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PLL, Ossilators and Frequency Synthesizers

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Sep 3, 2007
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frequency sintetizer

Could anyone tell me what difference exists between a PLL, an Ossilator and a frequency Synthesizer ?
Please elaborate your replies.
Thanks so much.

frequency sintetizer schematic

an oscillator,pll and frequency synthesizer all generates a particular frequency.....

take two oscillators of same frequency but from different sources....though they are same in terms of frequency they need not have same phase...(remember rate of change of phase is frequency..two signals having a phase difference but phase changing at same rate will have same frequency)

now in order to have oscillations at same frequency and phase we employ a negative feedback.....the system consists of an oscillator which generates frequencies based on the input voltage...a reference oscillator.... an phase detector which compares the phase of the reference and vco and generates an volgate output....(basically phase detector is an mixer) so we need an lpf to filter out higher frequencies....and the output of lpf fed to vco as input....... this is pll

now that we have achieved same phase and frequency....we are greedy to have a frequency output which is programmable in the sense we have an vco which operates at very high frequency compared to reference...we divide the output frequency by an frequency divider(a counter) and then compare the reference and the divider output and then the operation is same as described in previous para....
if we use an( divide by M ) then the output frequency will be M times Fref....if we use divide by 2 counter the o/p frequency will be 2 times....we can use an programmable divider to get an desired output frequency which is exactly in phase and frequency with input reference oscillator
this is frequency synthesizer.

u can refer to wikipedia, or razavi or any RF book for clear details

if this is useful to u dont forget to click helped me
simple frequency synthesizer

Thanks man,
I understand how these devices work but sure there is a difference between them perhaps in terme of implementation or utilisation.


of course there are...pll mainly used in clock generation process.....
frequency synthesizers in RF applications...and oscillators inbuilt in both....

pll ic with inbuilt vco

PLL is a indirect frequency synthesizer which is consist of PLL IC,VCO and referency crystal.
maybe this word is an explicit express of theses difference

A PLL is a very complex device that can work in some diferent maners like: filter, oscillator, Lock in, carrier recover, frequency sintetizer, etc.
An oscillator is a simple device that gives you a unique frequency.
Design of oscillators is a simple matter compared to design using PLL.

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