US 6,208,477 B1 · Hard disk drive having a built-in self-test for measuring non-linear signal distortion

Abstract

In a hard disk drive, a semiconductor chip includes a circuit used in a built-in self test (“BIST”) to determine an amplitude of a dibit echo for characterizing nonlinear distortion of a readback signal. Preferably, write precompensation is performed based on results of the BIST to minimize distortion attributable to intersymbol interference. A generator is used to generate a maximal length pseudo-random sequence. This maximal length pseudo-random sequence is input to a correlator which performs a correlation between the maximal length pseudo-random bit sequence and a readback signal responsive to the pseudo-random sequence that was stored onto a disk of the hard disk drive. In one embodiment, a seed value stored in memory is loaded into the generator upon detection of a synchronization signal read from the disk. With the appropriate seed value loaded into the generator, a specific pseudo-random bit sequence corresponding to a sample point of interest is then generated. The cross-correlation between this specific pseudo-random sequence with the readback signal produces a sample point corresponding to the dibit echo. By iteratively generating sample points corresponding to the echo, the peak amplitude of that dibit echo can be accurately estimated. The magnitude of the peak amplitude of the dibit echo is then used to characterize the nonlinear intersymbol interference, which in turn, can be used to perform write precompensation as well as other functions. With this semiconductor chip, a hard disk drive can accurately characterize nonlinear intersymbol interference in the field as part of a built-in self-test function.

Claims14

Dependent claims

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;
and
a controller for programming the register with a plurality of different seed values corresponding to locations of dibit echoes in the dibit extraction signal.

5 more elements

Dependencies are inferred from the claim text.

Hard disk drive having a built-in self-test for measuring non-linear signal distortion

Life of this patent

Hard disk drive having a built-in self-test for measuring non-linear signal distortion

Life of this patent

Abstract

Claims14