Analysis of bridging defects in sequential CMOS circuits and their current testability

Differences between controllability conditions for I/sub DDQ/ detectability iy in CMOS combinational and sequential circuits with bridging defects are presented. The usual detectability condition for current testability of bridges in combinational circuits is shown to fail for defective sequential circuits. A special class of bridges involving memory elements may change the state memorized in the element becoming current undetectable. Conditions for their occurrence have been investigated and their dependence on transistor size ratio and bridge resistance analyzed. A typical scan cell has been studied and its realistic bridges modifying the memorized state, identified.<>