Several methods improving the fault coverage in mixed-mode BIST are presented in this paper. The test is divided into two phases: the pseudo-random and deterministic. Maximum of faults should be detected by the pseudo-random phase, to reduce the number of faults to be covered in the deterministic one. We study the properties of different pseudo-random pattern generators. Their successfulness in fault covering strictly depends on the tested circuit. We examine properties of LFSRs and cellular automata. Four methods enhancing the pseudo-random fault coverage have been proposed. Then we propose a universal method to efficiently compute test weights.

The observations are documented on some of the standard ISCAS benchmarks and the final BIST circuitry is synthesized using the Column-Matching method.