Patent ID: 6750682
Filing Date: 2004-06-15
Classification: H03L

Abstract:
An apparatus for detecting a difference between frequencies, the apparatus comprising:a beat waveform generating unit which generates a beat waveform signal having a frequency which is equal to a difference between frequencies of a reference clock signal and a target clock signal; a reference-clock dividing unit which divides the reference clock signal by N, where N is an integer, to generate a divided reference-clock signal; and a frequency comparing unit which compares frequencies of the beat waveform signal arid the divided reference-clock signal, and generates a step out alarm signal which is a binary signal depending upon a polarity of a difference between the frequencies of the beat waveform signal and the divided reference-clock signal, wherein the frequency comparing unit includes, a first beat waveform generating unit which generates a first beat waveform signal having a frequency which is equal to a difference between frequencies of the beat waveform signal and the divided reference-clock signal; a delay adding unit which adds a delay of Â¼ period to the divided reference-clock signal to generate a delayed reference-clock signal; a second beat waveform generating unit which generates a second beat waveform signal having a frequency which is equal to a difference between frequencies of the beat waveform signal and the delayer reference-clock signal; and a phase comparing unit which compares phases of the first beat waveform signal and the second beat waveform signal obtains a polarity of a difference between the phases of the first beat waveform signal and the second beat waveform signal, and output the binary signal depending upon the obtained polarity.