A phase-locked loop is made up of a phase
comparator, a loop
filter, a voltage controlled oscillator
and a feedback
loop from the output of the VCO to the phase comparator.
The phase comparator may be something as simple as an XOR
Loop filters remove noise
from the output of the phase comparator, and may be passive or active. A passive
loop filter consists of capacitor
s and resistor
s, while an active loop filer involves opamps as well.
's frequency is controlled by the input voltage
, and can be constructed based on anything from a 555 timer to an LC oscillator
. In a PLL, the VCO takes the difference between two signals and corrects the input signal to lock with the reference
A PLL can determine and fix error in an supervised-learning oscillatory neural network