26. Inductive Coupling Noise in Multilayer Superconductive ICs

Large-scale rapid single flux quantum circuits primarily use passive transmission lines for routing signals among standard cells. This type of interconnect consists of driver/receiver circuits and a stripline or microstripline. This interconnect topology poses unique challenges on the routing process as the available routing resources are severely limited. Different alternative topologies have been considered to reduce the number of metal layers required by these structures. These topologies, however, increase the inductive noise between adjacent striplines as compared to topologies with additional ground planes. Another source of undesirable inductive coupling is the bias lines. Bias current distribution networks are connected to each cell. Despite the relatively small mutual inductance, high current within these bias lines can also couple to other circuits and transmission lines. Superconductive circuits are highly sensitive to inductance variations and parasitic coupling, further exacerbating this coupling issue. In this chapter, issues related to inductive noise coupling in multilayer superconductive ICs are discussed, and approaches to characterize and mitigate inductive noise in these systems are described. Guidelines to mitigate the deleterious effects of noise coupling are presented.