Frequency detector in phase locked loop circuit and frequency error detecting method

A frequency detector implementing a method capable of detecting a frequency error in a phase locked loop (PLL) circuit at high speed. The detector includes a run-length signal detecting unit detecting a run-length signal from a sampled radio-frequency (RF) signal in a frequency detection period, based on a predetermined distribution density of the run-length signal; a counter unit including at least one counter which counts the detected run-length signals in the frequency detection period; an edge counter controlling the frequency detection period by counting passing edges of the sampled radio-frequency signal; and a frequency error generating unit generating a frequency error in the frequency detection period, using the counting result output from the at least one counter and a predetermined reference value.