Magnetic disk apparatus and a thermal asperity compensation method of the same

A magnetic disk apparatus comprising:

• reproducing means for reproducing a signal recorded in a medium with a magnetoresistive element and outputting a reproduced signal;
• detecting means, having a predetermined detection level, for detecting thermal asperity from the reproduced signal;
• attenuating means for attenuating a predetermined low-frequency component of the reproduced signal output from said reproducing means in order to remove a thermal asperity component;
• variable gain amplifying means for amplifying the reproduced signal output from said attenuating means by using a variable gain;
• gain control means for controlling the gain of said variable gain amplifying means so as to make an amplitude of the reproduced signal output from said variable gain amplifying means constant;
• first hold means for holding gain control by said gain control means for a first predetermined period upon detection of the thermal asperity by said detecting means;
• sample means for sampling thee reproduced signal output from said variable gain amplifying means at a predetermined timing;
• phase control means for controlling a phase of sampling by said sample means so as to synchronize the sampling phase with the reproduced signal;
• second hold means for holding phase control of said phase control means for a second predetermined period upon detection of the thermal asperity by said detecting means;
• and
• control means for controlling the detection level of said detecting means, an attenuation property of said attenuating means, the first predetermined period of said first hold means, and the second predetermined period of said second hold means.

A method of compensating thermal asperity using a magnetic disk apparatus that includes:

• reproducing means for reproducing a signal recorded in a medium and outputting a reproduced signal;
• reproduced signal processing means having:
• a thermal asperity (TA) cancel filter for attenuating a TA component contained in the reproduced signal output from said reproducing means,
• a variable gain amplifier (VGA) for amplifying an output signal from the TA cancel filter at a variable amplifying rate,
• an automatic gain control (AGC) for controlling the amplifying rate of the VGA on the basis of an amplitude of the output signal from the TA cancel filter thus keeping an output signal from the VGA at a constant voltage level,
• an analog filter for subjecting the output signal from the VGA to a predetermined filtering process,
• an analog to digital converter (ADC) for converting the filtered signal from the analog filter into a digital signal in accordance with a reference clock,
• a digital filter for subjecting the output from the ADC to a predetermined signal process, and outputting a digital data, and
• a phase-locked loop (PLL) for generating the reference clock on the basis of the digital data from the digital filter;
• wherein the method comprises the steps of:
• setting a TA detection level;
• setting a resistance value of a rheostat of said cancel filter;
• setting a TA hold time of said AGC;
• setting a TA hold time of said PLL;
• and
• detecting a TA component from the reproduced signal by using the detection level set in the TA detection level setting step.

A thermal asperity compensation method of a magnetic disk apparatus, comprising the steps of:

• converting information recorded in a magnetic storage medium into an electrical signal by using a magnetoresistive element, and reproducing the information on the basis of the electrical signal, said electrical signal including thermal asperity;
• amplifying the electrical signal from said magnetoresistive element by a first amplifying circuit;
• amplifying the signal amplified by said first amplifying circuit by a second amplifying circuit such that an amplitude of an output from the second amplifying circuit is kept constant;
• detecting the thermal asperity of the signal amplified by said second amplifying circuit in accordance with a predetermined detection level;
• compensating for the thermal asperity using a filter having a characteristic of attenuating a thermal asperity component with a predetermined low-frequency range attenuation characteristic;
• holding a control operation of a sample timing by a PLL circuit for a predetermined PLL hold time upon detection of the thermal asperity;
• and
• holding a control operation for keeping the amplitude of the signal amplified by said second amplifying circuit constant for a predetermined AGC hold time upon detection of the thermal asperity.