Seagate Technology Incorporated

Robert F Smith

William D Huber

John C Kuklewicz

Terry A Aultman

A more linear duty cycle modulator is made by converting the sine wave bias into a triangle wave bias utilizing a sample and hold circuit as the base band signal is added; on readout, low pass filtering of the high frequency content of the duty cycle modulated waveform, the base band signal is recovered at full amplitude as if saturation recording was being utilized. In a further preferred approach, quadature amplitude modulation and demodulation is utilized.

Efficient linearization of saturation channels

A surface containing tracks of readable changes in state contains packets of servo control information. The packets of servo control information contain position information and additional information. The position information is amplitude encoded within a series of changes of state. The additional information is angle encoded within the same series of changes of state used to encode position information.

Method using magnetic disk servo pattern with buried identification

A second order PLL uses on-chip dynamically configurable compensation to permit varying loop bandwidth and damping ratio simultaneously in response to command signals. In a first embodiment, a type 2 PLL is compensated by synthesizing a two-pole lowpass filter, a zero, and a gain-programmable integrator. By appropriate selection of transfer function characteristics associated with each of these three building blocks, the open loop PLL transfer function may be remotely varied by scaling resistance or transconductance. In a second embodiment, a type 2 PLL is compensated using a simple series R-C in parallel with C configuration, wherein component selection results in a transfer function that permits relocation of a zero and a pole by varying a single resistance or transconductance. Such variation is preferably accomplished using ganged banks of resistors, remotely switched by associated metal-on-silicon transistors. In a hard disc data recovery application, wherein the recovered data bit rate varies as a function of read/write head position, generated control signals cause PLL compensation to be dynamically varied as a function of the data bit rate. This permits an optimized bandwidth and damping ratio to remain substantially constant over varying data bit rates. In other frequency agile applications, control signals commanding compensation configuration will be otherwise generated.

Method and apparatus for dynamic pole-zero reconfiguration for use with

For disk drives having dual element heads, an invention for providing self-calibration of hard-disk writer elements to reader elements offsets. A method is provided for positioning a reader element for reading information on a disk, and from the information read, determining a reference line for the writer element. The method may be incorporated into a hard-disk in the form of a self-calibration routine in memory. The self-calibration routine may be used for computing offsets for separate writer/reader elements in a dual head assembly. Also, apparatus are provided for self-calibration of hard-disk writer to reader element offsets.

Self-calibration for computer disk read/write offsets

A preamplifier configured for connection to a magnetoresistive transducer makes use of a first and second transistor connected in a common emitter differential pair configuration. The differential pair configuration has a pair of input terminals and a pair of output terminals. A first feedback circuit is included for providing feedback to at least one of a pair input terminals based on selected relatively slowly changing voltages between a pair of preamplifier output terminals. In this manner, the first feedback circuit minimizes differential voltages at the preamplifier output terminals. A second feedback circuit is provided for supplying feedback to at least one of the preamplifier input terminals based on relatively low frequency voltage magnitudes at one of the pair of input terminals. In this manner, a selected common mode voltage magnitude is maintained at one of the pair of input terminals.

Electronically coupled high-impedance magnetoresistive preamplifier

A shock load detection device mounted on a disk drive unit. The detection device is comprised of a piezoelectric polymer film encapsulated and electrically shielded by a metallic or metallic coated package. Electrical contacts are provided for on the piezoelectric polymer film and are connected to amplification and comparator circuitry which issues a write fault signal upon detection of external force in excess of a predetermined threshold. The shock sensor may be mounted on the computer disk drive of the unit in such a manner as to be at a 45.degree. angle to each of the x, y and z axis of the orthogonal coordinate system so that linear and torsional forces may be monitored.

Apparatus for sensing operating shock on a disk drive

A preamplifier circuit amplifies signals from a magneto-resistive element. The preamplifier circuit utilizes a voltage regulator to regulate one terminal of a magneto-resistive element at a predetermined voltage. A first feedback loop is used to minimize a differential DC component and a differential low frequency component of the differential output signal. A second feedback loop is utilized to cause a common mode component of the differential output signal to track an externally supplied reference voltage. The preamplifier of the present invention protects the magneto-resistive elements from short circuits of the disc medium, is powered by a single-ended power supply, and is capable of being coupled with other circuitry without physical coupling capacitors.

MR preamplifier having feedback loops for minimizing differential low

One or more active RC filter network stages of an electronically variable equalizer filter have R values which can be varied to maintain a substantially constant ratio of R values for each stage to vary the cutoff frequency of the equalizer filter while maintaining the relative shapes of the magnitude and phase characteristics of the equalizer filter. A control signal is generated to simultaneously vary the R values for the various network stages. The resistance value of the RC circuit of monostable multivibrator is controlled by control signal so that the multivibrator output pulse width is equal to a reference pulse width. The control signal is utilized to obtain the same R value for a number of other R values formed on a single substrate.

Electronically variable equalizer

A system for evaluating a recording system is disclosed, which includes a monostable multivibrator (MMV) for receiving the recovered data stream from the disc drive. The time constant of the MMV is controlled by a second, matched MMV which receives a fixed frequency input. By applying the output of this matched MMV to another input of the MMV receiving the recovered data, the time constant of the first multivibrator may be adjusted with the delay being a function of the period of the input frequency to the second multivibrator.

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San Jose, CA, United States of America

Robert F Smith