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A crystal-driven PLL locks both the phase and frequency to the reference crystal signal, thereby inheriting the crystal’s specified stability and accuracy, typically measured in parts per million (PPM). As a result, the frequency accuracy of the PLL output—expressed as a ±PPM deviation from the target output frequency—is effectively the same as that of the crystal reference. This is because the PLL maintains synchronization with the input signal in both phase and frequency.
Similarly, the resolution of timing modules such as PIT is determined by the accuracy of their reference clock source. Intermediate frequency dividers do not affect the overall accuracy in PPM, as they scale the frequency but not the relative timing precision.
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