GB1135378A - Improvements in or relating to electric circuits - Google Patents

Abstract

1,135,378. Frequency comparators. GENERAL ELECTRIC CO. Ltd. 21 Nov., 1967 [25 Nov., 1966], No. 53020/66. Heading H3A. Two frequencies are compared by generating two signals having a frequency equal to the difference between the input frequencies, the first signal representing the magnitude of the difference and the second the sense, the negative or positive excursion of the magnituderepresenting signal being inverted selectively in dependence upon the sense of the difference, to produce a D.C. output representing both sense and difference. As shown, an input and a reference signal are passed through frequency dividers which provide square waves of equal mark-space ratio. These waves pass to a coincidence circuit which produces a pulse train modulated in width by the difference frequency. This is filtered at 6 to produce the D.C. component of triangular waveform and this in turn is differentiated at 7 to produce a square wave the amplitude of which is proportional to the slope and thus the difference frequency but which is independent of the sense of the difference. The output of the divider 2 is also passed to a bi-stable circuit 10 so that successive half cycles allow respective sides of the bi-stable circuit to receive pulses from the divider to set the circuit to the corresponding state if it is not already there. The resulting output of the bi-stable circuit has a phase sense which represents the sense of the frequency difference and has a frequency equal to the difference. This, at 8, inverts one or other half cycle of the square wave from the differentiator 7 so that the output of 8 is a direct current having a magnitude and sense equal to the difference between the frequencies. The specification also describes a reversing switch suitable for block 8 (Fig. 3, not shown).