Seagate Technology Incorporated

Maxtor Corporation

Sperry Corporation

Memorex Corporation

William D Huber

Robert F Smith

Dennis C Stark

Rod J Swanson

William R McKee

Terry A Aultman

John C Kuklewicz

Nicholas Bucska

Bruce Buxton

Parallel coded spread spectrum communication for data storage

A data storage system achieves improved bandwidth efficiency using a modulated recording signal, channel linearization, and a compressor circuit for compressing peak amplitude of the recording signal. In a preferred embodiment, quadrature amplitude modulation and demodulation is utilized. Another embodiment achieves improved bandwidth efficiency using a recording medium having a substantially rectangular magnetic flux versus magnetic field intensity hysteresis characteristic and a substantially rectangular Kerr rotation versus magnetic field intensity hysteresis characteristic. Yet another embodiment achieves improved bandwidth efficiency using a storage medium having a substantially abrupt flux transition.

Efficient linearization of saturation channels

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.

A magneto-optical recording system achieves improved bandwidth efficiency using a modulated recording signal, recording channel linearization, and a MO medium having a low inter-granular exchange coupling and abrupt flux transitions.

Magneto-optical recording system employing linear recording and playback channels

An apparatus and method for detecting defects in the magnetic medium of a disk drive system includes sampling the output signal of the read channel of the system to provide a sampled output signal. In one embodiment, the sampled output signals from the read channel is squared. A delayed sampled output signal is also provided. The squared sampled output signal is summed with the delayed squared output signal. The square of the expected value of the sum of the squared sampled output signal and the delayed squared output signal is subtracted from the sum to provide a difference output signal. A threshold detector determines when the difference output signal of the subtraction means exceeds a predetermined threshold to provide an output signal indicative of a defect in the medium. One threshold detector determines when the absolute value of the difference output signal exceeds a predetermined threshold value. Another threshold detector determines when the difference output signal of the subtraction means exceeds either a predetermined upper threshold value or a predetermined lower value. The expected value may be a constant. In another embodiment, the absolute value of the sampled output signal and a delayed sampled absolute-value output signal are summed together.

Sampled data flaw detection for magnetic media

An improved data recording system incorporates a detection circuit directly into the data read channel circuitry of the recording system to provide the capability of automatic self-testing and mapping of media flaws. The flaw detection circuit outputs an error signal in response to distortions in the readback signal caused by a defect on the medium. Firmware code is utilized for controlling the scanning of the medium by the flaw detection circuit and for recording the locations of the defects on the medium in response to the error signal. The detection circuit itself comprises a phase-splitter for splitting the readback signal into in-phase and quadrature-phase components. These components are then squared and summed to generate a phase independent flaw signal having an amplitude modulated in relation to the locations of the defects.

Data recording system incorporating flaw detection circuitry

A media flaw detection apparatus having a sensitivity which is independent of the location of the flaw relative to the written test signal. The apparatus is equally sensitive to missing or extra bit defects. According to the invention, in-phase and quadrature-phase signals are heterodyned against the analog playback input signal. The resulting signals are squared and summed to produce a signal analogous to the effect of the flaw.

Media flaw detection apparatus for a magnetic disk drive with squaring

A read channel detector circuit for recovery of digital data from a readback waveform produced by a magnetic recording head is disclosed. The detector circuit includes a forward filter for slimming the rising edge and slurring the falling edge of an isolated input magnetic pulse. Quantized feedback techniques are then used to produce a compensating waveform which is substantially complimentary to the portion of the filtered waveform occurring after T.sub.min. The complimentary waveform is then added to the forward filter output to produce a waveform which is substantially a step function. This step function corresponds to a single digital transition, either positive-going or negative-going in a digital output sequence. The equalized waveform is then limited by a comparator to produce the desired digital output sequence. By slimming only the rising edge of the input magnetic pulse and by using quantized feedback techniques, the overall bandwidth of the system is conserved resulting in an increased binary signalling capability without substantial intersymbol interference.

Read channel detector with improved signaling speed

A read channel detector circuit for recovery of digital data from a readback waveform produced by a magnetic recording head is disclosed. The detector circuit includes a forward filter for slimming the rising edge and slurring the falling edge of an isolated input magnetic pulse. Quantized feedback techniques are then used to produce a compensating waveform which is substantially complimentary to the slurred falling edge of the isolated magnetic pulse. The complimentary waveform is added to the forward filter output to produce a waveform which is substantially a step function. This step function corresponds to a single digital transition, either positive-going or negative-going in a digital output sequence. The equalized waveform is then limited by a comparator to produce the desired digital output sequence. By slimming only the rising edge of the input magnetic pulse and by using quantized feedback techiques, the overall bandwidth of the system is conserved resulting in an increased binary signalling capability without substantial intersymbol interference.

Read channel detector for use in digital magnetic recording systems

Direct current null in the reproduction of a high density, digital, magnetic recording is equalized by the apparatus which first slims the magnetic head output pulse until one-half the main lobe time width of the pulse is equal to one-half the minimum time between polarity transitions, then, integrates the slimmed pulse, centers it about a zero reference voltage level, and finally, through a limiter, produces an output pulse signal which has abrupt output transitions whenever the centered, integrated pulse crosses the zero reference voltage level.

Equalization of DC null in reproducing a high density recording

A pulse improvement circuit for a magnetic readback system produces a data representative signal having symmetrical, equal-amplitude pulses of limited time widths. The circuit includes an equalizer made in accordance to a final transfer function produced as a result of a mathematical convolution of first and second transfer functions. The first transfer function is based on the theory of a matched filter for receiving a signal having data representative and non-white noise pulses contained therein to produce a filter signal having maximum signal to noise ratio. The second transfer function is based on the theory of a Papoulis window function for slimming the pulses contained in the filter signal. A specific circuit implementation of the final transfer function is an eight-pole, inductor-capacitor, ladder network for amplitude equalization coupled to an inductor-capacitor, lattice network including first and second order sections for phase equalization.

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San Jose, CA, United States of America

William D Huber