Mark S. Spurbeck

Interpolated timing recovery for hard disk drive read channels

We propose an architecture for hard disk drive read channels in which the signal from the read head is asynchronously sampled at a frequency slightly higher than the channel bit rate. Synchronous samples are subsequently computed by interpolation, and used by a conventional sequence detector such as a Viterbi detector for partial response. This architecture allows design of a fully digital PLL, including a digital ZPR function. In addition, the latencies of the ADC and FIR equalization filter do not contribute to loop delay. A cost effective, well performing implementation is described.

Least squares approximation of perfect reconstruction filter banks

Designing good causal filters for perfect reconstruction (PR) filter banks is a challenging task due to the unusual nature of the design constraints. We present a new least squares (LS) design methodology for approximating PRFBs that avoids most of these difficult constraints. The designer first selects a set of subband analysis filters from an almost unrestricted class of rational filters. Then, given some desired reconstruction delay, this design procedure produces the causal and rational synthesis filters that result in the best least squares approximation to a PRFB. This technique is built on a multi-input multi-output (MIMO) system model for filter banks derived from the filter bank polyphase representation. Using this model, we frame the LS approximation problem for PRFBs as a causal LS equalization problem for MIMO systems. We derive the causal LS solution to this design problem and present an algorithm for computing this solution. The resulting algorithm includes a MIMO spectral factorization that accounts for most of the complexity and computational cost for this design technique. Finally, we consider some design examples and evaluate their performance.