Partitioned Ohtomo Stability Test for Efficient Analysis of Large-Signal Solutions

A fundamental step in the design of electronic circuits is the verification that they are stable at least on a given set of external terminations, in order to avoid that the solution found be not observable in practice. This is especially true at microwave and millimeter-wave circuits, which are typically analyzed in the frequency domain rather than in the time domain. As a consequence, both in the linear and large-signal case, unstable solutions may be found instead of an observable one. Unfortunately, as compared to the linear case, the stability analysis of large-signal solutions is significantly more cumbersome. In particular, although it is possible to translate the small-signal tests based on the Nyquist principle to large-signal equivalents, the price to pay is a significant increase in matrix size. In the case of the Ohtomo test, which has only recently been applied to large-signal solutions, it is however possible to exploit the structure of the problem to significantly reduce the complexity and, therefore, simulation time. A real-world balanced amplifier is selected to validate the proposed method and illustrate its practical usage. The application of the method to a realistic monolithic circuit with a large number of devices is also presented.