Original Date: 01/23/1995
Revision Date: 01/18/2007
Best Practice : Quiescent Power Supply Current Testing
Sandia National Laboratories and the University of New Mexico have developed a test circuit based on the Keating-Meyer method to measure quiescent power supply current (IDDQ). This test circuit is a faster and more precise test circuit than those used in commercially available testers. IDDQ testing greatly reduces the number of test patterns and increases detection of fabrication defects of complementary metal-oxide semiconductor (CMOS) microelectronic circuits compared to traditional functional or stuck-at-fault testing.
Traditional automated test equipment has not been designed to accurately measure current at high test speeds. The few manufacturers that have this capability have faced trade-offs in trying to measure current with both speed and accuracy.
Efficient fault detection of integrated circuits at their functional outputs has become difficult because of increased complexity and gate count. Traditional testing assumes stuck-at faults that oversimplify the behavior of defects of CMOS integrated circuits. Boundary and full scan circuits have been added to component designs to help improve fault coverage above 95%, but low quality and reliability have persisted. IDDQ is the current required to power the CMOS integrated circuit after all logic transitions are made. In present CMOS integrated circuits, the magnitude of IDDQ is commonly less than 1 nA. However, when there is a defect such as a gate-to-source short, the quiescent current is one or more orders of magnitude higher. CMOS integrated circuits have complementary pairs of p-channel and n-channel transistor networks, with one pair on and the other off in the quiescent state. This allows one vector to test about 50% of the transistors. As the number of test patterns is increased, fault coverage increases rapidly. The number of test patterns for IDDQ testing has been proven to be orders of magnitude less than the number of patterns for stuck-at faults.
IDDQ testing technology has been transferred to industry through technical papers, tutorials, and presentations at test conferences. IDDQ testing has led to increased detection of common defects with smaller test patterns. Industry results have shown a 10 to 100-fold quality improvement by implementing IDDQ testing.
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