Clock-skew-controlled pipeline optimization in superconducting rapid single-flux-quantum circuits

This paper presents a clock-skew-controlled pipeline optimization method for superconducting rapid single-flux-quantum (RSFQ) circuits. Without changing the circuit’s cell-level topology (netlist connectivity, including the splitter-tree), the pipeline depth along each signal path can be flexibly adjusted by controlling the clock skew between adjacent logic cells. A quantitative relationship between clock skew and latency variation is derived to determine timing configurations at different pipeline depths. A 4-bit adder is designed using cells from the SIMIT Nb03 process library, and a stepwise reduction of its pipeline depth is carried out in simulation to validate the method. At a fixed clock frequency and bias margin, the circuit latency is reduced by 155 ps, while the number of Josephson junctions (JJs) is reduced by about 582.