Abstract: A method for characterizing a read channel of a disk drive by storing a pseudorandom number (PN) sequence at a first location on a recording surface of the disk drive, and storing the PN sequence at a second location on the recording surface. The PN sequence at the first location is read to generate a first playback signal, and a first dibit response is determined from the first playback signal. The PN sequence at the second location is read to generate a second playback signal, and a second dibit response is determined from the first playback signal. The first and second dibit responses are arithmetically combined to generate a combined dibit response in which at least some non-linear echoes are isolated.

Abstract: A sampled amplitude read channel is disclosed for magnetic disk storage systems utilizing a read head exhibiting a non-linear response such as a magneto-resistive (MR) read head. A sensor of the read head is adjusted to operate in a region of its response that provides optimum gain even though it may be a region of higher non-linearity. To compensate for the non-linearity introduced into the read signal, the read channel further comprises an adaptive non-linear correction circuit that is adaptively tuned by a least-mean-square (LMS) adaptation circuit. The analog read signal is sampled and the discrete time samples equalized into a desired partial response prior to sequence detection. The non-linear correction circuit is inserted into the read path prior to the sequence detector in order to attenuate the non-linear distortions that would otherwise degrade the performance of the sequence detector.