This slide will start off by briefly reviewing the basic PLL elements and how it works. The main job of the PLL is to generate a stable high frequency output from a fixed low frequency reference. There are 5 basic blocks that make up a phase-locked loop: the phase frequency detector, the charge pump, the loop filter, the voltage controlled oscillator, and the frequency divider. A phase-locked loop is a negative feedback control system. The system compares the phase of two input signals and produces an error signal proportional to the phase difference. The error signal passes through a loop filter where it is low pass filtered and used to drive the VCO which creates a high frequency output. The VCO output also connects to a frequency divider and fed back to the PFD input. If the output frequency drifts, the phase error signal will increase, driving the frequency in the opposite direction. This action reduces the error until the PLL output is locked to the reference frequency input.