System of referenceless clock and data recovery and frequency detector thereof

Abstract

A system of referenceless clock and data recovery and a frequency detector thereof has been provided. The output clock of the system initially works at the lowest frequency, the frequency of the output clock is monotonically increased in accordance with the control of the frequency detector, thereby gradually approximating a target value. The edge extraction circuit receives the data signal and the clock signal, identifies the transition edges of the signals and generates a data transition signal and a clock transition signal representing the transition edges of the data signal and the transition edges of the clock signal respectively. The edge detector then determines the data period of the data signal and the clock period of the clock signal. When the data period is smaller than half of the clock period, the edge detector generates a frequency-up signal and the frequency of the output clock is increased.