  Power integrity is becoming increasingly relevant due to increases in device
functionality and switching speeds along with reduced operating voltage. Large
current spikes at the device terminals result in electromagnetic disturbances
which can establish resonant patterns affecting the operation of the whole
system. These effects have been examined using a finite difference time domain
approach to solve Maxwell's equations for the PCB power and ground plane
configuration. The simulation domain is terminated with a uniaxial perfectly
matched layer to prevent unwanted reflections. This approach calculates the
field values as a function of position and time and allows the evolution of the
field to be visualized. The propagation of a pulse over the ground plane was
observed demonstrating the establishment of a complex interference pattern
between source and reflected wave fronts and then between multiply reflected
wave fronts. This interference which affects the whole ground plane area could
adversely affect the operation of any device on the board. These resonant waves
persist for a significant time after the initial pulse. Examining the FFT of
the ground plane electric field response showed numerous resonant peaks at
frequencies consistent with the expected values assuming the PCB can be
modelled as a resonant cavity with two electric and four magnetic field
boundaries.
