An Automatic Placement and Routing Methodology for Asynchronous SFQ Circuit Design

This article proposes an automatically placed and routed methodology for asynchronous single flux quantum (SFQ) circuits using passive transmission line lines and utilizing a commercial electronic design automation (EDA) tool, Cadence Innovus. At the cell level, dual rail SFQ asynchronous cells were developed to be implemented in the place and route methodology. Scripts were written that could convert any single rail netlist synthesized from behavioral Verilog using an EDA tool (such as Design Vision) containing single rail cells into dual rail asynchronous cells. Then, automatic placement and routing using Innovus was achieved through specific cell layout design choices that allowed the finished circuit design layout to pass checks by layout vs schematic and design rule check. Finally, back annotation was performed by reincorporating transmission line lengths from place and route stage in analog simulation to verify correct functionality of the design. As an example, a 4-b arithmetic logic unit design is used to illustrate the various stages of the methodology.