Patent ID: 7471158

Claim:
An automatic switching phase-locked loop (PLL), comprising: a phase detector receiving a reference signal and a feedback signal, and outputting a phase detection signal corresponding to the phase difference between the reference signal and the feedback signal; a charge pump receiving the phase detection signal and producing a pump current according to the phase detection signal; a band selector receiving a control voltage, producing a band selection signal and a voltage setting signal based the control voltage; a loop filter generating the control voltage corresponding to the pump current and setting the control voltage based on the voltage setting signal; a multi-band voltage control oscillator (VCO) coupled to the control voltage and the band selection signal, selecting one of a plurality of operating bands based on the band selection signal, and providing an output signal of a frequency within the selected operating band based on the control voltage; and a lock detector detecting whether the automatic switching PLL is locked, and outputting a lock signal corresponding to the detection result, wherein the band selector detects if the control voltage falls in a reference voltage range, and if so, the band selector produces neither the band selection signal to switch the operating band of the multi-band VCO nor the voltage setting signal to set the control voltage, or otherwise, produces the band selection signal to switch the operating band of the multi-band VCO and the voltage setting signal to set the control voltage, and wherein the band selector further receives the lock signal and further detects if the control voltage falls in one of at least one additional reference voltage ranges adjacent to the reference voltage range, and when detecting the control voltage in one of the at least one additional reference voltage range, producing neither the band selection signal nor the voltage setting signal until receiving the lock signal corresponding to a locked status of the automatic switching PLL.