What is the practical application of PLL?

[hysamir]

PLL application

I understand the pll and the use of it but i don't get one thing. In pll what we did is we used vco to generate about 2ghz frequency and then useing phase detector we compared with external clock which is running in phase. so my point is if we allready have crystal oscillator which is running in phase then what is the reason to generate another frequency and use pll? why can't i use crstal oscillator's frequency to do rest of my thing... (we did lab on pll in cmos)

i don't know whats the practical application of pll. let me know what u think...

 

[khouly]

Re: PLL application

the PLL has many application

about ur question u have a VCO with 2 GHz , and the phase detector to detect the phse difference between thr VCO and Xtal oscillaot "there is no Xtal oscillator running in 2 GHz"

but between the VCO and phase detector we usually insert a frequncy divider
and this called Frequncy synthizer

there are alot of applications of the pll

1) frequncy synthises
2) FM modulation , and demodulation
3) clock synchronization , and desewking

and many more

khouly

 

[Miguel Gaspar]

PLL application

Well in syncronos communication yo must send data and the clock, but both of them arrives contaminated by noise and afected by distortion. SO in the Rx you must regenerate the clock. That is only one of many applications of the PLL.

 

[bob_lv]

PLL application

You can use frequency synthesizer(PLL with divider) to get any frequency you want. But crystal oscillator can't do this.

 

[rjshmadala]

Re: PLL application

Hello hysamir,

suppose if u need mutiple frequenices.like in a transimitter u have to transmit data with various frequeincies( u need to allocate different channles for diffrent users), there how can u use a crystal osccilator which produce single frequency. and more ever it is very diffcult to produce high frequencies using crystal oscillators.and one more thing in communications u need to filter the data and u must process the data in reciver synchorunously. now a days ppl r able to process the data at a rate of 40Gb/s. which is very diffcult to achieve with crystal osciilator.so they generate this frequency with VCO and they are able to process.if ur able to find good crystal oscillator which works at high frequency that would be great. but we can use it for only single purpose (i.e) constant clock generation not for multiple frequeincies generation.

hope it understand

regards
rajesh