After more than 70 years of manufacturing development and more than a hundred billion square feet of boards produced, what could possibility be new in printed circuit board technology?
At DesignCon 2011, Jamal Izadian, founder of RFConnext, partnering with Julian Ferry, high speed engineering manager with Samtec, introduced a novel design for lower loss and higher bandwidth transmission lines using conventional circuit board manufacturing technology.
The new design, patents pending with RFConnext, "leverages the Heavyside condition, first derived for the transatlantic cable in the late 1860s by Oliver Heavyside," Izadian said.
The Heavyside condition identifies that signal degradation in an interconnect is not just about the conductor loss, described by the resistance, R, or the dielectric loss, described by the conductance, G, but optimal transmission depends on the ratio of R/L and G/C in a transmission line.
If these ratios are equal, even a high R or high G transmission line can provide low loss. But the challenge, Izadian said, is that limited to conventional transmission line design principles for circuit boards, just changing the cross section geometry does not affect the ratios very much.
In his new interconnect design, Izadian introduced an additional degree of freedom using drilled through holes which can independently affect each of the four transmission line terms.
"This extra degree of freedom lets us optimize the target impedance and the loss of transmission line structures." For example, when drilled in the signal path, the effective dielectric constant and dissipation factor is lowered by the fringe field lines passing through a larger fraction of air.
RFConnext refers to the new transmission line design as a Periodic Micro Transmission Line (PMTL).
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