Patent GB-829566-A (GB)
Title: Ferroelectric systems
IPC: G11C11/22
Filed: 1956-05-04
Abstract: 829,566. Circuits employing controlled non- linear capacitors. RADIO CORPORATION OF AMERICA. May 4, 1956 [May 31, 1955], No. 13945/56. Class 40 (9). The flow of alternating current in a circuit comprising two ferro-electric capacitors connected in series is inhibited when the capacitors are saturated in opposite respects by a positive resetting pulse, but is permitted to a degree determined by the reduction of charge when a negative setting pulse is applied, the flow of current continuing until such time as both capacitors are restored to their initial saturated state by a further resetting pulse. The two capacitors, 1, 2, Fig. 1, have substantiallyrectangular charge/voltage characteristics and are connected to an A.C. source 10 in series with a linear condenser 13 or other impedance which develops an output voltage V. Both capacitors 1, 2 require the same charge to saturate but may have different coercive voltages as shown by characteristics 32, 34 in Fig. 2. A further characteristic 30 applies to a ferro-electric capacitor 3 which requires both a higher saturating charge and coercive voltage and is connected to junction 25 in the A.C. circuit. The arrangement is controlled by pulses which are applied from a D.C. source 19 over an adjustable potentiometer 20 and a reversing switch 14. Initial saturation is effected by a positive resetting pulse 33 having an amplitude E 1 exceeding the combined coercive voltages of capacitors 2 and 3 and of sufficient duration t to saturate all the capacitors. As capacitors 1 and 2 are charge-saturated in opposite respects in the A.C. circuit, no current can flow from source 10 and the output voltage V is zero. Alternating current is permitted to flow by desaturating one or both of the capacitors 1, 2, the degree by which the total charge is reduced directly determining the current level and the resultant output voltage V. This reduction of charge is effected by a negative setting-pulse 36, the amplitude of which is determined by the potentiometer adjustment, and the duration t by the switch. When the condensers 1, 2 have dissimilar characteristics as shown, the amplitude of the setting pulse 36 controlling the charge reduction must lie between values higher than the sum of the coercive voltages of capacitors 3 and 1 and lower than the sum of the coercive voltages of capacitors 3 and 2 so that reduction of charge is confined to 3 and 1. Further control on the degree of charge reduction is exercised by the duration t of the pulse. The different characteristics of the capacitors may arise from the use of different dielectric materials or different dielectric thicknesses. The output voltage V determined by the reduction of charge continues indefinitely until the condenser 1 is resaturated by a further positive resetting pulse 33. The use of an asymmetric alternating voltage waveform 37 is described but it is stated that the wave may be symmetrical. In either case it is necessary for the peak voltage to be less than the combined coercive voltages of capacitors 3 and 1 or 3 and 2. It is stated that if capacitors 1 and 2 have the same characteristics, similar control of the output voltage is obtained but the reduction of charge is shared by the two units. The arrangement may be employed as a dynamic register of a binary input signal, the resetting pulse 36 recording a binary zero in terms of the output voltage and a setting pulse of predetermined amplitude recording a binary one. Modified arrangements are shown in Figs. 3 and 4. In Fig. 3, the capacitors 1, 2 have their junctionpoint 25 connected to negative setting and positive resetting sources 67, 70 by way of biased diodes 60 and 62, respectively. Coupling capacitors 73, 75 are used in Fig. 4 arrangement in which the bias potentials for the diodes are obtained from 77 and 79.