Hewlett-Packard Development Company, L.p.

Hewlett-Packard Company

Robert Philip Morling

Christopher Huw Williams

Andrew Hana

Richard D Barndt

Andrew David Brown

A digital data storage (DDS) system for reading DDS tapes employs a partial response maximum likelihood detection system which utilises redundancy in the 8-10 DC free modulation encoding to reduce low frequency noise. The system incorporates a time-varying trellis decoder which embodies some of the PR1 rules together with the rules regarding the charge state or the digital sum variation (DSV) implicit in 8-10 modulation coding. The decoder operates to reject low frequency noise such as that caused by crosstalk noise between adjacent tracks on the tape. The trellis topography has been considerably simplified by adopting a two step six state trellis which operates on bit pairs and in which the states relate to the current DSV value, and sign of the previous bit.

Data retrieval

A method of encoding a digital data stream for writing to a digital storage (DDS) format tape data storage medium comprises writing a byte stream to a preamble region, immediately preceding a user data region. The byte stream has a power spectrum substantially similar to a power spectrum of the user data region. An automatic gain control circuit responds to the preamble data stream in a substantially similar fashion to its response to the user data stream.

Equalization pre-amble region in digital data storage (DDS) format

An adaptive (FFE) filter 24 adaptively filters a signal and updates a plurality of coefficients stored on capacitors 69 to minimize the error between the filter output at 72 and a set of notional reference values supplied by a reference generator 74. The stored values of one or more coefficients are monitored and if the monitored coefficient or coefficients pass respective thresholds or leave respective ranges, indicating the onset of maladaption a default set of coefficients is forced.

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Robert Philip Morling