Semi-Analytical Estimation of On-Chip Intertwined Rectangular Transformer Parameters in 180 nm CMOS Technology

This paper presents the design methodology of an on-chip intertwined rectangular transformer in 180 nm CMOS technology intended for fully integrated LC oscillators. A simple model based on the physical interpretation of the transformer is presented. A method for fast estimation of inductance and magnetic coupling which takes into account the spacing between the turns is presented. Estimation of other parameters is given based on a combination of simple formulas, extraction from electromagnetic simulations and a fitting procedure. Four transformers with different turn ratios are simulated in HFSS and the results of the simulations to the fitted data of the lumped elements model are compared. The model's relative error of S-parameters compared to the simulations is less than 5% for inductors and 10% for the transformer in a high frequency range.