Issue link: https://iconnect007.uberflip.com/i/1512857
30 DESIGN007 MAGAZINE I DECEMBER 2023 High-speed PCB design is not as simple as sending a signal from the driver to the receiver over a transmission line. One should also con- sider the presence and interaction of the power distribution network (PDN) and how and where the return current flows. A logic sche- matic diagram masks detail crucial to the oper- ation of unintentional signal pathways vital to the understanding of signal performance, crosstalk, and electromagnetic emissions. e PCB designer needs to be able to visualize the connectivity of the return current flow to avoid large loop areas that increase series inductance, degrade signal integrity, and increase crosstalk and electromagnetic radiation. We think of a copper plane as a thick, solid plate of copper that can basically handle any Return Path Optimization amount of current we sink into it. It also serves to make the circuit layout easier, allowing the PCB designer to ground anything anywhere without having to run multiple tracks. at may well be the case with DC or very low-fre- quency analog circuits, but certainly not in the case of high-speed design. e return displace- ment current takes the path of least inductance in the nearest plane(s). Returning signal cur- rents tend to stay near their signal conduc- tors, falling off in intensity with the square of increasing distance. Ground impedance is at the root of virtually all signal and power integrity problems; low ground impedance is mandatory for both. is is readily achieved with a continuous ground reference plane but becomes increasingly Beyond Design by Barry Olney, IN-CIRCUIT DESIGN PTY LTD / AUSTRALIA