Analysis, design, and optimization of spiral inductors and transformers for Si RF ICs

TLDR

Silicon IC spiral inductors and transformers are analyzed via electromagnetic methods reduced to electrostatic and magnetostatic approximations, including substrate loss, and modeled with low‑order lumped circuits derived from two‑port measurements, using the custom CAD tool ASITIC for design and optimization. Measurements from 100 MHz to 5 GHz confirm good agreement with the theoretical predictions.

Abstract

Silicon integrated circuit spiral inductors and transformers are analyzed using electromagnetic analysis. With appropriate approximations, the calculations are reduced to electrostatic and magnetostatic calculations. The important effects of substrate loss are included in the analysis. Classic circuit analysis and network analysis techniques are used to derive two-port parameters from the circuits. From two-port measurements, low-order, frequency-independent lumped circuits are used to model the physical behavior over a broad-frequency range. The analysis is applied to traditional square and polygon inductors and transformer structures as well as to multilayer metal structures and coupled inductors. A custom computer-aided-design tool called ASITIC is described, which is used for the analysis, design, and optimization of these structures. Measurements taken over a frequency range from 100 MHz to 5 GHz show good agreement with theory.