Robust Limit Cycle Calculations of Oscillators

Standard approaches for limit cycle calculations of autonomous circuits exhibit poor convergence behavior in practice. By introducing an additional periodic probe voltage source, we can reformulate the system of autonomous differential algebraic equations (DAEs) as a system of non-autonomous DAEs with the constraint, that the current through the source has to be zero for the limit cycle. A one or a two stage approach now leads to a greater convergence domain, but in practice still additional techniques are necessary to improve robustness. The range of convergence towards the limit cycle for the initial probe amplitude can be expanded drastically by employing the affine invariance technique as damping strategy to Newton’s method.