Dynamic adjustment of a response characteristic of a phase-locked loop digital filter

A method for use with a phase-locked loop (PLL) that comprises a digital filter, an oscillator, and a time-to-digital converter (TDC), the method comprising:

• sampling, by the digital filter, at a discrete time in response to a reference clock signal received at the digital filter, wherein the digital filter comprises a discrete-time state-space filter;
• generating, by the oscillator, an output signal of the PLL in response to an output of the digital filter;
• determining, by the TDC, a phase difference between the output signal of the PLL and the reference clock signal;
• providing, by the TDC, a time signal to the digital filter, wherein the time signal is based on the phase difference and is representative of an instantaneous rate of operation of the PLL;
• and
• adjusting, by the digital filter, a response characteristic of the digital filter according to the time signal.

A phase-locked loop (PLL), comprising:

• means for filtering in a feedforward path of the PLL, wherein the means for filtering includes means for sampling at a discrete time in response to a reference clock signal;
• means for generating an output signal of the PLL in response to an output of the means for sampling;
• means for determining a phase difference between the output signal of the PLL and the reference clock signal;
• means for providing a time signal to the means for sampling, wherein the time signal is based on the phase difference and is representative of an instantaneous rate of operation of the PLL;
• and
• means for adjusting a response characteristic of the means for sampling according to the time signal.

A non-transitory computer-readable medium including program code stored thereon for use with a phase-locked loop (PLL) that comprises a digital filter, an oscillator, and a time-to-digital converter (TDC), the program code comprising instructions to direct the PLL to:

• sample, with the digital filter, at a discrete time in response to a reference clock signal received at the digital filter;
• generate, with the oscillator, an output signal of the PLL in response to an output of the digital filter;
• determine, with the TDC, a phase difference between the output signal of the PLL and the reference clock signal;
• provide, by the TDC, a time signal to the digital filter, wherein the time signal is based on the phase difference and is representative of an instantaneous rate of operation of the PLL;
• adjust, by the digital filter, a response characteristic of the digital filter according to the time signal, wherein the response characteristic is a sampling rate of the digital filter;
• modulate, by the digital filter, a filter coefficient of the digital filter in response to the time signal.