Guzik Technical Enterprises

Infinitum Solutions, Inc.

Hgst Netherlands, B.v.

Western Digital Technologies, Inc.

Hitachi Global Storage Technologies Netherlands B.v.

Alexander M Taratorin

Anatoli B Stein

Semen P Volfbeyn

Valeriy Serebryanskiy

Weldon Mark Hanson

Igor Tarnikov

Zhigang Bai

Lijie Guan

Suping Song

Changqing Shi

Yaguang Wei

Terence T Lam

Roger William Wood

Michael Kuok San Ho

Venkatesh Chembrolu

Supradeep Narayana

Juergen Heidmann

Anna Zheng

Henry Patland

Wade A Ogle

Lauri Viitas

Richard Leo Galbraith

John Thomas Contreras

Samir Y Garzon

Michael Paul Salo

Mark A Nichols

Alexander Tesler

Jing Lou

Dmitry Varsanofiev

Andrew Kogan

A magnetic recording write head has an electrically-conductive structure in the write gap between the write pole and the trailing shield and electrical circuitry for directing current through the write gap. The current through the electrically-conductive structure generates a circular Ampere field which, at the disk-facing end of the write pole, is substantially parallel to the disk-facing end of the write pole. The electrically-conductive structure in the write gap may be a STO or an electrically-conductive layer that is not part of a STO. The current direction through the electrically-conductive structure in the write gap is selected so that the generated Ampere field at the write pole end is in substantially the same direction as the magnetization direction of the write head side shields, which has been discovered to result in minimization of cross-track interference.

Magnetic recording write head with selected write gap current direction for minimization of cross-track interference

A real time digital trigger detection channel includes an event detector, a pulse former, a low pass filter, an analog-to-digital converter (ADC) and a Discrete Fourier Transform (DFT) processor coupled in series. The event detector is responsive to an applied input signal and the presence of information requiring digital trigger generation. The pulse former generates a pre-determined, limited length, stable pulse signal which is applied to an anti-aliasing, pulse shaping low pass filter. The resultant shaped pulse signal is converted to a sequence of sample values by the ADC, which in turn are applied to the DFT processor, which in turn calculates a discrete Fourier transform of the output sequence of ADC samples, performing trigger position calculation based on values determined by the DFT processor.

High resolution digital trigger detector

A method and apparatus for resolving time base-generated errors from sampling scope-based measurements. Mutually synchronized repetitive waveform-to-be-analyzed signals (WAS) and repetitive sinusoidal reference signals (RS) are respectively applied to a first channel and a second channel of a sampling scope. A time base generator applies a sampling signal to the first and second channels. An average sine wave period Tfor k samples of RS is determined, followed by determination of phase error &#x3c6;for each of the k samples, corresponding to phase differences between an ideal sine wave signal and the applied reference sinusoidal signal. Time base error values dfor k samples are calculated from d=&#x3c6;*T&#x3c0;. Error values dcorrect time base errors in the sampling signal, and the WAS is re-sampled at sampling times adjusted by d.

Time base correction method for high accuracy sampling scope-based measurements

A method and system for calibrating a time-interleaved digital to analog converter (DAC) provides equalization of frequency response misalignments in sub-DACs forming the DAC. In a calibration mode, test signals are applied to an DAC and output amplitudes and phases of are measured. From the measured values, complex values of the gains of the respective sub-DACs. h(F) are determined and a specified target frequency response T(F) for a tandem connection equalizer-DAC is determined. For each of a plurality of test frequencies, complex values of equalizer gains Eqare determined from Eq(F)=T(F)/h(F), to form equalizing frequency responses. Sets of equalizing coefficients C(p) pursuant to discrete Fourier transforms on Eq(F). In an operation mode, a digital input signal is transformed input into an equalized digital signal E(n) through use of the sets of equalizing coefficients C(p).

Equalization of sub-DAC frequency response misalignments in time-interleaved high-speed digital to analog converters

A digital down-converter with baseband equalization comprises a composite analog-to-digital converter (ADC) adapted to convert an applied RF analog signal to be processed to a digital signal, and then down-convert the digital signal to a baseband frequency region, and then perform equalization on the down-converted digital signal, thereby reducing distortions caused by introduction of spurious signals by the ADC.

Digital down converter with baseband equalization

A method, apparatus, and system are provided for implementing track following using signal asymmetry metrics monitored during read back in hard disk drives (HDDs). Signal asymmetry metrics monitored during read back are used together with a position error signal (PES) to correct and guide the position of a read sensor with respect to a written track in the HDD.

Implementing enhanced track following during read back using head asymmetry metrics in hard disk drives

Measurement of group delay for a device under test (DUT). A test signal includes (i) a low frequency sine wave f, (ii) sine wave harmonics at a high frequency f, (iii) L pairs of sideband components at frequencies k&#xb7;f&#xb1;2&#xb7;f, where k odd, and M pairs of sideband components at frequencies k&#xb7;f&#xb1;f, where k is even. At DUT output, (i) phase &#x3d5;at frequency fis measured, (ii) both sideband phase &#x3d5;(k) at frequencies k&#xb7;f+2&#xb7;fand phase &#x3d5;(k) at frequencies k&#xb7;f&#x2212;2&#xb7;ffor odd k, are measured, and (iii) both sideband phases &#x3d5;(k) at frequencies k&#xb7;f+fand &#x3d5;(k) at frequencies k&#xb7;f&#x2212;ffor even k, are measured. Group delay &#x3c4;at frequencies k&#xb7;F, are determined from: &#x3c4;=(&#x3d5;(k)&#x2212;&#x3d5;(k)&#x2212;4&#xb7;&#x3d5;)/(4&#xb7;f) for k odd, and &#x3c4;=(&#x3d5;(k)&#x2212;&#x3d5;(k)&#x2212;2&#xb7;&#x3d5;)/(2&#xb7;f) for k even.

Group delay measurement apparatus and method

A digital down converter with an equalizer translates an ADC output signal to a low frequency spectral region, followed by decimation. All operations of correction of the processed signal are carried out with a reduced sampling rate compared with sampling rates of the prior art. Equalization is performed only in a frequency pass band of the down converter. The achieved reduction of the required computation resources is sufficient to enable the down converter with equalization to operate in a real time mode.

Digital down converter with equalization

A digital down converter with equalization includes a composite ADC that performs demodulation of a received analog signal, converting the signal into in phase baseband signal and quadrature baseband signal. Equalization is performed to correct for misalignment of the frequency responses of the sub-ADCs in the composite ADC. In a form, ADC output signals are applied to a mixer array to frequency down-shift the digital form of the input signal, followed by digital filtering to effect convolutions of portions of the digital form of the input signal with a set of convolution coefficients determined so that the net processing is mathematically equivalent to down conversion with equalization. In another form, the ADC output signals are directly applied to a digital filter to effect both frequency down-shifting and convolutions, with filter coefficients determined so that the net processing is mathematically equivalent to down conversion with equalization.

A read head is tested by measuring the thermal magnetic fluctuation noise spectrum. A non-uniformity in the magnetic field of the free layer is produced and the thermal magnetic fluctuation noise spectrum is measured, with and/or without an external magnetic field applied. A peak in the thermal magnetic fluctuation noise spectrum can be used to derive the desired dimension of the free layer, such as track width and stripe height. The resulting measurement may then be fed back into the process control for the production of the read heads if desired. Additionally, the stiffness of the free layer and the strength of the reference layer may be determined using ferromagnetic resonance peaks in the thermal magnetic fluctuation noise spectrum.

Read sensor testing using thermal magnetic fluctuation noise spectra

Digital signal acquisition system is triggered when an input waveform matches a known reference waveform. This is achieved by calculating a stream of error metric values defined as a sum of absolute values of differences between incoming and reference samples. An error metric is calculated using only byte operations, which is advantageous for hardware implementation. A waveform trigger is determined by a sample index corresponding to a minimum value of the error metric and corresponds to a best match between input and reference waveforms. A waveform trigger is used for synchronous averaging and estimating time domain noise voltage. A reference waveform updates in poor SNR conditions to provide robust estimates of time domain noise by reducing reference waveform jitter.

Method and apparatus for data acquisition with waveform trigger

A two-stage digital down-conversion device for optimal detection of varying RF pulses incorporates a front end analog to digital converter (ADC), which samples an input RF signal and performs a first stage digital down conversion in wide bandwidth by means of two digital local oscillator multipliers, low pass filters and decimators. A stream of first stage quadrature I and Q samples is analyzed by a first stage I/Q processor. The I/Q processor generates an RF pulse trigger based on a first-stage envelope signal, center frequency and frequency span data which are used for a second stage narrow band digital down-conversion. The second stage digital down-conversion is based on mixing the first stage I and Q data samples with a second stage local oscillator, further low pass filtering and decimation using a second bandwidth. A stream of second stage I/Q quadrature samples has an optimal signal to noise ratio and allows accurate estimation of RF pulse parameters (magnitude, phase and frequency) by means of a second I/Q signal processor and/or by storing second I/Q data for subsequent processing and analysis.

Two-stage digital down-conversion of RF pulses

Disk drives with a Channel System and Write Driver Preamp architecture that dynamically adjusts the write driver's signal wave-shape depending on the write data signal pattern are described. The wave-shape control signal is generated in the Channel and transmitted to the Write Driver Preamp. Embodiments of the invention provide discrete n-level overshoot amplitude control using amplitude-level modulated (AML) signal. One embodiment implements a look-ahead strategy overshoot amplitude control where the overshoot amplitude for each transition depends only on the subsequent (following) bits in the data stream and not on any previously recorded data.

Disk drive with channel and preamp with dynamic write-current control for write head

A testing device tests a magnetic head with a read head structure including a read head element while applying an external magnetic field to the magnetic head. The testing device receives signals from the read head element and processes the signals to generate a spectral power density for the signals. The spectral power density is characterized for at least one frequency range. The characterization of the spectral power density is used to determine a characteristic of noise from the read head structure. The signals from the read head may be received with different applied magnetic fields and/or before or while thermally exciting the magnetic head. Additionally, a histogram of the signals may be generated and used to determine a second characteristic of the noise.

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Sunnyvale, CA, United States of America

Alexander M Taratorin