A Combination of Mixed FETD Method and SPICE to Simulate Nonlinear Multiport Circuits

A combination of the mixed finite-element time-domain method (MFETD) and SPICE solver is proposed in this letter to analyze the circuit response and crosstalk effects in complex microwave circuits with linear/nonlinear, passive/active components. The MFETD method in the EM part is adopted as an unconditionally stable time integration scheme to account for the low-frequency breakdown problem. SPICE is introduced to solve the nonlinear circuit equations in the circuit part by taking into account the coupling between multiport circuits. A microwave circuit based on an AD633 chip and an MCP3221 board is simulated to verify that this hybrid MFETD-SPICE method not only is superior in mesh flexibility to the finite-difference time-domain (FDTD)-based method but also exploits the well-developed open-source software SPICE to solve the nonlinear equations.