CrossCheck: A Cell Based VLSI Testability Solution

A new testability solution is proposed in which externally accessible test points are pre-designed into cells that comprise the VLSI designs. The test points are accessed through an on-chip grid of orthogonal probe and sense lines. The resultant VLSI design consists of a large number of test points through which test signals on every cell on the IC can be measured or modified to a limited extent. The sizable number of test points improves the testability of the designs by a very large factor. Additionally, analog measurement and signal injection capabilities allow detection of practical CMOS fault modes such as opens, shorts, open or closed FETs and even noise margins. The large observability of CrossCheck based designs reduces the automatic test pattern generation problem to one of providing control only. Several ISCAS benchmark designs are analyzed using CrossCheck cell libraries and fault models. The results show that over 97 percent coverage of a broad range of fault modes, such as opens and shorts, can be obtained on VLSI CMOS designs without the need for large computing resources.