Routing strategies for improving common mode filter performances in high speed digital differential interconnects

The propagation of the common mode noise on high speed differential traces has an impact on EMI and crosstalk toward nearby traces and electronic devices. A common mode filter, based on a simple planar electromagnetic bandgap, can be easily designed for filtering well-defined harmonics of the propagating common mode signal. The common mode portion of the signal can be reduced through the coupling to the electromagnetic bandgap cavity. This phenomena is obtained at the gap in the reference layer between two adjacent cavities. The electromagnetic principles are introduced and a systematic analysis is carried out in this work investigating the filter performances. The effect of the number of gap crossings on the depth of the filtering band is investigated and a compact layout configuration is introduced for saving layout area.