (9). [Also in Group XL (c)] Pulses are delayed by a magnetic core having a rectangular hysteresis characteristic which absorbs the leading portion of each pulse and extends the trailing portion, the duration of delay being determined by a delay control signal which adjusts the core flux from an initial saturated condition to a partially changed state. Two embodiments, Figs. 1 and 5, are described both of which operate on the principle that the leading portion of a pulse is absorbed in changing the core flux back from the partially changed state to the initial saturation level, and the trailing portion is extended by a flux resetting operation which adjusts the core flux to the previous partially changed state, this operation recurring cyclically as each pulse is received. As shown in Fig. 1, a core 12 having minor and major apertures 30, 32 is constructed so that the total cross-section of limbs 27, 28 adjacent the minor aperture 30 is equal to the minimum cross-section of limb 36, and is initially set to an overall saturated state by a clearing pulse Vc applied to a winding 34. The delay period is determined by a delay control pulse 60 applied to a winding 46 by way of a constantcurrent circuit which includes a PNP transistor 64 and a voltage clamping diode 70. The energy content of the control pulse 60 determines the degree of partial change of flux state, and results in inner and outer portions of the core having opposite stable states. The limbs 27, 28 adjacent the minor aperture then have respective different degrees of magnetization in the same direction, and the delay of the leading portion of the input pulse is brought about by utilizing it to restore both these limbs to the same state. This is effected by current in a winding 48 which flows when a PNP transistor 80 is rendered conductive by an input pulse 78 at terminal 74. During the leading portion of the input pulse, flux changes occur around the minor aperture and an output terminal 88 remains at a quiescent potential - 4 volts applied by a circuit comprising a- 50 v. potential resistor 96 and a - 4 v. clamping diode 81. When flux changes around the minor aperture terminate both limbs 27, 28 are saturated in the same sense and the earth potential at the emitter of transistor 80 appears at the output terminal. When this transistor is cut off by the trailing edge of the input pulse, a negative pulse passes over a condenser 92 of short time constant and brings a PNP transistor 86 to the conductive state. As a result an earth potential 94 continues the output pulse and the transistor remains conductive until the dissimilar flux states in the two core limbs are restored. Transistor 86 is then cut off and the delayed output pulse terminated. Maintenance of the transistor 86 in the conductive state to provide the necessary trailing portion delay is due to current over condenser 92 produced by induction in winding 48 during the dissimilar flux state restoration period. The fluxes are restored by a bias current in a resetting winding 50, which is neutralized for the duration of the input pulse by a current of greater amplitude and opposite sense in winding 48. A toroidal core 102 is used in the Fig. 5 embodiment in which initial saturation is effected by a clear pulse Vc in a winding 106. The partial change of flux in the core is effected by a pulse V SET which is applied by way of a transistor 128 to a set winding 122, the pulse duration determining the degree of delay. In this case, however, partial change is effected for each input pulse, a pulse V SET being applied coincidently with the trailing edge of an input pulse. The input pulses V IN are applied to a delay winding 134 over a transistor 142. The core is always in a state of partial change at this juncture due to the pulse. V SET immediately following the last input pulse, and an output pulse Vo does not appear until the delay time has elapsed and the core flux brought to its saturated state. At the termination of the input pulse, the pulse V SET is applied and performs the dual function of continuing the output pulse and partially changing the core flux in readiness for the next pulse. It is stated that delay control may be effected by a permanent magnet.