Importance

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Abstract

A phase locked loop device is provided. The phase locked loop device includes a phase/frequency detector, a charge pump, a low pass filter, a voltage-controlled oscillator, and a control unit. The phase/frequency detector generates a compared signal corresponding to a phase difference between a reference clock signal and a feedback clock signal. The charge pump coupled to the phase/frequency detector generates a pump current according to the compared signal. The low pass filter coupled to the charge pump generates an operating voltage corresponding to the pump current. The voltage-controlled oscillator coupled to the low pass filter generates an output clock signal in response to the operating voltage. The control unit coupled to the low pass filter and the voltage-controlled oscillator constrains the operating voltage to a predetermined voltage level when the frequency of the output clock signal is out of a predetermined frequency range.

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First Claim