Spice-Oriented Intermodulation Analysis Combining with MATLAB

It is very important to analyze the mixer and modulator circuits which are driven by multiple input frequencies. Volterra series methods are widely used for the frequency-domain analysis of nonlinear circuits, which can be applied to relatively strong nonlinear circuits. We compare properties of the above two methods using illustrative examples. In this paper, we propose a Spice-oriented HB method combining with MATLAB. Firstly, for the circuits containing nonlinear devices characterized by the special function, they are approximated by the Taylor series. Then, the Fourier coefficients can be calculated by MATLAB in the symbolic forms. Thus, the determining equations of HB method can be formulated by net-list in Spice simulator. It can be efficiently solved by the DC analysis of Spice, and the frequency-domain solutions are obtained. We found from examples that, although Volterra series method can be efficiently applied to weakly nonlinear circuits, it becomes erroneous to strong nonlinear circuits.