A design technique for embedded electromagnetic band gap structure in load board applications

A new design technique and analysis for an embedded electromagnetic bandgap (EBG) structure is presented. In modern multifunction designs, it may be required to integrate noise-sensitive analog circuits next to digital circuits. Here, digital switching noise can propagate through power/ground planes and affect analog circuit performance. It is important to block this effect. To prevent the noise propagation, an EBG-patterned power/ground plane can be an acceptable solution. However, difficulties arise when the EBG structure is put in a stripline-like environment; the embedded EBG structure loses the noise filtering function. The reason for the functional failure is analyzed, followed by a solution. The proposed solution has been demonstrated by both simulation and measurement. Simulation and measurement results demonstrate that the proposed embedded EBG structure can be effective for the desired noise isolation. The design technique is tested on a prototype load board for a 10-bit 3-GHz analog-to-digital converter from National Semiconductor. The suggested design technique for the embedded EBG structure includes three design parameters: 1) the potentials of the planes above and below the EBG layer; 2) the thicknesses of the dielectric layers above and below the EBG layer; and 3) the number and position of vias interconnecting the top and bottom planes.