Resistive Coupling Efficiency Criterion for Evaluating Substrate Shielding Structures of Transformers

Abstract

This letter presents a new way to evaluate the transformer substrate effect by computing its resistive coupling efficiency coefficient eta <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Kr</sub> . To assess eta <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Kr</sub> , a set of transformers with and without shielding structures was fabricated using standard 0.18-mum CMOS process. The resistive coupling factor eta <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Kr</sub> and efficiency eta <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Kr</sub> were extracted. It was found that substrate and shielding effects are better quantified with eta <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Kr</sub> than with G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> parameters. The larger the relative shielding dimensions, the higher the eta <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Kr</sub> is. With eta <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Kr</sub> as a figure of merit, we see clearly that a large 3-D patterned floating shield improves transformer performance more than a 2-D one. It was also found that shielding efficiency is correlated with shielding structure dimensions and that the performance of shielded transformers is less sensitive to temperature variations.