New wideband common-mode noise filter using quarter-wavelength resonator for high-speed differential signals

This work presents a novel, inexpensive and wideband common-mode noise suppression filter by using quarter-wavelength resonator. The quarter-wavelength resonator can provide a shorting path for common-mode return current of differential interconnects around the resonance frequency of the open stub. The feasibility of cascading several open stubs is proposed to achieve the wideband bandwidth over a broad GHz range. Numerical results indicate the rejection band of the proposed filter ranges from around 4.27GHz to 8.2GHz by over 20dB for cascading three different lengths of open stubs. The location of open stub underneath and parallel to the differential traces greatly facilitates implementation of common-mode noise filter in multilayer structures and multiple differential signaling pairs for high-speed digital systems, e.g. USB3.0 and HDMI. Importantly, in term of eye diagrams, signal integrity of the differential signals is not degraded within the wide bandwidth of the proposed common-mode noise filter.