A common-mode suppressor for eliminating common-mode noise in high frequency differential data transmission systems and an associated method includes a long coiled differential transmission line configured to transfer data between a source and a load. The differential transmission line comprises a first conductive wire and a second conductive wire which are inductively and capacitively coupled and are laterally aligned or vertically aligned with each other. Further, the differential transmission line is matched for differential signals and un-matched for common-mode noise.