Patent Application
20050068751
A printed circuit board may have a “signal layer” with signal traces (e.g., conductive paths) that electrically connect components, such as processors and other integrated circuits. The printed circuit board may also have one or more voltage planes, such as a power plane and a ground plane, to provide power to the components.
In some cases, electromagnetic resonance between voltage planes (e.g., between a power plane and a ground plane) may increase the impedance associated with a printed circuit board. For example, reflections back and forth between the edges of a power plane and a ground plane can result in electromagnetic resonance that increases the impedance characteristics of a printed circuit board.
To reduce the resonance and improve impedance characteristics, passive elements, such as surface mounted capacitors, can be provided on the printed circuit board. This approach, however, may increase the cost of the printed circuit board—especially when the design needs to meet requirements associated with a high-performance processor (e.g., a processor with a high frequency clock signal might require a large number of surface mounted capacitors).
The printed circuit board 100 also includes a signal layer (the top surface) with signal traces 190 (e.g., conductive paths) that electrically connect components, such as processors and other integrated circuits. In some cases, electromagnetic resonance between the voltage planes 120, 130 may increase the impedance associated with the printed circuit board 100.
To reduce the resonance and improve impedance characteristics, discrete passive elements (e.g., resistors and capacitors) might be used to terminate the edges of the voltage planes 120, 130. This approach, however, might increase the cost of the printed circuit board 100.
According to some embodiments, a floating trace 240 is provided on the signal layer. The floating trace 240 is an electrically conductive path, such as a strip line or a microstrip line routed along the signal layer, that is electrically connected to the second voltage plane 230. For example, the floating trace 240 might be electrically connected to the second voltage plane 230 via a plated through hole 250 (e.g., that passes through a hole 260 in the first voltage plane 220). Note that the signal layer may include an number of floating traces (with each trace being electrically connected to the second voltage plane 230 and not being directly connected other traces on the signal layer). For example, a second floating trace 242 is illustrated in
Note that the floating trace 240 may have a resistance that is (i) proportional to the length of the trace 240 and (ii) inversely proportional to the cross-sectional area of the trace 240. Moreover, the substrate between the traces 240, 242 may inherently provide some capacitance. As a result, the overall impedance associated with the apparatus 200 may be damped or reduced, especially at resonant frequencies, without using discrete passive components (e.g., surface mounted resistors and capacitors). That is, the parasitic resistance and capacitance associated with the floating traces 240, 242 may improve the efficiency of the power delivery system (e.g., the voltage planes 220, 230).
The printed circuit board 500 also includes a signal layer (the top surface) with signal traces (not illustrated in
As illustrated in
The following illustrates various additional embodiments. These do not constitute a definition of all possible embodiments, and those skilled in the art will understand that many other embodiments are possible. Further, although the following embodiments are briefly described for clarity, those skilled in the art will understand how to make any changes, if necessary, to the above description to accommodate these and other embodiments and applications.
Although some embodiments have been described with respect to a power plane and/or a ground plane, any type of voltage plane may be associated with a floating trace on a signal layer. Moreover, although specific components have been used as examples, a floating trace may be associated with any type of component, including an Application Specific Integrated Circuit (ASIC), a processor such as a Central Processing Unit (CPU), a memory device, a package, a chipset, a and/or a motherboard. Similarly, although specific routing paths and geometries have been illustrated for a floating trace, floating traces may be routed along any path in the signal layer.
The several embodiments described herein are solely for the purpose of illustration. Persons skilled in the art will recognize from this description other embodiments may be practiced with modifications and alterations limited only by the claims.
