Spread spectrum#Spread-spectrum clock signal generation

With spread spectrum clocking, abbreviated SSC, in the synchronous digital equipment, a specific clock signal (clock ) is understood to minimize electromagnetic interference. In this case, the clock signal is varied continuously in a certain frequency range, it is thereby artificially provided with a so-called jitter.

Background

A synchronous digital system is driven by a clock. This periodic clock signal usually has a very narrow frequency range. The radiated energy is thus reduced to a very small bandwidth. To minimize the potential for interference, is varied by means of spread spectrum ( Spread Spectrum Data Sheet ) the frequency in a certain frequency band. With a 1 GHz processor, for example, the clock is varied in the range from 999.5 to 1000.5 MHz.

The radiated and disturbing amount of energy remains the same, but now is spread over a larger frequency range and thus the noise power is reduced at a specified frequency.

Application in the computer field

For computers, SSC is implemented with the following components:

• Processors
• Motherboard (PCI - Express)
• Hard Drives
• Disk Controller
• Flat panel displays

Possible Problems

Activated SSC can lead to different problems related to computer hardware. Especially with SATA drives that are attached to SAS RAID controllers with SAS expander chips, it may happen that the hard drives are not recognized by the RAID controller.