At-speed test is not necessarily an AC test

A measure for assessing how well a given generator can apply AC patterns to the logic it is intended to drive is proposed. It is shown that this measure, called the AC strength, is both easily computable and gives a direct indication as to how good the generator is in performing its AC test task. Also proposed is an alternative to the special latch design for AC test. This alternative uses normal LSSD (level sensitive scan design) latch design, and pays special attention to the way the circuit inputs are connected along the scan chain. It is shown that by connecting the inputs in a special way, the AC test potential is greatly enhanced, and the hardware overhead, in most cases, will be negligible.