Pseudo-Random Pattern Generator Design for Column-Matching BIST

This paper discusses possibilities for a choice of a pseudorandom pattern generator that is to be used in combination with the column-matching based built-in self-test design method. The pattern generator should be as small as possible, whereas patterns generated by it should guarantee satisfactory fault coverage. Weighted random pattern generators offer this. Several weighted pattern generator designs are proposed and their effectiveness is evaluated in this paper. Moreover, two methods for computing the weights are compared. The column-matching method is primarily intended for a test-per-clock BIST, i.e., test patterns are applied to the tested circuit in parallel. Pseudorandom vectors obtained by an LFSR are modified here by a combinational circuit, to obtain deterministic test patterns. The number of inputs of this block corresponds to the width of the LFSR, the outputs correspond to the tested circuit inputs. This paper discusses possibilities of a reduction of the LFSR width.