Abstract
The relationship between LSI operation modes and radiated emission, and reduction measures were studied by using Test LSI. Output operation that drives many external traces radiates a large amount of emission. Insufficient return paths for external trace currents at LSI mounted area result in high frequency current loops, which excite the power and ground plane and cause widely distributed high frequency currents over the PCB. Putting ferrite on LSI package and covering LSI package with copper sheet effectively reduce the extent of the current distribution over the PCB and reduce the emission.
