Finding Characteristic Polynomials for LFSMs Used as Test Pattern Generators

– A built–in Test Pattern Generation (TPG) mechanism that is very popular for pseudorandom or pseudo–exhaustive TPG is a shift register whose initial portion is configured as a Linear Feedback Shift Register (LFSR), or some other kind of a Linear Finite State Machine (LFSM). A fundamental problem that exists in this mechanism is the presence of linear dependencies among the bit sequences produced by different stages. A formula that relates the linear dependencies with the characteristic polynomial of any kind of LFSM has been recently found. In this work we show how the computation of this formula can be made faster. This allows the faster computation of an appropriate characteristic polynomial for the target LFSM so that linear dependecies are minimized.