method for switching the operation mode of a pll circuit and a circuit for controlling the operating mode of a pll circuit

摘要

A method of switching the mode of a PLL circuit which has a high-speed mode and a normal mode, which allows the PLL circuit to be locked up at a high speed. The PLL circuit (20) includes a phase comparator (23) and a charge pump (25) for generating a current depending on a comparison output signal from the phase comparator. The mode switching method includes the steps of detecting whether a current output terminal of the charge pump is in a high impedance state, and switching the mode of the PLL circuit from the high-speed mode to the normal mode or from the normal mode to the high-speed mode when the high impedance state is detected. IMAGE