Common-Mode Conversion Noise Mitigation With Embedded Coupled Lines in Differential Serpentine Delay Microstrip Lines

In this article, a novel method to suppress differential-to-common mode conversion noise in differential serpentine delay microstrip lines (DSDMLs) is proposed. To suppress the remnant mode conversion noise, embedded coupled lines are adopted in the parallel traces section of DSDMLs. Embedded coupled lines can minimize the timing delay between even- and odd-modes in the parallel traces section. In specific dimensions, embedded coupled lines propagate even- and odd-mode signals with the same velocity without changing the differential-mode impedance, so DSDMLs with embedded coupled lines can suppress differential-to-common mode conversion noise without degrading differential-mode signal quality. In simulations, the proposed DSDMLs exhibit about 93.0% suppression of the peak common-mode conversion voltage compared with conventional DSDMLs, regardless of the length of the parallel traces section of DSDMLs. The performance of our proposed DSDMLs is verified by conducting measurements with millimeter-scale test boards in the frequency and time domains. The test board exhibited 78.7% suppression of common-mode conversion noise without degrading the differential insertion loss compared with conventional DSDMLs. Simulations and measurement results exhibited good agreement.