Doubt regarding PLL.. may be a foolish question....

[DEV123]

I have seen analogy between voltage follower and PLL somewhere telling that both uses negative feedback. ie voltage follower tries to track input voltage where as PLL tracks input signal's frequency and phase. Ok right.

But I know that voltage follower amplifies current signal too.
My doubt is that, to follow the input phase or frequency why do we need a complicated control system. Just a piece of wire would work , isn't it? To filter noise a LPF will do know, so actually is PLL to avoid jitter etc, What is the real aim of using PLL.

I know what I am asking is really foolish, but I need to know where I am wrong, need peace in this matter, please help.

 

[keith1200rs]

PLLs are normally used in circuits/systems that have some dividers in them so the output frequency is higher or lower than the reference frequency by a precise amount. A common use is in radios. From a single 10MHz crystal you can generate a local oscillator 10.7MHz away from the desired receive frequency in the FM 88-108MHz band, for example, in 100kHz steps. PLLs can also be used for other purposes, such as generating phase shifted clocks.

Keith.

 

[DEV123]

then why expanations say track freq. and phase

 

[keith1200rs]

The PLL itself tracks frequency and phase but is usually part of a synthesizer. See https://en.wikipedia.org/wiki/Frequency_synthesizer in particular

which shows the divider.

Keith

 

[DEV123]

Yes I agreed , but the basic explanation of any PLL includes frequency divider as an optional element. without freq divider can you explain me this device.

https://cnx.org/content/m14477/latest/ECE463PLLblockdiagram4.png

 

[keith1200rs]

It is a PLL where the VCO output is the same frequency as the input frequency. What do you want to know about it? Normally it wouldn't be used on its own but with some programmable dividers.

Keith.

 

[DEV123]

What does Track mode in PLL refer to actually then? I am basically trying to understand PLL. I am referring basic to block diagram in

https://cnx.org/content/m14477/latest/ECE463PLLblockdiagram4.png

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This is a link giving explanation of PLL.
http://cnx.org/content/m14477/1.7/
It says

A Phase-Locked Loop (PLL) is a commonly-used tool in many aspects of Communications to create a Maximum-Likelihood estimate of a "noisy" sinusoid.

What is a maximum likelihood estimate of noisy signal means.