Control method for selecting frequency band and related clock data recovery device

A clock data recovery device, comprising:

• a phase detector, for generating a phase detecting signal according to a data frequency of a serial data stream and a recovery frequency of a recovery clock and for generating retimed data according to the serial data stream and the recovery clock;
• a charge pump, coupled to the phase detector for generating a current signal according to the phase detecting signal;
• a low pass filter, coupled to the charge pump for generating a locking voltage according to the current signal;
• a multi-bands voltage-controlled oscillator, coupled to the low pass filter for operating at an operating frequency band of a plurality of frequency bands according to a band selecting signal and generating the recovery clock according to the locking voltage and the operating frequency band;
• a voltage range generating unit, for generating a locking voltage range according to a range control signal;
• a comparing unit, coupled to the voltage range generating unit and the low pass filter for generating a high locking signal according to the highest voltage of the locking voltage range and the locking voltage and generating a low locking signal according to the lowest voltage of the locking voltage range and the locking voltage;
• and
• a control module, coupled to the comparing unit, the charge pump, the voltage range generating unit and the multi-bands voltage-controlled oscillator for generating the band selecting signal and the range control signal.