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Electromagnetic Interference (EMI) is a major challenge for designers of today’s electronic devices, and clock signals can be a major source of EMI on the circuit board. Traditional filtering and shielding can be costly and inefficient. On the other hand, a very effective and efficient approach to reduce EMI emissions is to use spread spectrum clock generation (SSCG). Spread spectrum is the frequency modulation of the source clock at a much lower modulation rate, typically 30 to 60 kHz. Radiated emissions are minimized by spreading energy around the center of the source frequency. This technique spreads EMI over a wider frequency range, reducing peak emission at every harmonic. The Si512xx clock family can be customized at the factory to support a specific spread profile, percentage, modulation rate or type based on the customer system requirement. The figure shown here shows a spectrum plot of a 64 MHz clock before and after spread spectrum clocking being applied. The energy peaks of 64 MHz and its higher order harmonics are reduced for more than 10 dB with a ±1% spread percentage. It is worth mentioning here that the Si51210 (6-pin device) is an excellent candidate for a standalone EMI reduction device, receiving an input frequency between 3 to 166 MHz, and applying SSCG to the desired output. Due to its small size, the footprint can be easily placed between the system clock (non Spread) and the destination when designing the PCB. In case an EMI test failure happens in the product testing stage, the Si51210 can be easily populated to solve the problem and avoid costly and time consuming board debug and redesign.
