Patent GB-793799-A (GB)
Title: Improvements in logical elements
IPC: H03K19/162
Filed: 1955-04-25
Abstract: 793,799. Parametrically-excited resonators. INTERNATIONAL BUSINESS MACHINES CORPORATION. April 25, 1955 [April 28, 1954], No. 11855/55. Class 40 (4). An electrical device having non-linear reactance and an inherent resonant frequency, such as a crystal diode or a ferro-magnetic inductor with self-capacity, is energized by an amplitudemodulated power signal Ps and by a control signal Si<SP>1</SP>, the fundamental or chosen subharmonic frequencies of which lie at or near the resonant frequency, the arrangement being such that the control signal amplitude is insufficient by itself to establish resonant oscillation, and a mode of oscillation determined by the control signal can only arise when the control and power signals are simultaneously present and the power signal exceeds a certain critical amplitude. The basic arrangement is shown in Fig. 5 in which a crystal diode O couples power and output channels formed respectively by waveguides EG and AC. The diode is biased by a voltage of the order 0.1 to 0.2 volts, and is energized over the power channel by an alternating signal Ps, the frequency f1of Ps being of such value that the diode produces a subharmonic output signal Si of frequency f1/n (1000-10,000 Mc/s.) in the region of its resonant frequency. The production of this subharmonic signal is dependent, however, on the level of the power signal f exceeding a certain critical value, while the phase relationship of the output signal obtained is indefinite since it has as many equally-spaced possible phase values as the order n of the subharmonic frequency. For this frequency to have one particular and predetermined phase relationship, a weak control signal Si<SP>1</SP> of the same frequency and of the phase required is applied to the diode over the output channel during the period when the level of Ps is raised through the critical value. Termination of signal Si occurs when the level of the power signal Ps is reduced below the critical value. Conditions of operation are that the amplitude variation of Ps should occur at a much lower frequency than the frequency f1 of the power signal, and that each channel should present little attenuation to its allotted frequency but high attenuation to the frequency in the other channel. It is stated that coaxial cables may alternatively be used and that the sources of frequency may be magnetrons or klystrons. It is stated that O may alternatively be a wound saturable magnetic core tuned by its selfcapacity in the frequency range of one to several Mc/s., the channels in this case being formed by transmission lines or by ordinary wiring to which the core is inductively coupled. Arrangements are described in which a number of units each consisting of a crystal diode form circuits for performing logical operations. Command-compliance operation. Two interconnected units O 1 , O 2 , Fig. 8, have their subharmonic outputs Six, Si 2  arranged to act in opposition. The respective power signals Ps 1 , Ps 2 , Fig. 9 (a) and (b), are amplitude-modulated at a much lower frequency and have relative phase displacements such that the level S1 of Ps 1  is raised through the critical value before the level S2 of Ps 2 , and remains above this value until a corresponding increase in the level S2 of Ps2 occurs. The phase of the subharmonic output Si 1  of O 1  is determined by a weak signal Si<SP>1</SP> as previously described, which signal could originate in a further unit. The subharmonic output Si<SP>1</SP> constitutes the phase-determining signal Si<SP>1</SP> 2  of unit O 2 , since it is present when O 2  commences to generate a subharmonic oscillation as a result of Ps 2  rising above the critical value. Due to the relative phase displacement of the amplitude-modulated power signals Ps 1 , Ps 2 , action in the reverse direction O 2  #O 1  cannot occur, and the condition arises that information represented by the output phase of O 1  determines the phase output of O 2  in a command-compliance relationship. A moderate degree of attenuation is included in the output channels to prevent possible influence on the operation of O 2  by the weak signal Si<SP>1</SP>. The unit O 2  could be caused to produce an output having a different subharmonic phase relationship to that of O 1  by introducing a phase shift in the output channel connecting O 1  and O 2 , This would necessitate spacing O 1  and O 2  by a distance, e.g. 30 to 3 cms, of the same order as the wavelength of the subharmonic frequency. Cyclic control of three units. Commandcompliance operation of three units A, B, C in tandem may also be obtained by arranging the respective amplitude-modulated power signals to have the relative and cyclic phase relationships shown in Figs. 11 (a) to (c). It is possible for only two adjacent units at most to produce subharmonic outputs simultaneously, with the result that operating conditions are obtained whereby the subharmonic phase of A controls that of B, B controls C, C controls A and so on., but A, B and C cannot directly influence the phase of C, A or B respectively. If a phase delay corresponding to one-third of the cyclic time of the amplitude-modulated power signal is included in the power channel of a particular unit such as B, the direction of control is reversed and B determines the phase of A. Simplified circuit rotation. Each crystal diode unit is denoted by a square, Fig. 12 (b), and a line representing the output channel. The power channel is omitted, but the cyclic position of the subharmonic output as determined by the power signal is shown by a letter A, B or C. A command-compliance arrangement of two units is shown, and the case when a delay in a power channel causes a reversal of control is illustrated by Fig. 13, the reversal of control direction, viz: B to A, being denoted by the symbol #I. In the particular case of second harmonic output, the subharmonics produced by a unit have one of two possible phase relationships, viz: positive or negative. If no phase-shift arises in the signal channel between two units in tandem, both units will produce subharmonics, in turn, having the same positive or negative phase. This is an " affirmative " connection, and since there is an absence of logical processing, no indication is given in the simplified circuits. If, on the other hand, there is a phase shift of #, a positive phase subharmonic from one unit becomes a negative phase subharmonic in the next unit and vice versa. This is a " negative " or " NOT " connection and is denoted by the letter n beneath the line connecting two units. The letter P indicates a permanent source of subharmonic frequency. Majority operation. A single B unit, Fig. 14, connected to an odd number of A units, generates a subharmonic of a particular phase relationship, positive or negative, according to the majority of like phase relationships produced by the A units. Disjunction or logical OR operation. A single B unit, Fig. 15, is associated with two A units and a permanent source P of subharmonic frequency. As unit B follows the majority of its inputs, and since P is always positive in phase, a majority of positive phases is obtained if and only if at least one A unit is positive. Conjunction or logical AND operation. The arrangement, Fig. 16 (a), is identical with Fig. 15 except that the permanent source P of subharmonic frequency has a negative phase relationship. As a result the subharmonics applied to B produce a positive output if and only if both A units are positive. For three inputs, the arrangement shown in Fig. 16 (c) is used. Implication operation. In a further modification of Fig. 15, Fig. 16 (b), the output of one A unit has a negative phase relationship. Hence the output of B is positive if and only if the input to the upper A unit is negative and/or the lower A unit positive. Parity sensing. In Fig. 16 (d), three subharmonic inputs are applied to the A units on the left, and logical operations are performed on three separate B units. The output of the upper unit B is positive when two or all of the A units are positive (majority), the lower B unit is positive if and only if all the A units are positive (AND), and the centre B unit is positive if and only if all the A units are negative (NOT AND). Unit C is positive if and only if the outputs of the upper and centre B units are both negative. The final output is obtained from the single A unit on the right and is positive if and only if either C or the lowest B is positive (OR), i.e. if one or three only of the inputs to the A units on the left are positive. Binary addition. The majority and parity sensing arrangements, Figs. 14 and 16 (d), may be employed to determine the carry digit and the sum digit in binary addition, the three inputs A being the digits of the two addends and the carry digit from the preceding stage. Power and subharmonic frequency sources. Suitable delays are incorporated in the power supply channels so that the various units may operate as classes A, B or C, the fundamental frequency 1000-30,000 Mc/s. being derived from a magnetron or klystron and amplitudemodulated by a controlling oscillator at a frequency in the order of 17-1000 Mc/s. The permanent signal source is obtained from a similar generator operating at about 500 to 15,000 Mc/s., the second harmonic being locked to the fundamental frequency source. Monitoring. Since the amplitude of the subharmonic is determined by that of the power signal, a proportion of the output can be employed, after rectification, in maintaining the individual units in proper adjustment. A suggested application is automatic variation of the forward bias of the diodes with regard to their operating temperatures and ages, and control of the source of power signals. Wave-shaping. It is stated that amplification of the modulating frequency occurs when the unit produces a subharmonic, output and that a modulated signal of the wa