Configuration and controlling method of fractional-N PLL having fractional frequency divider

摘要

The provided fractional frequency divider includes a divider controlling unit for generating a divider selection signal in response to a dual-edge triggering of an input signal and a frequency dividing unit coupled to the divider controlling unit for dividing the frequency of the input signal by one of an integer and a fractional dividers in response to the dual-edge triggering and the divider selection signal to generate the output signal of the fractional frequency divider. An operation of the frequency dividing unit is not suppressed when the integer divider is employed, the operation of the frequency dividing unit is not suppressed for a period of the input signal and is suppressed for half of that period, and this cycle is kept on recurring when the fractional divider is employed. The fractional-n PLL having the fractional frequency divider is also provided.