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Automated Video Test Card With Self-Test Mechanisms Disclosure Number: IPCOM000036737D
Original Publication Date: 1989-Oct-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 7 page(s) / 132K

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Pinera, CV: AUTHOR


This article describes a video test card (VTC) which allows accurate testing of digital and analog video signals without reliance on visual verification by a test operator.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 41% of the total text.

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Automated Video Test Card With Self-Test Mechanisms

This article describes a video test card (VTC) which allows accurate testing of digital and analog video signals without reliance on visual verification by a test operator.

Testing of video display controllers traditionally uses visual

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methods to verify their proper operation. Test operators visually determine if the displayed screen is correct or defective. As graphics boards move to higher resolutions and the number of colors available increases, visual verification becomes unreliable.

Signature analysis has been successfully used to test digital video signals. Signature analysis is a technique where a long serial bit stream is compressed into a cycle redundancy code or "signature". Missing bits or bits in incorrect positions can be detected with signature analysis. This disclosure describes a VTC to test analog and digital video signals using signature analysis techniques.

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The VTC disclosed herein is shown in block diagram form in Fig. 1. A digital multiplexer (MUX) allows the individual selection of up to fourteen digital signals from the card under test (CUT). The digital signals requiring testing are the digital video lines driving a digital-to-analog converter (DAC) on an analog video board or simply the digital video on strictly digital video output boards. Other related digital signals on the CUT are also verified using these lines.

The VTC DAC supplies the reference voltages when verifying the red video signal. The video level is set to a static level and the VTC DAC is used to "window" that value to determine if it is within specifications. This procedure is performed for all video levels.

The comparators are used to perform the actual analog-to-digital conversion. Each comparator output is readable from the bus. The comparator outputs also connect to the digital multiplexers so signatures can be taken with the board running at speed to verify operation of the video DAC in its operational mode.

The signature analysis unit forms the basis for CUT verification and self-test of the VTC. The signature analysis unit verifies serial

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bit streams using signature analysis techniques which provide a highly accurate indication of whether the bit stream is correct. A self-test mode allows the test software to generate test signatures via software to verify proper operation of the signature analyzer.


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CUT control logic allows the VTC to take control of the digital video bus on the CUT as well as the video sync signals to provide a way for testing the DAC under controlled conditions. If the CUT is designed with manufacturing testability in mind, it will have a way to disable the digital circuits supplying data to the DAC as well as a way to disable the dot clock, vertical sync, horizontal sync, and blanking signals. The VTC can take control of these signals and provide stable patterns to the DAC to allow precise testing wi...