International Business Machines Corporation

Wayne Leung Cheung

Ju-Hi John Hong

Kok-Kia Chew

Karl Arnold Belser

David W Albrecht

Stephen A Jove

John Jeffrey Stephenson

Francis Edward Mueller

Chung Chuan Liu

Thinh Huu Nguyen

Louis Joseph Serrano

Mohamad Towfik Krounbi

Michael Paul Salo

Chorng-Kuang Wang

Kevin Roy Vannorsdel

Donald Lee Clare

Scott Arthur Thomas

Mohammed Amine Hajji

Chenhuei J Chaing

Dave Anthony Freitas

A preamplifier system is provided for use with a magneto-resistive (MR) sensor. Included is an alternating current (AC) coupling module connected to the MR sensor for blocking a direct current (DC) voltage associated with an input signal, and filtering low frequency noise associated with the input signal. Also provided is a gain stage module coupled to the AC coupling module. The gain stage module includes a plurality of cascode field effect transistors (FETs) configured for amplifying the input signal, while reducing intrinsic noise and increasing operational bandwidth. Coupled to the gain stage module is a control circuit for feeding back an output of the gain stage module for bias regulation and disturbance rejection.

CMOS low-noise MR read head pre-amplifier circuit

A method and apparatus for providing matched differential MR biasing and pre-amplification. Tightly matched and well centered low-level MR bias voltage is provided directly to the sensing element for controlled input-impedance differential pre-amplification without common-mode voltage level control with loops.

Method and apparatus for providing matched differential MR biasing and pre-amplification

A magneto-resistive (M-R) head has a read element with a servo sensing width as wide as a data track width and a data sensing width of less than one data track width. The two read sensing widths are achieved by using a single read element having a center electrical contact from the M-R read element that effectively reduces the sensing width of the read element. In a first embodiment, the servo sensing width comprises a first portion of the read element and the data sensing width comprises a second, smaller portion of the read element. In a second embodiment, the servo sensing width comprises the entire read element width and the data sensing width comprises a portion thereof. In yet another embodiment, abutting read elements are constructed to enable separate optimization of each sensing width. The wide servo sensing width permits use of a wide servo pattern having servo bursts as wide as a data track width. A position error sensing (PES) signal produced with the wide servo read element and wide servo pattern has increased linearity and accuracy.

Disk drive with wide servo burst pattern and wide servo sensing element

A multi-track density direct access storage device is disclosed. In accordance with a preferred embodiment of the present invention, a direct access storage device for data storage within a data processing system comprises a housing, a rotatable spindle, at least one disk, and several heads. The disk is fixedly mounted to the rotatable spindle, and the rotatable spindle is rotated by a motor within the housing. A first disk surface of the disk has a first track density and a second disk surface of the disk has a second track density; wherein the second track density is preferably greater than the first track density. Each of the several heads contains a transducer to read and write information from and to the disk during the disk rotation. Under this configuration, the lower storage density it first disk surface is utilized to store data that are frequently accessed while the higher storage density second disk surface is for storage capacity supplementation such that the total data storage capacity of the direct access storage device can be increased without degrading the data-accessing performance.

Multi-track density direct access storage device

A digital servo system for a disk drive provides servo information signal demodulation. The system includes a digital demodulator including a burst signal accumulator that accumulates terms according to respective burst timing intervals to produce a digital, quadrature position error signal (PES). The demodulator also can include a dibit burst filter with synchronous dibit sampling preferably implemented as a Hilbert Transform filter. Alternatively, the demodulator does not include a filter and a squarer and, instead, the squarer comprises a sum-and-squarer that sums the squares of odd and even digitized samples. In another embodiment, the system employs a digital demodulator having a digital squarer that removes any phase component of the digitized servo information signal and includes a burst signal accumulator that accumulates the squared terms according to respective burst timing intervals to produce the PES. The demodulator may include a filter comprising a harmonic notch filter. A spilt burst servo pattern for the servo control system is comprised of half-width transitions that can be written in a signal pass of a recording head and therefore has no phase misalignment between adjacent flux patterns.

Digital pes demodulation for a disk drive servo control system using synchronous digital sampling

Access can be optimized to data strings hierarchically organized on a single disk drive where the data strings are address map defined and recorded in bands of contiguous tracks on a frequency usage basis. The bands are arranged such that each of the most frequently used strings are out-of-phase recorded several times on a counterpart track where the band is located toward the outer disk diameter. The least frequently used strings and sequential data strings are stored elsewhere on the same or other surfaces. A group of three or more bands provides for a more refined partitioning of the data strings on a frequency of usage or a recency of usage basis. The read/write transducer has its idle position over the outer diameter.

Method and apparatus for optimizing access to coded indicia

A servo pattern has bursts that are constructed from two frequencies in a complementary arrangement so that the servo pattern frequencies alternate in adjacent servo tracks. The servo pattern is decoded by a pair of digital notched filters so that each filter notches out readback signal data from a different one of the frequencies to form a combined PES signal produced from each respective frequency and to control movement of the head servo. The complementary arrangement of the servo bursts decreases signal gain differences between the frequencies and improves the accuracy of servo position information. The digital notched filter provides efficient processing of the readback signal and enhances easier selection of filter parameters and easier design of the servo processing circuitry. The servo pattern uses less disk surface area as compared with typical dual or quadrature servo patterns and can be recorded on the disk using fewer servo write steps.

Digital demodulation of a complementary two-frequency servo PES pattern

A multi-track density direct access storage device is disclosed. In accordance with a preferred embodiment of the present invention, a direct access storage device for data storage within a data processing system comprises a housing, a rotatable spindle, at least one disk, and several heads. The disk is fixedly mounted to the rotatable spindle, and the rotatable spindle is rotated by a motor within the housing. A first disk surface of the disk has a first track density and a second disk surface of the disk has a second track density; wherein the second track density is preferably greater than the first track density. Each of the several heads contains a transducer to read and write information from and to the disk during the disk rotation. Under this configuration, the lower storage density first disk surface is utilized to store data that are frequently accessed while the higher storage density second disk surface is for storage capacity supplementation such that the total data storage capacity of the direct access storage device can be increased without degrading the data-accessing performance.

Servo pattern bursts are recorded with two frequencies that are detected using heterodyne detection with oscillators at the same frequency as the respective recorded frequencies. The two frequencies are selected to be orthogonal so the sensed servo pattern of one frequency is zero when detected with the detecting circuitry of the other frequency. The servo pattern bursts of the two frequencies are placed close together on the disk so they are sensed simultaneously so that, with orthogonality processing, a PES signal from a three phase pattern is sufficient to provide a robust linear signal, thereby eliminating one of the bursts from a quadrature pattern and reducing the disk surface area needed in each track for the servo pattern by 25% or more.

Two frequency servo PES pattern

An apparatus, system and method are described for generating a continuous and linear position signal generated from stitched position error signal (PES) components, for use by a servo control system in positioning a transducer with respect to a storage surface. Continuity is achieved by providing a normalization stage in the servo control loop for correcting discontinuities at the stitch points with minimal impact to the PES zero-crossing points. According to a first preferred embodiment normalization is applied using an algorithm determined by the width of the read transducer. According to a second preferred embodiment, normalization is selectively applied near the stitch points of the PES components, but is not applied at their zero-crossing points. In another preferred embodiment, a first normalization algorithm is applied near the stitch points, and a second normalization algorithm is applied at the zero-crossing points. In a fourth embodiment, a smoothing function is applied between the stitch points and zero-crossings to smooth the transition from normalized to unnormalized signal contributions or from signal contributions normalized in a first manner to signal contributions normalized in a second manner. A further aspect of the present invention is to determine whether the PES exceeds a nominal value and if so, to hold the PES at the nominal value at each stitch point.

Disk drive servo sensing gain normalization and linearization

A digital servo control system for a disk drive provides asynchronous servo information signal demodulation. The system includes a digital demodulator having a digital squarer that removes any phase component of the digitized servo information signal and includes a burst signal accumulator that accumulates the squared terms according to respective burst timing intervals to produce a digital, quadrature position error signal (PES). The demodulator also can include a filter comprising a harmonic notch filter preferably implemented as a Hilbert Transform filter. Alternatively, the demodulator does not include a filter and squarer and, instead, the squarer comprises a sum-and-squarer that sums the squares of odd and even digitized samples. A split burst servo pattern for the servo control system is comprised of half-width transitions that can be written in a single pass of a recording head and therefore has no phase misalignment between adjacent flux patterns.

Quadrature servo pattern disk providing asynchronous digital PES

Asynchronous digital PES demodulation disk drive servo control system

A servo system accurately detects and processes signals from servo patterns encoded on magnetic storage disks using weighted accumulation, for use in precisely positioning read/write heads with respect to tracks of data contained on the disks. After servo patterns are sensed by reading them from a disk, the resultant servo signals are processed by weighted accumulation circuitry to provide a position signal, which may be decoded to ascertain the positioning error of the read/write head and to apply any corrections that might be needed. In one embodiment, an amplitude position signal is generated by multiplying the servo signal by complementary quadrature weighting signals, then squaring each quadrature output signal, summing them, and taking the square root of the summed signal. In another embodiment, a phase position signal is generated by multiplying the servo signal by complementary quadrature weighting signals, dividing one of the multiplied signals by the other to provide a quotient signal, and then generating a signal corresponding to the arctangent of the quotient signal. The invention may be implemented with analog or digital circuitry. In an analog embodiment, the quadrature output signals are created using multipliers to multiply the servo signal by complementary analog quadrature weighting signals. In a digital embodiment, the output quadrature signals are created using latches to sample the servo signal at predetermined intervals, selectively multiplying sampled signals by predetermined quadrature weighting signals, and accumulating the resulting signals.

Asynchronous position error signal detector employing weighted

A demodulator for a servo control system receives a servo signal that is produced from reading a servo pattern that comprises a repeating sequence of trigonometric-compensated, phase-encoded magnetic flux transitions that extend continuously across the width of a servo track and includes a burst cosine phase detector that samples the amplitude of the servo signal at regular intervals and produces burst sample data, from which the demodulator produces a position error signal that is a substantially linear function of the servo head position relative to the servo track width. Because a plurality of amplitude samples is taken from each cycle of the servo signal, an increased signal-to-noise ratio can be obtained for the servo signal. The superior signal characteristics permit smaller and less complex demodulator elements to be used, thereby reducing the overall servo control system complexity. The burst cosine phase detector multiplies the servo signal samples with a predetermined set of reference coefficients to produce a linear phase difference that indicates the servo head radial position.

Phase-compensated servo pattern and position error-sensing detector

A disk head position control system having a disk head controller that moves a disk head relative to a surface of a magnetic media disk encoded with a plurality of tracks of a quadrature burst pattern includes a burst pattern that comprises an asynchronous, multi-frequency track address code having burst pattern transitions that extend across the width of a track and are arranged in staggered fashion in alternate tracks such that no transitions between adjacent tracks are aligned in the disk radial direction.

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San Jose, CA, United States of America

Wayne Leung Cheung