Novel Double Clamp Methodology to Reduce Shielded Cable Radiated Emissions Initiated by Electronic Device Switching

A new "double clamp methodology" (DCM) is proposed that can suppress a cable's peak radiated emission in a band centered around noise frequency (f noise pk ) that is generated by common-mode (CM) electrical noise current flowing in any product containing pulsed switching devices connected to a shielded cable. DCM is a cable grounding technique that clamps or terminates a shielded cable in two places. The first shield clamp at the switching device output uses traditional well-known cable termination techniques, e.g., 360° low inductance shield connection to ground. A second shield clamp can be placed at a predetermined cable length from the first, where the cable resonant frequency is known to have ultralow CM impedance at noise frequency f noise pk . The cable loop between shield clamp terminations sets up a resonant low impedance at f noise pk that diverts CM current to the ground plane inside the product, so CM current entering a shielded cable is reduced as well as radiated electric field emissions. Analytical and measurement techniques are provided to determine the correct cable clamp length. Experimental test results confirm DCM effectively controls CM noise current and resulting peak radiated emissions by 12 dB·μV/m (~4×), without external suppression components added.