My teachers told me that the output of PLL circuit is same as its input but i am not able to understand if the output of PLL is same as its input then why we are using it... Please help

 

Well your teachers told you wrong. It depends on the context of the question and situation.

 

The output and input will be in phase but they have different frequencies. Thus you can generate an output frequency that is some multiple of the input frequency. If the input is from a crystal oscillator you can generate accurate output frequencies with the accuracy determined by the oscillator accuracy. That's how frequency synthesizers work.

 

The output and input will be in phase but they have different frequencies. Thus you can generate an output frequency that is some multiple of the input frequency. If the input is from a crystal oscillator you can generate accurate output frequencies with the accuracy determined by the oscillator accuracy. That's how frequency synthesizers work.

Input and output can have the same frequency. As an example, a PLL with a VCXO can stabilize a jittery or noisy input signal.

 

Hello,

The following page of the educypedia contains a lot of links with information on pll's ;
http://educypedia.karadimov.info/electronics/pll.htm

bertus

 

Input and output can have the same frequency. As an example, a PLL with a VCXO can stabilize a jittery or noisy input signal.

I somehow figured someone would come up with an exception to my generality.

 

Hello,

There is also a system that locks on any multiple of the reference, called the Huff and Puff VFO stabilization.
Hans Summers has a couple of examples here:
http://www.hanssummers.com/huffpuff.html

Bertus

 

I somehow figured someone would come up with an exception to my generality.

Yeah, leave it to the old nitpicker.

 

I liked this tutorial when I tried to grasp PLLs.