The tracking range of a phase locked loop (PLL)

The range of frequencies over which the PLL can maintain lock with the incoming signal is called Lock Range or Tracking Range

In PLL (phase-locked loop), the capture range is always less than the lock range.

PLL is used to select the desired frequency channel in communication circuits.

The different states of PLL are:

Lock Range:

When PLL is in lock state it can track frequency changes in the incoming signal.

The range of frequencies over which the PLL can maintain lock with the incoming signal is called Lock Range or Tracking Range

Capture Range:

The Range of frequencies over which the PLL can acquire the lock with an input signal is called capture range.

Free Running state:

Initially, no input signal is applied. Under this condition, the phase detector and Low pass filter outputs will be zero. At this time, VCO operates at free-running frequency. This is the normal operating frequency of VCO.