PLL bandwidth and its impact on PLL output clock jitter

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    Question: What is PLL bandwidth and how does it impact PLL output jitter?



    A PLL behaves as a low pass filter as a result of the loop filter in its architecture. PLL bandwidth is determined by this low pass filter bandwidth. Consider the case where the cut off frequency of the PLL low pass filter band is 10 MHz. If the PLL input signal has noise at a frequency below the PLL cut off frequency, the jitter will be passed to the clock output signal. Any input signal noise at a frequency above the PLL cut off frequency will be attenutated at 20 dB/decade due to the low pass filter rolloff.