Identifying the main nonlinear contributions: use of multisine excitations during circuit design

Modeling and understanding the nonlinear behavior of analog and RF circuits is essential for good design of telecommunication systems. Classical Volterra series give the designer this necessary insight, but they are only valid for weakly nonlinear systems and they are difficult to edit. To overcome these limitations, we developed a technique to identify, quantify and qualify the sources of nonlinear behavior in analog and RF circuits by combining the information obtained by a set of simulations that use periodic excitation signals with a given power spectrum and arbitrary phases. The paper describes and demonstrates this approach by the analysis of the cascade of a BiCMOS power preamplifier and power amplifier with adaptive biasing for 5 GHz wireless local area networks (WLAN). The approach is applicable to weakly and strongly nonlinear systems, which is demonstrated by pushing the amplifier into compression. Furthermore, it provides useful design information, such as the contribution of each subcircuit to the overall nonlinear behavior.