On the design and analysis of unmatched LFSR pattern generators in pseudorandom testing

An area efficient design of unmatched pattern generators with dynamic connections for circuits with many inputs is presented. For a circuit with n inputs, instead of requiring n flip-flops, the design needs only m + [n/m] flip-flops and a connection mapping network. m flip-flops are used to construct a primary LFSR (linear feedback shift register) for pattern generation. The other [n/m] flip-flops form a secondary LFSR that dynamically changes the connections between the primary LFSR outputs and circuit inputs by controlling the mapping network. Experiments show that the proposed design is less costly in area as compared to matched designs and also achieves better test quality than either the matched or unmatched designs with static connections