Missing Bit Detection in Surface Analysis Testing
Original Publication Date: 1984-Dec-01
Included in the Prior Art Database: 2005-Feb-06
Two retriggerable single shots are triggered at positive and negative thresholds, respectively, of a read-back nominally sinusoidal waveform from a magnetic disk surface being tested. The single-shot outputs, which are one and a half times the nominal period of the waveform in duration, are applied to a NAND gate. If either input falls, the NAND gate output indicates a "missing bit", which is indicative of a defect in the medium. A suitable circuit is shown in Fig. 1. The read-back signal from the disk surface is applied to an input terminal and its positive and negative excursions compared with threshold levels set by positive and negative digital-to-analog converters. Fig. 2, Fig. 3 and Fig. 4 illustrate the operation of the circuit on various types of input waveform.