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Multi-Threshold Surface Analysis Tester

IP.com Disclosure Number: IPCOM000034178D
Original Publication Date: 1989-Jan-01
Included in the Prior Art Database: 2005-Jan-26
Document File: 3 page(s) / 70K

Publishing Venue

IBM

Related People

Anderson, PM: AUTHOR [+3]

Abstract

This article describes a tester which measures surface defects of magnetic disks and, in doing so, features (1) Multiple test the thresholds for fast data assembly, (2) a signal distribution design which minimizes measurement, inaccuracies, and eliminates calibration headaches, (3) a self-clocking data path which easily handles input signals over a wide frequency range, and (4) digitally programmable parameters related to disk drive rotation speed. (Image Omitted) The desired results are achieved using a multiple-threshold measurement system. It features a self-clocking data path to easily handle input signals over a wide frequency range. The signal distribution design minimizes measurement inaccuracies and calibration requirements.

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Multi-Threshold Surface Analysis Tester

This article describes a tester which measures surface defects of magnetic disks and, in doing so, features (1) Multiple test the thresholds for fast data assembly, (2) a signal distribution design which minimizes measurement, inaccuracies, and eliminates calibration headaches, (3) a self-clocking data path which easily handles input signals over a wide frequency range, and (4) digitally programmable parameters related to disk drive rotation speed.

(Image Omitted)

The desired results are achieved using a multiple-threshold measurement system. It features a self-clocking data path to easily handle input signals over a wide frequency range. The signal distribution design minimizes measurement inaccuracies and calibration requirements. Also, all parameters related to drive rotation speed are made digitally programmable for use with variable-speed drives. Surface analysis testing consists of generating a test reference based on the peak level of the signal to be tested, and then comparing each peak of the signal to thresholds set at various percentages of that reference. The comparison circuitry looks for "defect" signal peaks that are significantly different in amplitude from the reference. Referring to Fig. 1, the gain of the Input Amp is first set by closing the Gain Control loop. The amplified Test Signal is sampled by the Envelope Follower to generate a Dynamic Reference, or a slowly- moving voltage which follows overall signal level variations while ignoring quick variations or "defects". The Integrator, set to integrate with reference to Vref, acts to further filter the envelope of the Test Signal. The digital Sample/Hold, in the sample mode, allows the Gain Control line to follow the filtered envelope. Vref is equal to the desired peak signal level, and the gain-control loop has enough gain that Test Signal peak level ends up equal to Vref. With the gain set, the Gain Control line is held digitally in the Sample/Hold so the gain remains constant. Surface analysis testing can be done using either the Dynamic Reference or the Static Reference, as chosen by the Analog Switch. The Dynamic Reference is useful for "missing-bit" testing, while the Static Reference is necessary for "extra-bit" testing. The Static Reference is set by the Integrator, now working with reference to ground, integrating a Track Average. This Track Average value is digitally held by the Static Reference output of the Sample/Hold circuitry. Both references are can be used with variable-speed drives, because the Envelope Follower response time and the Integrator time constant are both digitally programmable. The Multiplying Digital-to-Analog (D-to- A) CONVERTERS SET THE TEST THRESHOLDS AT THE DESIRED PERCENTAGE OF THE Test Reference. The Test Signal is then compared to the Test Thresholds by the Multi-Threshold Self-Clocking Detector, and the resulting Data is clocked, one Data "word" per Test Signal peak, to the data ha...