Abstract: In a pulse width modulated read signal channel for an optical disk drive, a data-transition threshold is maintained for data detection by a threshold tracking circuit that estimates the amplitude centerline data-transition threshold from the most recent maximum and minimum values of the read signal waveform. To improve the accuracy of the response of the centerline estimator, the threshold is increased or decreased based on the phase error at each read signal transition through the data-transition threshold. In addition, defects in the optical recording media are detected, and a defect present signal is used to inhibit the transition phase error input to the centerline estimator. This prevents the estimator from moving the threshold to an incorrect stable level. In addition, the defect present signal boosts the error feedback in the centerline estimator. The estimator then more quickly follows the read signal waveform.

Abstract: A method and apparatus for detecting peaks in a signal which comprises an alternating polarity waveform including a plurality of points. A selected point in the signal is designated. Thereafter, a threshold value for the selected point is established utilizing a prior threshold value associated set off with spaces with a point prior to the selected point as follows:(m(n)=t0*ax(n)+t1*m(n-1)wherein n is the point identifier, m(n) is the threshold value, t0 is a fixed positive constant less than one, t1 is a fixed positive constant less than one, ax(n) is the absolute value of the input signal, and m(n-1) is the prior threshold value for the prior point. In this manner the threshold value may be adjusted for fluctuations in amplitude of the signal. Next, the selected point is compared with the threshold value to determine whether or not the selected point is within a predetermined distance of the threshold.

Abstract: A method and apparatus for detecting peaks in a signal which comprises an alternating polarity waveform including a plurality of points. A selected point in the signal is designated. Thereafter, a threshold value for the selected point is established utilizing a prior threshold value associated set off with spaces with a point prior to the selected point as follows:(m(n)=t0*ax(n)+t1*m(n-1))wherein n is the point identifier, m(n) is the threshold value, t0 is a fixed positive constant less than one, t1 is a fixed positive constant less than one, ax(n) is the absolute value of the input signal, and m(n-1) is the prior threshold value for the prior point. In this manner the threshold value may be adjusted for fluctuations in amplitude of the signal. Next, the selected point is compared with the threshold value to determine whether or not the selected point is within a predetermined distance of the threshold.

Abstract: A digital phase lock loop channel is provided for threshold detection of a pulse width modulated binary data stream that has negative and positive transitions defining one binary state of the data stream. A threshold-establishing and transition-detecting network receives this data stream and provides a first output of one polarity corresponding to the detection of a positive transition, a second output of an opposite polarity corresponding to the detection of a negative transition, and a time-of-arrival output corresponding to a positive and a negative transition. A first and a second digital PLL is provided, each PLL having a transition input, a time-of-arrival input, a phase-error input, a phase error output a data-valid output, and a data output. Each PLL has an internal digital phase detector network connected to receive its transition input and its time-of-arrival input, and each PLL is operable to generate the phase error output therefrom.

Abstract: A tape drive subsystem discloses that variable length symbols can be used to reliably identify data stored on the tape. Machine controlling procedures are disclosed to encode and decode data for the reliable sensing of the serial number of a media, especially tape cartridges, having different track densities. The subsystem detects the serial number of the media and corrects, or at least detects, error patterns. A variable length symbol code is encoded in a plurality of groups with each group having a "one" being represented as an erase gap ERG signal covering a first two units of a group, and a "zero" is represented as one unit of an ERG signal, both followed by four units of an Inter Block Gap IBG signal.