spread spectrum clocking_xilinx pre-production_Free running

The following detailed description is directed to technologies for adaptive spread-spectrum clocking to limit interference in a target band. The circuitry of many electronic and computing devices include an oscillator or clock circuit that continuously generates a clock signal needed for the operation of synchronous digital components of the device, including processors, memory, communication components, and the like. For example, a hard-disk drive (“HDD”) device may include a clock circuit for generating the operational clock for internal dynamic random-access memory (“DRAM”). The DRAM clock circuit of the HDD may generate electromagnetic interference (“EMI”) that interferes with other components of the HDD or systems that implement the HDD and/or exceeds allowable EMI limits.

To limit EMI generated by the DRAM operational clock or other clock circuit, spread-spectrum clocking (“SSC”) may be utilized. SSC schemes vary the frequency of the clock signal in a limited range around a base frequency. The rate of change in the clock frequency is referred to as the “modulation rate” and the range over which the frequency is varied is referred to as the “deviation range.” Since SSC spreads EMI energy in the frequency domain through the deviation range, peak EMI at the base frequency and its harmonics may be significantly reduced. However, while peak EMI is reduced, the range of frequencies over which electromagnetic energy is radiated may be expanded around the base frequency and its harmonics.

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