The numerical simulation of integrated circuits represents an essential part for cheap and time effective circuit design. It provides all
interesting signals, voltages, currents and resulting datas. New developments in the production engineering demand a higher abstraction
level for circuit element models which may cause difficulties for the numerical analysis. Well-known problems are higher index configurations of
the resulting differential algebraic systems (DAEs) and inconsistent initial values. Due to the large dimension of many circuits, the
localization of problematic circuit configurations becomes difficult. Here we elaborate special structures of equation systems arising from the
modified nodal analysis (MNA) - one of the most used modelling technique that enables an automatic generation of the network equations and
preserves the circuit structure. Exploiting this structure and assuming certain modelling criteria one can guarantee low index systems, supply
consistent initial values and handle discontinuities of the solutions. In this way convergence of standard integration methods for the time domain
analysis is guaranteed. The model criteria are circuit element related and can be simply checked by the model designer.