Method and apparatus for performing digital thermal asperity detection

Abstract

An improved thermal asperity detector is disclosed for detecting short thermal asperities using a variable time threshold. The thermal asperity detector includes a saturation detector, and a comparator system. The comparator system may include a polarity latch, a processor, a level comparator and a timing comparator. The saturation detector compares a programmable saturation threshold to an A/D sample to generate an enable signal in response to the A/D sample exceeding the saturation threshold. The polarity latch receives the A/D sample and the enable signal, and records the most significant bit of the A/D sample to identify the polarity of the saturation and to provide an output signal representative thereof in response to the enable signal. The processor generates a threshold level control signal based upon a programmable level threshold and the polarity latch output signal. The level comparator compares the A/D sample and the output from the polarity latch in response to the enable signal, and generates a timing output signal to a timing comparator in response to the comparison of the A/D sample and the output from the polarity latch. The timing output signal represents a number of succeeding A/D samples that surpasses the dynamically shifted level threshold. The timing comparator compares the timing output signal from the level comparator and a programmable time threshold in response to the enable signal. Finally, the timing comparator generates a thermal asperity indication when the succeeding A/D samples surpass the dynamically shifted level threshold for the programmable time threshold.