To add another $0.02 worth...
There are two mechanisms for radiation: transmission line fields, and ground noise. The fringing fields from the trace determine the radiation. Therefore, the height of the trace above the gnd plane (coupling) determines the radiation by this mechanism. The ground noise is the most interesting. The higher the voltage drop across ground, the higher the radiation. The voltage drop is determined by the mutual inductance between the trace and the gound plane, and the current through the trace. Assuming the trace is already as low as convenient, one would then seek to limit the current. Terminating the trace in its characteristic impedance results in (typically) MUCH higher currents than terminating in the high input impedance of the trace. Lower current, lower ground noise. However, the reflection must be contended with. Termination at the source assures only one reflection, an acceptable situation. Mark --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
