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Method of Module In-Place Testing Without Backdriving

IP.com Disclosure Number: IPCOM000043366D
Original Publication Date: 1984-Aug-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 2 page(s) / 41K

Publishing Venue

IBM

Related People

Kranz, RH: AUTHOR [+4]

Abstract

This article describes a method of module in-place testing (MIPT) which allows testing of integrated circuit modules in-circuit without backdriving other modules, thereby making cards which contain modules testable using MIPT techniques. Referring to Fig. 1, traditional in-circuit module testing techniques require backdriving module A, designated Q1, while exercising module B, designated Q2. A tester probe makes contact with the pin of Q1, as shown in Fig. 2. If Q1 is off, the tester probe can change the voltage of the connecting land pattern with relatively little difficulty. For this case, Q2 can easily be tested.

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Method of Module In-Place Testing Without Backdriving

This article describes a method of module in-place testing (MIPT) which allows testing of integrated circuit modules in-circuit without backdriving other modules, thereby making cards which contain modules testable using MIPT techniques. Referring to Fig. 1, traditional in-circuit module testing techniques require backdriving module A, designated Q1, while exercising module B, designated Q2. A tester probe makes contact with the pin of Q1, as shown in Fig. 2. If Q1 is off, the tester probe can change the voltage of the connecting land pattern with relatively little difficulty. For this case, Q2 can easily be tested. If Q1 is on, however, then the method used to make the base of Q2 positive is for the tester probe to supply excessive current to Q1 for a short period of time and force the collector voltage positive to a one state. For transistor- transistor logic (TTL) circuits, typically, 3 volts at 300 milliamps or less for 5 milliseconds or less is used. Because of the short time duration, Q1 is not heated to a high enough temperature to cause failure. This procedure cannot be used with many technologies because the printed circuit within the module cannot tolerate the backdrive current. The technique described herein provides for a circuit configuration shown in Fig. 3 wherein the tester connects to both ends of the land pattern and makes use of the resistance of the land pattern to eliminate the backdrive current flowing through Q1. In operation, capacitor C1 is charged to a positive DC voltage (Vt) through resistor R1 and diode D1. When the tester is ready to apply a pulse to the base of Q2, the field-effect trans...