Power supplies, power lines, lightning, computer equipment, and electronic components are all potential sources of electromagnetic interference (EMI) that may affect the performance of electronic components. EMI can be conducted from one component to another via electrical pathways in a single system or be transmitted through airwaves. Devices that need to communicate via RF intentionally emit electromagnetic signals that can interfere with other equipment, but even devices that are not designed to emit electromagnetic signals may unintentionally contribute to EMI noise. FCC regulations limit allowed emissions from certain classes of devices, such as computing equipment and microwave ovens, but this does not guarantee that electronic components will not be damaged by EMI from consumer products.
Nearly every electronic device or component is capable of generating EMI, and it is important to consider EMI exposure as part of circuit design because of the damage it can do to electronic components including timing devices. Phase noise and phase jitter of oscillators may increase substantially in the presence of external sources of EMI. It is possible to reduce EMI reaching the oscillator through board-level shielding or filtering, but this approach is not always successful. By evaluating the electromagnetic susceptibility (EMS) of various oscillators, we can determine factors that contribute to EMS and understand how proper oscillator design can minimize detrimental effects of EMI on clock performance.