'Institute of Electrical and Electronics Engineers (IEEE)'
Abstract
Common-mode rejection filters operating at microwave frequencies have been the
subject of intensive research activity in the last decade. These filters are of interest for
the suppression of common-mode noise in high-speed digital circuits, where differential
signals are widely employed due to the high immunity to noise, electromagnetic
interference (EMI) and crosstalk of differential-mode interconnects. These filters can
also be used to improve common-mode rejection in microwave filters and circuits
dealing with differential signals. Ideally, common-mode stopband filters should be
transparent for the differential mode from DC up to very high frequencies (all-pass),
should preserve the signal integrity for such mode, and should exhibit the widest and
deepest possible rejection band for the common mode in the region of interest.
Moreover, these characteristics should be achieved by means of structures with the
smallest possible size. In this article, several techniques for the implementation of
common-mode suppression filters in planar technology are reviewed. In all the cases,
the strategy to simultaneously achieve common-mode suppression and all-pass behavior
for the differential mode is based on selective mode-suppression. This selective mode
suppression (either the common or the differential mode) in balanced lines is typically
(although not exclusively) achieved by symmetrically loading the lines with symmetric
resonant elements, opaque for the common-mode and transparent for the differential
mode (common-mode suppression), or vice versa (differential-mode suppression).MINECO, Spain-TEC2013-40600-R, TEC2013-41913-PGeneralitat de Catalunya-2014SGR-15