A Degree-of-Freedom Based Synthesis Scheme for Sequential Machines with Enhanced BIST Quality and Reduced Area

This paper reports a novel approach to design efficient BIST structures for sequential machines (FSMs) with reduced gate area. In a PRPG based BIST structure, an FSM shows limited testability due to three kinds of states, viz., the unreachable states, the hard-to-exit states, and the hard-to-reach states. A metric, referred to as degree-of-freedom (DOF) in FSM states has been introduced that quantifies the BIST quality of an FSM. Analysis of DOF enables efficient state encoding to ensure high BIST quality as well as low gate area of the resulting FSM. A genetic algorithm (GA) based graph embedding approach is adopted to solve the state encoding problem. Experimental results on benchmark circuits show that the proposed scheme improves the BIST quality significantly simultaneously reducing the gate area of the resultant machine.[PUBLICATION ABSTRACT]