Patent ID: 6208477
Filing Date: 2001-03-27
Classification: G11B

Abstract:
A hard disk drive providing a built-in self-test for measuring non-linear distortion of a readback signal through dibit extraction, the hard disk drive comprising:a disk having a recording surface storing a recorded block including a recorded string of bits defining a first phase of a maximal length pseudo-random sequence generated by a predetermined polynomial;head and read channel for producing the readback signal responsive to the recorded block;built-in self-test circuit operative during the self test including:a signal generator for generating a reference signal having a sequential block including a sequential string of bits defining a second phase of the maximal length pseudo-random sequence;a correlator responsive to the readback signal and the reference signal for producing a plurality of cross-correlation values representing part of a dibit extraction signal;a programmable resister for storing a seed value for controlling the phase of the sequential string of bits; anda controller for programming the register with a plurality of different seed values corresponding to locations of dibit echoes in the dibit extraction signal.