System and method for calibrating damping factor or analog PLL

An integrated phase-locked loop (PLL) and calibration system responsive to a calibration enable signal `CAL` for maintaining a damping factor .delta. of the PLL at a constant value, said integrated system comprising:

• a phase detector means for comparing the phases of an output signal of the PLL and a reference input signal to produce an error signal based on any phase difference;
• a charge pump coupled to receive the error signal and a reference current signal I.sub.r, said charge pump ouputting of a source/sink direction a charge current I.sub.c proportional to the reference current I.sub.r and having a direction determined by the error signal;
• a filter coupled to receive the charge current I.sub.c and provided therefrom a voltage control signal V.sub.c ;
• a voltage controlled oscillator (VCO) coupled to the filter to receive at an input the voltage control signal V.sub.c and generate therefrom a frequency output F.sub.0, the frequency output F.sub.0 of the VCO comprising an output signal of the PLL;
• at least one of said charge pump, said filter and said VCO having a component value within a predefined tolerance;
• sensing means for dynamically determining the damping factor .delta. of the PLL;
• and
• current generation means coupled to the sensing means and the charge pump for generating the reference current I.sub.r, said current generation means including means for automatically calibrating the reference current I.sub.r in response to the calibration enable signal `CAL` and the dynamically determined damping factor .delta. such that the damping factor .delta. of the PLL is automatically dynamically maintained at said constant value notwithstanding variation of the component value within its predefined tolerance due to process, temperature or power supply variation.

A method for calibrating a phase-locked loop (PLL) circuit in response to a calibration enable signal `CAL`, the PLL circuit having a plurality of components including a phase comparator coupled to a charge pump which receives a reference current I.sub.r and outputs therefrom a proportional source/sink charge current I.sub.c to a filter which provides a control voltage V.sub.c to a voltage controlled oscillator (VCO) that outputs a frequency signal F.sub.0, the PLL circuit having a damping factor .delta. which is a function of the charge current I.sub.c, at least one component of said plurality of components having a component value within a predefined tolerance, said calibrating method comprising the steps of:

• (a) receiving the calibration enable signal `CAL`;
• (b) dynamically sensing the damping factor .delta. of the PLL;
• and
• (c) automatically adjusting the reference current I.sub.r in response to the calibration enable signal `CAL` received in said step (a) and the damping factor .delta. dynamically sensed in said step (b) such that the damping factor .delta. is maintained at a pre-chosen constant value notwithstanding variation of the component value of the at least one component within its predefined tolerance due to process, temperature or power supply variation.