Patent GB-778883-A (GB)
Title: Improvements in and relating to non-linear circuits
IPC: G11C19/12
Filed: 1955-05-20
Abstract: 778,883. Electric digital-data-storage apparatus. NIPPON TELEGRAPH & TELEPHONE PUBLIC CORPORATION. May 20, 1955 [May 28, 1954], No. 14681/55. Class 106 (1). [Also in Group XXXIX] Binary information is represented by the two possible phases of a sub-harmonic frequency f which is produced from an excitation source of frequency 2f by a non-linear inductive or capacitive reactor forming part of a tuned circuit, the selection of one sub-harmonic phase being determined by a pilot signal of frequency f applied to the tuned circuit directly. The operating conditions are such that the pilot signal by itself cannot establish resonance, but if the excitation frequency 2f is applied at the same time to the non-linear reactor to produce the sub-harmonic frequency f, the tuned circuit is brought into resonance in phase with the pilot signal. Thereafter the pilot signal exercises no further control and may be terminated without affecting the sub-harmonic output. Basically the operation is due to the phenomena that an oscillation is built up in a tuned circuit if a parameter of the circuit, such as a non-linear inductance, is cyclically varied. This effect is known as the " parametric excitation of oscillations " and is discussed in the Specification with reference to the publications " Nonlinear Vibrations " by J. J. Stoker, 1950, and " Ordinary Non-Linear Differential Equations," by N. W. McLachlan, 1950. A complete unit is shown in Fig. 1a, in which a non-linear reactor M formed by two cores has windings L1, L1<SP>1</SP> connected to an excitation source O of frequency 2f and to a D.C. source B which biases the cores in the region where maximum variation of permeability occurs. Further windings L2, L2<SP>1</SP> connected in opposition are associated with a condenser C to form a tuned circuit which is connected over a switch S2 to a pilot signal source 02 of frequency f. When the excitation source 01 is connected to the reactor, the tuned circuit is brought into resonance and provides an amplified output of frequency f at terminals T2, T2<SP>1</SP> the phase of which is determined by switch S2 connecting the pilot signal to the tuned circuit either directly or over a phase-reversing transformer. Once the excitation frequency produces a sub-harmonic condition, the amplified output of selected phase persists independently of 02 or the position of S2, and the arrangement thus functions as a memory. Termination of sub-harmonic oscillation is effected by either disconnecting the excitation source or varying its frequency, or by changing the value of the bias potential. Mention is made of alternative units, Figs. 1b and 1c, which use non-linear barium titanate capacitors C1, C2 with the optional provision of a linear capacitor C. It is suggested that both components in the tuned circuit may be non-linear. The pilot signal source 02 may be a thermionic oscillator, or a similar " parametrically excited " unit, Figs. 3a to 3c. In these Figures Z denotes an impedance coupling of two units, Y an admittance coupling, and L5 a mutual inductance coupling. If unit P1 is brought into resonance of a particular phase and the coupling is resistive, then unit P2 will oscillate in the same phase when excited by frequency 2f. The arrangement constitutes a shift register since P1 can be then taken out of use by terminating its excitation frequency without affecting P2. Information may be transferred in either direction according to the sequence of connecting and interrupting the excitation frequency 2f to the individual units. Where the coupling element is reactive, a similar phase shift of exciting frequency 2f is made so that the particular phase of the voltage transferred from one unit to the other is maintained. On the other hand, a phase-inverting element such as a transformer may be used between two units to deliberately reverse the phase of the transferred voltage. Detection of the transferred binary information represented by phase for the purpose of D.C. polarity control of apparatus such as a thermionic valve circuit may be effected by the use of a ring modulator or frequency modulation detector and a reference frequency of standard phase. Input signals represented by D.C. polarity may be converted into pilot frequency signals by the use of a ring modulator or a second-harmonic type of magnetic amplifier, Fig. 4a, having a synchronized saturating frequency of f/2. Alternatively a magnetic bridge, Fig. 4b, providing a second harmonic output may be used, the output being obtained at terminals t2, t2<SP>1</SP>. Various applications in electrical computing are described as follows: Delay circuit or shifting register. The " parametrically excited " units are represented in Fig. 7a by PA-PE and are linked by coupling impedances Z. Information present at every third unit such as PA, PD is transferred through the delay circuit by repeated operations involving application of the excitation frequency to the adjacent units in the direction of transfer (PB, PE) and subsequently terminating the excitation of the original units (PA, PD). " AND " circuits. Fig. 8a illustrates an AND circuit for two variables applied from unit Px, Py to a single unit Pd. The logical AND operation is determined by a further unit Po which combines an output having a phase representing binary zero with the outputs of Px and Py. All the units produce sub-harmonic voltages of equal magnitudes. A circuit for three variables x, y and z is shown in Fig. 8b. Two reference units Po may be used, or alternatively a single Po unit may be associated with two coupling impedances. " OR " circuits. The logical OR operation may be performed by circuits identical with the AND circuits, Figs. 9a and 9b (not shown), except that the output of the Po unit or units has a phase representing binary one. " NOT " circuits. The output of a unit, Fig. 10, is reversed in phase by a transformer T. Alternatively the other output terminal t2 may be used.