Phase locked loop with phase rotation for spreading spectrum

A phase-locked loop with phase rotation for spreading spectrum, comprising:

• a phase detector, which receives a reference clock signal and a feedback clock signal to thereby produce an error signal;
• a charge pump, which is connected to the phase detector in order to convert the error signal into a current signal;
• a filter, which is connected to the charge pump in order to convert the current signal into a voltage signal;
• a voltage-controlled oscillator (VCO), which is a ring oscillator connected to the filter in order to produce N clock signals with a same frequency based on the voltage signal, wherein the N clock signals have phases θ0 to θN-1 respectively, and θj indicates a phase lead of 2π/N over θj+1, for j=0, 1, . . . , N−2;
• and
• a selector, which is connected to the VCO in order to select one from the N clock signals based on a predetermined sequence to thereby produce a target clock signal;
• wherein the selector sequentially selects the clock signals with the phases θ0, θ1, θ2, . . . , θN-1 respectively as the target clock signal when an up spectrum spreading operation is performed, sequentially selects the clock signals with the phases θ0, θN-1, θN-2, . . . , θ2, θ1 respectively as the target clock signal when a down spectrum spreading operation is performed, and sequentially selects the clock signals with the phases θ0, θ1, θ2, . . . , θN-1, θ0, θN-1, . . . , ←N-2, . . . , θ2, θ1 respectively as the target clock signal when a spectrum spreading is operated by centering on a frequency of the target clock signal, such that frequency of the target clock frequency is spread evenly within a fixed frequency range and energy of the target clock signal is distributed evenly in frequency domain.