Geometry Optimization of Planar Spiral Inductors operating at 5G mid-band frequencies

This paper discusses a simplified methodology and optimization of geometry for designing of Planar Spiral Inductors. The existing method to calculate Inductance of a spiral i.e., the Greenhouse algorithm and other popularly used Spiral Inductor models are revisited. The parasitics and their effects on the spiral, quality factor, and range of operation at higher frequencies are discussed. The aim is to offer a simple method for extracting the geometric parameters of the Spiral Inductor for required Inductances are derived considering the given design constraints. The layout specifications can be chosen based on the requirements of the Quality Factor, the frequency range of operation. The layout parameters for 2nH, 5nH, and 10nH are derived for the outer dimensions in micrometers. The algorithm is implemented in Matlab and the Spiral Inductors designs are simulated in Sonnet EM tool on 180nm CMOS technology. The results are found to have overall deviations less than 10% for the thickness of 1 nm with a frequency range of operation in mid-bands of 5G spectrum and operational range almost till double the frequency corresponding to the maximum Quality Factor.