A Novel Wideband Common-Mode Suppression Filter for Gigahertz Differential Signals Using Coupled Patterned Ground Structure

A novel simple wideband common-mode suppression filter

“…It is found the insertion loss for the CM in the wide stopband is approximately less than 15 dB within 3.6-9.5 GHz. The cutoff frequency is defined by 15 dB, which is sufficient for solving the signal integrity and EMI issues in high-speed digital circuit applications [1,5]. However, there exists a stub, named as point a, the insert loss Scc21 at point a is about −13 dB, which is over −15 dB and needs to be further suppressed.…”

“…With two optimized C-shaped DGS pattern on ground planes, it achieves a broad stopband width while it has a small area. The area of the proposed filter is only 75% of the CM filter in reference [1] while it has a wider stopband than that of the latter.…”

“…Differential signals have been widely used in high-speed digital circuits because they have advantages of low radiated emission and good immunity performance for common mode (CM) noise. However, because of unbalanced routing, patterned ground plane and clock skew, a significant amount of CM noises are easily generated in practical circuits [1]. They are responsible for electromagnetic interference (EMI) emissions problems which degrade the signal integrity of the high-speed circuit system.…”

“…The conventional methods using discrete components are difficult to realize a large noise reduction effect in wide frequency range. Recent CM filter designs include electro-magnetic bandgap (EBG) filter [2,3] and defected ground structure (DGS) filter [1,4,5,6,7]. The EBG filter is effective to reduce CM noise at the GHz band.…”

“…Reference [5] demonstrated a CM filter using periodic DGS can achieve a broad stopband from 3.3 GHz to 5.7 GHz, of which the size is about 15 mm by 30 mm. Reference [1] demonstrated that a CM DGS filter adopting two U-shaped and one H-shaped DGS cell can achieve a broad stopband from 3.6 GHz to 9.1 GH-z. The stop-band width and the size of the filter are 5.5 GHz and 10 mm by 10 mm respectively.…”