Abstract: A disc drive storage system is disclosed that employs sector level and track level error correction systems (ECS), wherein the track level error correction capability is increased by interleaving the track level redundancy. In the preferred embodiment, each sector on the disc is divided into three interleaves or codewords with sector level redundancy generated for each interleaved codeword. The track level redundancy is then generated by combining the interleaved codewords separately according to a predetermined error correction operation (e.g., byte XOR) to form an interleaved redundancy sector. During readback, the sector level ECS generates an erasure pointer corresponding to an uncorrectable codeword within a sector for use by the track level ECS. In this manner, the track level ECS can correct up to three uncorrectable sectors when three sectors contain a single uncorrectable codeword in separate interleaves.

Abstract: In an image acquisition system, which produces at least one image, each of which is scorable with reference to at least one image quality criterion, a control system is provided for optimizing the image quality criterion. Typically, the image quality criterion is at least in-part established by an exposure parameter. When considered as an apparatus, the present invention includes a number of components which cooperate together to automatically and continually adjust the value of the exposure parameter to optimize the image quality criterion. An image acquisition means is provided to obtain one or more acquired images under selected exposure characteristics. A transform system is provided for receiving the one or more acquired images and developing an energy distribution map, or histogram, of at least a portion of the one or more acquired images.

Abstract: A rate 5/7, d=0 channel code encodes a Gray code servo track address into channel data recorded on a magnetic disk; a PR4 sliding threshold Viterbi sequence detector detects the recorded servo track address upon read back; a cost effective d=0 decoder decodes the recorded servo track address into its Gray code representation; and a 1/1+D filter decodes the Gray code track address into its binary representation. Detecting the servo data with a PR4 Viterbi sequence detector, which is already provided in a read channel for detecting user data, increases the data density of the storage system. The cost and complexity of the decoder is reduced by encoding/decoding the Gray code track address in sections of five bits.

Abstract: A sampled amplitude read channel reads user data and embedded servo data stored on a magnetic medium by detecting digital data from a sequence of discrete time interpolated sample values. A write frequency synthesizer generates a write clock for writing digital data to the magnetic medium at a predetermined baud rate for a selected zone, and upon read back, a read frequency synthesizer generates a fixed sampling clock at a frequency slightly higher than the write frequency at the outer zone. A sampling device samples the analog read signal at this fixed sampling rate across the data zones and servo wedges to generate a sequence of discrete time channel samples that are not synchronized to the baud rate. Before sampling, an analog receive filter processes the read signal to attenuate aliasing noise without having to adjust its spectrum across data zones or servo wedges. A discrete time equalizing filter equalizes the channel samples according to a predetermined partial response (PR4, EPR4, EEPR4, etc.).

Abstract: An error correction system (20) operates on clock cycles to decode a sequence of error correcting symbols (R(x)) received from a disk drive (24), and alternatively to encode data in a codeword for storage on a disk drive. The system includes a generator (30) which, during decoding, receives symbols of the sequence during a plurality of reception clock cycles. During the reception clock cycles the generator generates error pattern bits, regenerated CRC values, syndromes, and parity values. Also during the reception clock cycles the generator uses the regenerated CRC values and CRC symbols of the sequence to generate CRC check values. An error address determinator (90) uses the syndromes and parity values to determine, during a last of the reception clock cycles, a reference address (L) of an error burst in a data symbol portion of the sequence. An error pattern generator (80) then efficiently inserts the error pattern bits at the reference address in an output error pattern during a very next clock cycle.

Abstract: A method and apparatus for computing, in real time, the coefficients C.sub..tau. (n) of a time varying FIR filter according to an optimum singular value decomposition (SVD) algorithm. The coefficients of a plurality of FIR filters are represented by a M.times.N matrix A.sub.M.times.N, where M is the number of FIR filters and N is the number of coefficients in the impulse response of each FIR filter (i.e., the number of filter taps). The A.sub.M.times.N matrix is factored into F.sub.M.times.N and G.sub.N.times.N matrices, and a singular value decomposition of the A.sub.M.times.N matrix is computed as A.sub.M.times.N =U.sub.M.times.N .cndot.D.sub.N.times.N .cndot.V.sub.N.times.N, where U.sub.M.times.N is a M.times.N unitary matrix, D.sub.N.times.N is a N.times.N diagonal matrix {.sigma..sub.1, .sigma..sub.2, . . . , .sigma..sub.N }, .sigma..sub.i are the singular values of A.sub.M.times.N (and .sigma..sub.1 .gtoreq..sigma..sub.2 . . . .gtoreq..sigma..sub.N .gtoreq.0), and V.sub.N.times.N is a N.times.

Abstract: A rate 16/17 ENDEC is disclosed which encodes 16 bit input data words into 17 bit codewords according to at least one predetermined code constraint, such as an RLL (d,k) constraint. The encoder encodes the high and low byte of the input data word using the same mapping circuitry which reduces its cost and complexity. The codewords are transferred through a communication channel, such as a computer disc storage device, and upon reception (or readback) the first 8 bits of the 17 bit codeword are decoded independent from the last 8 bits which prevents error propagation. That is, the first 8 bits of the codeword are decoded into a high byte of the decoded data word, and the last 8 bits of the codeword are decoded into a low byte of the decoded data word independent from one another.

Abstract: A sliding mode controller for controlling a read/write head actuator in a magnetic disk drive storage system wherein a voice coil motor connected to the actuator operates to adjust the position of the read/write head over a selected data track recorded on a magnetic medium. The sliding mode controller comprises a technique for reducing chatter associated with the inherent operation of such a controller--rapid switching between gains to force the observable phase states to follow a predetermined phase state trajectory. While tracking the centerline of a selected track, the sliding mode controller generates a motor control command by multiplying an actuator position error and an actuator position error velocity by respective switching gains. When seeking to a new track, the controller reduces switching noise by disabling the actuator position error and generating the motor control signal responsive to the actuator position error velocity alone.

Abstract: A write-once optical disk data recorder automatically calibrates a laser during a write data operation and using write pulses focussed to a disk. First, the laser is calibrated using a non-focussed laser beam. Each sector of the disk has a laser checking or test area, such as an automatic laser power correction field (ALPC) of two byte lineal extent. During a first write operation after a power up or disk load, a pulse width modulated (PWM) laser test signal is recorded using a laser power level set using the non-focussed laser beam and an indicated desired recording power level on the disk. The recorded laser test signal is read back. The length of the read back laser test signal is measured. The measured length is then compared with a desired length of the PWM laser test signal that indicates a desired laser power level. That is, as laser recording power levels increase, a resultant recorded signal grows in size. This property is used to measure laser power for calibrating laser operation.