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Phase Locked Loop

A phase locked loop is a feedback control system made up of a phase comparator and a Voltage Controlled Oscillator (VCO).  The system is designed so that the VCO maintains a constant phase angle relative to a reference signal.  The phase comparator compares the input signal with the one generated by the VCO and adjusts the VCO through a feedback loop.  Below is the block diagram of a PLL and the transfer function.  

The gain of the phase comparator can be found by dividing the supply voltage Vcc by pi radians.  

Frequency vs Capacitance

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