Cables connected to a device carry unwanted transient signals and other disturbances to
other devices. This is the general conducted emission definition . The
conducted emissions are measured with voltage and current measurements on the cables.
Such measurement methods are standardized, for instance, for automotive appliances in
The voltage measurement method measures the conducted emissions only on the power and
eventually the ground cable on a LISN (Line Interface
Simulation Network). However, that is of utmost relevance,
because the disturbances on the power supply are distributed to other devices by the
power delivery network. The current measurement method with a coupling coil measures the
common mode current on a multi-wire cable harness. The measured conducted emissions are
initiated by galvanic coupling, electric and magnetic near field coupling, and even from
radiated far fields. Transient signals and disturbances on the cables also cause radiated
emission. Thus, every PCB emission mechanism that causes radiated emissions from cables
attached to the PCB is also relevant for the conducted emissions. The following
description of emission mechanisms from the PCB, therefore does not further distinguish
between radiated and conducted emission mechanisms.
All radiated and conducted emission measurement methods have different measurement
sensitivities for different emission frequency ranges and different emission coupling
mechanisms. This is the main reason for the application of different methods for device
EMC compliance measurements.
Emission from PCBs can be classified based on the following two main mechanisms:
C. Poschalko: The Simulation of Emission from Printed Circuit Boards under a Metallic Cover