Patent GB-820957-A (GB)
Title: Improvements in or relating to analogue computing apparatus
IPC: H03K3/53
Filed: 1956-06-25
Abstract: 820,957. Electric analog calculating. ZENITH RADIO CORPORATION. June 25, 1956 [July 2, 1955], No. 19631/56. Class 37. [Also in Group XL (c)] A computer for the product of second and third analog voltages or currents divided by a first such analog comprises resonant circuits for developing first and second signals of amplitudes representing alternating time functions decremental from amplitude values proportional respectively to the first and second analog voltages or currents, a load circuit, and gating means for applying a signal derived from the second signal to the load during a time interval determined by instantaneous coincidence in a comparator between the amplitude characteristics of the first signal and the third analog voltage or current to develop in the load a signal analogous to the required function. In Fig. 1 a source of unidirectional voltage U is connected in series with normally open electronic switch 11 and a parallel resonant circuit 16, while a second source of unidirectional voltage B is connected in series with normally open electronic switch 12 and a parallel resonant circuit 17; the switches being closed at intervals over short periods by timing pulse generator 15 to shock excite the identical resonant circuits to produce damped sinusoidal oscillations from the respective initial amplitude values of U and B. The oscillatory voltage across 16 is applied to comparator 14 also receiving a unidirectional voltage A, which at instantaneous equality between the inputs generates a sampling pulse applied to electronic switch 13 to connect the instantaneous value of the oscillatory voltage across 17 to capacitance 31, which is repeatedly charged on successive operative cycles to develop a voltage P representing (Figs. 3, 4, not shown) AB/U for fixed or variable values, provided that the highest frequency of variation of voltage A is not greater than the frequency of oscillation of the resonant circuits. The sampling pulse frequency may be greater or less than the oscillation frequency (Figs. 5, 6, not shown). Fig. 7 shows an electronic switch wherein triode V2 is connected in a normally cut-off blocking oscillator circuit with triple wound transformer T1; the anode of V2 being connected to the anode of trigger triode V1 normally passing a low current. A positive control pulse at the grid of V1 initiates a stroke of the blocking oscillator to develop a high amplitude pulse at transformer winding 5, 6 which drives the bridge connected diodes V3 to V6 conducting so that the capacitance C3 in parallel with resistance R3 is charged to the peak pulse voltage, and has a large time constant, so that in absence of the transformer pulse the cathodes V4, V6 are biased positively and the anodes of V3, V5 are biased negatively, so that terminals X, X<SP>1</SP>, at which the cathodes of V3, V5 are respectively joined to the anodes of V4, V6, are open circuited ; while for the duration of the positive control pulse the connection between terminals X, X<SP>1</SP> is bilaterally conducting. Fig. 8 shows a comparator wherein triode V7 is connected with triple wound transformer T2 in a blocking oscillator circuit; V7 normally passing a small current and having its grid returned to earth over a diode V8 poled to normally prevent feedback through transformer winding 7, 8. Comparison voltages are applied over terminals Z, Z<SP>1</SP>, Y, Y<SP>1</SP> to opposite sides of diode V8 to bias it in opposition, and if terminal Y is driven more positive than Y<SP>1</SP> by a comparison voltage, diode V8 conducts and the feedback path is completed so that the blocking oscillator strikes to develop a pulse across the transformer output winding connected to output terminals S, S<SP>1</SP>. Capacitance-resistance circuit C6, R7 in the triode grid circuit is charged by each pulse, and has a time constant sufficiently long to disable the comparator for a time longer than the longest time for which voltage Y, Y<SP>1</SP> is likely to exceed Z, Z<SP>1</SP>. A buffer amplifier may be connected between resonant circuit 17 and switch 13 in Fig. 1 and switches 11, 12 may be operationally synchronized with the zero values of current in the inductive limbs of resonant circuits 16, 17 by a modification equalizing the timing frequency with the natural frequency of the resonant circuits (Fig. 9) wherein switches 11, 12 are impulsed by the output of a comparator circuit similar to that shown in Fig. 8, wherein input Z, Z<SP>1</SP> is derived by amplifying the voltage across a resistance in series with the inductance of resonant circuit 16; the input Y, Y<SP>1</SP> being short-circuited, so that timing pulses are developed in phase with each passage of the inductance current through zero.