Fractional clock generator with low power and low noise

1. A clock generator comprising:

a delta-sigma modulation, DSM, for generating a division control signal and a phase control signal;

an oscillator, for generating an oscillation signal with a first frequency;

an adjustable frequency divider, for performing a division operation on the oscillation signal according to the division control signal, to generate a first division signal and a second division signal, wherein the first and second division signals have a second frequency;

a phase interpolator, PI, for performing a phase interpolation operation on the first and second division signals according to the phase control signal, to generate an output signal with an output frequency, wherein the first frequency is greater than the second frequency;

a frequency detector, coupled to the PI, for receiving a ratio signal and a reference signal, and comparing a frequency of the reference signal to the output signal according to the ratio signal, to generate a comparison signal; and

a low-pass filter, LPF, connected between the frequency detector and the DSM, for filtering high-frequency noise of the comparison signal;

wherein the first frequency is an integer multiple of the second frequency.

2. The clock generator of claim 1 , wherein the second division signal is generated by delaying the first division signal by a clock cycle, wherein the clock cycle is an oscillating period of the oscillation signal.

3. The clock generator of claim 2 , wherein a phase of the output signal is between a phase of the first division signal and a phase of the second division signal.

4. The clock generator of claim 1 , wherein the PI comprises:

a first interpolator module, including a plurality of buffers connected between the first division signal and an interpolated node;

a second interpolator module, including a plurality of buffers connected between the second division signal and the interpolated node; and

an output buffer, coupled to the interpolated node, for outputting the output signal.

5. The clock generator of claim 1 , wherein the reference signal is in a reference frequency.

6. The clock generator of claim 5 , wherein the DSM receives the filtered comparison signal for generating the division control signal and the phase control signal, to indicate the adjustable frequency divider to perform a division operation, the PI to perform a phase interpolation operation, so that a ratio of the output frequency to the reference frequency is a fraction.

7. The clock generator of claim 5 , wherein the frequency detector comprises:

a first D-flip flop, including a data input terminal coupled to a system power supply, a frequency input terminal connected to the output signal, a data output terminal for generating a first comparison signal, and a reset terminal;

a second D-flip flop, including a data input terminal coupled to the ground, a frequency input terminal connected to the reference signal, a data output terminal for generating a second comparison signal and a reset terminal;

a digital circuit, for receiving the ratio signal, the first comparison signal and the second comparison signal, and comparing the output frequency to the reference frequency, to generate the comparison signal; and

a NAND gate, including a first data input terminal for receiving the first comparison signal, a second data input terminal for receiving the second comparison signal, and a data output terminal connected between the reset terminal of the first D-flip flop and the reset terminal of the second first D-flip flop.

8. The clock generator of claim 5 , further comprising:

a phase-lock loop, PLL, coupled to the PI, for filtering the high-frequency noise of the DSM.