Abstract: The present invention provides a frequency-sampling circuit and method for characterizing a health condition of a test unit attached to a power supply. The frequency-sampling circuit is connected externally to the test unit. The circuit comprises an inductor and a capacitor connected in series at an output. When switched, the circuit resonates with an AC loop current to produce a damped-frequency response at the output. Frequency measurements of this response are processed to generate SoH or RUL estimates for the test unit. The voltages applied within the frequency-sampling circuit are limited, which in turn limits the AC loop current to avoid loading the power supply. Incorporating the inductance and capacitance with in the frequency-sampling circuit allows the circuit to be configured for different classes of test units having a wide range of characteristic impedances.

Abstract: A prognostic cell is used to predict impending failure of a useful circuit or circuits in a host IC. Increasing the stress on the prognostic cell relative to the useful circuit shifts the failure distribution of the cell along the time axis. The relative amount of time between the useful circuit failure and prognostic cell trigger point is the “prognostic distance”. The prognostic distance is controlled by designing in the excess stress applied in test device(s), by setting the threshold for triggering in the comparison circuit or by both. Prediction accuracy is enhanced by using multiple test devices to oversample the underlying failure distribution and triggering the failure indicator when a certain fraction fail.