CLOCK JITTER IN A SERVO-DERIVED CLOCKING SCHEME FOR MAGNETIC DISK DRIVES

The performance of a simple servo-derived clocking scheme for magnetic disk recording channels is presented, Using a theoretical model, the bit clock jitter is analyzed by computer simulation, and it is shown t hat in the bit clock jitter the mechanical component (velocity jitter) is more influential than the jitter component which originates from t he position noise in the detected clock mark readback pulse, Cancellat ion error of an eccentricity jitter component between writing and read ing moments due to PLL (Phase-Locked Loop) gain variation can be reduc ed by a feed-forward eccentricity suppression technique, Part of simul ation results are verified by jitter measurements using an experimenta l recording channel, a patterned magnetic disk and an MR/Inductive hea d, Bit clock jitter of less than 2.5 ns(rms) is obtained for a spindle with air-bearing, supporting the analytical results, The simple servo -derived clocking scheme can be used in magnetic disk drives with a da ta rate of 20 Mbit/s or more.