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Creating a Data Window for Fast Video Signals

IP.com Disclosure Number: IPCOM000043224D
Original Publication Date: 1984-Jul-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 3 page(s) / 40K

Publishing Venue

IBM

Related People

Ko, MA: AUTHOR

Abstract

Measurement of fast video signals is quite difficult. This article describes a method by which a data window for measuring such signals can be created. Large display video signals with relatively small pulse widths, e.g., on the order of 20 nanoseconds, present a problem in terms of measurement. Because of the rapid speed involved, measurement of such signals is not easily accomplished with conventional methods. In [*], a method was suggested for manipulating the data rate, in other words, slowing down the signal to a rate that can be handled by the measuring device. While this method is of value in the process of logic verification, it has unfortunate drawbacks when applied to the manufacturing card test area, where the detection of faults, not verification of logic, is the main goal.

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Creating a Data Window for Fast Video Signals

Measurement of fast video signals is quite difficult. This article describes a method by which a data window for measuring such signals can be created. Large display video signals with relatively small pulse widths, e.g., on the order of 20 nanoseconds, present a problem in terms of measurement. Because of the rapid speed involved, measurement of such signals is not easily accomplished with conventional methods. In [*], a method was suggested for manipulating the data rate, in other words, slowing down the signal to a rate that can be handled by the measuring device. While this method is of value in the process of logic verification, it has unfortunate drawbacks when applied to the manufacturing card test area, where the detection of faults, not verification of logic, is the main goal. It has been found that when the signal is slowed down in this manner, some faulty components that cannot operate at high speed do work properly at such a lower speed, thereby eluding fault detection.

Since measurement in real time is thus necessary to ensure fault detection, the task then is to set up a data window so that the continuous data stream can be divided into measurable segments. One such window is the display frame. Each frame consists of an even field and an odd field. By measuring the video signal between two successive transitions of the frame from even to odd or vice versa, a consistent result can be obtained, if one assumes the frame is configured to display a static test pattern. One method of establishing such a window might be to arrange for the processor in the card test station to monitor the even-to-odd transition and thus enable emergence of the video signal exclusively inside the data window. An external counter could then make measurements and display the result. Unfortunately, the problem with such a method is that the types of test equipment currently available are not fast enough to handle such signals. By the time the even-to-odd transition is detected and the data window is set up, several even-to-odd transitions would have elapsed, resulting in an inconsistent data window. Another method considered ha...