Look-Ahead Maximum Likelihood Data Detector for Optical Disk Drives

A simple maximum likelihood detector is described for system-on-chip (SoC) implementation for optical disk drives. As compared to the Viterbi detector (VD) commonly used for storage devices, this detector offers a solution for the speed bottleneck of the VD and less hardware complexity. Using look-ahead samples eliminates the need for a path memory and also resolves the speed bottleneck so that only a “select” operation is required within a clock cycle by moving the other two operations “add” and “compare” out of a clock cycle loop. Another advantage of this detector is that the target sample values can be constructed at the current sample time. This means that sample error can be estimated with significantly less delay for adaptive control loops. This detector is based on two-dimensional boundary functions, which can be readily derived by a simple procedure for finding a set of error events in the respective signal transition and envelope groups. This detector is currently used in a Samsung DVD super-multi-SoC.