SERVO CIRCUITRY FOR COUNTING TRACKS ON AN OPTICAL STORAGE MEDIUM

摘要

Servo circuitry (406) for counting tracks on an optical storage medium (412) is disclosed. The servo circuitry is comprised of a differential phase detector (420) and a digital phase-locked loop (436). The differential phase detector receives four signals (A-D) from a quad-photodetector (410) and correlates the four signals into a first correlation signal (CORR P) and a second correlation signal (CORR N). The digital phase-locked loop receives an adjustable amplification value along with the positive correlation signal (CORR P) and the negative correlation signal (CORR N). The digital phase-locked loop generates a track count signal based on the adjustable amplification value, the positive correlation signal, and the negative correlation signal. The track count signal represents track crossings on the optical storage medium. The digital phase-locked loop advantageously has an adjustable bandwidth based on the amplification value. The servo circuitry counts tracks on both CDs and DVDs.