What is the single most critical improvement that needs to be made on the board (PCB) to reach >10Gbs data rates (DK, DF, T-Line routing)?
There is one critical improvement in a board that must be made and one improvement in the transceivers that drive a high speed signal. All resonances from stubs, of any sort, must be kept short enough so that their resonance frequency is above about 5 x the Nyquist frequency, or above about 25 GHz, for 10 Gbps signals. The resonance frequency of a stub is 1500 GHz/length (in mils). For the resonant frequency to be above 50 GHz, (Fres > 10 x Nyquist)requires the stub length to be shorter than 30 mils. In addition to using strictly a point to point routing architecture, it is important to use vias with residual stubs shorter than 30 mils. This can be achieved by backdrilling or using blind or buried vias. This is the one most important feature of a board to achieve 10 GHz operation. FR4 has another limitation related to its losses. If the transceivers have pre-emphasis and equalization, they can overcome as much as -30 dB of dielectric and conductor losses. This combination can enable co
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