Systems and methods of real-time frequency calibration for segmented voltage controlled oscillator based phase-lock loop

A method of real-time frequency calibration for a phase-lock loop (PLL) that is based on a segmented voltage controlled oscillator (VCO), the segmented VCO comprising at least one VCO core, the method comprising:

• receiving a request to lock the PLL to an output frequency;
• searching in a look-up table for a segment selection signal corresponding to the output frequency, and operating a current VCO core based on the segment selection signal to lock the PLL to the output frequency, the look-up table is established using steps comprising performing frequency sweeping to each VCO core of at least one VCO core and establishing the look-up table based on frequency ranges of multiple frequency segments of each VCO core, wherein when performing frequency sweeping to any VCO core, enabling the VCO core under sweeping and disabling all other VCO cores, and using the PLL to sweep each frequency segment among the multiple frequency segments, when the PLL transitions from an unlock status to a lock status, or from a lock status to an unlock status, identifying a lower bound and an upper bound of a frequency range for each frequency segment;
• obtaining a tuning voltage inputting to the current VCO core and determining whether the tuning voltage is in a normal operation range,
• responsive to the tuning voltage exceeding the normal operation range, adjusting the segment selection signal for segment switching from a current frequency segment in the current VCO core to another frequency segment in the current VCO core, or from the current frequency segment in the current VCO core to another frequency segment in another VCO core, until the tuning voltage is within the normal operation range with the PLL being locked to the output frequency.