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Patent Issued for Storage Device Having Degauss Circuitry with Ramp Generator for Use in Generating Chirped Degauss Signal

July 23, 2014

By a News Reporter-Staff News Editor at Electronics Newsweekly -- From Alexandria, Virginia, VerticalNews journalists report that a patent by the inventors Mazur, Paul (Cottage Grove, MN); Norman, Robert A. (Bloomington, MN); Gleason, Jeffrey A. (Burnsville, MN); Hoque, Anamul (Lakeville, MN), filed on July 24, 2012, was published online on July 8, 2014.

The patent's assignee for patent number 8773817 is LSI Corporation (San Jose, CA).

News editors obtained the following quote from the background information supplied by the inventors: "Disk-based storage devices such as hard disk drives (HDDs) are used to provide non-volatile data storage in a wide variety of different types of data processing systems. A typical HDD comprises a spindle which holds one or more flat circular storage disks, also referred to as platters. Each storage disk comprises a substrate made from a non-magnetic material, such as aluminum or glass, which is coated with one or more thin layers of magnetic material. In operation, data is read from and written to tracks of the storage disk via a read/write head that is moved precisely across the disk surface by a positioning arm as the disk spins at high speed.

"The storage capacity of HDDs continues to increase, and HDDs that can store multiple terabytes (TB) of data are currently available. However, increasing the storage capacity often involves shrinking track dimensions, bit lengths or other features in order to fit more data onto each storage disk, which can lead to a variety of problems, including degraded on-track recording performance, as well as off-track recording performance issues such as adjacent track erasure.

"A number of techniques have been developed in an attempt to further increase storage capacity. For example, a technique known as shingled magnetic recording (SMR) attempts to increase storage capacity of an HDD by 'shingling' a given track over a previously written adjacent track on a storage disk. In another technique, referred to as bit-patterned media (BPM), high density tracks of magnetic islands are preformed on the surface of the storage disk, and bits of data are written to respective ones of these islands. Other techniques include, for example, heat-assisted magnetic recording (HAMR) and microwave-assisted magnetic recording (MAMR). The HAMR technique utilizes a laser to locally preheat an area on the disk surface prior to recording in that area. In the MAMR technique, an additional write head is configured to emit an AC magnetic field that excites ferromagnetic resonance in the media, building up energy that eases the process of writing data.

"HDDs often include a system-on-chip (SOC) to process data from a computer or other processing device into a suitable form to be written to the storage disk, and to transform signal waveforms read back from the storage disk into data for delivery to the computer. The SOC has extensive digital circuitry and has typically utilized advanced complementary metal-oxide-semiconductor (CMOS) technologies to meet cost and performance objectives. The HDD also generally includes a preamplifier that interfaces the SOC to the read/write head used to read data from and write data to the storage disk. As is well known, the read/write head may comprise, for example, separate read and write heads.

"The preamplifier generally comprises one or more write drivers that provide corresponding write signals to the write head in order to write data to the storage disk. Such write signals are generally characterized as current signals, but may alternatively be characterized as voltage signals. Data bits are usually each stored as group of media grains oriented in a common magnetization direction (e.g., up or down). In order to record a given data bit, the write driver generates a write signal that transitions from a negative write current to a positive write current, or vice-versa, where the magnitude of the write current from zero to its peak value may be in the range of about 15 to 65 milliamperes (mA), although different values can be used.

"At the completion of a given write operation, the write head may exhibit remanent magnetization after the write current has been turned off. This residual magnetization or 'domain lock up' can be the cause of a phenomenon known as erase after write (EAW), where a non-energized (i.e., zero write current) head is seen to erase or degrade previously-written areas of the disk. These previously-written areas may comprise user data or even fixed servo sectors that are used to control the tracking of the radial position of the write head. In order to address the EAW problem, a degauss signal may be applied to the write head by the preamplifier immediately after completion of the write operation.

"The typical degauss signal waveform includes current pulses of alternating polarities that repeat at a fixed frequency and decay in steady state amplitude over time. It is also known to vary the frequency of the degauss signal waveform. Waveforms of this type are referred to as 'chirped' degauss signal waveforms. See U.S. application Ser. No. 13/186,445, filed Jul. 19, 2011 in the name of J. S. Goldberg et al. and entitled 'Magnetic Storage Device with Chirped Write Head Degaussing Waveform,' which is commonly assigned herewith and incorporated by reference herein."

As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventors' summary information for this patent: "Illustrative embodiments of the invention provide HDDs or other types of disk-based storage devices that exhibit enhanced operating performance through the use of degauss circuitry including at least one ramp generator for use in generating a chirped degauss signal. For example, such a ramp generator may be configured to generate a current ramp for application to a current controlled oscillator.

"In one embodiment, an HDD or other disk-based storage device comprises a storage disk, a write head configured to write data to the disk, and control circuitry coupled to the write head. The control circuitry comprises at least one write driver and degauss circuitry associated with the write driver. The degauss circuitry is configured to generate a chirped degauss signal to be applied to the write head by the write driver. The degauss circuitry comprises a ramp generator configured to generate a ramp signal for controlling a frequency of at least a portion of a waveform of the chirped degauss signal.

"The ramp signal generated by the ramp generator may comprise a current ramp that is applied to a control input of a current controlled oscillator of the degauss circuitry. In such an arrangement, the ramp generator may illustratively comprise a first programmable digital to analog converter configured to generate a start frequency current of the current ramp responsive to a start frequency control signal, and a second programmable digital to analog converter configured to generate a stop frequency current of the current ramp responsive to a stop frequency control signal, with the first and second programmable digital to analog converters independently setting the respective start and stop frequency currents of the current ramp. The ramp generator may further comprise a reference circuit, an output circuit, slew rate control circuitry configured to control a rate of transition of the current ramp between the start frequency current and the stop frequency current, and switching circuitry configured to control biasing of the reference circuit responsive to a degauss mode signal. More particularly, the switching circuitry responsive to the degauss mode signal controls biasing of the reference circuit between the start frequency current and the stop frequency current in conjunction with initiation of a degauss mode of operation. Also, the switching circuitry further controls coupling of the output circuit to the slew rate control circuitry.

"One or more of the embodiments of the invention provide significant improvements in disk-based storage devices. For example, by providing a degauss signal waveform in which the frequency of the degauss signal can be more easily and accurately controlled, improved write head demagnetization is achieved after each of a plurality of write operations in which data is written to the storage disk, thereby better avoiding problems such as EAW and leading to enhanced overall performance."

For additional information on this patent, see: Mazur, Paul; Norman, Robert A.; Gleason, Jeffrey A.; Hoque, Anamul. Storage Device Having Degauss Circuitry with Ramp Generator for Use in Generating Chirped Degauss Signal. U.S. Patent Number 8773817, filed July 24, 2012, and published online on July 8, 2014. Patent URL:

Keywords for this news article include: Electronics, LSI Corporation, Digital To Analog.

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Source: Electronics Newsweekly

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