Weighted Random Patterns for BIST Generated in Cellular Automata

The paper presents a design method for Built-In Self Test (BIST) that uses a cellular automaton (CA) for test pattern generation. We have extensively studied the quality of generated patterns and we have found several interesting properties of them. The proposed CA can generate weighted random patterns which can be used instead of linear feedback shift register (LFSR) sequences, the fault coverage is higher. There is no need of reseeding the CA in order to generate patterns with different weights. The CA is formed by T flip-flops and does not contain any additional logic in the feedback. We proposed a new scheme of test pattern generation for BIST where the CA serves as a test pattern generator. It is formed by a modified scan chain flip-flops. A number of experiments were done with ISCAS 85 and 89 benchmark circuits. We compared the quality of the generated test patterns with the quality of the patterns generated in an LFSR and with the quality of modified test patterns with several different global test pattern weights. The proposed CA can be advantageously used in BIST.