POWERTEST: a tool for energy conscious weighted random pattern testing

Due to the increasing use of portable computing and wireless communications systems, energy consumption is of major concern in today's VLSI circuits. With that in mind we present an energy conscious weighted random pattern testing technique for Built-In-Self-Test (BIST) applications. Energy consumption during BIST operation can be minimized while achieving high fault coverage. Simple measures of observability and controllability of circuit nodes are proposed based on primary input signal probability (probability that a signal is logic ONE). Such measures help determine the testability of a circuit. We developed a tool, POWERTEST, which uses a genetic algorithm based search to determine optimal weight sets (signal probabilities or input signal distribution) at primary inputs to minimize energy dissipations. The inputs conforming to the primary input weight set can be generated using cellular automata or LFSR (Linear Feedback Shift Register). We observed that a single input distribution (or weights) may not be sufficient for some random-pattern resistant circuits, while multiple distributions consume larger area. As a trade-off, two distributions have been used in our analysis. Results on ISCAS benchmark circuits show that energy reduction of up to 97.82% can be achieved (compared to equi-probable random-pattern testing with identical fault coverage) while achieving high fault coverage.