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February 2014 • The PCB Design Magazine 33 stops—preventing reflection—which is what impedance matching is all about. Figure 5 illustrates the improved waveform of the matched bifurcated line of Figure 4. This technique, for matching branched lines, is not often used due to the difficulty of fabricating traces of widely varying impedance on the same substrate. Also, space limitations beneath FPGAs limit the width of the thicker trace. Another is- sue with this technique lies with the loop re- turn currents created within the network. If one of the bifurcated traces is located on a different layer to the other, the return current will be ref- erenced to different planes. When this occurs, a potentially large loop area is created, with a cor- responding increase in radiated emissions. GND EFFECTIVE RoUTING oF MULTIPLE LoADS continues beyond design Figure 4: A matched bifurcated transmission line. Figure 5: The resultant waveform of the matched line.