VCO gain self-calibration for low voltage phase lock-loop applications

A phase-locked loop (PLL) circuit having a voltage-controlled oscillator (VCO) is automatically calibrated for VCO center frequency and VCO gain during power up or responsive to a calibration signal. The VCO has several input voltage versus output frequency operating curves. During a calibration phase, proper VCO center frequency is selected by selecting one of the operating curves. VCO gain is then determined using the selected VCO operating curve. If the value of VCO gain is not within predetermined limits, VCO gain is adjusted accordingly, and the process of selecting a VCO operating curve and determining VCO gain is repeated.