Read channel

Abstract

An improved read channel for storage and communication application particularly useful in optical storage applications. The improved read channel includes a Viterbi sequence detector tuned to a preferred partial response target well suited to sensing of pulses in the waveforms typical of optical storage read heads. In particular, the read channel of the present invention implements pulse and sequence detection for a partial response target having a spectral null at the Nyquist frequency and having a relative minimum between zero and the Nyquist frequency. In other words, the partial response target of the improved read channel is not a monotonic decreasing function between zero and the Nyquist frequency as is known in present read channels. More specifically, in the preferred embodiment, the partial response target of the read channel includes a spectral null at the Nyquist frequency and another spectral null at half the Nyquist frequency. The improved read channel further includes state logic in the Viterbi sequence detector that processes two discrete samples in parallel. Parallel processing of multiple samples improves the read channel performance for application in ever increasing bit density storage and communication applications. The preferred embodiment of the present invention also includes selectable waveform shaping features to improve the flexibility of utilizing the read channel in a variety of applications. Specifically, the present invention includes a reshaping filter, a prefilter and DC offset circuit that may be selected to adapt the waveform as required for application to the slicer and to adapt as required for application to the sequence detector.