Shiver Me Timers! Using Spread Spectrum Clock Generators

Most methods used for EMI suppression have hardly changed in the last quarter century. The standard tool kit has largely consisted of components that filter and shield, and methods for improving layout. While these tools have become refined over time, nothing much in the kit would have seemed alien to an RF designer of a generation ago. It was only in the last decade or so that a truly new approach was proposed, the spread spectrum clock generator (SSCG). It reduces EMI by modulating the clock frequency, thereby spreading radiated energy over a frequency range wider than the bandwidth of the standard receiver used to measure emissions. At any one frequency, the detected emission falls. Spread spectrum techniques are hardly new. The tale of their invention is oft-told, and usually begins with the filing of a 1942 patent by George Antheil and the actress Hedy Lamarr. The patent disclosed a method of frequency hopping used to immunize radio controlled torpedoes from jamming. In the last two decades, the technique has become a fixture in the communications industry because of its advantages in range, immunity and security. The use of spread spectrum clock generation to reduce emissions in digital devices was first proposed in a paper presented at the 10th Annual Power Electronics Seminar at the Virgini