Fractional frequency divider and frequency synthesizer

摘要

A fractional frequency divider comprises: a fractional frequency divider circuit configured to, by using an integer frequency division signal obtained by dividing an input signal by an integer frequency division ratio, generate a fractional frequency division signal into which the input signal is divided by a fraction frequency division ratio; a latch circuit configured to capture a frequency control signal representing a specified fraction frequency division ratio in synchronization with the fractional frequency division signal; and a control circuit configured to generate an integer control signal for setting an integer frequency division ratio corresponding to a specified fraction frequency division ratio in synchronization with an integer frequency division signal, based on a captured frequency control signal. The fractional frequency divider circuit updates the integer frequency division ratio by referring to the integer control signal in synchronization with the input signal.