A Time-Constant Calibrated Phase-Locked Loop With a Fast-Locked Time

A time-constant calibrated phase-locked loop with a fast-locked time is presented. A variable capacitance multiplier (VCM) is developed to adjust the equivalent capacitance in the loop filter. And a calibration circuit is used to allow the time constant of the loop filter to track with the reference clock. By using the proposed time-constant calibration circuit and the VCM, the fast acquisition time is achieved and the loop capacitance is also multiplied. A prototype has been fabricated in a 0.35-mum CMOS process to demonstrate the proposed circuit