US Patent 11923859 High-resolution and agile frequency measurement

An apparatus for generating a frequency estimate of an output signal includes a reference signal generator configured to generate a reference clock signal. The apparatus includes frequency estimation circuitry configured to generate a cycle count based frequency estimation of the output signal based on the reference clock signal and a clock cycle count of the output signal. The frequency estimation circuitry further generates a fractional frequency estimation of the output signal based on the reference clock signal and a plurality of time-to-digital conversion phase samples of the output signal. The frequency estimation circuitry further generates the frequency estimate of the output signal using the cycle count based frequency estimation within a range and a frequency error determined from the fractional frequency estimation. The plurality of time-to-digital conversion phase samples and the cycle count based frequency estimation use a same number of reference clock cycles of the reference clock signal.