A. Mels, F. Zachariasse, NXP Semiconductors, Nijmegen, Netherlands

Summary: Starting from the concept of the shmoo edge as a smooth transition from 100% fail to 100% pass, we have developed a model of LADA signal strength. By combining this model with a suitable measure for image quality, we derived equations for the acquisition time needed to discern a LADA response from the background noise. Comparison of the model to experimental data shows that it is indeed a realistic representation. For weak signals, we show that the optimal condition, for minimum acquisition time, is at the 50% pass/fail point of the shmoo plot. Under these conditions, the acquisition time decreases quadratically with an increase in laser-induced timing shift, or a decrease in jitter. We investigated a number of ways to improve the LADA response. Performing LADA at reduced supply voltages appears to be a promising avenue to achieve this. In some device types, it results in a 7-fold reduction in acquisition time. In conclusion the model offers a quantitative tool to estimate the feasibility of a given LADA measurement and a guide to optimising the required experimental set-up.