David E Call

US Patent:

7564236, Jul 21, 2009

Filed:

Jul 1, 2008

Appl. No.:

12/166163

Inventors:

David Ernest Call - Folsom CA, US
Hardayal Singh Gill - Palo Alto CA, US

Assignee:

Hitachi Global Storage Technologies Netherlands B.V. - Amsterdam

International Classification:

G01R 33/09
G11B 5/33
G11B 5/39

US Classification:

324210, 360313, 360319

Abstract:

A method for testing magnetic heads formed on a wafer to detect the presence of thermal induced popcorn noise resulting from thermal fly height control. The method includes performing a quasi test on a magnetic head, the quasi test being performed over 400 or more cycles of magnetic field application. For additional test accuracy, the write head can be cycled while 400 or more cycles of magnetic field are generated.

US Patent:

8040131, Oct 18, 2011

Filed:

Jul 1, 2008

Appl. No.:

12/166078

Inventors:

David Ernest Call - Folsom CA, US
Ciaran Avram Fox - Sunnyvale CA, US
Robert Langland Smith - Sunnyvale CA, US
Chin-Yu Yeh - San Jose CA, US

Assignee:

Hitachi Global Storage Technologies Netherlands B.V. - Amsterdam

International Classification:

G01R 33/12

US Classification:

324210

Abstract:

A method for testing a magnetic head to determine whether the magnetic head is unacceptably affected by temperature variations. The test includes testing the magnetic head at different temperatures and measuring either or both of a signal amplitude and a signal asymmetry of a signal from the magnetic head at the different temperatures. If signal amplitude or signal asymmetry vary excessively as a result of the temperature change then the head can be scrapped.

US Patent:

56028067, Feb 11, 1997

Filed:

Jun 28, 1995

Appl. No.:

8/495967

Inventors:

Patrick C. Arnett - Morgan Hill CA
David E. Call - Hollister CA
Blair I. Finkelstein - Tucson AZ
Glen A. Jaquette - Tucson AZ
Ernesto E. Marinero - Saratoga CA

Assignee:

International Business Machines Corporation - Armonk NY

International Classification:

G11B 1100

US Classification:

364 13

Abstract:

A light intensity, direct overwrite, magneto-optical system generates signals such that, during the formation of a recording mark on an optical disk, a laser is driven a) at a pedestal power level, then b) at a quench power level for a first quench period t. sub. 1, the quench power level being less than the pedestal power level, then c) at a write power level for a write period t. sub. 2 whereby the reference bit becomes oriented in the writing direction, the write power level being greater than the pedestal power level, then d) at the quench power level for a second quench period t. sub. 3, and then e) at the pedestal power level until the formation of another recording mark begins. The system is provided with a controller to determine optimal lengths of the quench periods t. sub. 1 and t. sub. 3, thereby reducing thermal interference between closely spaced recording marks.

US Patent:

51723654, Dec 15, 1992

Filed:

Sep 11, 1991

Appl. No.:

7/757743

Inventors:

David E. Call - Tucson AZ
Blair I. Finkelstein - Tucson AZ
Catherine S. Singer - Poughkeepsie NY

Assignee:

International Business Machines Corporation - Armonk NY

International Classification:

G11B 7125

US Classification:

369116

Abstract:

Method and apparatus for predicting the approach of semiconductor laser diode end-of-life from the power vs. current characteristic curve of the diode thereby obviating the need for nonvolatile memory. Current measurements are taken for three power levels and the linear slope of the characteristic curve at the high power level is compared to the linear slope at low power levels. When the comparison exceeds predetermined criteria, a flag is raised.

US Patent:

56403810, Jun 17, 1997

Filed:

Mar 8, 1996

Appl. No.:

8/612993

Inventors:

David Ernest Call - Hollister CA
Stephen J. Hrinya - San Jose CA
Jerry Elden Hurst - San Jose CA
Glen Alan Jaquette - Tucson AZ
Anthony Juliana - San Jose CA

Assignee:

International Business Machines Corporation - Armonk NY

International Classification:

G11B 700

US Classification:

369116

Abstract:

An optical disk recorder employs laser drive signals having diverse current or power levels. A scaling digital-analog-converter (DAC) supplies a scaled reference signal to a plurality of scaled DACs. The scaled DACs supply the diverse laser drive signals. Calibrating the scaling DAC calibrates the scaled DACs. A base array of DACs include not only the scaling DAC but a plurality of base array DACs. Such base array DACs control reading operations as well as supplying a threshold current. The threshold current is that laser drive signal current level below which laser 25 does not emit a laser beam. During writing, the CUT current is added to the laser drive currents supplied by the scaled DACs. A desired CUT current is determined by calculating a slope of the laser drive current to emission of radiation. Then the slope is extrapolated to a zero emission point below which no coherent emission of radiation occurs.

US Patent:

55263291, Jun 11, 1996

Filed:

Jan 30, 1995

Appl. No.:

8/381617

Inventors:

John E. Bish - Tucson AZ
David E. Call - Hollister CA
Glen A. Jaquette - Tuscon AZ
Judson A. McDowell - Tuscon AZ
Arturo A. Mojica - Tucson AZ
Lawrence D. Tipton - Tucson AZ

Assignee:

International Business Machines Corporation - Armonk NY

International Classification:

G11B 700

US Classification:

369 32

Abstract:

The present invention provides a method and an apparatus to accurately and consistently distinguish blank sectors from written sectors on optical media despite drive and media variations. A readback envelope threshold is established each time optical media is mounted into an optical drive. In one embodiment, the gain of readback amplifiers are set to a first level, the optical head seeks to and reads a sector or set of sectors on the optical disk known to have information recorded thereon and a first readback envelope generated. The gain of the readback preamplifier is then set to a second level, the optical head seeks to and reads another sector or set of sectors known to have information recorded thereon and a second readback envelope generated. The readback threshold is calculated from the amplitudes of the first and second envelopes. Once the threshold has been calculated for a disk, the drive can scan for a blank sector by comparing the amplitude of the sector's readback envelope with the threshold: if the amplitude is less than the threshold, and no other written format feature is readily indicated the sector can be classified as being blank and it is safe to write to the sector.

US Patent:

53831756, Jan 17, 1995

Filed:

Dec 17, 1992

Appl. No.:

7/992525

Inventors:

Blair I. Finkelstein - Tucson AZ
David E. Call - Tucson AZ

Assignee:

International Business Machines Corporation - Armonk NY

International Classification:

G11B 700

US Classification:

369121

Abstract:

A laser control system for use with an erasable optical disk device to minimize laser feedback during a recording operation. Focus control circuits are utilized to establish a slightly defocused condition prior to a recording operation and maintaining that slightly defocused condition throughout the recording operation. Defocusing the write beam significantly reduces feedback and thereby significantly increases pulse-to-pulse repeatability of the write pulse amplitude at the optical disk.

US Patent:

53094611, May 3, 1994

Filed:

Jul 29, 1992

Appl. No.:

7/921894

Inventors:

David E. Call - Tucson AZ
Glen A. Jaquette - Tucson AZ
Julian Lewkowicz - Tucson AZ

Assignee:

International Business Machines Corporation - Armonk NY

International Classification:

H01S 300

US Classification:

372 38

Abstract:

A drive circuit for a laser which has the capability of eliminating transient conditions when switching a high frequency modulator on or off, and including elements for maintaining desired depth of modulation. These capabilities are included in a circuit that automatically compensates for changing conditions due to temperature, laser characteristics and fluctuations in media reflectivity.