Digital maximum likelihood detector for class iv partial response

Abstract

A high speed all digital detector for Class IV partial response signalling, particularly to such detector wherein the detector recorded signals are precoded, is based upon a recognition that 1-D.sup.2 filters correspond to a pair of 1-D filters responsive to alternate bits. A detector in accordance with the present invention includes a decision making circuit for maximum likelihood sequence estimation (MLSE) that has operated at a speed of at least 120 megabits per second. Such a detector makes decisions by comparing a current signal sample S.sub.n with a stored, or pointer, signal sample S.sub.p and the prior state (T.sub.IN) of the system. When a decision as to a current sample can be made, the decision is stored serially in a memory for later reading out as part of a completely detected stream. When a decision cannot be made as to a current sample, the current sample is stored with an indication of the position of that sample in the data stream. When a decision cannot be made as to a current sample, the detector can make a decision in respect to the last stored sample (before it is replaced by the current sample) and that decision is stored in memory at the previously indicated position for later readout in proper sequence.