Digital peak-threshold tracking method and apparatus

Abstract

A peak-detection threshold circuit for digitally adjusting an analog peak-threshold level in a magnetic storage read channel. A digital scheme is used to monitor both the positive (PX) and negative (NX) peaks detected in an analog signal. For both positive and negative thresholds T.sub.P and T.sub.N, intermediate peak thresholds T.sub.M are established at selectably lower levels than the peak-detection threshold T.sub.P /T.sub.N. Analog signal peaks are detected when the analog signal crosses the intermediate peak threshold T.sub.M. The corresponding peak-detection threshold T.sub.P /T.sub.N is then compared to the analog peak amplitude. If the intermediate peak threshold T.sub.M and the corresponding peak threshold T.sub.P /T.sub.N are both exceeded by the analog signal, a digital 'increment' error flag bit is generated. If only the intermediate peak threshold T.sub.M is exceeded by the analog signal, a digital 'decrement' error flag bit is generated. No error is generated unless the signal exceeds the intermediate peak threshold T.sub.M. The increment and decrement error flags are stored sequentially in an error flag history register, which is evaluated to select a digital 'added value' for the corresponding stored digital peak threshold V.sub.P /V.sub.N. The 'added values' are continuously created (one per peak) to create a continuously updated digital value V.sub.P /V.sub.N for each peak-detection threshold. The analog peak-detection threshold level T.sub.P /T.sub.N is generated merely by converting the corresponding stored digital value V.sub.P /V.sub.N to an analog current. Several prioritized mask registers permit selection from among various 'added value' magnitudes for variable-speed threshold movement responsive to the variation of analog signal peak levels.