spread spectrum clocking_xilinx pre-production_Free running(4)

The routine 200 includes step 202, where a target band for the adaptive SSC mechanism is identified。 The target band may comprise an operational frequency range of a component of the device or system implementing the device。 For example, the target band may represent a WWAN receiving band utilized by a laptop computer or other portable system for mobile Internet access, such as the GSM900 receiving band (925-960 MHz)。 From step 202, the routine 200 proceeds to step 204, where the frequencies within the deviation range around the base frequency of the SSC scheme are correlated with the target band。

For example, an SSC scheme with a base frequency of 320 MHz, a +/−10,000 ppm deviation range, and a 32 kHz modulation rate may radiate substantial electromagnetic energy around the third harmonic of the clock base frequency between approximately 950。4 MHz and 969。6 MHz。 This frequency range overlaps a portion of the target band of 925-960 MHz, specifically between 950。4 MHz and 960 MHz。

The routine 200 proceeds from step 204 to step 206, where the adaptive SSC mechanism modulates the clock signal at a higher modulation rate for those clock frequencies correlated with the target band。 For example, the clock signal may be modulated at a frequency of 60 kHz for clock frequencies between approximately 316。8 MHz and 320 MHz (correlated to the 950。4-960 MHz overlap with the target band identified in step 204 above)。spread spectrum clocking Conversely, at step 208, the adaptive SSC mechanism modulates the clock signal at a lower modulation rate for those clock frequencies not correlated with the target band。

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