Detector hardware complexity of high-order partial response magnetic read channels is a major obstacle to high data rate operation and reduced area and power consumption. The method presented here reduces the complexity of single-step and two-step implementations of the Viterbi detector by applying a distance-enhancing code that eliminates some states from the code trellis. The complexity of the detector is further reduced by eliminating less-probable branches from the trellis. This is accomplished by a simple control mechanism that uses the signs of the consecutive input samples. The reduced set of add-compare-select (ACS) units is dynamically assigned to the detector states, decreasing the complexity of the Viterbi detector by roughly 50%. This method is demonstrated on high-order partial response systems with the E/sup 2/PR4 target and an 11-level/32-state target. The simulation results show negligible bit error rate (BER) degradation for signal-to-noise ratios In the range of operation of contemporary disk drive read channels.

A new trellis code for partial-response magnetic recording channels, that eliminates most frequent errors while keeping the code trellis invariant in time, is proposed. Previously published codes either had lower code density or resulted in time varying trellises with a period of 9, thus requiring a higher complexity of detectors. The new code introduces dependency between codewords to achieve the same coding constraints as an 8/9 code, with the same code density, resulting in a trellis that has a period of two. The new trellis code eliminates two states in every second step of the E/sup 2/PR4 trellis, requiring a 14-state two-step sequence detector.