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5.2.5
Modulation Shape
The 'Modulation Shape' is the form of signal which is used to modulate the main output clock signal.
There are two shapes: 'Triangle' and 'Dual Triangle'. 'Triangle' provides a first-stage EMI improvement
(SSCG_PERIOD_JITTER = 0). The 'Dual Triangle' mode (SSCG_PERIOD_JITTER = any other value
than 0) provides second-stage EMI improvement.
Triangle (SSCG_PERIOD_JITTER = 0)
A single triangular shape with a constant period (SSCG_PERIOD value) is used for
modulation. Within the four phases of a single period, the internal SSCG_FSTEP unit
increments or decrements the modulation frequency.
'Dual Triangle' (SSCG_PERIOD_JITTER = any other value than 0)
This shape is used when the duty cycle of the working period of the modulated output signal is
intentionally 'jittered' or expanded (using the SSCG_PERIOD_JITTER register) to level out
small peaks in the frequency spectrum of the modulated clock signal. As a consequence, the
amplitude of the 'second triangle shape' is also slightly higher than that of the first, increasing
the average overall frequency (this could be corrected to avoid overstepping the 666 MHz
barrier by reducing the SSCG_FSTEP value). The SSCG_FOFFSET setting can shift the
transition phases, also modifying the average overall modulation frequency (if SSCG_FSTEP
is not changed). The final modulation shape is essentially the result of continuously alternating
between two different triangle shapes.
Version 1.30
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