Spread Spectrum - 1.0 English

Clocking Wizard for Versal ACAP LogiCORE IP Product Guide (PG321)

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1.0 English

When Spread Spectrum (SS) is selected, CLK_OUT3 and CLK_OUT4 are not available. Divide values of these outputs are used for SS modulation frequency generation. There are four modes available for Spread Spectrum Mode:


The available modulation frequency range is 25 – 250 kHz.

Spread Spectrum calculation details are described in the following figures:

Figure 1. Spread Spectrum Mode (Center Spread)
Figure 2. Spread Spectrum Mode (Down Spread)
Note: Input_clock_frequency is in Hz.

For spread:

  • If (SS_Mode = CENTER_HIGH):
  • If (SS_Mode = CENTER_LOW):
  • If (SS_Mode = DOWN_HIGH):
  • If (SS_Mode = DOWN_LOW):

In the above equatons, M is CLKFBOUT_MULT_F, D is DIVCLK_DIVIDE, and O is respective CLKOUTX_DIVIDE.

For Modulation Frequency:
  • O2 and O3 are calculated by the write_device_image in implementation. Same calculation is done in the wizard to get actual modulation frequency value.
  • Then based on what O2 and O3 is calculated, the actual modulation frequency is calculated:
    • If (SS_Mode = CENTER_HIGH or SS_Mode = CENTER_LOW)
    • If (SS_Mode = DOWN_HIGH)
    • If (SS_Mode = DOWN_LOW)
Important: Actual modulation frequency may deviate within +/- 10% of the requested modulation frequency for some settings.