Accelerated Simulation Technique for Low Bit Error Probability Estimation of Rapid Single Flux Quantum Logic Cells

The elevated operating temperatures of high-Tc superconductor (HTS) rapid single flux quantum (RSFQ) logic cells lead to higher thermal noise and this can be a major limiting factor in the development of working circuits of this kind. Determining the thermally induced bit error probability (BEP) of a circuit is therefore extremely important. If the BEP of a circuit is high enough it can be directly measured by running a circuit simulation over many clock cycles and counting the faulty bits. However, the BEP's required are very low and these simulations take enormous amounts of time. We propose a general method that can be applied to any circuit, to quickly and easily determine its BEP, without requiring the identification of any specific error-prone junctions or the understanding, application and solving of any complicated and computationally intensive mathematical formulas. By varying the temperature that a circuit is simulated at, the amount of noise introduced into the system can be controlled: the higher the temperature, the more noise introduced, and the higher the observed BEP. The BEP is measured at various higher-than-normal temperatures where it can be measured quickly and relatively accurately, and a parametric model is then fitted to the data collected that describes the BEP as a function of temperature. Extrapolation of this model estimates the BEP at the required operating temperature.