Noise Coupling in Heavily and Lightly DopedSubstrate from Planar Spiral

Noise Coupling in Heavily and Lightly Doped Substrate from Planar Spiral Inductor Tony Yeung, Alan Pun, Zhiheng Chen, Jack Lau, Fran cois J.R. Cl ement Dept. of Electrical & Electronic Engineering, The Hong Kong University of Science & Technology Center for Integrated Systems, Stanford University, Stanford, CA 94305 Abstract| Recently, much studies have been done to include on-chip inductors for wireless communication IC design. The large area metal plane of the spiral inductor can form large capacitor to the silicon substrate. At high enough frequency, excitation of the inductor will induce noise to the substrate. In this paper, we will present the simulation results of the coupling e ect of a planar spiral inductor on heavily and lightly doped substrate by using a compact model of the substrate. Results show that the insertion of a P+ di usion guard ring can reduce about 15dB of noise for lightly doped substrate and 7dB of noise for heavily doped substrate at 3GHz. Variation in the size of the P+ di usion guard ring a ects the e ciency of noise reduction and also the inductance. Results show that in order to optimize for inductance, the side length of the guard ring needs to be twice the side length of the inductor and the guard ring can only reduce about 6dB of noise for lightly doped substrate and 1.5dB of noise for heavily doped substrate at 3GHz.