Abstract: A discrete time servo demodulation technique incorporated within a sampled amplitude read channel to demodulate embedded servo field information stored on a magnetic medium. The servo field information is transduced by a read head into an analog signal, and converted to a sequence of sample values in the read channel. The demodulation technique is responsive to the sample values and includes a discrete time peak detector for detecting servo data, and a discrete time servo burst amplitude detector for measuring the amplitude of servo bursts. Peaks are detected in the analog read signal by sensing a change of slope from the sequence of sample values. The peaks are qualified by polarity in that a peak is detected only if its polarity is opposite in sign from the previous peak. The servo burst amplitudes are measured by interpolating, rectifying, and accumulating the sequence of sample values corresponding to the servo bursts.

Abstract: In a sampled amplitude read channel for magnetic recording, a nonlinear discrete time decimation filter in a negative feed back loop adjusts a DC offset in an analog read signal from a magnetic read head without distorting the read signal. In sampled amplitude recording, adding the samples of an isolated positive pulse to the samples of an isolated negative pulse generates the DC offset of the discrete time sample values. A decimation filter adds the sample values from a positive pulse to the sample values of a negative pulse in order to detect and pass the DC offset in the read signal. The detected discrete time DC offset from the discrete time decimation filter is converted into an analog DC offset signal and subtracted from the analog read signal in a negative feedback loop. A running average decimation filter removes the DC offset during acquisition, and a decision-directed decimation filter removes the DC offset during tracking.