Multiparameter optimization of RSFQ circuits using the method of inscribed hyperspheres

Rapid Single Flux Quantum (RSFQ) circuits must be designed with large operating margins because of variations in the fabrication process. We describe a routine to optimize the yield, rather than the critical margin, of RSFQ circuits, based on the method of inscribed hyperspheres. The operating region is mapped out with a minimum of circuit simulations taking into account the relative size of the process variations. The method is effective for as many as nine parameters. We show that the standard optimization of critical margin will often give a seriously wrong result for multidimensional parameter space.<>