Maxtor Corporation

Agere Systems Inc.

Syquest Technology, Inc.

Mastor Corporation

Rosser S Wilson

Michael R Spaur

Michael J Mayo

Peter D Butler

Frank Seuberling

In a system having an input signal set with at least two signals having mutually exclusive frequencies f and f being part of the input signal set, whose amplitude is represented in an input digital representation, the amplitudes of each of the at least two signals are digitally represented. A digital representation of the frequency of each of the signals is derived. A digital representation of the sine function and of the cosine function of the frequency of each of the signals is derived based on the digital representation of the frequency. The digital representations of each of the sine and cosine functions is mixed with the input digital representation to derive digital representations of the sine and cosine functions of each of the signals. The digital representations of the sine and cosine functions of each of the signals are processed to derive a digital representation of the amplitude of each of the signals.

Digital processing of pilot-tone amplitudes

A headerless, fault-tolerant sample-data servo pattern, comprising an alternating sequence of first and second servo sectors, with the first servo sectors each including a partial track address and circumferential orientation information, and the second servo sectors each including a full track address, provides an absolute indication of a read/write head's circumferential orientation along a given track on a magnetic disk which is robust in the presence of defects in the magnetic recording medium.

Disk with fault-tolerant sample-data servo pattern

Apparatus for detecting data track misregistration is described. The present invention involves the interaction of a microprocessor with a demodulator. Microcode within the microprocessor initiates a misregistration scan of all data tracks at specific intervals to generate a calibration offset table that is used to direct the heads during the subsequent interval. A demodulator obtains the peak values of calibration servo bursts, displaced one-half of the track width to either side of a track, and outputs a timing pulse proportional to their respective peak voltage values. A timer within the microprocessor extracts the time values, and the misregistration displacement is calculated by the comparison of the inner burst and outer burst time values. The calculated displacement is used in the offset table for subsequent disk references.

Method and apparatus for detecting data track misregistration

A sample data position error signal detection means is described. This invention is suited for use in a digital sector servo in a magnetic media disk drive environment. In particular, the invention relates to the detection and presentation in digital form of position error signals (PES) representative of magnitude and sign of recording head displacement from a track centerline. The circuits disclosed provide a digital representation of PES suitable for direct application to a digital signal processor which controls overall servo positioning operations. The invention detects the PES by an integration method and incorporates the innovation of requiring only two integrators to demodulate a PES having an arbitrarily large number of phases. The invention uses a phaselock oscillator having a hybrid digital/analog phase detector to generate the coherent carrier sequence for synchronous detection of PES. A further innovation of the invention is the use of a fully digital automatic gain control circuit (AGC). Prior embodiments of position demodulators have employed analog AGC approaches which are more sensitive to disk surface flaws and which cannot easily be made adaptive. Furthermore, such features as exponentiation of AGC gain control level can be readily incorporated with no penalty to circuit complexity.

Sample data position error signal detection for digital sector servo

A phase lock loop for a sector servo system. A servo phase lock loop oscillator provides the control timing function of the servo. Initially, the PLO is locked in frequency to a frequency reference obtained from a counter/timer in a digital signal processor (DSP) used to control the servo system. Subsequent to acquisition of the nominal operation frequency, the PLO is caused to lock in turn to gap and frame character markers derived from the digital information encoded into the servo burst. Transition between PLO reference sources is commanded by the microprogram running in the DSP, based upon microprogram assessment of servo PLO status. The PLO outputs timing control tags to the servo control logic and PES demodulator, a reference clock to the file read/write channel, and interrupt pulses to the DSP to synchronize DSP operation with the servo hardware, and initiate periodic DSP computation of the control algorithm.

Phase lock loop for sector servo system

A sample data position error signal detection means. This invention has application in a digital servo in a magnetic media disk drive environment. In particular, the invention relates to the detection in digital form of position error signals (PES) representative of magnitude and sign of recording head displacement from a track center line. The circuits disclosed provide a digital representation of PES suitable for direct application to a digital signal processor which controls overall servo positioning operations. The invention detects the PES by employing a digital integrator which comprises a register and adder. The composite servo data is first amplified by variable gain amplifier and then undergoes low pass filtering before being digitized by an analog to digital converter (ADC). The digital integration is performed by accumulating a constant number of ADC samples in the register. Before being accumulated in the register, the sampled servo data is alternately multiplied by plus or minus one, using an exclusive-OR gate cascade interposed between the ADC output and adder input. The multiplication of the sampled servo data by plus one or minus one is required for synchronous rectification. Upon completion of accumulation of a prescribed number of ADC samples, the contents of the register are transferred to a temporary buffer pending interrogation by the servo controlled digital signal processor.

Synchronous digital detection of position error signal

In the present invention, a single sector counter and accompanying multiple buffer registers are used to provide the sector count for a plurality of recording zones. Initially, the sector counter is validated by synchronizing it with an index mark. In one embodiment, an angular position sensing counter counts a clock having a frequency and phase to match the occurrence of segments in a reference zone. A look up table or computation provides an offset value representing the difference between each reference zone segment boundary, and the occurrence of the next consecutive sector in each of the recording zones. Additional logic generates periodic sector pulses once the zone transition has been accomplished, and provides means to prevent generation of shortened sector intervals. This permits rapid validation of the sector signal so that it is no longer necessary to wait for the index in a hard-sectored drive before establishing the sector position when changing zones. This improves the latency of the disk drive and overall system performance.

Zone density sector counter

A fault tolerant servo index scheme is described. The present invention provides a servo index pattern and detection method which can be utilized to any servo scheme, including, but not limited to, sector servo and dedicated surface servo. The servo pattern of the preferred embodiment of present invention is a twelve bit pattern chosen to limit the side lobes of an autocorrelation plot of the pattern with a template of the pattern. In this manner a greater number of errors can be tolerated while still permitting index identification. Initially, the entire servo pattern on a servo track is detected in sequence at the bit rate. Each twelve bit sequences of bits is compared to a template of the servo pattern and the number of bits whose position and value ('1' or '0') match the template are determined. Whenever a threshold level (less than the total number of bits in the pattern) of 'hits' takes place it assumed that the index has been detected. By minimizing the magnitude of the side lobes of the correlation plot, the threshold can be set between somewhere between complete correlation and the side lobe number. The lower the side lobe, the greater the number of errors which can be tolerated while still indicating an index identification. In one embodiment of the present invention, twelve bit sequence of the servo pattern are compared to a sequential series of templates in which a three bit burst error is implemented. Therefore, even if three consecutive index pattern bits are damaged the index can still be detected.

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Menlo Park, CA, United States of America

Rosser S Wilson