PCB Routing guidelines - Part 5

What are the various sources of radiation the PCB design engineer has to deal with in a PCB?

If we stick to common scenarios and keep aside the high speed circuitry, we can list the following sources that could cause radiation.

• The clock circuitry that is inside the IC can cause radiation
• The external oscillator used for generating the clock for the main components like micro controller, processor, FPGA, etc. 
• There could be clock tree on the PCB where clock buffers used and they require careful attention
•  The I/O signals that are routed on the PCB which form a long antenna when routed to till the external peripherals or when routed long on the PCB
• The radiation that may arise from the cables connected to the on-board connectors. This board can couple onto the circuit around the connector.
• High speed traces having longer return path for the signal.
• High speed traces routed over a void on the PCB. In another way, discontinued return path for the signals.
• The power circuit and especially the switchers that switch at a higher frequency and can couple noise to output.

Whatever may be the source the primary responsibility of the PCB engineer is to see that the ground return path is as close as possible to the main signal and they have to ensure to eliminate the bigger loop areas. Also, the PCB engineer has to ensure that there is enough room between the oscillator circuits and the circuitry around so that there is no chance of noise coupling.