Power and Signal Integrity and Electromagnetic Emission; the Balancing Act of Decoupling, Planes and Tracks

The noise voltage in the reference or ground of a printed circuit board is often the cause of unwanted radiated emission. Power supply planes attribute to the noise voltage. By replacing the power supply planes by tracks, the noise voltage in the reference or ground can be considerably reduced, which leads to a dramatic reduction of the radiated electromagnetic fields. This has been shown using transmission line equations for a general two-conductor line. Simulation and measurements results confirm the beneficial effect of removing power planes. A reduction of 50 dB in radiated electromagnetic field strength was obtained. The question was raised whether (or not) the signal integrity is negatively influenced by using power tracks instead of planes. Several printed circuit boards have been built and measured, showing that signal integrity remains while reduction of radiated emission is achieved.