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A Simple Method to Accurately Predict PLL Reference Spur Levels Due to Leakage Current

A Simple Method to Accurately Predict PLL Reference Spur Levels Due to Leakage Current

Presented is a simple model that can be used to accurately predict the level of reference spurs due to charge pump and/or op amp leakage current in a PLL system. Knowing how to predict these levels helps pick loop parameters wisely during the early stages of a PLL system design.

The phase locked loop (PLL) is a negative feedback system that locks the phase and frequency of a higher frequency device (usually a voltage controlled oscillator, VCO) whose phase and frequency are not very stable over temperature and time to a more stable and lower frequency device (usually a temperature compensated or oven controlled crystal oscillator, TCXO or OCXO). As a blackbox, the PLL can be viewed as a frequency multiplier.

 

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