Finding Best Voltage and Frequency to Shorten Power-Constrained Test Time

In a digital test, supply voltage (V-DD), clock frequency (f(test)), peak power (P-MAX) and test time (TT) are related parameters. For a given limit P-MAX = P-MAXfunc, normally set by functional specification, we find the optimum V-DD = V-DDopt and f(test) = f(opt) to minimize TT. A solution is derived analytically from the technology-dependent characterization of semiconductor devices. It is shown that at V-DDopt the peak power any test cycle consumes just equals P-MAXfunc and f(test) is fastest that the critical path at V-DDopt will allow. The paper demonstrates how test parameters can be obtained numerically from MATLAB, or experimentally by bench test equipment like National Instruments' ELVIS. This optimization can cut the test time of ISCAS'89 benchmarks in 180nm CMOS into half.