Disk drive having built-in self-test system for characterizing performance of the drive

A method for computing a sequence of channel metrics {Γn} for characterizing the performance of a disk drive, the method comprising the steps of:

• reading a plurality of bit cells stored on a recording surface in the disk drive to produce a noise-corrupted read signal;
• generating a sequence of observed samples {yn}, the sequence of observed-samples {yn} forming a sequence of observed-sample sequences {Yn}, each observed sample sequence Yn having an earliest observed sample and a latest observed sample;
• providing a sequence of expected samples {wn}, the sequence of expected samples forming a sequence of expected-sample subsequences {Wn}, each expected-sample subsequence Wn having an earliest expected sample and a latest expected sample;
• computing a sequence of channel metrics {Γn}, each channel metric Γn being a function of a distance determined from one of the observed-sample subsequences Yn to the corresponding expected-sample sequence Wn, each channel metric Γn being independent of the earliest observed sample in every prior observed-sample subsequence Yn and the earliest expected sample in every prior expected-sample subsequence Wn;
• and
• computing a mean μΓ of the channel metrics Γn;
• computing a standard deviation σΓ of the channel metrics Γn;
• computing a ratio of the mean μΓ to the standard deviation σΓ, the ratio (μΓ/σΓ) corresponding to a signal to noise ratio.

A method for estimating a bit error rate for a disk drive, the method comprising the steps of:

• reading a plurality of bit cells stored on a recording surface in the disk drive to produce a noise-corrupted read signal;
• generating a sequence of observed samples {yn} responsive to the noise-corrupted read signal, the sequence of observed samples {yn} forming a sequence of observed-sample subsequences {Yn}, each observed-sample subsequence Yn having an earliest observed sample and a latest observed sample;
• providing a sequence of expected samples {wn}, the sequence of expected samples forming a sequence of expected-sample subsequences {Wn}, each expected-sample subsequence Wn having an earliest expected sample and a latest expected sample;
• computing a sequence of channel metrics {Γn}, each channel metric Γn being a function of a distance determined from one of the observed-sample subsequences Yn to the corresponding expected-sample subsequence Wn, each channel metric Γn being independent of the earliest observed sample in every prior observed-sample subsequence Yn and the earliest expected sample in every prior expected-sample subsequence Wn;
• computing a mean μΓ of the channel metrics {Γn};
• computing a standard deviation σΓ of the channel metrics {Γn};
• computing a ratio of the mean μΓ to the standard deviation σΓ, the ratio (μΓ/σΓ) corresponding to a signal to noise ratio;
• and
• estimating the bit error rate from the ratio (μΓ/σΓ).

A disk drive having a normal mode of operation and a built-in self-test mode of operation for producing a sequence of channel metrics {Γn}, the disk drive comprising:

• a recording surface having a plurality of bit cells;
• a transducer for reading the plurality of bit cells to produce a noise-corrupted read signal;
• a sampler responsive to the noise-corrupted read signal for generating a sequence of observed samples {yn}, the sequence of observed-samples {yn} forming a sequence of observed-sample sequences {Yn};
• an expected sample generator operative during the built-in self-test mode of operation for providing a sequence of expected samples {wn}, the sequence of expected samples forming a sequence of expected-sample subsequences {Wn};
• channel metrics computer for computing a sequence of channel metrics {Γn}, each channel metric Γn being a function of a distance determined from one of the observed-sample subsequences Yn to the corresponding expected-sample sequence Wn;
• and
• a ratio computer for computing a mean μΓ of the channel metrics Γn, a standard deviation σΓ of the channel metrics Γn, and a ratio of the mean μΓ to the standard deviation σΓ, the ratio (μΓ/σΓ) corresponding to a signal to noise ratio.

A disk drive having a normal mode of operation and a built-in self-test mode of operation for producing a sequence of channel metrics {Γn}, the disk drive comprising:

• a recording surface having a plurality of bit cells;
• a transducer for reading the plurality of bit cells to produce a noise-corrupted read signal;
• a sampler responsive to the noise-corrupted read signal for generating a sequence of observed samples {yn}, the sequence of observed-samples {Yn} forming a sequence of observed-sample sequences {Yn};
• an expected sample generator operative during the built-in self-test mode of operation for providing a sequence of expected samples { wn}, the sequence of expected samples forming a sequence of expected-sample subsequences {Wn};
• channel metrics computer for computing a sequence of channel metrics {Γn}, each channel metric Γn being a function of a distance determined from one of the observed-sample subsequences Yn to the corresponding expected-sample sequence Wn, the channel metrics computer comprising:
• equation circuitry for implementing a plurality of equations to compute a plurality of different channel metrics Γn;
• and
• an equation selection matrix for selecting between the different channel metrics Γn computed by the equation circuitry, the selection based on a selected number of the expected samples {wn}, the equation matrix generating a selected channel metric Γn;
• and
• an accumulator for accumulating the selected channel metric Γn.

A method for computing a sequence of channel metrics {Γn} for characterizing the performance of a disk drive comprising a recording surface having a plurality of bit cells and a transducer for reading the plurality of bit cells to produce a noise-corrupted read signal, the method comprising the steps of:

• sampling the noise-corrupted read signal to generate a sequence of observed samples {yn}, the sequence of observed-samples {yn} forming a sequence of observed-sample sequences {Yn};
• generating, during the built-in self-test mode of operation, a sequence of expected samples {wn}, the sequence of expected samples forming a sequence of expected-sample subsequences {Wn};
• computing a sequence of channel metrics {Γn}, each channel metric Γn being a function of a distance determined from one of the observed-sample subsequences Yn to the corresponding expected-sample sequence Wn, the step of computing the channel metrics comprising the steps of:
• computing a plurality of different channel metrics Γn;
• and
• selecting between the different channel metrics Γn based on a selected number of the expected samples {wn} to generate a selected channel metric Γn ;
• and
• accumulating the selected channel metric Γn.