GB1362206A - Apparatus for synthesising polyphase sine waves - Google Patents

Abstract

1362206 Waveform changing G & E BRADLEY Ltd 28 Jan 1972 [29 Jan 1971] 3517/71 Addition to 1206941 Heading H2F In apparatus for synthesizing polyphase sine waves, a non-sinusoidal (e.g. square wave) source 10 feeds a chain of frequency dividers 11 ... 16 which provide a primary non-sinusoidal oscillation of frequency f and further first phase oscillations of multiple frequency 3f, 5f &c., the components of the Fourier series of the further oscillations having the same relationship to one another as those of the primary oscillation f; the frequencies and phases of the further oscillations being such that when combined at 18, with the primary oscillation f, cancellation of the significant harmonics takes place so that the resultant output is sinusoidal. The dividing chain includes a stage 15 which divides by n (where n is equal to the required number of phases) and has n outputs which are fed to further combining means (not shown) together with appropriate further harmonic-cancelling oscillations so as to provide sinusoidal outputs at the other phases. Fig. 1 shows part of a system for providing a three-phase output. A square wave source 10 of frequency 30,030 f is fed to the dividing chain 11 ... 16, having the division ratios shown, to provide a square wave at the fundamental frequency f. Further dividers provide the harmonic-cancelling square waves 3f ... 15f, which are fed to a summing circuit 18 comprising weighted resistors 17, 23 ... 28. The first phase output is obtained from an amplifier 19 via an optional filter 20. Dividers 15, 30 ... 33 have a ratio of 3 and provide outputs displaced by 120 degrees so as to supply fundamental and harmonic-cancelling oscillations to further summing circuits (Figs. 2 and 3, not shown).