Broadband cyclotomic tone detector

摘要

A system (1000) for estimating the frequency of a tone input utilizes sample rate restriction in successive stages and processing by digital cyclotomic filters at each stage. The tone input (2001) is first transformed in network (1100) to yield two quadrature tones. Digitizer (1200) converts the two tones into data words. Buffer (1300) comprises two essentially identical storage arrangements wherein data words are stored and then supplied to succeeding stages. Frequency-shifting unit (1400) effects modulus-one multiplication by processing appropriately selected data words. Word pairs and frequency-shifted versions thereof are processed by cyclotomic filters (1500). Sequential decimation in the system effects a successively refined estimate to the tonal frequency. During each stage of decimation, the filters are configured to provide symmetric coverage of the subband containing the estimate. Configuration information is provided by decision unit (1600) via threshold comparison of the outputs from the filters and controller (1700) provides control information to the elements of the system. Rate reduction occurs on a 4:1 basis for each stage of decimation. The first frequency interval covered is one-fourth the initial sampling rate, and each stage of decimation causes a factor of four refinement in the estimate. The filters are structured as the equivalent of four filter pairs at each stage of decimation, two of the four pairs are of first order, whereas the other two are of second order.