Frequency Generation
High-frequency electromagnetic emission peaks occur at integer multiples of a circuit’s fundamental operating or switching frequency. These narrow-band signals, known as harmonic radiation spikes, arise from non-linearities in semiconductor switches or fast transition times in clock circuits. The presence of these spikes can cause a printed circuit board assembly to fail electromagnetic compatibility standards.
High-speed digital signals on board traces are a primary source of these emissions.
Mitigation Technique
Board design strategies reduce the amplitude of unwanted high-frequency emissions at their source or prevent them from radiating. To control harmonic radiation spikes, layout designers implement decoupling capacitors close to active device pins and route critical signal traces with continuous ground reference planes. Series termination resistors can also slow down the rise times of digital pulses.
These board layout decisions are critical for reducing noise generation before it reaches the shielding stage. Shielding enclosures or board-level metal cans block the remaining radiated energy from escaping the product housing.
Diagnostic Measurement
Spectrum analysis identifies the exact frequencies and amplitudes of the unwanted emission peaks during compliance testing. Engineers tracking harmonic radiation spikes use near-field probes to scan the board assembly for localized radiation hot spots. This measurement identifies which traces or components require further shielding or filtering.
