Abstract: Methods and apparatus are provided for measuring the performance of a read channel. A number of detection techniques, such as SOVA and maximum-a-posteriori (MAP) detectors, produce a bit decision and a corresponding reliability value associated with the bit decision. The reliability value associated with the bit decision may be expressed, for example, in the form of log likelihood ratios (LLRs). The reliability value can be monitored and used as a performance measure. The present invention provides a channel performance measure that generally correlates directly to the BER but can be collected in less time.

Abstract: A device and process to compensate for asymmetrical qualities of an analog input signal, if present, and generate a timing signal. The timing signal is then used for analog to digital conversion.

Abstract: A pseudo-random bit interleaver and de-interleaver comprising a source for generating pseudo-random numbers and transformation logic that transforms each pseudo-random number generated by the source into a plurality of different pseudo-random numbers. Each of the transformed pseudo-random numbers identifying a parity equation to which an incoming bit will be assigned for computing parity.

Abstract: User data is read from a medium having servo data and user data encoded thereon. The user data is read with a read/write head that is operable in a write mode and a read mode. Servo data is read in a time window following a transition from write mode to read mode, with a frequency passband that has a first low frequency corner. User data is read from the medium after expiration of the time window, with a frequency passband that has a second low frequency corner that is lower than the first low frequency corner.

Abstract: Methods and apparatus are provided for programmable codeword encoding and decoding. Data blocks are represented as a number of codewords. Data is encoded into one or more full size codewords and at least one truncated codewords. Typically, data is encoded and decoded using one or more full size codewords and one truncated codeword. The truncated codewords are a two-dimensional array having a number of columns (or rows or both) less than the full size codeword. In this manner, the disclosed truncated codewords are adaptable to various system parameters that affect code rate.

Abstract: Methods and apparatus are provided for measuring the performance of a read channel. A number of detection techniques, such as SOVA and maximum-a-posteriori (MAP) detectors, produce a bit decision and a corresponding reliability value associated with the bit decision. The reliability value associated with the bit decision may be expressed, for example, in the form of log likelihood ratios (LLRs). The reliability value can be monitored and used as a performance measure. The present invention provides a channel performance measure that generally correlates directly to the BER but can be collected in less time.

Abstract: A pseudo-random bit interleaver and de-interleaver comprising a source for generating pseudo-random numbers and transformation logic that transforms each pseudo-random number generated by the source into a plurality of different pseudo-random numbers. Each of the transformed pseudo-random numbers identifying a parity equation to which an incoming bit will be assigned for computing parity.

Abstract: User data is read from a medium having servo data and user data encoded thereon. The user data is read with a read/write head that is operable in a write mode and a read mode. Servo data is read in a time window following a transition from write mode to read mode, with a frequency passband that has a first low frequency corner. User data is read from the medium after expiration of the time window, with a frequency passband that has a second low frequency corner that is lower than the first low frequency corner.

Abstract: The present invention relates to a method of providing error margin information for threshold errors associated with a digital peak detector. The method comprises comparing a plurality of peak sample values associated with the digital peak detector to a threshold margin test level and incrementing a counter each time the threshold margin test level exceeds one of the plurality of peak sample values. The value associated with the counter relates to an amount of threshold margin associated with the digital peak detector. The present invention also relates to a method of providing error margin information for peak shift errors associated with a digital peak detector. The method comprises identifying relevant peak sample data points associated with each of a plurality of detected peaks and determining a peak shift amplitude associated with each of the detected peaks using the identified relevant peak sample data points.

Abstract: The present invention relates to a method of providing error margin information for threshold errors associated with a digital peak detector. The method comprises comparing a plurality of peak sample values associated with the digital peak detector to a threshold margin test level and incrementing a counter each time the threshold margin test level exceeds one of the plurality of peak sample values. The value associated with the counter relates to an amount of threshold margin associated with the digital peak detector. The present invention also relates to a method of providing error margin information for peak shift errors associated with a digital peak detector. The method comprises identifying relevant peak sample data points associated with each of a plurality of detected peaks and determining a peak shift amplitude associated with each of the detected peaks using the identified relevant peak sample data points.

Abstract: A circuit to process a coded information sequence received from a transmitter, by determining a value for a metric indicative of the relative quality for each of best candidates to be selected as the sequence is actually transmitted, selecting if said coded information sequence is to be decoded in accordance with either E2 PR4 (1,k) or in accordance with EPR4 (0,k); and, using a common trellis to share circuitry between the E2PR4 (1,k) and EPR4 (0,k) detectors to reduce overall complexity.