Phase Locked Loop Basic Components and Fundamental Operations

Phase locked loop or its acronym as PLL is a type of servo loop. Despite, PLL performs its functions based on the incoming radio frequency signal; each basic criterion present in the component or loop in terms of loop stability and other similar parameters remain same. According to EC faculty members of top engineering colleges in India, PLL comprises of three prime elements, which include

Phase Detector or Comparator

Phase detector or comparator circuit block present in the loop plays major role to compare phases of two different signals and later on, generates voltage signal based on difference on phases present in between two different signals.

Loop Filter

Loop Filter of Phase Locked Loop is mainly useful for filtering out output from the detector component. Even loop filter removes any signal of the component, for which comparison of phase takes place via VCO line. In addition, the component governs different types of characteristics present in the loop and its respective stability feature.

VCO or Voltage Controlled Oscillator

VCO implies a suitable circuit block that mainly generates output in the form of radio frequency signal. One can control the frequency of this component and swing over suitable operational frequency band for PLL device.

Fundamental Operation of PLL

Basic concept associated with the operation of Phase Locked Loop is simple and easy, as depicted here. EC professors of top engineering colleges in India said that the operation starts with connecting signal that comes from VCO and reference signal within the detector. After this, output signal from phase detector passes via loop filter and later on, applied across VCO or Voltage Controlled Oscillator.

VCO or Voltage Controlled Oscillator that remains within Phase Locked Loop produces a suitable signal that enters component of phase comparator. Comparator or detector compares the incoming reference signal with the signal that comes from the oscillator component and produces a resulting difference or any error voltage. Here, difference or error voltage is comparable with the phase difference in between two types of signals.
 

Error signal that comes from phase detector will pass through suitable low pass filter that governs most of the properties of PLL and thereby, removes any type of high frequency elements present over the signal. Once you apply error signal from the filter towards control terminal of oscillator, you will be able to calculate the tuning voltage.

Sense of any variation in the voltage signal should be able to reduce difference between phases and thereby, frequency in between two different signals. Initially, loop will remain out of the lock; while error voltage will be able to pull the frequency of the oscillator towards the reference signal, until or unless it remains unable to reduce the error signal further and later on, loop comes to the locked condition.

Whenever PLL or Phase Locked Loop remains in lock, it produces steady state of error voltage. Now, by the help of an amplifier circuit in between VCO and phase detector, the loop reduces the actual error present in between two different signals to least possible values or levels. However, some amount of voltage always remains present across control terminal of the oscillator, as it puts on the correct value of frequency.

In conclusion, PLL is a versatile building block in modern industries dealing with radio frequency electronics.