Editing Spread spectrum (section)

=== Background ===
Practical synchronous digital systems radiate electromagnetic energy on a number of narrow bands spread on the clock frequency and its harmonics, resulting in a frequency spectrum that, at certain frequencies, can exceed the regulatory limits for electromagnetic interference (e.g. those of the [[Federal Communications Commission|FCC]] in the United States, [[JEITA]] in Japan and the [[International Electrotechnical Commission|IEC]] in Europe).

Spread-spectrum clocking avoids this problem by reducing the peak radiated energy and, therefore, its electromagnetic emissions and so comply with [[electromagnetic compatibility]] (EMC) regulations. It has become a popular technique to gain regulatory approval because it requires only simple equipment modification. It is even more popular in portable electronics devices because of faster clock speeds and increasing integration of high-resolution LCD displays into ever  smaller devices. As these devices are designed to be lightweight and inexpensive, traditional passive, electronic measures to reduce EMI, such as capacitors or metal shielding, are not viable. [[Active EMI reduction]] techniques such as spread-spectrum clocking are needed in these cases.