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.
Linghui Zhang (Thu,) studied this question.