About Divider, Multiplier and PLL

Divider

Refers to the N frequency division is changed the frequency to 1/N. The period becomes N times.

A piezoelectric reaction occurs when the quartz crystal is energized. Vibrates at a fixed frequency and generates a pulse signal whose voltage changes according to a fixed period. The high frequency signal goes to the frequency divider, which is converted to a low frequency signal.

Multiplier

N multiplier is changed the frequency to N times. The period becomes 1/N times.

In modern communication, people usually need more higher and stable output frequency. Although the LC crystal oscillator can work out higher frequency, the stability is not good, at the same time crystal oscillator has higher stability and accuracy, but the fundamental frequency is too low. In wireless communication industry, frequency synthesis technology (such as PLL) can obtain high frequency signals from low-frequency quartz crystal oscillator.

Phase Locked Loop (PLL ) Circuit

PLL is a closed-loop feedback control system. The PLL composed of as below parts :

1.Phase Comparator：A frequency comparison is made between the input reference signal and the feedback loop signal.

2.Loop Filter：Implemented by frequency divider,Reference base signal to reduce the output of the VCO into the same level.

3.Voltage Controlled Oscillator: According to the input voltage, A periodic signal corresponding to the frequency is output.

4.Feedback Loop

You may want to know: 

What is the difference between the crystal resonator and oscillator?