could anyone tell me what is the role of PLL in this image?

[Osawa_Odessa]

Hi, could anyone tell me what is the role of PLL in this image?

I attached the paper just in case you need more information.

 

[kalbun]

I think this is a classical PLL-VCO chain, even if the image does not show the feedback from the VCO output to the PLL.

 

[Osawa_Odessa]

Hi, thanks for help, do you mean that the VCO belongs to PLL block?
Another question. TXCO is an oscillator then its frequency is equal to the frequency of VCO?

 

[kalbun]

Hi, thanks for help, do you mean that the VCO belongs to PLL block?
Another question. TXCO is an oscillator then its frequency is equal to the frequency of VCO?

According to the paper, yes. I read it very quickly, but I remember that VCO is considered as part of the PLL block.

No, the frequency of VCO varies, and the PLL is indeed used to maintain it at a frequency depending from the PLL settings. The TCXO is used as reference oscillator, basically its precision (expressed in PPM) gives the precision of the whole chain.

For a description of PLL principles, I suggest you the Wikipedia. There is an article in the english section, very precise and very clear.