Experimental Study on Crosstalk Reduction between Integrated Inductors up to Millimeter-Wave Regime

Amount of inductors and transformers in highly integrated mm-wave multi-channel data communication and radar transceivers is steadily increasing with the growing complexity of the chips. Driven on one hand by higher integration of phased-array transceivers, e.g., for 5G applications, yet on the other hand by the demand for cost and chip area reduction, inductors need to be placed densely close to each other. This causes unwanted interferences coupled via inductors between different parts of the integrated system, resulting in SNR degradation, reduced data rates and nonlinear distortion effects. This paper presents an experimental study on coupling between on-chip inductors and investigation of various crosstalk reduction techniques for highly integrated SoCs up to mm-wave frequencies. We compare different orientations of 8-shaped inductors and discuss a rotated version of the 8-shape coil, which provides an additional improvement of 10 dB over the entire frequency range. Two-port measurements of coupled inductors connected single-endedly are performed up to 145 GHz. Additionally, 4-port measurements are done up to 70 GHz. We propose analyzing the crosstalk mechanisms by converting the measured S-parameters into the mixed-mode representation. Test structures were realized in 28 nm bulk CMOS technology node.