PhaseShifts andLinear Dependencies

Two-dimensional scandesign isawidely usedBIST a,|= °11111I1100100 architecture forpseudo-random andpseudo-exhaustive testing. 2 = °1111 o 1 o 11 oo 1 o However, linear dependencies thatarise duetotheproperties ofthetest-pattern generators inusehavea negative impact a3= o1000I1Io1 o 11o onfault coverage. Toalleviate thisproblem, networks ofXOR a, gates knownasphase shifters areoften used. Existing techniques_F (b) forselecting phaseshifts, suchasthose basedonlarge channelS= = separations, leadtoinadequate removal oflinear dependencies. In Scach C this paperwepresent forthefirst timeamethodfortheselection T ofappropriate channel phase shifts toexplicitly minimize linear dependencies. Experimental results corroborate theeffect ofthe approach inincreasing fault coverage.