Mathematical behavior of integration methods with non continuous first derivative devices in circuit simulation

Computation of MOS transistor channel currents in SPICE transient analysis may give rise to unrealistic oscillations when charge-control models are used for MOS devices in connection with the trapezoidal integration method: this problem is related to the criterion used to estimate the truncation error associated to the last computed timepoint. A new algorithm for step-size control and choice of the integration method in SPICE transient analysis, based on computation of a Local Error Estimate (LEE), has been developed which avoids the above mentioned oscillations. The algorithm has been implemented in SPICE and preliminary results show that it does not give rise to oscillations while imposing a low overhead on the computational effort