Multi-state preamplifier for disk drives

A preamplifier for a magnetic recording disk drive comprising:

• a means for selecting a current-sensing mode of the preamplifier when a value representing a resistance of a selected MR element is greater than a first threshold value;
• a means for selecting a voltage-sensing mode of the preamplifier when the value representing the resistance of the selected MR element is less than the first threshold value less a value representing a range of uncertainty of said first threshold value;
• a means of selecting the voltage-sensing mode when the value representing the resistance of the selected MR element is not less than the first threshold value less the value representing a range of uncertainty of said first threshold value and, a value representing an impedance of an interconnect line coupled to the selected MR element is greater than a second threshold value;
• and
• a means of selecting the current-sensing mode when the value representing the resistance of the selected MR element is not less than the first threshold value less the value representing a range of uncertainty of said first threshold value and, the value representing an impedance of the interconnect line coupled to the selected MR element is not greater than the second threshold value.

A method of selecting a preamplifier mode for a magnetic recording disk drive comprising the steps of:

• selecting a current-sensing mode of the preamplifier when a value representing a resistance of a selected MR element is greater than a first threshold value;
• selecting a voltage-sensing mode of the preamplifier when the value representing the resistance of the selected MR element is less than the first threshold value less a value representing a range of uncertainty of said first threshold value;
• selecting the voltage-sensing mode when the value representing the resistance of the selected MR element is not less than the first threshold value of less the value representing a range of uncertainty of said first threshold value and, a value representing an impedance of an interconnect line coupled to the selected MR element is greater than a second threshold value;
• and
• selecting the current-sensing mode when the value representing the resistance of the selected MR element is not less than the first threshold value less the value representing a range of uncertainty of said first threshold value and, the value representing an impedance of the interconnect line coupled to the selected MR element is not greater than the second threshold value.

A method for choosing a voltage-sensing or a current- sensing mode for a preamplifier for a magnetic recording disk drive comprising the steps of:

• loading values representing a resistance of a selected MR element and an impedance of an interconnect line coupled to the selected MR element;
• comparing the value representing resistance of the selected MR element with a first threshold value;
• selecting the current-sensing mode when the value representing resistance of the selected MR element is greater than the first threshold value;
• comparing the value representing resistance of the selected MR element with the first threshold value less a value representing a range of uncertainty of said first threshold value when the value representing resistance of the selected MR element is not greater than the first threshold value;
• selecting the voltage-sensing mode when the value representing resistance of the selected MR element is less than the first threshold value less the value representing a range of uncertainty of said first threshold value;
• comparing the value representing an impedance of the interconnect line coupled to the selected MR element with a second threshold value when the value representing resistance of the selected MR element is not less than the first threshold value less the stored value representing a range of uncertainty of said first threshold value;
• selecting the voltage-sensing mode when the value representing the impedance of the interconnect line coupled to the selected MR element is greater than the second threshold value;
• and
• selecting the current-sensing mode when the value representing the impedance of the interconnect line coupled to the selected MR element is less than the second threshold value.

A method for choosing a voltage-sensing or a current-sensing mode for a preamplifier for a magnetic recording disk dive comprising the steps of:

• selecting a read/write head having a write element and an MR element for reading and a corresponding data track on a disk surface;
• writing a magnetic signal on a first segment of the data track with the write element at a first frequency and writing a magnetic signal on a second segment of the data track with the write element at a second frequency, wherein the second frequency is higher than the first frequency;
• switching the preamplifier to the voltage-sensing mode;
• reading, with the MR element, the first segment of the data track at the first frequency to obtain a first amplitude of an output signal from the preamplifier, and reading, with the MR element, the second segment of the data track at the second frequency to obtain a second amplitude of an output signal from the preamplifier, and recording a first amplitude difference representing the difference between said first amplitude and said second amplitude read in the voltage-sensing mode;
• switching the preamplifier to the current-sensing mode;
• reading, with the MR element, the first segment of the data track at the first frequency to obtain a first amplitude of an output signal from the preamplifier, and reading, with the MR element, the second segment of the data track at the second frequency to obtain a second amplitude of an output signal from the preamplifier, and recording a second amplitude difference representing the difference between said first amplitude and said second amplitude read in the current-sensing mode;
• comparing the first amplitude difference and the second amplitude difference to determine the sensing mode having a smaller value of the amplitude difference;
• assigning the sensing mode having the smaller value of the amplitude difference as an assigned sensing mode for the selected MR element;
• and
• recording the assigned sensing mode for the selected MR element.