On the charge sharing problem in CMOS stuck-open fault testing

The charge-sharing problem associated with the detection of CMOS stuck-open faults is analyzed. It is shown that this problem cannot be ignored if high-quality tests are required, and that assuming the worst-case condition and using conventional testing techniques may dramatically reduce the detectability of stuck-open faults. The authors present a layout-driven method to characterize this problem and show that by a monitoring of the current supply this problem becomes much easier to solve. Through the use of current supply monitoring a very high improvement factor, which can easily offset the error caused by imprecise estimations of capacitance, has been obtained. It is demonstrated that by slight modification of the layout of a circuit the charge-sharing problem can be eliminated. A robust test generation procedure is also presented.