Abstract: A method and apparatus for detecting a high flying condition of a transducer head in a computer disk drive is provided. The method and apparatus allow the detection of high fly write events that occur over one or a small number of data sectors. In addition, the present invention provides a method and apparatus for detecting high fly write events with a great deal of sensitivity. The method and apparatus of the present invention provide quick response and high sensitivity by monitoring the strength of a signal derived from data written to the disk, and signaling a high fly write event if the monitored signal strength in connection with a particular piece of data is less than a stored high fly write number corresponding to that piece of data by a predetermined amount.

Abstract: A method and apparatus for detecting a high fly write condition in a disk drive is disclosed. Amplitudes of automatic gain control (AGC) fields are used in connection with determining whether a high fly write condition exists in a disk drive, since the amplitude of an AGC field read by a head is generally related to the flying height of the head. In one embodiment, a calibration process is performed to obtain average amplitudes of AGC fields on a zone-by-zone basis for a head associated with a disk surface. These average amplitudes of AGC fields are then stored onto the disk surface for later use. When a write operation is to be performed, the head measures the amplitude of the AGC field associated with a data sector onto which a block of data is to be stored. The measured amplitude of the AGC field is compared to the average amplitude of the AGC fields for the zone associated with the AGC field being read.

Abstract: A method and apparatus for detecting a high fly write event in a computer disk drive is provided. The method and apparatus allow the detection of high fly write events occurring over very short time spans. In addition, the present invention provides a method and apparatus for detecting high fly write events with a great deal of sensitivity. The method and apparatus of the present invention provide quick response and high sensitivity by monitoring the strength of a signal derived from a servo sector position burst or a group of bursts, and signaling a high fly write event if the monitored signal strength is less than a predetermined or threshold amount.

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.

Abstract: Apparatus and method for calibrating the drive current circuit of a semiconductor laser diode subject to reflected optical feedback from a target surface such an an optical recording disk. The method makes use of two power output vs. drive current characteristic curves for the laser, one curve for in focus condition and one for out of focus condition, wherein the curves exhibit an asymptotic region at high power levels (P.sub.2). Measurement of drive current (I.sub.2) power level P.sub.2 is taken under an out of focus condition. Measurements of drive current at a predetermined low power level P.sub.1 are taken for both (I.sub.1) and in focus condition (I.sub.3). The linear slope of the in focus curve can thus be calculated to set desired power levels.

Abstract: An optical disk recorder has a laser driven by a digital analog converter (DAC). During initialization a pair of comparators actuated at minimum and at maximum power levels for actuating a microprocessor to calibrate a DAC 23 between the minimum and maximum power levels rended of digital input changed to the DAC. The same comparators can be used during normal recording and reading operations for detecting under and over power conditions of the laser. Procedures for the calibration and over power and under power detection are described.

Abstract: A data detection circuit employing either amplitude or transition location techniques to adjust a detection threshold for following shifts in baseline of the signal being detected. In the amplitude version, the midway amplitude value between a detected succession of positive and negative peaks adjusts the detection threshold such that threshold adjustment occurs in one detection period and is used in the immediately-following detection period. In the transition-position detection, the relative location in time of successive transitions, represented by samples of the transition of a read signal, are integrated and averaged for providing detection which tracks baseline shifts. In all cases, shifting of detection threshold is always immediately adjacent the usage of a detection threshold which continually follows a shifting DC baseline of the input signal.

Abstract: Recording operations for an optical disk recorder are calibrated by adjusting recording power level (light intensity) such that a permissible crosstalk can be detected in adjacent erased tracks. Following the power level calibration, pulse duration or width is calibrated for a predetermined symmetry of recorded pulses along the calibration track. Various sequences and procedures are described. Calibration occurs at a plurality of radially spaced-apart tracks.

Abstract: A focus acquire circuit for use in optical systems, such as optical data recorders and players, uses up to three parameters signals to indicate an in-focus condition. The zero crossing of a focus error signal is combined with a signal indicating that the focus error signal has approached a peak value and with a signal indicating a change in laser drive signal amplitude to indicate an in-focus condition. Various circuit details are illustrated showing how the three parameters cna be combined together for indicating an in-focus condition.

Abstract: An optical information-bearing-signal recorder employs thermally-induced recording of ablative, material movement, material phase change, magneto-optic or similar technologies. Synchronous noise in the recording is reduced by employing a heat-inducing energy pulse, coherent light for example, shaped to have an initial recording-initiating intensity amplitude followed by a recording-sustaining amplitude. The duration of the recording-initiating amplitude portion is constant for all lengths of signals being recorded. When a rotating optical disk is employed as a record-bearing medium, the recording-initiating and recording-sustaining amplitudes are increased with increasing radius of the recording on the disk.

Abstract: An electromagnetic transducer particularly of the magneto-resistive (MR) type is biased by an inductive circuit means and operates within the linear portion of its characteristic curve. The inductive circuit means is interconnected to the output terminals of said transducer. An amplifier means is connected to the output terminals of the transducer and the inductive circuit means. The amplifier means is also biased by the inductive circuit means. The biasing scheme is enhanced when a gyrator is used as the inductive circuit means.

Abstract: Two magnetoresistive (MR) elements are connected with two matched impedance elements in a bridge arrangement for sensing magnetic flux manifesting information recorded on magnetic media. An alternating current (AC) bias is applied to the bridge's input, and short-term variations in the bridge output signal envelope are detected as representing recorded information. Long-term (average) variations in the signal envelope are also detected and used to adjust the AC bias to maintain a constant average envelope. Additional bridge inputs may be connected in parallel with the first, and the additional bridges' outputs used to derive additional information signals without any additional AC bias adjustment circuits.