Abstract: Techniques for early detection of degradation in NAND Flash memories by measuring the dispersion of the threshold voltages (VT's), of a set (e.g. page) of NAND Flash memory cells during read operations are described. In an embodiment of the invention the time-to-completion (TTC) values for the read operation for the memory cells are used as a proxy for dispersion of the threshold voltages (VT's). A Dispersion Analyzer determines the dispersion of the set of TTC values. In one embodiment the delta between the maximum and minimum TTC values is used as the dispersion measurement. If the measured TTC dispersion differs by more than a selected amount from a reference dispersion value, a warning signal is provided to indicate that the page of memory has degraded. The warning signal can be used to take appropriate action such as moving the data to a new page.

Abstract: The embodiments of the invention in this disclosure describe techniques for early warning of degradation in NOR Flash memories by estimating the dispersion of the threshold voltages (VT's), of a set of NOR Flash memory cells during read operations. In an embodiment invention the time-to-completion (TTC) values for the read operation for the memory cells are used as a proxy for dispersion of the threshold voltages (VT's). If the measured TTC dispersion differs by more than a selected amount from the reference dispersion value, a warning signal is provided to indicate that the page of memory has degraded significantly. Higher level components in the system can use the warning signal to take appropriate action. Since every cell's VT position in an ideal distribution can be estimated, the data from each cell can have a confidence level assigned based on deviation from the mean of an ideal distribution.

Abstract: Techniques are provided for iteratively decoding data recorded on a data storage device. An iterative decoder decodes the data using multiple decoding iterations to correct errors. In multiple iterations of the iterative decoder, a post processing block generates soft information, and a decoder applies a minimum sum decoding algorithm to a low density parity check (LDPC) code to generate extrinsic information based on the soft information and updated soft information.

Abstract: Embodiments of the present invention relate to the detection of synchronization marks in data storage and retrieval. To detect a synchronization mark, embodiments of the present invention require both pattern matching and proper phase alignment, following a repeating synchronization field. According to one particular embodiment, proper phase alignment following a repeated four bit synchronization field, is utilized in conjunction with pattern matching, to identify a synchronization mark. By allowing a synchronization mark to be identified only with proper phase alignment at the earliest possible occurrence of the synchronization mark, accuracy of synchronization mark detection may be improved.

Abstract: A Flash memory system and a method for data management using the system's sensitivity to charge-disturbing operations and the history of charge-disturbing operations executed by the system are described. In an embodiment of the invention, the sensitivity to charge-disturbing operations is embodied in a disturb-strength matrix in which selected operations have an associated numerical value that is an estimate of the relative strength of that operation to cause disturbances in charge that result in data errors. The disturb-strength matrix should also include the direction of the error which indicates either a gain or loss of charge. The disturb-strength matrix can be determined by the device conducting a self-test in which changes in the measured dispersion value are provoked by executing a selected operation until a detectable change occurs. In alternative embodiments the disturb-strength matrix is determined by testing selected units from a homogeneous population.

Abstract: A Flash memory system and a method for data management using the system's sensitivity to charge-disturbing operations and the history of charge-disturbing operations executed by the system are described. In an embodiment of the invention, the sensitivity to charge-disturbing operations is embodied in a disturb-strength matrix in which selected operations have an associated numerical value that is an estimate of the relative strength of that operation to cause disturbances in charge that result in data errors. The disturb-strength matrix can also include the direction of the error which indicates either a gain or loss of charge. The disturb-strength matrix can be determined by the device conducting a self-test in which charge-disturb errors are provoked by executing a selected operation until a detectable error occurs. In alternative embodiments the disturb-strength matrix is determined by testing selected units from a homogeneous population.

Abstract: The embodiments of the invention in this disclosure describe techniques for early warning of degradation in NOR Flash memories by estimating the dispersion of the threshold voltages (VT's), of a set of NOR Flash memory cells during read operations. In an embodiment invention the time-to-completion (TTC) values for the read operation for the memory cells are used as a proxy for dispersion of the threshold voltages (VT's). If the measured TTC dispersion differs by more than a selected amount from the reference dispersion value, a warning signal is provided to indicate that the page of memory has degraded significantly. Higher level components in the system can use the warning signal to take appropriate action. Since every cell's VT position in an ideal distribution can be estimated, the data from each cell can have a confidence level assigned based on deviation from the mean of an ideal distribution.

Abstract: Techniques for early detection of degradation in NAND Flash memories by measuring the dispersion of the threshold voltages (VT's), of a set (e.g. page) of NAND Flash memory cells during read operations are described. In an embodiment of the invention the time-to-completion (TTC) values for the read operation for the memory cells are used as a proxy for dispersion of the threshold voltages (VT's). A Dispersion Analyzer determines the dispersion of the set of TTC values. In one embodiment the delta between the maximum and minimum TTC values is used as the dispersion measurement. If the measured TTC dispersion differs by more than a selected amount from a reference dispersion value, a warning signal is provided to indicate that the page of memory has degraded. The warning signal can be used to take appropriate action such as moving the data to a new page.

Abstract: A Flash memory system and a method for data management using the embodiments of the invention use special test cells with Early Degradation Detection (EDD) circuitry instead of using the actual user-data storage cells are described. The Flash memory test cells can be made to serve as a “canary in a coal mine” by being made more sensitive than the standard cells by using experimentally determined sensitive write VT and variable read VT. Techniques for early degradation detection (EDD) in Flash memories measure the dispersion of the threshold voltages (VT's), of a set (e.g. page) of NAND Flash memory cells during read operations. In an embodiment of the invention the time-to-completion (TTC) values for the read operation for the memory cells are used as a proxy for dispersion of the threshold voltages (VT's). A Dispersion Analyzer determines the dispersion of the set of TTC values.

Abstract: A system corrects errors in a bit stream. The system includes an encoder and a decoder. The encoder encodes the bit stream using a low density parity check code by inserting parity check bits into the bit stream to generate codewords. The decoder decodes the codewords using parity check equations that are based on the low density parity check code. The parity check bits may comprise no more than four percent of the bits in the codewords of the low density parity check code. The low density parity check code can have a minimum separation of at least 7 between any two ones in each row of a parity-check matrix that is based on the low density parity check code. The encoder and the decoder can be defined in hardware using logic circuits that are interconnected to implement a trellis based on the low density parity check code.

Abstract: A system corrects errors in a codeword. The system includes a channel that sorts reliability numbers of symbols in the codeword to create an ordered list of candidate erasure locations. The system also includes a generalized minimum distance decoder that iteratively processes the ordered list of candidate erasure locations and at least two syndromes of the codeword using a single-shot key equation solver to generate an error locator polynomial and an error evaluator polynomial. The generalized minimum distance decoder processes the least reliable candidate erasure locations first within the ordered list of candidate erasure locations.

Abstract: A detector generates a detected sequence, and a post processor generates probability values that indicate the likelihood of a plurality of error events in the detected sequence. The post processor partitions the values into first and second subsets. The post processor selects a first most likely value from the first subset of the values and a second most likely value from the second subset of the values. The post processor generates a bit reliability based on the first and the second most likely values.

Abstract: Techniques are provided that generate bit reliabilities for a detected sequence. A detector generates the detected sequence. According to one embodiment, a post-processor finds a first set of combinations of one or more error events in the detected sequence satisfying a complete set or a subset of error correction constraints corresponding to the first bit value, finds a second set of combinations of one or more error events in the detected sequence satisfying a complete set or a subset of error correction constraints corresponding to the second bit value, selects a first most likely combination of one or more events of the first set and a second most likely combination of one or more events of the second set, and generates a bit reliability based on the first and the second most likely values.

Abstract: A data storage device includes a first filter that generates a short DC equalization target in response to a read back signal generated from magnetic patterns that are recorded on a storage medium using perpendicular recording. The data storage device also includes a first detector that generates an output sequence in response to the short DC equalization target. The data storage device also includes a high pass filter that attenuates DC components of the short DC equalization target and that passes low frequency components of the short DC equalization target above a cutoff frequency to generate a filtered signal. The data storage device also includes a second detector that processes the output sequence in response to the filtered signal.

Abstract: The invention includes apparatus and methods that allow a data storage device perform an enhanced data recovery procedure (DRP) that includes obtaining a new digital sampling of the voltages for the failing unit of data by re-reading the analog signal and converting it to digital form using an analog-to-digital conversion (ADC) using a fixed phase clock signal. The data samples are re-interpolated using a programmable delay line. The digital values representing the voltages are stored a buffer so that the data can be processed repeatedly using varying parameters as part of the data recovery procedure. Optionally the samples stored in the buffer can be processed in the reverse direction (from end of sector to beginning of sector) without requiring modification of the standard Viterbi detector since it inherently works on data processed in either direction.

Abstract: Embodiments of the present invention relate to the detection of synchronization marks in data storage and retrieval. According to one embodiment, synchronization marks are detected from the output of a matched filter, upstream of the Viterbi detector. This approach avoids the delay associated with the latency of the Viterbi output, thereby allowing time to align parity framing and to properly start the time-varying trellis. Certain embodiments disclose 34- and 20-bit primary synchronization marks located at the beginning of a data region. Other embodiments disclose 16-, 20-, and 24-bit embedded synchronization marks located within a data region.

Abstract: Embodiments of the present invention relate to the detection of synchronization marks in data storage and retrieval. To detect a synchronization mark, embodiments of the present invention require both pattern matching and proper phase alignment, following a repeating synchronization field. According to one particular embodiment, proper phase alignment following a repeated four bit synchronization field, is utilized in conjunction with pattern matching, to identify a synchronization mark. By allowing a synchronization mark to be identified only with proper phase alignment at the earliest possible occurrence of the synchronization mark, accuracy of synchronization mark detection may be improved.

Abstract: A system corrects errors in a codeword. The system includes a channel that sorts reliability numbers of symbols in the codeword to create an ordered list of candidate erasure locations. The system also includes a generalized minimum distance decoder that iteratively processes the ordered list of candidate erasure locations and at least two syndromes of the codeword using a single-shot key equation solver to generate an error locator polynomial and an error evaluator polynomial. The generalized minimum distance decoder processes the least reliable candidate erasure locations first within the ordered list of candidate erasure locations.

Abstract: A system corrects errors in a bit stream. The system includes an encoder and a decoder. The encoder encodes the bit stream using a low density parity check code by inserting parity check bits into the bit stream to generate codewords. The decoder decodes the codewords using parity check equations that are based on the low density parity check code. The parity check bits may comprise no more than four percent of the bits in the codewords of the low density parity check code. The low density parity check code can have a minimum separation of at least 7 between any two ones in each row of a parity-check matrix that is based on the low density parity check code. The encoder and the decoder can be defined in hardware using logic circuits that are interconnected to implement a trellis based on the low density parity check code.

Abstract: A data storage device includes a first filter that generates a short DC equalization target in response to a read back signal generated from magnetic patterns that are recorded on a storage medium using perpendicular recording. The data storage device also includes a first detector that generates an output sequence in response to the short DC equalization target. The data storage device also includes a high pass filter that attenuates DC components of the short DC equalization target and that passes low frequency components of the short DC equalization target above a cutoff frequency to generate a filtered signal. The data storage device also includes a second detector that processes the output sequence in response to the filtered signal.