Mechanism Analysis and Experiment of the Effects of the Guard Ring on the Inductors Performance

The grounded guard ring (GGR) is widely used to suppress the electromagnetic coupling (EMC) among adjacent inductors and reduce crosstalk with other components. However, the GGR will affect the performance of the inductor itself. To intuitively and deeply analyze the mechanism of the effects of GGR on the performance of inductors, an equivalent circuit model of inductors was adopted. Then, the substrate doping (SD) and EMC effects are introduced to characterize the mechanism of the GGR effects. To verify the correctness and rationality of the mechanism analysis, the inductors with and without GGR are taped-out using a standard 180-nm CMOS process. Then, the experimental results of the effects of GGR on the performance of inductors are presented. Furthermore, the equivalent model parameters are extracted based on measured S-parameters of two kinds of inductors. Finally, the experimental results are consistent with the mechanism analysis of the GGR effects, which has important guiding significance for the design of the subsequent GGR to improve the inductor and circuit performance.

I. Introduction

In recent years, with the advent of the Internet of Things and the fifth-generation (5G) communications, low-cost and highly integrated CMOS millimeter-wave (mm-wave) circuits have become a research hotspot [1], [2], [3]. To increase the integration density of chips, the individual components on-chip should be placed as close as possible. Consequently, it leads to the adjacent sensitive components, especially inductors, which will suffer from performance degradation and further impact the whole circuit. The main reason is due to the electromagnetic coupling (EMC) and crosstalk [4]. An efficient way to solve this problem is employing guard rings to the periphery of the inductors. These guard rings greatly increase the isolation of the inductors [5], [6], [7]. However, using guard rings also affect the performance of the inductor itself, such as inductance (), quality factor (-factor), and self-resonance frequency (SRF) [8], [9]. Most studies in grounded guard rings (GGRs) are focused on discussing why GGR can increase isolation and reduce substrate noise [10], [11], [12]. According to the author’s knowledge, there are rarely discussed the effects of the guard ring on the performance of the inductors in great depth. Therefore, the motivation for this letter is to intuitively and deeply analyze the mechanism of the effects of GGR on the performance of inductors.