MarginX: Simple and Fast Circuit Parameter Optimization Tool for Superconductor Circuits

For integrated circuit design, optimizing circuit parameters is crucial to achieve wide operating margins and high yields, even in the presence of fluctuations and variations in device characteristics. In this paper, we report the development of a new circuit parameter optimization tool for superconductor integrated circuits, leveraging the latest analog circuit simulator and the center of gravity method. The developed optimization tool, implemented in C++, utilizes a parallel processing algorithm for highspeed optimization. By using only the phase information of the Josephson junction to distinguish the correct behavior of the circuit, this tool can be applied not only to conventional single flux quantum (SFQ) circuits but also to superconductor circuits whose behavior is not based on a 2π phase change. We optimized several SFQ logic gates and compared the margin expansion and optimization time with conventional optimization tools. Our tool achieved an optimization time of less than 2% of that of conventional tools in most cases. This optimization tool facilitates the rapid parameter optimization of any superconductor circuits containing various types of Josephson junctions.