A multi-band clock generator includes a phase-locked loop (PLL) integrated circuit responding to first and second clock signals, and includes a multi-band voltage controlled oscillator (VCO) responding to a multi-bit control word that sets a frequency characteristic curve of the VCO. The multi-band clock generator also includes an adaptive frequency calibration (AFC) circuit responding to the first and second clock signals, and the AFC circuit is configured to look-up a first multi-bit control word during an operation to lock an output clock signal generated by the VCO to a first frequency characteristic curve associated with the first multi-bit control word.