Comparison of time-step sizes for stability and convergence in transient analysis of MOSFET circuits

In transient analysis of an MOSFET circuit using the forward algorithm, the time-step size has an upper bound imposed by the stability. While, in using the backward algorithm, the time-step size may also have an upper bound, since the Newton-Raphson method used therein may not converge if the time-step size is too large. From the calculation made in this investigation it is found that for the ring oscillator the maximum time-step sizes for a converging backward algorithm are larger than those for a stable forward algorithm only by a factor not greater than eight. For most cases studied, this factor is even less than the number of Newton-Raphson iterations required for convergence