GENERATION OF VECTOR PATTERNS THROUGH RESEEDING OF MULTIPLE-POLYNOMIAL LINEAR FEEDBACK SHIFT REGISTERS

In this paper we perform a comparative analysis of the encoding efficiency of BIST schemes based on reseeding of single polynomial LFSR's as well as LFSR's with fully programmable polynomials. Full programmability gives much better encoding efficiency. For a testcube with s carebits we need only s+4 bits in contrast to s+19 bits for reseeding of single polynomials, but since it involves solving systems of nonlinear equations it is not applicable to realistic cases. We propose a new BIST scheme where the generator can operate according to a number of primitive polynomials. The testcubes are encoded as the polynomial identifier and a seed. We present models of the encoding efficiency of this scheme and demonstrate, both theoretically and through extensive simulations, that such a scheme with 16 polynomials approaches the efficiency of the scheme based on full polynomial programmability, essentially preserving the computational simplicity of single reseeding