A broadband reduced equivalent circuits for on-chip millimeter-wave asymmetrical transformer

Abstract

A broadband reduced equivalent circuit based on the lumped approximations has been developed for the four-port asymmetrical transformer. The proposed model consists of four ideal transformers and five driving-point admittances. The four-port scattering parameters are converted to respective driving-point admittances, which are then fitted with rational function approximation. The proposed equivalent circuit is characterised by its accuracy and lesser number of elements compared to conventional model. The modelling method is validated by electromagnetic simulation for a four-port asymmetrical transformer with 0.13-μm SiGe BiCMOS aluminium process. The agreements between the electromagnetic data and model simulation are excellent in the frequency range up to 80.1 GHz. This modelling method can also be used for other asymmetrical devices such as spiral inductor, which is discussed in this article.

Keywords:

• broadband equivalent circuit
• asymmetrical transformer
• scattering parameters
• rational function
• spiral inductors