Electromagnetic interference (EMI), also called radio frequency interference (RFI) degrades or limits the effective performance and reliability of electronic circuits. Here we will discuss on the possible noise generators/sources of EMI. To improve the noise immunity, often EMI protection circuits are necessary in critical applications such as healthcare equipment, aerospace control systems, defense/military electronic equipment, and in automotive safety systems.

Broadcast transmitters, two-way radio transmitters, paging transmitters, and cable TV are potential sources of RFI and EMI. Other possible sources of interference include a wide variety of devices, such as doorbell transformers, toaster ovens, electric blankets, ultrasonic pest control devices, electric bug zappers, heating pads, and touch controlled lamps. Multiple CRT computer monitors or televisions sitting too close to one another can sometimes cause a “shimmy” effect in each other, due to the electromagnetic nature of their picture tubes, especially when one of their de-gaussing coils is activated.

Electromagnetic interference at 2.4 GHz can be caused by 802.11b and 802.11g wireless devices, Bluetooth devices, baby monitors and cordless telephones, video senders, and microwave ovens.

Switching inductive loads, such as electric motors, often cause interference, but it is easily suppressed by connecting a snubber circuit, a resistor in series with a capacitor, across the switch. Switched-mode power supplies can be a source of EMI, but have become less of a problem as design techniques have improved, such as integrated power factor correction.

Integrated circuits are often a source of EMI, but they must usually couple their energy to larger objects such as heatsinks, circuit board planes and cables to radiate significantly. On integrated circuits, important means of reducing EMI are: the use of bypass or decoupling capacitors on each active device (connected across the power supply, as close to the device as possible), rise time control of high-speed signals using series resistors, and VCC filtering.