Calibration systems and methods for setting PLL gain characteristics and center frequency

摘要

Calibration systems and techniques for phase-locked loops (PLLs) provide precise setting of the center frequency and/or uniform voltage controlled oscillator (VCO) gain characteristics. Center frequency is calibrated by imposing a selected center frequency at the output of the PLL and driving the control voltage Vc across the PLL's filter to a predefined, steady state voltage indicative of PLL circuit calibration. The approach can be employed to calibrate any imposed VCO frequency output. VCO gain calibration is accomplished by employing the center frequency calibration technique only with a low frequency point imposed on the VCO output. A high frequency point on the transfer function is calibrated by applying a known voltage across the filter and driving the VCO output to a corresponding calibration frequency. Once a low frequency point and a high frequency point are calibrated, the slope of the VCO transfer function is defined. Various integrated PLL/calibration system embodiments are presented.