HIGHER HARMONICS COMPENSATION IN PHASE LOCKED LOOP

摘要

PROBLEM TO BE SOLVED: To compensate for external disturbances caused by higher harmonics introduced into a phase locked loop in a revolving storage medium. SOLUTION: Adverse effects caused by higher harmonics external disturbances of a phase locked loop is reduced by higher harmonics compensation. The compensation may always exist in the loop or could be switched over when a loop lock is obtained. External disturbances within the bandwidth of the loop are compensated by using an additional integration pole or a bump (a resonance) filter. External disturbances outside the bandwidth of the loop are compensated for employing a low pass filter or a notch (a nonresonance) filter. As an alternative plan, cancel signals may be generated and added as feed forward signals. In a repeated type control system, the version in which residual errors are filtered in the previous rotation of a medium is used as feed forward signals and the adverse effects of the higher harmonics are canceled.