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Circuit Isolation Technique for Module-In-Place Testing

IP.com Disclosure Number: IPCOM000044391D
Original Publication Date: 1984-Dec-01
Included in the Prior Art Database: 2005-Feb-05
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Kugler, CJ: AUTHOR

Abstract

Integrated circuit (I/C) modules are electrically isolated while "in- circuit" on a printed circuit (PC) board. A common technique of PC board testing is Module-In-Place-Testing (MIPT). This requires the ability to electrically isolate every I/C module (or region) on the PC board. Several methods are available to do this, e.g., tri-stating, degating, power plan isolation, etc. However, many commonly available I/C modules do not provide this capability. It still is possible to test some of these devices "in circuit" through overdrive techniques (also known as backdriving). Another method is to insert extra circuitry on the PC board to provide the isolation capability (for increased testability of the PC board).

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Circuit Isolation Technique for Module-In-Place Testing

Integrated circuit (I/C) modules are electrically isolated while "in- circuit" on a printed circuit (PC) board. A common technique of PC board testing is Module-In- Place-Testing (MIPT). This requires the ability to electrically isolate every I/C module (or region) on the PC board. Several methods are available to do this, e.g., tri-stating, degating, power plan isolation, etc. However, many commonly available I/C modules do not provide this capability. It still is possible to test some of these devices "in circuit" through overdrive techniques (also known as backdriving). Another method is to insert extra circuitry on the PC board to provide the isolation capability (for increased testability of the PC board). The isolation needed is provided here by adding a diode between every I/C module and the ground plane of the PC board, as shown in the drawing. The source is increased by one diode drop. During testing, a "bed of nails" fixture makes contact to every device terminal to provide stimulus and measure signals. When ground is supplied to any selected I/C module by a tester, only that selected I/C module can power up. All other I/C module diodes are back biased. Thus, electrical isolation of all modules is achieved. The ability to use tri-state and other techniques to isolate is not affected. Overdriving is no longer a necessity. Testability is very high due to the ability to use "free state" module test pa...