Roger W Cox

US Patent:

49221957, May 1, 1990

Filed:

Dec 19, 1988

Appl. No.:

7/286391

Inventors:

Roger W. Cox - Monroeville PA

Assignee:

Westinghouse Electric Corp. - Pittsburgh PA

International Classification:

G01R 23165

US Classification:

324158MG

Abstract:

An extraneous frequency detector especially suited for analyzing the three-phase output of a variable speed constant frequency (VSCF) generator generates in a sample-and-hold circuit amplitude samples of a phase selected by a multiplexer for application to a discrete time analog filter in the form of a switched capacitor high pass filter. A control circuit generates dual-phase non-overlapping clocking signals which control the sampling rate of the sample-and-hole circuit and the switching rate of the switched capacitor filter. Two modes of operation are provided for the single filter circuit by generating the clocking signals for the first mode of operation at a first frequency which is at least twice the frequency of the highest order harmonic of interest such that all frequencies above the fundamental are detected. In the second mode of operation, the clocking signals are generated at the fundamental frequency. This produces aliasing of the fundamental frequency and all harmonics resulting in a comb filter which detects all frequencies above a few hertz except for the fundamental and its harmonics.