spread spectrum clocking_xilinx pre-production_Free running(8)

It will be further appreciated that the HDD device 300 may not include all of the components shown in FIG。 3, may include other components that are not explicitly shown in FIG。 3 or may utilize an architecture completely different than that shown in FIG。 3。 Further, the HDD device 300 is described for illustrative purposes, and it will be further appreciated that the embodiments described herein may be applied to any electronic device implementing spread-spectrum clocking for one or more components。

FIG. 4 shows at 402 a triangular frequency modulation profile associated with a conventional SSC scheme for a clock signal having base frequency of 320 MHz, a deviation range of ±10,000 ppm and a modulation rate of 32 kHz. FIG. 4 further shows at 404 a frequency modulation profile for an adaptive SSC scheme according to embodiments described herein. The adaptive SSC profile 404 shown is for a 320 MHz clock configured to reduce interference in a target band of 925-960 MHz, corresponding to the GSM900 receiving band from the example above. In this adaptive SSC scheme, the rate of change in clock frequency, or “modulation rate,” is higher for those clock frequencies in the deviation range that correlate to the target band than those clock frequencies that do not interfere.

Specifically, the modulation rate of the adaptive SSC profile 404 is higher, e.g. 60 kHz, for clock frequencies in the 316.8-320 MHz frequency range 410 (correlated to the 950.4-960 MHz overlap of the third harmonic with the target band) and lower, e.g. 20 kHz, for clock frequencies in the 320-323.2 MHz frequency range 408. Since the clock signal will spend less time in the lower half (316.8-320 MHz) of the deviation range and more time in the upper half (320-323.2 MHz), the amount of electromagnetic energy radiated in the lower half of the clock frequency range will be less than that radiated in the upper half of the clock frequency range. This is also true for all harmonics of 320 MHz base frequency.

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