Characterization, design and modeling of on-chip interleaved transformers

Abstract

This report aims to provide a comprehensive review of the project, characterization, design and modeling of on-chip interleaved transformers. Investigation, modeling, and performance optimization of silicon-based on-chip transformers are deliberately addressed. Complete characterization of monolithic planar interleaved transformers was performed based on 3D EM (Electromagnetic) simulations. The effect of layout geometry on the transformer’s performance was investigated. The number of turns of the octagonal spiral, the inner radius of the spiral, the metal line width, and the metal spacing were each varied independently, while the other parameters were kept unchanged. The conclusion of the report could serve as useful design guidelines. Various loss mechanisms that degrade the transformer’s performance were examined. A scalable model has been proposed to represent the RF characteristics of different transformer designs. All the RLC model elements were formulated as functions of the transformer’s geometrical and process parameters. Thus, the flexibility to tailor the transformer design becomes possible for any RF applications. Verification with accurately calibrated EM simulations demonstrated the accuracy of the performance predication and the scalability for a wide range of transformers’ layout.

A 5GHz Gilbert Cell mixer was finally designed to test the capability of the proposed transformer. The transformer works as an input balun to generate differential signals. Resonant tuning was added to reduce the losses between input and output ports. The designed mixer offers high conversion gain, excellent isolations, as well as good linearity and noise performances.