Abstract: An apparatus and method are disclosed for decoding servo data recorded on a magnetic disk drive and detecting pinned layer reversals and signal errors, for example, errors due to noise. The servo data is encoded using wide-bi-phase encoding. This encoding is detected by a magneto-resistive sensor that senses the magnetization in domains passing by the sensor. The decoder includes an A/D converter for sampling the signals emitted by the sensor, to provide a sequence of the encoded data. A trellis, such as a Viterbi trellis, is employed to decode the samples generated by the converter. The trellis includes nodes representing states, connected by paths representing transitions, among the nodes. A quality value is generated for the transitions, the quality value representing the distance between each sample in the sequence output by the A/D converter and a corresponding expected sample.

Abstract: A disk drive clock circuit includes a servo clock generator and a disk locked frequency converter. The servo clock generator generates a servo clock signal in response to servo information read from a data storage disk in a disk drive. The disk locked frequency converter responds to the servo clock signal by generating a modified clock signal having a different frequency, and adjusts timing of an edge of the modified clock signal in response to a timing event identified from the servo information read from the disk. The disk locked frequency converter can include a divide-by-n counter that is configured to divide the frequency of the servo clock signal by a number n to generate the modified clock signal. The disk locked frequency converter can reset the divide-by-n counter to a defined value in response to the timing event. The modified clock signal can thereby be phase locked to the servo information on the disk.

Abstract: A disk drive clock circuit includes a servo clock generator and a disk locked frequency converter. The servo clock generator generates a servo clock signal in response to servo information read from a data storage disk in a disk drive. The disk locked frequency converter responds to the servo clock signal by generating a modified clock signal having a different frequency, and adjusts timing of an edge of the modified clock signal in response to a timing event identified from the servo information read from the disk. The disk locked frequency converter can include a divide-by-n counter that is configured to divide the frequency of the servo clock signal by a number n to generate the modified clock signal. The disk locked frequency converter can reset the divide-by-n counter to a defined value in response to the timing event. The modified clock signal can thereby be phase locked to the servo information on the disk.

Abstract: A majority detector for error recovery provides hard and soft majority detection.