In a single-ended circuit where either signal or power is returned to the source through a ground line, noise filtering can be accomplished by using a shunt (bypass) capacitor and/or series inductor or inductive element such as a ferrite bead. In a balanced or un-grounded transmission system (two-wire line), a different kind of component is needed to address noise that may be picked up in common to the balanced pair of conductors. Although schematically it looks like an ordinary transformer turned on its side, the common mode choke is easily and specifically identified by its two polarizing dots, indicating the winding structure unique to this kind of device. The common mode choke’s windings are arranged in order to provide for the attenuation of common mode noise currents while still allowing the relatively free passage of differential (single-ended) signal currents. No ground connection is required for the common mode choke to function as an EMI suppression device.