Frequency level detection method and spread spectrum clock frequency level detection apparatus of the spread spectrum clock

摘要

PROBLEM TO BE SOLVED: To provide a method and apparatus for detecting a frequency level of a spread spectrum clock in which, for a spread spectrum clock having a frequency modulated over a plurality of frequency levels in a fixed modulation cycle, the frequency level of the spread spectrum clock is detected.;SOLUTION: A pulse generating circuit 48 generates a pulse at fixed period intervals by comparing a countable value of a reference clock with a value stored in a setting register 46. An SSC count value obtained by counting the number of spread spectrum clocks SSC_CLK for the fixed period is held in a counter buffer 51 and compared with various thresholds stored in a setting register 53 via a comparator circuit 55, and thereby a frequency level of the spread spectrum clock SSC_CLK at that time point is detected.;COPYRIGHT: (C)2011,JPO&INPIT