Maximum likelihood servo detector for detecting an error correcting servo code recorded on a disc storage medium

Abstract

A disc storage system servo code detector is disclosed that provides enhanced error correction capabilities during both tracking and seeking by increasing a minimum distance d between valid codewords and by increasing a minimum distance {circumflex over ( )}d from the signal space between adjacent codewords to the decision boundaries of all other valid codewords. The signal space with respect to the minimum distances is not a limiting aspect of the invention; however, in the preferred embodiment the codewords are selected to maximize the minimum distances in Euclidean space. Thus, the read signal is sampled and equalized according to a partial response spectrum, and maximum likelihood detection is employed to detect the servo codewords in Euclidean space. The code rate is selected according to certain design criteria such as the amount of error correction desired, the data density, and the cost and complexity of the encoder/decoder circuitry. After selecting the code rate and number of bits per codeword, a computer search is carried out to find a subset of codewords large enough to encode the track addresses while providing large minimum distance values for d and {circumflex over ( )}d .