Radio frequency (RF) circuit board topology
View Patent ↗An interconnection structure for interconnecting circuitry on a first conductive layer to circuitry on a second conductive layer is provided. The interconnection structure of the present invention comprises a signal conductor via surrounded by a plurality of ground vias. The plurality of ground vias shield the signal conductor via, thus providing electrical isolation for the conductor via from the rest of the circuitry. One feature of the present invention is that the plurality of ground vias can be modified, adjusting their diameters and their placement relative to the signal conductor via, in order to affect the overall characteristic impedance of the interconnection structure. This feature is useful when propagating high frequency signals between signal traces on different conductive layers of a printed circuit board. In view of the high frequencies used in today's wireless communication systems, the interconnection structure proposed aids in the practical implementation of radio frequency modules by mitigating the effects of impedance discontinuities ordinarily present at signal trace-to-via transition regions.
1. A multilayer printed circuit board for use in a radio frequency communication system, said multilayer printed circuit board comprising:
at least two conductive layers, each conductive layer having a conductive trace formed thereon which terminates at a via pad;
an interconnection structure comprising:
a center signal conductor via connected at each end to a via pad on one of said at least two conductive layers, wherein said signal conductor via is for propagating electrical signals between conductive traces on different conductive layers of said printed circuit board;
a plurality of ground vias surrounding said signal conductor via, said plurality of ground vias having a position relative to said signal conductor via based upon-a desired overall impedance of said interconnection structure;
at least one inner ground metal layer, each inner ground metal layer corresponding to one of said conducting layers, each inner ground metal layer having a ground pullback section cut away in a region surrounding said signal conductor via, each inner ground metal layer providing a ground return path for said corresponding conductive layer, each inner ground metal layer further comprising a ground extension section corresponding to a section of said conductive trace on said corresponding conductive layer, said ground extension section protruding into said ground pullback section and being unconnected to said signal conductor via, each inner ground metal layer being immediately adjacent said corresponding conductive layer, said section of said conductive trace being isolated from a ground plane of said conductive layer.
2. A multilayer primed circuit board according to claim 1 wherein said cut away ground pullback section of said at least one inner ground metal layer has a radius greater than the radius of said via pad.
3. A multilayer printed circuit board according to claim 1 wherein said plurality of ground vias have a diameter based upon the desired overall impedance of the interconnection structure.
4. A multilayer printed circuit board according to claim 1 wherein said cut away ground pullback section is concentric with said center signal conductor via and has a radius greater than the radius of said via pad.
5. A multilayer printed circuit board according to claim 1 wherein said board is used in an antenna selection module for connecting at least one of a plurality of radio pans to at least one of a plurality of antenna ports.
6. A multilayer printed circuit board according to claim 1 wherein each of said plurality of ground vias are substantially the same distance from said centre signal conductor via.
7. A multilayered printed circuit board according to claim 1 wherein said ground extension section extends said ground metal layer into said ground pullback region adjacent said section of said conductive trace on said corresponding conductive layer.
8. A multilayer printed circuit board according to claim 1 wherein each conductive layer has at least one Corresponding inner ground metal layer.
9. A multilayer printed circuit board according to claim 8 wherein an inner conductive layer has two corresponding inner ground metal layers, said inner conductive layer being between said corresponding inner ground metal layers.