GB715344A - Improvements in or relating to electrical equipment of the kind adapted to provide an electric signal which is substantially proportional to the product of two quantities - Google Patents

Abstract

715,344. Electric analogue computors. GENERAL ELECTRIC CO., Ltd., and KIRKNESS, R. H. March 23, 1953, [Dec. 21, 1951.] No. 30061/51. Class 37. In equipment of the kind which provides an electric signal substantially proportional to the product of two given quantities A and B, an oscillator 5 and a phase-splitting network 6 supply two oscillations having the same frequency but a relative phase difference of 9o degrees to two modulators i and 2 where each is amplitudemodulated by signals. representing one of the two quantities A and B; the two amplitude-modulated oscillations are fed simultaneously to a circuit 8 of which the characteristic at least approximately follows a square law, and a device 9 derives a signal having a magnitude dependent upon the product of the two quantities A and B from an oscillatory component in the output of the circuit 8 which has a frequency twice that of the oscillations supplied by the oscillator 5. Thus the input to the squaring circuit 8 may be written A sin (wt + °) + B cos (wt + °), its output then being proportional to the square of this expression, which can be shown to be equal to ¢[(A<SP>2</SP>+B<SP>2</SP>) + (B<SP>2</SP>-A<SP>2</SP>) cos a(wt+°)]+AB sin 2 (wt+°). The last term has an amplitude proportional to the required product AB, and this component is selected by means of the phase-sensitive device 9 to which a frequency doubler 11 supplies an oscillation of the required double frequency through a phase-shifting network I3 which is adjusted so that there is no output from the device 9 when either of the given quantities A and B is zero. In an alternative arrangement the oscillations in quadrature supplied to the modulators i and 2 are produced as described in Specification 703,192, [Group XL(c)]. The modulators i and 2 may be of the type described in Specification 715,353, [Group XL(c)]. The squaring circuit may be as shown in Fig. 2, comprising two matched pentodes 2 and 22 having a common anode load resistor 23, the input signals being supplied in anti-phase to the control grids 24 and 25 by means of a phase-splitting network 26.