EMI problems? Part two: Where does EMI come from?
Every electronic device, including cell phones, creates both good and bad characteristics. Cell phones these days offer the convenience of talking to friends, family, and business associates from just about anywhere. However, they also have the potential to produce EMI signals—and those signals are only part of the problem. The evolution of these devices exceeds the basic phone services by including smartphone capabilities.
Neighboring equipment and circuits do not expect this type of EMI noise. Cell phones rely on high levels of RF energy to do their jobs. Although they comply with regulations, they may become sources of unintended EMI to susceptible devices.
PCBs, clock circuits, oscillators, digital circuits, and processors also can be sources of EMI in circuits. Electromechanical devices that switch currents produce EMI during make-or-break operations. These EMI signals do not necessarily have a negative effect on other electronic equipment. The spectral content and intensity of an EMI signal determine whether it has the potential for an unexpected response from a susceptible circuit.
It is better to stop the interfering signal at its source, rather than allow it to propagate through circuits. As for vehicles, carmakers are constructing more vehicle bodies with plastic, which becomes a problem when you need to find a low-impedance ground or provide shielding.
Once the signals are free and roaming about, they stand a chance of entering your sensitive systems and wreaking havoc. Next month’s column will detail how the EMI signal travels through the medium to get to your circuits.
Bonnie Baker is a senior applications engineer at Texas Instruments and author of A Baker’s Dozen: Real Analog Solutions for Digital Designers.