Improved Microwave Circuit Design Flow Through Passive Model Yield And Sensitivity AnalysisSource: Modelithics, Inc.
This application note presents a method for improved design flow with a goal of cost-effective first-pass design success. Typically, when an RF/Microwave design has to be fine-tuned to fit the design criteria, a design engineer will use the built-in optimization capability in the EDA tool. In a typical case, the optimization engine has to deal with ten or more variables such as component values that can be changed, and at least three to four goals. In the case of a microwave filter, example goals would include in-band insertion loss and return loss, cutoff frequency and out of band rejection. The large number of criteria that the optimization engine has to deal with creates a landscape of ‘solutions’ that are more or less random. No matter which optimization engine one will use, not all possible outcomes will be tested simply because this would be too time consuming.
In this paper we propose a solution that maps the impact that individual components have on sub-system performance so that a good trade-off can be made with regard to component values and tolerance (low tolerance=more expensive, larger tolerance=less expensive). This will ultimately lead to lower manufacturing costs and improved yield. The proposed solution requires accurate passive component models that allow yield analysis by means of a tolerance setting, something that is close to impossible with commonly used S-parameter file-based component representations. By combining Modelithics Global Models™ for passive RLC components  with AWR microwave Office we allow the software to find an optimal solution that does not only reach the design goal, but will also help the design engineer find an optimum component tradeoff and a high yield.