Importance

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Abstract

A circuit (100) for generating a ratio signal indicating a ratio of frequency error to signal magnitude of an input signal includes an FM ratio detector (110) and a sigma-delta analog-to-digital converter (130). The FM ratio detector (110) is responsive to the input signal and generates a magnitude signal and an error signal. The magnitude signal is representative of a magnitude of the input signal and the error signal is representative of a frequency error of the input signal relative to a preselected frequency. The sigma-delta analog-to-digital converter (130), which is responsive to the filtered magnitude signal and the filtered error signal, generates a stream of logic '1's' and logic '0's' that are indicative of a ratio of the filtered error signal to the filtered magnitude signal. Thus, the sigma-delta analog-to-digital converter generates the ratio signal (132).

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First Claim