AND9015 - A Solution for Peak EMI Reduction with Spread Spectrum Clock Generators

What is the problem? Electromagnetic Interference is the Electromagnetic emission from a device or a system that interferes with the normal operation of another device or a system (external source). It is also referred to as Radio Frequency Interference (RFI). EMI is caused by electromagnetic induction or electromagnetic radiation emitted from an external source. Conducted EMI and Radiated EMI are the two types of electromagnetic interference. Conducted EMI is caused by the physical contact of the conductors where as radiated EMI is caused by induction (without physical contact of the conductors). EMI is an unwanted RF energy that interferes with other systems’ normal operation. It is the excess radiated energy from the interfering device or the system, beyond the limits of electromagnetic compliance. Disturbances experienced in local receiving equipments such as television, radio, and cell phones are examples of interference due to unwanted RF energy which is EMI. With TV reception as an example, the poor picture quality seen could be due to EMI. Interference may prevent reception altogether, may cause only a temporary loss of a signal, or may affect the quality of the sound or picture produced by the interfered equipment. Radio frequency interference can occur due to the harmonic frequencies of the interfering device or equipment even if the interfering device itself is not operating at the interfered frequency. This interference is unwanted by the user as this would affect the normal operation of the device or system. Why it is to be contained? Legal limits have been imposed on electromagnetic emissions from all digital equipments and apparatus intended for general population, by monitoring bodies like the Federal Communication Commission (FCC) in the USA, the International Special Committee for Radio Interference (CISPR) in Europe, VCCI in Japan etc. Many countries now have similar requirements for products to meet some level of Electromagnetic compatibility (EMC) regulation. CISPR sets standards for radiated and conducted electromagnetic interference. The FCC has two classes of radiation levels, stated as Class A and Class B. Class A devices are digital devices intended for use in commercial, industrial or businesses and not intended for use by the general public or in the home. Class B digital devices are intended to be used in the home but could also be used elsewhere. The regulations and regulators are in place to ensure that the emissions from devices / systems released to market do not interfere with the normal functioning of other devices / systems already in the market. Non−compliant products are at risk of being recalled which can negatively impact brand image. Thus ensuring EM compliance for products becomes critical for company’s success. With faster clock speeds, lower voltage/power requirements due to the recent advances in the semiconductor and computing technology coupled with the explosion of the wireless technologies, Electromagnetic compatibility (EMC) is becoming one of the most important standard requirements in the new technology world.