Abstract: A magnetic recording disk has a textured test band that is radially spaced from the textured landing zone and that typically has laser-induced bumps with an average height substantially different from the average height of the laser-induced bumps in the textured landing zone. The bumps in both the test band and the textured band are formed in spiral tracks because the disk is simultaneously rotated and translated radially while the texturing laser is pulsing the disk. However, because the bumps in the textured band are not formed until after the average height of the bumps in the test band have been measured by a second analyzing laser, the two spiral tracks are separate and discontinuous.

Abstract: An analyzing laser system determines a physical characteristic of a repetitive texture pattern formed on a substrate surface. In one embodiment the system uses diffracted laser light to compute the average height of texturing bumps on a substrate surface. A laser beam is directed to the substrate surface and overlaps a group of individual marks or bumps formed in a repetitive pattern. A scanning linear photodector array receives light diffracted from the surface. The digitized output of the array is the angular distribution of diffracted light intensities. In the preferred embodiment for determining the average height of laser-induced bumps formed on a specular magnetic recording disk substrate, the angular positions of the first and second diffraction peaks or rings are determined and the intensities are integrated around those diffraction peaks or rings.

Abstract: A method is provided for making crater shaped bumps on a calibration disk which can be used for calibrating a PZT slider, the PZT slider in turn being used for detecting predetermined asperities on a production run magnetic disk. The crater shaped bumps emulate predetermined asperities of production run magnetic disks and especially asperities which are undesirable and would cause the production run disk to be discarded after testing by the PZT slider. Crater shaped bumps which emulate undesirable asperities on current production runs of magnetic disks have a diameter in the range of 10 to 25 .mu.m and a peripheral ridge with a height h.sub.r above a nominal surface of the calibration disk in the range of 75 to 120 nm. Close tolerance crater shaped bumps with this configuration can be made by impinging two or more pulses of laser energy on the same location of a calibration disk. By increasing the number of pulses the height of the peripheral ridge progressively increases.

Abstract: Quantization noise in oversampled digital data can be reduced by processing including alternate steps of lowpass filtering and so-called code projection, in cases where the set of discrete-time signals corresponding to quantized-signal data is a convex set. Corresponding specific methods are disclosed for simple analog-to-digital conversion, "dithered" analog-to-digital conversion, and first- and second-order single-path .SIGMA..DELTA.-conversion. For example, in the case of simple analog-to-digital conversion, code projection involves replacing sample values by quantization-threshold values in those cases where, after filtering, a sample value lies in a different quantization interval as compared with the corresponding value of quantized-signal data.

Abstract: The disclosure pertains to parallel analog-digital converters, the first comparator stage of which give a so-called thermometer scale, formed by a sequence of logic "ones" and logic "zeros". According to the disclosure, a corrector stage is added on in series with the comparator stage. If a comparator of the first stage accidentally gives a logic value opposite that given by the two neighboring comparators, the corrector stages forces the accidentally erroneous value to assume the same value as that the values given by the two neighboring comparators, if and only if these values are equal. The disclosed device can be applied to signal processing ADCs.