A Decoupling-Capacitor Electromagnetic Bandgap Structure for Ultrawideband Power Line Filtering

Discrete decoupling capacitors (decaps) in power line noise filtering has been suffered from limited bandwidth within a few hundred of MHz for a long time, due to the unavoidable parasitic series inductance (ESL). This paper made a significant breakthrough, which successfully breaks the ESL limitation of discrete capacitors and greatly broadens the effective decoupling bandwidth. A novel electromagnetic bandgap (EBG) structure formed by periodic decoupling capacitors, namely decoupling-capacitor electromagnetic bandgap (DCEBG) structure, which exhibits EBG characteristic instead of inductance in the high-frequency range where the inductive impedance of capacitors dominated, is proposed. Measurement and simulation data show that the decoupling bandwidth of capacitors is extended by about two orders of magnitude at the higher cutoff frequency, as well as one order of magnitude at the lower cutoff frequency. Furthermore, folded DCEBG structures are also proposed for geometry flexibility. Equivalent circuit models are developed to analyze the coupling among capacitors, vias and power lines. The test board of the proposed structures achieves -30 dB decoupling bandwidth from 22 kHz up to beyond 10 GHz. The other obvious advantage of the proposed structure is very compact in size. This work brought the decoupling performance into a new benchmark.