High-performance servo channel for nanometer head positioning and longitudinal position symbol detection in tape systems
In a tape system, the core of the reel-to-reel and track-following servomechanisms is the servo channel, which processes the servo signal generated by a servo reader reading a timing-based servo pattern. The servo channel estimates essential servo parameters, including tape velocity, head lateral position, and longitudinal tape position. The achievable precision of the various estimates determines how densely data can be placed on tape. In this paper, the architecture and the design of a highperformance synchronous servo channel (SSC) are presented. The channel performance is evaluated by means of analytical bounds on the estimation error, simulations, and experimental results, which demonstrate that the proposed servo channel is instrumental to achieve head positioning with nanometer accuracy and reliable detection of longitudinal position information in tape systems. Methods for the estimation of servo parameters with enhanced precision and of dynamic tape-to-head skew by dual SSCs operating on adjacent servo bands are also presented and their performance evaluated.