Methodology
Worst-case analysis is the analysis of a device (or system) that assures that the device meets its performance specifications. These are typically accounting for tolerances that are due to initial component tolerance, temperature tolerance, age tolerance and environmental exposures (such as radiation for a space device). The beginning of life analysis comprises the initial tolerance and provides the data sheet limits for the manufacturing test cycle. The end of life analysis provides the additional degradation resulting from the aging and temperature effects on the elements within the device or system.
This analysis is usually performed using SPICE, but mathematical models of individual circuits within the device (or system) are needed to determine the sensitivities or the worst-case performance. A computer program is frequently used to total and summarize the results.
A WCCA follows these steps: 1) Generate/Obtain circuit model 2) Obtain Correlation to validate model 3) Determine sensitivity to each component parameter 4) Determine component tolerances 5) Calculate the variance of each component parameter as sensitivity times absolute tolerance 6) Use at least two methods of analysis (e.g. hand analysis and SPICE or Saber, SPICE and measured data) to assure the result 7) Generate a formal report to convey the information produced
The design is broken down into the appropriate functional sections. A mathematical model of the circuit is developed and the effects of various part/system tolerances are applied. The circuit's EVA and RSS results are determined for Beginning-of-Life and End-of-Life states.
These results are used to calculate part stresses and are applied to other analysis. In order for the WCCA to be useful throughout the product’s life cycle, it is extremely important that the analysis be documented in a clear and concise format. This will allow for future updates and review by other than the original designer. A compliance matrix is generated that clearly identifies the results and all issues.
Read more about this topic: Worst-case Circuit Analysis
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