Analysis of the intermodulation distortion and nonlinearity of common-base SiGeC HBTs.

The aim of this paper is to study the nonlinearities of a common base RF transistor in order to identify the intrinsic origin of distortion. In this paper we introduce the Volterra theory through the CMNA (Compacted Modified Nodal Analysis) method to establish the output nonlinearities of the building block as a function of the transistor equivalent circuit elements. This method was applied to 0.25 mum SiGeC BiCMOS technologies for comparison purpose. The 2nd and 3rd nonlinear orders of the intermodulation output current were derived. The full expression was used to identify the dominant contributors of the nonlinearity and to provide a simplified expression. The role of the current-gain linearity and the difference between the high and low frequency performances were explained.