GB1005868A - Improvements in electrical analogue computing circuit arrangements - Google Patents

Abstract

1,005,868. Analogue calculating circuits. ELECTRIC & MUSICAL INDUSTRIES Ltd. Dec. 1, 1961 [Dec. 1, 1960], No. 41259/60. Heading G4G. [Also in Division H4] An arrangement for performing division includes a source of signals representing a first variable, a second source of signals representing a second variable and two function generators to which the signals from the first and second sources are applied and from which are derived two signals, each substantially representing the logarithm of the respective variable. These logarithmic signals are fed to an arrangement for producing a linear combination thereof and the combined signal is fed to a generator having a transfer co-efficient substantially representing a hyperbolic function. An output signal derived from the hyperbolic function generator represents the quotient of particular functions of the two variables, the particular functions being determined by the choice of hyperbolic function and the linear combination. In one embodiment of the invention, for determining the ratio U/V, two time varying voltage signals U and V are applied to the inputs 1 and 2 of the circuit and by means of the resistors 3, 5 and 8 and an amplifier 4 they are added together and inverted to produce a signal representing - (U+V). This signal is applied to the input of the logarithmic function generator 11. It is also applied through a resistor 9 (value R) to the input of an amplifier 7 to whose other input is applied the signal U through a resistor 6 (value R/2) so that the amplifier 7 gives an output representing V - U. This output is fed to the logarithmic function generator 12. The two logarithmic function generators 11, 12, which consist of conventional diode circuits, have their outputs applied via the resistors 13 and 14, each of value R, to the amplifier 15, whose feed-back resistor 17 has a value R/2. A signal corresponding to the function ¢ [log (U + V) - log (V - U)] is produced at the amplifier output. This signal is applied to a tanh function generator 16 to deliver a function tanh ¢ [log (U + V) - log (V - U)] which is equal to U/V. It is said that the " tanh " function is particularly easy to generate by means of diode function generators, provided the function U is restricted to the range V>U> - V. Other embodiments of the invention include an arrangement for producing an approximate result wherein the " tanh " generator and the preceding summing amplifiers are replaced by a pair of differencing valves with a large resistance in the common cathode lead. Further, if the tanh function generator is replaced by a hyperbolic secant function generator, the circuit delivers a signal proportional to the ratio between the geometric and arithmetic means of the signals applied to the logarithmic function generators, because 2xy/x + y = sech ¢ log y/x.